Gear Review 2016

Gear Review 2016

What bits of kit impressed me in 2016?

One or two for sure, but not as many as you might think, but here are the things that have made it into my office for keeps, or made my ‘wants list’!

Nikon D500.

Buy Here: Calumet Photographic

%name Gear Review 2016

Every time I grab hold of one of these 1.5x crop DSLR bodies I find myself wanting one more and more – cracking little camera.

I find the new Nikon auto focus system works better on this body than it does on the lamentable D5.

The 10 frames per second frame rate will drop noticeably to around 7fps with continuous dynamic tracking, but that’s not a bad thing really.

Get an XQD card (a big one!), and the battery pack with a D5 battery in it will give the auto focus that little extra ‘umph’.

Nikon 300mm f4 PF lens.

Buy Here: Calumet Photographic

%name Gear Review 2016

Les Peel (Hi Les!) turned up here the other day with one of these 300mm PF lenses on his D500 – and honestly, it blew me away!

I’ve seen very mixed reviews about this lens, and to be honest I’d not given it a second thought ever since it was launched.  But the D500/300mm PF combo that Les brought here staggered me in terms of sharpness and auto focus speed; I even slung the lens on my D800E, and got the same results.

Yes, I agree with with some of the negatives put forward by some; too many elements give give a certain ‘flatness’ to its images, and don’t even think about pointing it at the sun, because the fresnel will make a mess!  But in terms of sports/action photography the idea of using it is a more appealing thought than that of swinging a 300 f2.8 all day.

Please bare in mind though that my opinion is based solely on the use of ONE example.

Canon 1DX Mk2.

By Here: Calumet Photographic

%name Gear Review 2016

This camera isn’t just an ‘upgrade’ to the 1DXMk1 – far from it.  For me the Mk1 was a reliable, steady and highly predictable dance partner.

The Mk2 is a bit of an animal by comparison – like switching from a slow waltz at the local town hall to a full-on Argentine Tango with some sultry hooker in a down-town bar in Beunos Aries!

I took one to Norway back in September for a week (1DX that is, not the sultry hooker), and it mystified my for at least 3 days because I was treating it like a Mk1.

For me it needs a small firmware ‘fettle’ on the AF, but the level of performance with this Mk2 is exceptional.  And now the ADC is integral with the sensor (a la Nikons Sony sensors) the image quality has shot through the roof.

If you own a Mk1 and you are still debating the trade-in then STOP IT and get a move on – times a’wastin..!

Canon 200-400mm f4

Buy Here: Calumet Photographic

%name Gear Review 2016

Still ranks as my favored lens for wildlife photography, not quite the blistering speed and resolution of the behemoth below, but it’s a very close second.  The versatility of 200-560mm comes in mighty handy, and it totally wipes the floor with the Nikon alternative.

Canon 500mm f4 USM Mk2.

Buy Here: Calumet Photographic

%name Gear Review 2016

Oh my, what a lump of glass. Far lighter than its predecessor, and better balanced if you ask me; I can shoot this lens hand-held all day long – simply stunning image quality and so sharp and fast in the auto focus department that it makes me want to cry!

Both it and it’s zoom cousin above represent huge chunks of investment so you have got to NEED either one.  But both of them are worth every single penny if you ask me.

G-Tech G-Raid 8TB Removable Drive

Buy Here: Calumet Photographic
%name Gear Review 2016

I have to admit to being a bit of a G-Drive fan-boy – yep, they’re slightly pricey!

But if you spend thousands on your camera bodies and lenses, and your images are your lifes work, then wincing at the cost of somewhere bullet-proof to store said images is the action of an idiot.

My images are stored on two 4TB internal drives and both of these are cloned to an 8TB internal RAID 0 pair.  This RAID 0 pair is backed up to the 8TB G-Drive unit.  Being on a ‘cheese grater’ MacPro I have no Thunderbolt connections.  But this G-Drive unit is plenty fast enough for my needs across USB 3.0

It’s fast, reliable, very quiet and gives me dual backup for off-site storage for not a lot of money in the grand scheme of things.

 

G-Tech G-Drive EV ATC 1TB USB 3 Hard Drive

Buy Here: Calumet Photographic

%name Gear Review 2016

I’ve had a couple of these 1Tb USB 3.0 portable G-Drives for over a year now – I use them for storage and backup when I’m away, and they have performed flawlessly in that time.

Based around the modular G-Drive system the internal Evolution series drive can be easily removed from the ruggedised water-proof case with little or no effort.

To free up the usb ports on my MacBook Pro I’ve just upgraded the external cases to Thunderbolt (yes, my MBP is the sensible one !). So now the drives can be used on either my MBP or Richs’ Vaio.

Eizo ColorEdge CS2420 24.1″ Wide Gamut Monitor

Buy Here: Calumet Photographic

%name Gear Review 2016

As yet this baby hasn’t made it into my office because I don’t need a new monitor.  But in about another 3 to 4 months that’ll be a different story, because my back light hours are long-since past already, and the extreme right edge of my LP2475W is getting slightly dark.

But am I going to replace it with a ColourEdge or SpectraView Reference – am I heck as like!

No, it’ll be this CS2420.  Calumet Birmingham have one of these in permanent use – God only knows how old it is or how many hours it has on the back light.  But I calibrated it the other week using my ColorMunki Photo via the MBP running a 10 bit connection over Display port to mini Display port and was mightily impressed:

Screen Shot 2016 12 21 at 14.51.38 600x375 Gear Review 2016

The CS2420 (wire frame) compared to AdobeRGB1998 – impressive for under £600.

I must stress that I treat any monitor as ‘dumb’ – I don’t use any of the software-based calibration utilities that come with the monitor, nor do I use the silly little sensor that drops down from the top bezel on some Eizo CE’s.

When you have a print coming off the printer that looks exactly like the original image (not the damn soft-proof like some folk forget) then you know your colour management is set up perfectly.

And this CS2420 Eizo enables me to do just that – for under £600 – a bargain!

Speaking of printing, my last recommendation is a printing paper.

