The format rhetoric seems to be heating up again. Maybe it never cooled off. In the last 7 or 8 years, I’ve owned and made many images with APS-C (with crop factors between 1.3 and 1.5), full frame (FF), and 33×44 (MF, or crop MF, depending on your level of precision – and maybe your agenda). During that time, I’ve also used larger MF cameras, and a 72×96 mm Betterlight back that has an effective sensor area that’s larger than anything you can fit onto 120 film until you pass 6×9. That’s pretty much the range of sizes available to serious photographers except Four-Thirds and Micro Four-Thirds. After all that experience and all the testing I’ve done, I’m pretty confident that I understand the broad benefits and drawbacks of format choices.
First off, let me hasten to point out that there are indeed image quality implications of format choice. People often invoke the concept of equivalence, which Joseph James explains so well here, to argue the point that choosing a smaller format does not mean choosing lower image quality. Other people say that equivalence is baloney. Neither is correct. Equivalence, as defined by James, is a true analysis of an idealized reality, and is perfectly accurate within its constraints. The people who say that format choices don’t affect image quality are ignoring the limitations of equivalence. Those that say it’s bunkum are ignoring how well it works if you use it within its limits.
What are the limits of equivalence? You need the following to all be true:
- Same resolution in pixels across all formats compared.
- Full well capacities the same in all formats compared.
- Same color filter array (CFA) performance across formats
- Ideal lens designs only.
In the real world, usually none of those things precisely apply. Let’s look at how they affect the findings of equivalence.
A state of the art MFT sensor is 20 MP. The current generation of CMOS BSI 645-ish sensors are 150 MP. The almost-order-of-magnitude difference in pixel count means there’s about a three to one difference in resolution. If you print at all large, that’s a huge advantage to the larger format. Even the difference between MFT and the highest-res FF sensors, which are running around 60 MP, is significant.
Could we build 150 MP MFT sensors? Sure, we could; it might even be easier than making the sensor in the IQ4 150 MP. But could any manufacturer sell that sensor profitably? I doubt it. It wouldn’t have anywhere near the dynamic range of the big sensor – see #2 above – and there would be issues with the current crop of MFT lenses. They’d have to charge near-Phase-One prices for the cameras, and almost all of the target group of customers would opt for the real thing.
Given a design and a wafer-processing technology, the number of electrons that can be stored at a photosite is mainly a function of the area of that photosite. That sets the limit on the highlight detail that can be retained. The low limit is set by the read noise, which is not a strong function of pixel pitch. The dynamic range is related to the ratio of the two, with a few other factors thrown in depending on the particular flavor of DR we’re talking about. But in general, as you make the sensor smaller and keep the pixel count the same, you lower the FWC drastically, and give the shadow noise a gentle nudge southward. The result is that the DR of the smaller sensor is lower than that of the larger one. If the sensor sizes aren’t that different, the loss of DR in making the sensor smaller isn’t too great. If the gap between the sizes is a chasm, so is the DR hit for the smaller sensor.
Now that we’ve mostly made the transition to back-side-illumination (BSI), it’s not as important as it used to be, but it used to be that the dirty secret of some sensors was that, with some lenses well away from the lens axis, the light could come through one CFA dye and land on the photosite that was under a different CFA dye. That meant that the color information was contaminated and would be decoded improperly. This is called CFA crosstalk, and gets worse as the pitch gets finer, because an offset of, say, 1 micrometer (um) is only 15% of the pitch of a 6 um pitch sensor, but 45% of the pitch of a 2 um sensor. You can make the CFAs thinner as the sensor pitch drops, but it’s not possible to make it proportional. I vaguely remember that there’s also something similar going on with microlenses.
As the format gets larger, the f-stop required for the same depth of field (DOF) and diffraction gets narrower. When you’re considering ideal lenses, that doesn’t make any difference. But in the real world, it’s a heck of a lot easier to design and manufacture a great f/4 lens than a great f/1.4 lens. Decreasing the aperture just makes everything easier.
- Off-axis bokeh can be better because the size of the ray bundle is decreased.
- Vignetting is less of an issue.
- The behavior on the transition from in to out of focus is more ideal.
- Off-axis aberrations are decreased.