Brilliant Museum Inkjet Paper – SilverGloss Natural 300gsm

Buy Here: Calumet Photographic

%name Gear Review 2016

Brilliant by name, and rather brilliant by nature!

I love this paper. It’s quite heavy and substantial at 300gsm, and has quite a large gamut.  I use it all the time in my venerable Epson 4800 – and that’s with the ‘canned profile’ and Lyson ink for Gods sake.

It gives exceptional prints using Calumet/Brilliant own ‘canned’ profiles on the Canon 9500Mk2 and Pixma Pro 1, and the Epson SC-P600/800.  I’ve no reason to think it won’t work in other printers that have a profile listed on the Brilliant website, but I haven’t tried them!  And Canon actually produce their own Pixma Pro 1 profile for this paper too, links below:

Mac OSX El Capitan version

Windows 10/8/7/Vista version

You will find the profile in one of the sub folders in the download.

And speaking of the Pixma Pro 1

Buy Here: Calumet Photographic

%name Gear Review 2016

A 12 ink A3+ printer that I really do rate – for a ‘plastic fantastic’ desktop printer.

I know it’s been around for a while now, so it’s not new like the Epson SC-P600/800 printers – but then again, I’m not overly partial to either of those.  Not that there’s anything wrong with the printers – it’s just the stupid driver installations I can’t get on with – pathetically over-complicated.

Basically the Pixma Pro 1 is ‘plug ‘n go’ once the driver is installed and it produces the best quality prints I’ve seen out of a Canon DTP since the venerable old 3500Mk2 ended production.

The light weight head is supposed to help prevent clogs – though the real cause of head clogs is low humidity inside the printer.

No ‘plastic fantastic’ printer is designed for regular long print runs; that’s the purview of the big medium format jobs.  But for someone who wants to print a handful of A3 prints per week this printer should suit them down to the ground.

Canon 5DMk4.

A lot of you will be wondering why I’ve not mentioned or listed the Canon 5DMk4.  Short answer is I’ve not finished testing it yet – I do the job thoroughly!  No good saying it works brilliantly, then have the thing erupt in a ball of flame after 2 months a la S7 Edge is it?

I just need to do some final dynamic range testing on it, and to that end I’ll be using the new and older versions of the ubiquitous 16-35 f2.8

So there we go, 10 goodies of varying cost that I’ve considered as ‘wish list worthy’ in 2016; some new and some not so new.

Remember, these are just the opinions of some fat geezer in Cheshire!

SHAMELESS PLUG ALERT

I’ve just brought out my Basic Milky Photography Workflow training, available HERE

Add the discount code BLOG25DEC at the checkout to get 25% off all available downloads – either my Auto Focus Guide for Birds in Flight or my Milky Way Workflow, or BOTH!

Money – it’s such a dirty word, but we all need it!

I wish I could afford to give this training away, but I have to support a family and my photography and photo training are my only income.

I know most of you will try to shop around for bargains and not buy from the referral links in the above post – and that’s okay.

But these posts take time to produce when you type with two fingers like me, and that’s time I’m not earning money to pay the electricity bill et al.

If you could make a small donation via the DONATE button below it would mean a lot folks – seriously, it would.

This blog gets visited by a LOT of people from all walks of life and from all across the planet.  If just 20% of my visitors donated between £5 and £10 per year then I could go full time on reviewing gear in depth the moment it became available to buy or hire for a few weeks.

Manufacturers like Canon and Nikon will never ‘lend’ me anything for review simply because they can’t trust me to say nice things about them.

Retailers make very little in the way of profit on a per item basis. Especially on bodies and lenses, the margins are ridiculous, even your local green grocer couldn’t operate on some of the narrow margins.  So retailer sponsorship here in the UK isn’t a feasible proposition either.  Calumet are good in lending me items from their ‘hire stock’ but that just costs them money in lost hire revenue; which in turn leads to broken up and protracted review times.

So please folks, if you want me to find the bugs in something – so you don’t have to waste your hard earned cash and find them yourself, then please consider making a donation.

Many thanks and Seasons Greeting to all.

Autofocus Drill-down

Long Lens Autofocus Considerations.

If you read my previous post about the 1Dx sensor you will have seen that I mentioned my, as yet unfinished, tome about long lens autofocus for wildlife photography.  It’s a frustrating project because I keep having to change various bits to make them simpler, re-order certain paragraphs etc.

But I thought I’d blog-post something here that I expand on in the project, and it’s something an awful lot of people NEVER take into consideration.

As a Nikon user I’m used to the vagaries of the Nikon AF system and I manage to work with it just fine – I have to!

But photographers who don’t shoot wildlife, and don’t use 400mm or 500mm lumps of glass as their “standard lens” might not find the vagaries I bitch about quite so apparent; indeed some might not come across them at all.

As a wildlife photographer I shoot in crappy light, I shoot with slow lenses (both in terms of f-number and focus speed), I shoot low contrast subjects on equally low contrast backgrounds, I’m constantly shooting brown-on-brown, grey on grey etc, I shoot stupidly small subjects….the list goes on!

For years, good wildlife photography has been done by pushing camera/lens capabilities beyond their performance design parameters; and this particularly applies to our “expectations” of our latest and greatest AF system – be it Canon or Nikon.

I find so many people who come to my workshops etc. are not even aware of this one simple fact – sharp focus requires more work AND increased speed of work by the lens AF motor the closer a subject is to the camera.

Just try looking at the delineations on the focusing ring of a lens:

D3C6337 900x599 Autofocus Drill down

Canon 200-400 focused at 20 meters. (Lens porn WARNING: This lens will cause movements in the front-of-trouser department).

Look at the scale and note the distance between 20m and 50m marks – that distance is indicative of the amount of work required of the autofocus controller and motor to move from 20m to 50m or vice versa.

Now look where the 10m mark is – it requires FAR MORE work from the focus controller and motor to move from 20m to 10m, than it did to move the 30 meters from 50m to 20m.