If you take a lens of the same design and scale it up from one format to another twice the linear dimensions, the length of the lens will double, and its volume and weight will go up by a factor of eight. But if it can be two stops slower, and equivalence says it can, it may be just as long, but it will be a whole lot lighter.
And there’s yet another benefit; the lens can be simpler – a lot of the complexity of fast lens designs is there to deal with issues that wouldn’t be significant at all if the lens were slower.
Are you with me? Equivalence is fine as far as it goes, but there are practicalities that mean that the constraints of the theory don’t apply to all aspects of the universe in which we happen to live.
So far, we’ve been talking only of the technical challenges of camera and lens design and manufacture. But business rears its ugly — ugly only to the person who wants to be able to model everything — head.
Designing for the market
When your cameras cost a bundle, you design lenses that are not as constrained by manufacturing cost (cogs) as they would be if most of your sales came from Best Buy. So, even if the designs had to be as complicated as those for smaller formats, the companies making lenses for the big ones would be shooting higher. Couple that with the fact that the slow lenses needed for bigger formats are better inherently and easier to design, and you’ve got a recipe for the lenses getting better as the format gets bigger.
Price and volume
There’s another effect that runs in the same direction as the one immediately above as you go from MFT to APS-C to FF but reverses course above that. High volume makes lenses cheaper on a per-lens basis, and having a big market means that lens designers can cater to niches within that market. Put those two together and you’re going to see a lot of time and effort being spent on the high-end full-frame market. This isn’t enough to counteract the advantages of medium format lenses, but it’s a countervailing tendency.
There are those who want to future-proof their work, but most of us make images with one or more uses in mind. Over the last 30 years, we’ve seen the image quality from any give format size increase dramatically, to the point where a format a couple of sizes down from another can easily produce images that outshine what its big brother could have done some time ago. But, 4K displays – and 8K coming soon – to the contrary, our needs for image quality are not growing nearly as fast as the cameras themselves are advancing. Trees don’t grow to the sky. Although they are increasingly technically possible, the likelihood of digital 6×9 cm, 4×5 inch, and 8×10 inch area-capture formats in mass production is vanishingly small*. Indeed, the question is whether, five or six years hence, any new cameras larger than 33×44 mm will be shipping in other than boutique quantities. As time goes by, 33×44 will be in danger.
Formats and perspective
For the purposes of this discussion, let’s define perspective as the arrangement, location, orientation, and size of three-dimensional objects captured by a camera that represents the scene in two dimensions. Let’s limit ourselves to rectilinear lenses. Most camera lenses strive for, and usually come quite close to, rectilinear reproduction. Fisheye lenses are a notable exception, as are the anamorphic lenses used with some motion-picture cameras.** With that definition limitation, perspective is determined by camera location (to be precise, the location of the entrance node of the lens) and the field of view, not by format.
There are people who will tell you that medium format renders perspective differently from full frame cropped to 4:3. There are people who will tell you that the earth is flat. There are people who say that MF compresses space more than smaller formats. There are people who say that Stanley Kubrick filmed Neil Armstrong’s first lunar steps on a set in Borehamwood, England.
The illusion of depth
Photographs are flat. Absent trickery such as that used for stereo imagery (goggles, glasses, prisms, etc), they look flat for the most part. Yet there is sometimes a three-dimensional quality to them, where some objects seem to be in front of others, and subjects stand out strikingly from backgrounds. This is sometimes called “3D pop” and is prized by many. The effect is the result of many things beside perspective: color relationships (like chromostereopsis), the brain’s exaggeration of vertical distance, texture gradients, depth of field, elevation, and the like. When these all work in consonance, the illusion is more powerful. When they offer opposite clues, it is weak or non-existent.
One to the depth-cue generators is the nature of the transition from in-focus to out-of-focus parts of the image. The details of this transition are a function of the particular lens design under consideration. The behavior is quite complicated. It is not too hard – especially for cameras with automatic focus bracketing – to examine this transition with a point-source target. It is next to impossible – at least for me – to look at such a sequence of images and come to conclusions about what they say about the likelihood of 3D pop with any given lens. It has been my experience that relatively simple lens designs are better at creating the effect than the staggeringly complex ones that we’re seeing more and more of these days. Leica aficionados say that Leica lenses are unique in consistently delivering this quality. That has not been my experience, but I do have one Leica lens, the 90/2 Apo Summicron M ASPH, that sometimes seems to produce it.