On top of that extra work, if we are tracking a subject moving at 10 meters per second the lens takes 3 seconds to move from 50m to 20m, but then has to move a lot FASTER as well to cover the extra workload moving from 20m to 10m in just 1 second.

Then you wonder why your Nikon D40 + Sigma 50-500mm is crap at doing “birds in flight”; you never realise that your autofocus system is bag of spanners and powered by a hamster on a wheel…….it’s just not fast enough kids

Autofocus accuracy is nothing without speed if you are wanting to do productive wildlife photography.

As I alluded to before, as a photographer of the old wildlife I, and YOU will always encounter problems that users in other photographic disciplines may not, or if they do then the problem has a lot less impact than it does for us.

Think of it this way – a sports photographer will use a 500mm f4 to photograph a 6 foot tall overpaid git who’s 25m to 70m away, on a sunny Saturday afternoon or under a squillion watts of flood lighting; and he’s looking for a 6×12 for the back page of the Sunday Sport.  I’ll use the same lens to photograph a cute Red Squirrel at 5m to 7m in a gloomy wood in the middle of winter and I’m looking for a full size, full resolution image for stock.

SquidgerPor 900x620 Autofocus Drill down

Red Squirrel – this is basically the FURTHEST DISTANCE you could shoot at with a 500mm lens and still get a meaningful composition. Click for larger view.

Note the distance – 631/100 – that means 6.31 meters. Aperture is f8, so DoF is around 7 centimeters.

The image is UNCROPPED as are all the other images in this post

We don’t really want to be any further away because “his cuteness” will be too small in the frame:

The factors effecting subject distance choice are:

  1.  lens resolving power – small, fine details need to be as close as possible.*
  2.  sensor resolving power – we need as many pixels as possible covering the subject.*
  3.  auto focus point placement accuracy – if the subject is too small in the frame, point placement is inaccurate.
  4. general “in camera” composition

*These two are inextricably intertwined

I’ve indicated the active focus point on the above image too  because here’s a depth of field “point of note” – autofocus wastes DoF.  Where is the plane of focus? Just between the eyes of the squirrel.

Assuming the accepted modern norm of DoF distribution – 50/50 – that’s 3.5 centimeters in front of the plane of focus, or indicted AF point, that will be sharp.  Only problem there is that the squirrel’s nose is only around 1 centimeter closer to the camera than the AF point, so the remaining 2 .5 centimeters of DoF is wasted on a sharp rendition of the fresh air between its nose and the camera!!

Now let’s change camera orientation and go a bit closer to get the very TIGHTEST shot composition:

SquidgerLs 900x370 Autofocus Drill down

Red Squirrel – this is basically the CLOSEST DISTANCE you could shoot at with a 500mm lens and still get a meaningful composition. Click for larger view

The subject distance is 5.62 meters. Aperture is f6.3 so DoF is around 4.4 centimeters.

Now let’s change photographic hats and imagine we are a sports photographer and we are spending a Saturday afternoon photographing a bunch of over-paid 6 foot tall gits chasing a ball around a field, using the very same camera and lens:

HUPor 900x608 Autofocus Drill down

He’s not over-paid or chasing a ball, but this is the CLOSEST distance we can shoot at with this orientation and still get a “not too tight” composition of a 6 foot git! “Shep’s” not a git really – well, not much! Click to enlarge

The distance for this shot is 29.9 meters. Aperture is f6.3 so DoF is around 1.34 meters.

HULs 900x602 Autofocus Drill down

And here we are at the CLOSEST distance for this horizontal camera orientation – still not too tight. Click to enlarge.

The distance here is 50.1 meters. Aperture is f6.3 so DoF is around 3.79 meters.

So with this new “sports shooter” hat on, have we got an easier job than the cold, wet squirrel photographer?

You bet your sweet life we have!

The “Shepster” can basically jump around and move about like an idiot on acid and stay in sharp focus because:

  1. the depth of field at those distances is large.
  2. more importantly, the autofocus has VERY little work to do along the lens axis, because 1 or 2 meters of subject movement closer to the camera requires very small movements of the lens focus mechanicals.

But the poor wildlife photographer with his cute squirrel has so much more of a hard time getting good sharp shots because:

  1. he/she has got little or no depth of field
  2. small subject movements along the lens axis require very large and very fast        movement of the lens focus mechanicals.

So the next time you watch a video by Canon or Nikon demonstrating the effectiveness of their new AF system on some new camera body or other; or you go trawling the internet looking for what AF settings the pros use, just bear in mind that “one mans fruit may be another mans poison” just because he/she photographs bigger subjects at longer average distances”.

Equipment choice and its manner of deployment and use is just not a level playing field is it…but it’s something a lot of folk don’t realise or think about.

And how many folk would ever consider that a desired “in camera” image composition has such a massive set of implications for autofocus performance – not many – but if you put your brain in gear it’s blindingly obvious.

Please consider supporting this blog.

This blog really does need your support. All the information I put on these pages I do freely, but it does involve costs in both time and money.

If you find this post useful and informative please could you help by making a small donation – it would really help me out a lot – whatever you can afford would be gratefully received.

Your donation will help offset the costs of running this blog and so help me to bring you lots more useful and informative content.

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MTF, Lens & Sensor Resolution

MTF, Lens & Sensor Resolution

I’ve been ‘banging on’ about resolution lens performance and MTF over the last few posts so I’d like to start bringing all these various bits of information together with at least a modicum of simplicity.

If this is your first visit to my blog I strongly recommend you peruse HERE and HERE before going any further!

You might well ask the question “Do I really need to know this stuff – you’re a pro Andy and I’m not, so I don’t think I need to…”

My answer is “Yes you bloody well do need to know, so stop whinging – it’ll save you time and perhaps stop you wasting money…”

Words used like ‘resolution’ do tend to get used out of context sometimes, and when you guys ‘n gals are learning this stuff then things can get a mite confusing – and nowhere does terminology get more confusing than when we are talking ‘glass’.

But before we get into the idea of bringing lenses and sensors together I want to introduce you to something you’ve all heard of before – CONTRAST – and how it effects our ability to see detail, our lens’s ability to transfer detail, and our camera sensors ability to record detail.

Contrast & How It Effects the Resolving of Detail

In an earlier post HERE I briefly mentioned that the human eye can resolve 5 line pairs per millimeter, and the illustration I used to illustrate those line pairs looked rather like this:

5LPmm MTF, Lens & Sensor Resolution

5 line pairs per millimeter with a contrast ratio of 100% or 1.0

Now don’t forget, these line pairs are highly magnified – in reality each pair should be 0.2mm wide.  These lines are easily differentiated because of the excessive contrast ratio between each line in a pair.

How far can contrast between the lines fall before we can’t tell the difference any more and all the lines blend together into a solid monotone?

Enter John William Strutt, the 3rd Baron Rayleigh…………

Rayleigh MTF, Lens & Sensor Resolution

5 line pairs at bottom threshold of human vision – a 9% contrast ratio.

The Rayleigh Criterion basically stipulates that the ‘discernability’ of each line in a pair is low end limited to a line pair contrast ratio of 9% or above, for average human vision – that is, when each line pair is 0.2mm wide and viewed from 25cms.  Obviously they are reproduced much larger here, hence you can see ’em!

SensorContrast copy MTF, Lens & Sensor Resolution

Low contrast limit for Human vision (left) & camera sensor (right).

However, it is said in some circles that dslr sensors are typically limited to a 12% to 15% minimum line pair contrast ratio when it comes to discriminating between the individual lines.

Now before you start getting in a panic and misinterpreting this revelation you must realise that you are missing one crucial factor; but let’s just recap what we’ve got so far.

  1. A ‘line’ is a detail.
  2. but we can’t see one line (detail) without another line (detail) next to it that has a different tonal value ( our line pair).
  3. There is a limit to the contrast ratio between our two lines, below which our lines/details begin to merge together and become less distinct.

So, what is this crucial factor that we are missing; well, it’s dead simple – the line pair per millimeter (lp/mm) resolution of a camera sensor.

Now there’s something you won’t find in your cameras ‘tech specs’ that’s for sure!

Sensor Line Pair Resolution

The smallest “line” that can be recorded on a sensor is 1 photosite in width – now that makes sense doesn’t it.

But in order to see that line we must have another line next to it, and that line must have a higher or lower tonal value to a degree where the contrast ratio between the two lines is at or above the low contrast limit of the sensor.

So now we know that the smallest line pair our sensor can record is 2 photosites/pixels in width – the physical width is governed by the sensor pixel pitch; in other words the photosite diameter.

In a nutshell, the lp/mm resolution of a sensor is 0.5x the pixel row count per millimeter – referred to as the Nyquist Rate, simply because we have to define (sample) 2 lines in order to see/resolve 1 line.

The maximum resolution of an image projected by the lens that can be captured at the sensor plane – in other words, the limit of what can be USEFULLY sampled – is the Nyquist Limit.

Let’s do some practical calculations:

Canon 1DX 18.1Mp

Imaging Area = 36mm x 24mm / 5202 x 3533 pixels/photosites OR LINES.

I actually do this calculation based on the imaging area diagonal

So sensor resolution in lp/mm = (pixel diagonal/physical diagonal) x 0.5 = 72.01 lp/mm

Nikon D4 16.2Mp = 68.62 lp/mm

Nikon D800 36.3Mp = 102.33 lp/mm

PhaseOne P40 40Mp medium format = 83.15 lp/mm

PhaseOne IQ180 80Mp medium format = 96.12 lp/mm

Nikon D7000 16.2mp APS-C (DX) 4928×3264 pixels; 23.6×15.6mm dimensions  = 104.62 lp/mm

Canon 1D IV 16.1mp APS-H 4896×3264 pixels; 27.9×18.6mm dimensions  = 87.74 lp/mm

Taking the crackpot D800 as an example, that 102.33 lp/mm figure means that the sensor is capable of resolving 204.66 lines, or points of detail, per millimeter.

I say crackpot because:

  1. The Optical Low Pass “fights” against this high degree of resolving power
  2. This resolving power comes at the expense of S/N ratio
  3. This resolving power comes at the expense of diffraction
  4. The D800E is a far better proposition because it negates 1. above but it still leaves 2. & 3.
  5. Both sensors would purport to be “better” than even an IQ180 – newsflash – they ain’t; and not by a bloody country mile!  But the D800E is an exceptional sensor as far as 35mm format (36×24) sensors go.

A switch to a 40Mp medium format is BY FAR the better idea.

Before we go any further, we need a reality check:

In the scene we are shooting, and with the lens magnification we are using, can we actually “SEE” detail as small as 1/204th of a millimeter?

We know that detail finer than that exists all around us – that’s why we do macro/micro photography – but shooting a landscape with a 20mm wide angle where the nearest detail is 1.5 meters away ??

And let’s not forget the diffraction limit of the sensor and the incumbent reduction in depth of field that comes with 36Mp+ crammed into a 36mm x 24mm sensor area.

The D800 gives you something with one hand and takes it away with the other – I wouldn’t give the damn thing house-room!  Rant over………

Anyway, getting back to the matter at hand, we can now see that the MTF lp/mm values quoted by the likes of Nikon and Canon et al of 10 and 30 lp/mm bare little or no connectivity with the resolving power of their sensors – as I said in my previous post HERE – they are meaningless.

The information we are chasing after is all about the lens:

  1. How well does it transfer contrast because its contrast that allows us to “see” the lines of detail?
  2. How “sharp” is the lens?
  3. What is the “spread” of 1. and 2. – does it perform equally across its FoV (field of view) or is there a monstrous fall-off of 1. and 2. between 12 and 18mm from the center on an FX sensor?
  4. Does the lens vignette?
  5. What is its CA performance?

Now we can go to data sites on the net such as DXO Mark where we can find out all sorts of more meaningful data about our potential lens purchase performance.

But even then, we have to temper what we see because they do their testing using Imatest or something of that ilk, and so the lens performance data is influenced by sensor, ASIC and basic RAW file demosaicing and normalisation – all of which can introduce inaccuracies in the data; in other words they use camera images in order to measure lens performance.

The MTF 50 Standard

Standard MTF (MTF 100) charts do give you a good idea of the lens CONTRAST transfer function, as you may already have concluded. They begin by measuring targets with the highest degree of modulation – black to white – and then illustrate how well that contrast has been transferred to the image plane, measured along a corner radius of the frame/image circle.

MTF100 50 101 900x290 MTF, Lens & Sensor Resolution

MTF 1.0 (100%) left, MTF 0.5 (50%) center and MTF 0.1 (10%) right.

As you can see, contrast decreases with falling transfer function value until we get to MTF 0.1 (10%) – here we can guess that if the value falls any lower than 10% then we will lose ALL “perceived” contrast in the image and the lines will become a single flat monotone – in other words we’ll drop to 9% and hit the Rayleigh Criterion.

It’s somewhat debatable whether or not sensors can actually discern a 10% value – as I mentioned earlier in this post, some favour a value more like 12% to 15% (0.12 to 0.15).

Now then, here’s the thing – what dictates the “sharpness” of edge detail in our images?  That’s right – EDGE CONTRAST.  (Don’t mistake this for overall image contrast!)

Couple that with:

  1. My well-used adage of “too much contrast is thine enemy”.
  2. “Detail” lies in midtones and shadows, and we want to see that detail, and in order to see it the lens has to ‘transfer’ it to the sensor plane.
  3. The only “visual” I can give you of MTF 100 would be something like power lines silhouetted against the sun – even then you would under expose the sun, so, if you like, MTF would still be sub 100.

Please note: 3. above is something of a ‘bastardisation’ and certain so-called experts will slag me off for writing it, but it gives you guys a view of reality – which is the last place some of those aforementioned experts will ever inhabit!

Hopefully you can now see that maybe measuring lens performance with reference to MTF 50 (50%, 0.5) rather than MTF 100 (100%, 1.0) might be a better idea.

Manufacturers know this but won’t do it, and the likes of Nikon can’t do it even if they wanted to because they use a damn calculator!

Don’t be trapped into thinking that contrast equals “sharpness” though; consider the two diagrams below (they are small because at larger sizes they make your eyes go funny!).

ContrastUnsharp MTF, Lens & Sensor Resolution

A lens can have a high contrast transfer function but be unsharp.

SharpLowContrast MTF, Lens & Sensor Resolution

A lens can have low contrast transfer function but still be sharp.

In the first diagram the lens has RESOLVED the same level of detail (the same lp/mm) in both cases, and at pretty much the same contrast transfer value; but the detail is less “sharp” on the right.

In the lower diagram the lens has resolved the same level of detail with the same degree of  “sharpness”, but with a much reduced contrast transfer value on the right.

Contrast is an AID to PERCEIVED sharpness – nothing more.

I actually hate that word SHARPNESS; and it’s a nasty word because it’s open to all sorts of misconceptions by the uninitiated.

A far more accurate term is ACUTANCE.

acutance MTF, Lens & Sensor Resolution

How Acutance effects perceived “sharpness”.

So now hopefully you can see that LENS RESOLUTION is NOT the same as lens ACUTANCE (perceived sharpness..grrrrrr).

Seeing as it is possible to have a lens with a higher degree resolving power, but a lower degree of acutance you need to be careful – low acutance tends to make details blur into each other even at high contrast values; which tends to negate the positive effects of the resolving power. (Read as CHEAP LENS!).

Lenses need to have high acutance – they need to be sharp!  We’ve got enough problems trying to keep the sharpness once the sensor gets hold of the image, without chucking it a soft one in the first place – and I’ll argue this point with the likes of Mr. Rockwell until the cows have come home!

Things We Already Know

We already know that stopping down the aperture increases Depth of Field; and we already know that we can only do this to a certain degree before we start to hit diffraction.

What does increasing DoF do exactly; it increases ACUTANCE is what it does – exactly!

Yes it gives us increased perceptual sharpness of parts of the subject in front and behind the plane of sharp focus – but forget that bit – we need to understand that the perceived sharpness/acutance of the plane of focus increases too, until you take things too far and go beyond the diffraction limit.

And as we already know, that diffraction limit is dictated by the size of photosites/pixels in the sensor – in other words, the sensor resolution.

So the diffraction limit has two effects on the MTF of a lens:

  1. The diffraction limit changes with sensor resolution – you might get away with f14 on one sensor, but only f9 on another.
  2. All this goes “out the window” if we talk about crop-sensor cameras because their sensor dimensions are different.

We all know about “loss of wide angles” with crop sensors – if we put a 28mm lens on an FX body and like the composition but then we switch to a 1.5x crop body we then have to stand further away from the subject in order to achieve the same composition.

That’s good from a DoF PoV because DoF for any given aperture increases with distance; but from a lens resolving power PoV it’s bad – that 50 lp/mm detail has just effectively dropped to 75 lp/mm, so it’s harder for the lens to resolve it, even if the sensors resolution is capable of doing so.

There is yet another way of quantifying MTF – just to confuse the issue for you – and that is line pairs per frame size, usually based on image height and denoted as lp/IH.

Imatest uses MTF50 but quotes the frequencies not as lp/mm, or even lp/IH; but in line widths per image height – LW/IH!

Alas, there is no single source of the empirical data we need in order to evaluate pure lens performance anymore.  And because the outcome of any particular lens’s performance in terms of acutance and resolution is now so inextricably intertwined with that of the sensor behind it, then you as lens buyers, are left with a confusing myriad of various test results all freely available on the internet.

What does Uncle Andy recommend? – well a trip to DXO Mark is not a bad starting point all things considered, but I do strongly suggest that you take on board the information I’ve given you here and then scoot over to the DXO test methodology pages HERE and read them carefully before you begin to examine the data and draw any conclusions from it.

But do NOT make decisions just on what you see there; there is no substitute for hands-on testing with your camera before you go and spend your hard-earned cash.  Proper testing and evaluation is not as simple as you might think, so it’s a good idea to perhaps find someone who knows what they are doing and is prepared to help you out.   Do NOT ask the geezer in the camera shop – he knows bugger all about bugger all!

Do Sensors Out Resolve Lenses?

Well, that’s the loaded question isn’t it – you can get very poor performance from what is ostensibly a superb lens, and to a degree vice versa.

It all depends on what you mean by the question, because in reality a sensor can only resolve what the lens chucks at it.

If you somehow chiseled the lens out of your iPhone and Sellotaped it to your shiny new 1DX then I’m sure you’d notice that the sensor did indeed out resolve the lens – but if you were a total divvy who didn’t know any better then in reality all you’d be ware of is that you had a crappy image – and you’d possibly blame the camera, not the lens – ‘cos it took way better pics on your iPhone 4!

There are so many external factors that effect the output of a lens – available light, subject brightness range, angle of subject to the lens axis to name but three.  Learning how to recognise these potential pitfalls and to work around them is what separates a good photographer from an average one – and by good I mean knowledgeable – not necessarily someone who takes pics for a living.

I remember when the 1DX specs were first ‘leaked’ and everyone was getting all hot and bothered about having to buy the new Canon glass because the 1DX was going to out resolve all Canons old glass – how crackers do you need to be nowadays to get a one way ticket to the funny farm?

If they were happy with the lens’s optical performance pre 1DX then that’s what they would get post 1DX…duh!

If you still don’t get it then try looking at it this way – if lenses out resolve your sensor then you are up “Queer Street” – what you see in the viewfinder will be far better than the image that comes off the sensor, and you will not be a happy camper.

If on the other hand, our sensors have the capability to resolve more lines per millimeter than our lenses can throw at them, and we are more than satisfied with our lenses resolution and acutance, then we would be in a happy place, because we’d be wringing the very best performance from our glass – always assuming we know how to ‘drive the juggernaut’  in the first place!

Please consider supporting this blog.

This blog really does need your support. All the information I put on these pages I do freely, but it does involve costs in both time and money.

If you find this post useful and informative please could you help by making a small donation – it would really help me out a lot – whatever you can afford would be gratefully received.

Your donation will help offset the costs of running this blog and so help me to bring you lots more useful and informative content.

Many thanks in advance.

 

Lens Performance

I have a friend – yes, a strange concept I know, but I do have some – we’ll call him Steve.

Steve is a very talented photographer – when he’ll give himself half a chance; but impatience can sometimes get the better of him.

He’ll have a great scene in front of him but then he’ll forget things such as any focus or exposure considerations the scene demands, and the resulting image will be crap!

Quite often, a few of Steve’s character flaws begin to emerge at this juncture.

Firstly, Steve only remembers his successes; this leads to the unassailable ‘fact’ that he couldn’t possibly have ‘screwed up’.

So now we can all guess the conclusive outcome of that scenario can’t we……..that’s right; his camera gear has fallen short in the performance department.

Clairvoyance department would actually be more accurate!

So this ‘error in his camera system’ needs to be stamped on – hard and fast!

This leads to Steve embarking on a massive information-gathering exercise from various learned sources on ‘that there inter web’ – where another of Steve’s flaws shows up; that of disjointed speed reading…..

The terrifying outcome of these situations usually concludes with Steve’s confident affirmation that some piece of his equipment has let him down; not just by becoming faulty but sometimes, more worryingly by initial design.

These conclusions are always arrived at in the same manner – the various little snippets of truth and random dis-associated facts that Steve gathers, all get forcibly hammered into some hellish, bastardized ‘factual’ jigsaw in his head.

There was a time when Steve used to ask me first, but he gave up on that because my usual answer contravened the outcome of his first mentioned character flaw!

Lately one of Steve’s biggest peeves has been the performance of one or two of his various lenses.

Ostensibly you’ll perhaps think there’s nothing wrong in that – after all, the image generated by the camera is only as good as the lens used to gather the light in the scene – isn’t it?

 

But there’s a potential problem, and it  lies in what evidence you base your conclusions on……………

 

For Steve, at present, it’s manufacturers MTF charts, and comparisons thereof, coupled with his own images as they appear in Lightroom or Photoshop ACR.

Again, this might sound like a logical methodology – but it isn’t.

It’s flawed on so many levels.

 

The Image Path from Lens to Sensor

We could think of the path that light travels along in order to get to our camera sensor as a sort of Grand National horse race – a steeplechase for photons!

“They’re under starters orders ladies and gentlemen………………and they’re off!”

As light enters the lens it comes across it’s first set of hurdles – the various lens elements and element groups that it has to pass through.

Then they arrive at Becher’s Brook – the aperture, where there are many fallers.

Carefully staying clear of the inside rail and being watchful of any lose photons that have unseated their riders at Becher’s we move on over Foinavon – the rear lens elements, and we then arrive at the infamous Canal Turn – the Optical Low Pass filter; also known as the Anti-alias filter.

Crashing on past the low pass filter and on over Valentines only the bravest photons are left to tackle the the last big fence on their journey – The Chair – our camera sensor itself.

 

Okay, I’ll behave myself now, but you get the general idea – any obstacle that lies in the path of light between the front surface of our lens and the photo-voltaic surface of our sensor is a BAD thing.

Image Path1 900x426 Lens Performance

The various obstacles to light as it passes through a camera (ASIC = Application Specific Integrated Circuit)

The problems are many, but let’s list a few:

  1. Every element reduces the level of transmitted light.
  2. Because the lens elements have curved surfaces, light is refracted or bent; the trick is to make all wavelengths of light refract to the same degree – failure results in either lateral or longitudinal chromatic aberration – or worse still, both.
  3. The aperture causes diffraction – already discussed HERE

We have already seen in that same previous post on Sensor Resolution that the number of megapixels can effect overall image quality in terms of overall perceived sharpness due to pixel-pitch, so all things considered, using photographs of any 3 dimensional scene is not always a wise method of judging lens performance.

And here is another reason why it’s not a good idea – the effect on image quality/perceived lens resolution of anti-alias, moire or optical low pass filter; and any other pre-filtering.

I’m not going to delve into the functional whys and wherefores of an AA filter, save to say that it’s deemed a necessary evil on most sensors, and that it can make your images take on a certain softness because it basically adds blur to every edge in the image projected by the lens onto your sensor.

The reasoning behind it is that it stops ‘moire patterning’ in areas of high frequency repeated detail.  This it does, but what about the areas in the image where its effect is not required – TOUGH!

 

Many photographers have paid service suppliers for AA filter removal just to squeeze the last bit of sharpness out of their sensors, and Nikon of course offer the ‘sort of AA filter-less’ D800E.

Side bar note:  I’ve always found that with Nikon cameras at least, the pro-body range seem to suffer a lot less from undesirable AA filtration softening than than their “amateur” and “semi pro” bodies – most notably the D2X compared to a D200, and the D3 compared to the D700 & D300.  Perhaps this is due to a ‘thinner’ filter, or a higher quality filter – I don’t know, and to be honest I’ve never had the desire to ‘poke Nikon with a sharp stick’ in order to find out.

 

Back in the days of film things were really simple – image resolution was governed by just two things; lens resolution and film resolution:

1/image resolution = 1/lens resolution + 1/film resolution

Film resolution was a variable depending on the Ag Halide distribution and structure,  dye coupler efficacy within the film emulsion, and the thickness of the emulsion or tri-pack itself.

But today things are far more complicated.

With digital photography we have all those extra hurdles to jump over that I mentioned earlier, so we end up with a situation whereby:

1/Image Resolution = 1/lens resolution + 1/AA filter resolution + 1/sensor resolution + 1/image processor/imaging ASIC resolution

Steve is chasing after lens resolution under the slightly misguided idea the resolution equates to sharpness, which is not strictly true; but he is basing his conception of lens sharpness based on the detail content and perceived detail ‘sharpness’ of his  images; which are ‘polluted’ if you like by the effects of the AA filter, sensor and imaging ASIC.

What it boils down to, in very simplified terms, is this:

You can have one particular lens that, in combination with one camera sensor produces a superb image, but in combination with another sensor produces a not-quite-so-superb image!

On top of the “fixed system” hurdles I’ve outlined above, we must not forget the potential for errors introduced by lens-to-body mount flange inaccuracies, and of course, the big elephant-in-the-room – operator error – ehh Steve.

So attempting to quantify the pure ‘optical performance’ of a lens using your ‘taken images’ is something of a pointless exercise; you cannot see the pure lens sharpness or resolution unless you put the lens on a fully equipped optical test bench – and how many of us have got access to one of those?

The truth of the matter is that the average photographer has to trust the manufacturers to supply accurately put together equipment, and he or she has to assume that all is well inside the box they’ve just purchased from their photographic supplier.

But how can we judge a lens against an assumed standard of perfection before we part with our cash?

A lot of folk, including Steve – look at MTF charts.

 

The MTF Chart

Firstly, MTF stands for Modulation Transfer Function – modu-what I hear your ask!

OK – let’s deal with the modulation bit.  Forget colour for a minute and consider yourself living in a black & white world.  Dark objects in a scene reflect few photons of light – ’tis why the appear dark!  Conversely, bright objects reflect loads of the little buggers, hence these objects appear bright.

Imagine now that we are in a sealed room totally impervious to the ingress of any light from outside, and that the room is painted matte white from floor to ceiling – what is the perceived colour of the room? Black is the answer you are looking for!

Now turn on that 2 million candle-power 6500k searchlight in the corner.  The split second before your retinas melted, what was the perceived colour of the room?

Note the use of the word ‘perceived’ – the actual colour never changed!

The luminosity value of every surface in the room changed from black to white/dark to bright – the luminosity values MODULATED.

Now back in reality we can say that a set of alternating black and white lines of equal width and crisp clean edges represent a high degree of contrast, and therefore tonal modulation; and the finer the lines the higher is the modulation frequency – which we measure in lines per millimeter (lpmm).

A lens takes in a scene of these alternating black and white lines and, just like it does with any other scene, projects it into an image circle; in other words it takes what it sees in front of it and ‘transfers’ the scene to the image circle behind it.

With a bit of luck and a fair wind this image circle is being projected sharply into the focal plane of the lens, and hopefully the focal plane matches up perfectly with the plane of the sensor – what used to be refereed to as the film plane.

The efficacy with which the lens carries out this ‘transfer’ in terms of maintaining both the contrast ratio of the modulated tones and the spatial separation of the lines is its transfer function.

So now you know what MTF stands for and what it means – good this isn’t it!

 

Let’s look at an MTF chart:

Nikon 500mmf4MTF Lens Performance

Nikon 500mm f4 MTF chart

Now what does all this mean?

 

Firstly, the vertical axis – this can be regarded as that ‘efficacy’ I mentioned above – the accuracy of tonal contrast and separation reproduction in the projected image; 1.0 would be perfect, and 0 would be crappier than the crappiest version of a crap thing!

The horizontal axis – this requires a bit of brain power! It is scaled in increments of 5 millimeters from the lens axis AT THE FOCAL PLANE.

The terminus value at the right hand end of the axis is unmarked, but equates to 21.63mm – half the opposing corner-to-corner dimension of a 35mm frame.

Now consider the diagram below:

ImageCircle 853x900 Lens Performance

The radial dimensions of the 35mm format.

These are the radial dimensions, in millimeters, of a 35mm format frame (solid black rectangle).

The lens axis passes through the center axis of the sensor, so the radii of the green, yellow and dashed circles correspond to values along the horizontal axis of an MTF chart.

Let’s simplify what we’ve learned about MTF axes:

Modi500mmf4MTF Lens Performance

MTF axes hopefully made simpler!

Now we come to the information data plots; firstly the meaning of Sagittal & Meridional.   From our perspective in this instance I find it easier for folk to think of them as ‘parallel to’ and ‘at right angles to’ the axis of measurement, though strictly speaking Meridional is circular and Sagittal is radial.

This axis of measurement is from the lens/film plane/sensor center to the corner of a 35mm frame – in other words, along that 21.63mm radius.

ImageCircle21 900x708 Lens Performance

The axis of MTF measurement and the relative axial orientation of Sagittal & Meridional lines. NOTE: the target lines are ONLY for illustration.

Separate measurements are taken for each modulation frequency along the entire measurement axis:

ImageCircle31 900x708 Lens Performance

Thin Meridional MTF measurement. (They should be concentric circles but I can’t draw concentric circles!).

Let’s look at that MTF curve for the 500m f4 Nikon together with a legend of ‘sharpness’ – the 300 f2.8:

MTF2 900x545 Lens Performance

Nikon MTF comparison between the 500mm f4 & 300mm f2.8

Nikon say on their website that they measure MTF at maximum aperture, that is, wide open; so the 300mm chart is for an aperture of f2.8 (though they don’t say so) and the 500mm is for an f4 aperture – which they do specify on the chart – don’t ask me why ‘cos I’ve no idea.

As we can see, the best transfer values for the two lenses (and all other lenses) is 10 lines per millimeter, and generally speaking sagittal orientation usually performs slightly better than meridional, but not always.

10 lpmm is always going to give a good transfer value because its very coarse and represents a lower frequency of detail than 30 lpmm.

Funny thing, 10 lines per millimeter is 5 line pairs per millimeter – and where have we heard that before? HERE – it’s the resolution of the human eye at 25 centimeters.

 

Another interesting thing to bare in mind is that, as the charts clearly show, better transfer values occur closer to the lens axis/sensor center, and that performance falls as you get closer to the frame corners.

This is simply down to the fact that your are getting closer to the inner edge of the image circle (the dotted line in the diagrams above).  If manufacturers made lenses that threw a larger image circle then corner MTF performance would increase – it can be done – that’s the basis upon which PCE/TS lenses work.

One way to take advantage of center MTF performance is to use a cropped sensor – I still use my trusty D2Xs for a lot of macro work; not only do I get the benefit of center MTF performance across the majority of the frame but I also have the ability to increase the lens to subject distance and get the composition I want, so my depth of field increases slightly for any given aperture.

Back to the matter at hand, here’s my first problem with the likes of Nikon, Canon etc:  they don’t specify the lens-to-target distance. A lens that gives a transfer value of 9o% plus on a target of 10 lpmm sagittal at 2 meters distance is one thing; one that did the same but at 25 meters would be something else again.

You might look at the MTF chart above and think that the 300mm f2.8 lens is poor on a target resolution of  30 lines per millimeter compared to the 500mm, but we need to temper that conclusion with a few facts:

  1. A 300mm lens is a lot wider in Field of View (FoV) than a 500mm so there is a lot more ‘scene width’ being pushed through the lens – detail is ‘less magnified’.
  2. How much ‘less magnified’ –  40% less than at 500mm, and yet the 30 lpmm transfer value is within 6% to 7% that of the 500mm – overall a seemingly much better lens in MTF terms.
  3. The lens is f2.8 – great for letting light in but rubbish for everything else!

Most conventional lenses have one thing in common – their best working aperture for overall image quality is around f8.

But we have to counter balance the above with the lack of aforementioned target distance information.  The minimum focus distances for the two comparison lenses are 2.3 meters and 4.0 meters respectively so obviously we know that the targets are imaged and measured at vastly different distances – but without factual knowledge of the testing distances we cannot really say that one lens is better than the other.

 

My next problem with most manufacturers MTF charts is that the values are supplied ‘a la white light’.

I mentioned earlier – much earlier! – that lens elements refracted light, and the importance of all wavelengths being refracted to the same degree, otherwise we end up with either lateral or longitudinal chromatic aberration – or worse still – both!

Longitudinal CA will give us different focal planes for different colours contained within white light – NOT GOOD!

Lateral CA gives us the same plane of focus but this time we get lateral shifts in the red, green and blue components of the image, as if the 3 colour channels have come out of register – again NOT GOOD!

Both CA types are most commonly seen along defined edges of colour and/or tone, and as such they both effect transferred edge definition and detail.

So why do manufacturers NOT publish this information – there is to my knowledge only one that does – Schneider (read ‘proper lens’).

They produce some very meaningful MTF data for their lenses with modulation frequencies in excess of 90 to 150 lpmm; separate R,G & B curves; spectral weighting variations for different colour temperatures of light and all sorts of other ‘geeky goodies’ – I just love it all!

 

SHAME ON YOU NIKON – and that goes for Canon and Sigma just as much.

 

So you might now be asking WHY they don’t publish the data – they must have it – are they treating us like fools that wouldn’t be able to understand it; OR – are they trying to hide something?

You guys think what you will – I’m not accusing anyone of anything here.

But if they are trying to hide something then that ‘something’ might not be what you guys are thinking.

What would you think if I told you that if you were a lens designer you could produce an MTF plot with a calculator – ‘cos you can, and they do!

So, in a nutshell, most manufacturers MTF charts as published for us to see are worse than useless.  We can’t effectively use them to compare one lens against another because of missing data; we can’t get an idea of CA performance because of missing red, green and blue MTF curves; and finally we can’t even trust that the bit of data they do impart is even bloody genuine.

 

Please don’t get taken in by them next time you fancy spending money on glass – take your time and ask around – better still try one; and try it on more than 1 camera body!

 

Please consider supporting this blog.

This blog really does need your support. All the information I put on these pages I do freely, but it does involve costs in both time and money.

If you find this post useful and informative please could you help by making a small donation – it would really help me out a lot – whatever you can afford would be gratefully received.

Your donation will help offset the costs of running this blog and so help me to bring you lots more useful and informative content.

Many thanks in advance.

 

Please note, I’ve not written this blog article for any other reason than to make its readers aware of the facts – no one pays me in cash or kind for any products mentioned in this article; it is written purely for information purposes; you do with this information “what you will”!

If you have any questions please feel free to drop me a line via email at tuition@wildlifeinpixels.net