The MF look
In some circles – and the fact that I’m so acutely aware of this, Lord help me, is an indication that I need to get out more – there are currently fervid conversations (I’m being generous with that noun) about the presence or absence of something called the “MF look”. This look, like the “Zeiss look” or the “Leica look”, is not precisely defined, and its source not nailed down, but my personal belief is that there is a signal buried underneath all that noise, even though the SNR is well under one. I think that a part of the look stems from better off-axis performance of MF lenses, which occurs for the reasons described above: they’re slower and they’re better. A big part of it probably comes from the way that MF lenses handle the transition from in to out of focus: they are by and large simpler, have lower high-order aberrations that come from correction of low-order ones. Another part of it is a result that the photographers who use MF are as a group more accomplished than those using smaller formats. Even if they aren’t consciously juggling depth-cue generators to get them all pointed in the same direction, some of them have enough experience that they may be able to make it happen at will.
MF is not unique in having a look. We’ve all seen videos made with small-sensor cameras and noted the generally unappealing lack of subject separation that occurs because they don’t have lenses that are fast enough (consider that to emulate the look of an f/2 lens on a Super 35 sensor with a 1/3 inch sensor (6 mm diagonal), you’d need a lens faster than f/0.5, which is impossible with refractive optics).
Netting it out
- For IQ, size matters, and bigger is better
- But bigger is heavier and more expensive, too – and therefore less popular – and niche markets aren’t where you’re likely to find price/performance stars.
- Once an image is good enough for its intended use, there is little point in making it better, especially if doing so involves large amounts of cash and great inconvenience.
- There is no magic.
*There are already A-size and B-size line-capture cameras readily available at low prices. They are optimized for macrophotography. We usually call them scanners.
**Have you ever look at out-of-focus background point sources in movies made with anamorphic lenses? Weird.
I agree with pretty much everything you wrote.
One thing I wish were tested/understood more is the global contrast of a lens. There are tests of flare, but MTF tests are as I understand it normalized to the global contrast.
You pointed out that larger format lenses can achieve the same performance with fewer elements due to the smaller relative aperture. Perhaps this results in higher contrast?
Is this a general pattern among the top-performing lenses?
As I understand it, manufacturers put their best coatings on the mega-element-count lenses, but what if they put them on something like a 4-group or 5-group lens for a medium format cameras? Or a Tessar? (my Contax 45 Tessar has pretty poor coatings and exhibits a surprising amount of flare)
I don’t know why manufacturers of high-end lenses would be parsimonious in allocating their best coatings. First off, if the lens has relatively few elements, there are similarly few surfaces that need coating. Second, I don’t think that a low element count is necessarily the cheapest way to design a lens — look at Leica. It is true that fewer surfaces means less reflection and therefore less need for exotic coatings, so maybe there is truth to what you’re saying. I don’t really know. I do know that Zeiss said that they used their best coatings on their V-series ‘blad lenses when they were marketing the heck out of the T* technology, and those weren’t all high element count lenses.
I think global contrast was a big deal in the film era, but I think it’s less important now that we can put the white and black points wherever we want them.
Erik Kaffehr says
I would mostly agree, with a few points to make.
1) It seems that lens design are getting more complex these days. Gone are the simple double Gauss designs in both 24×36 and small medium format.
2) 24×36 lenses are also getting pretty expensive.
3) I don’t see the connection between off axis performance and the 3D effect.
I would also mention that my Hasselblad T* lenses are quite to flare, sort of indicating that newer technology may produce better results.
“3) I don’t see the connection between off axis performance and the 3D effect.”
Did I claim such a connection?
Erik Kaffehr says
Mea culpa! I was thinking about the 3D effect, but your writing was about the MF look. Sorry!
What I may ask is also: “What constitutes a look?”
In my book a look may be something that sets an image apart. So, if you have say ten pictures, of which five are shot with MFD, it would be possible to pick those five when the images are displayed side by side.
My experience shooting MFD (Hasselblad V) and Sony is that it is not really the case on processed images. On unprocessed images the aspect ratio is a perfect giveaway, of course.
Very clearly, I think that in many cases there will be an advantage of images shot on GFX 50 compared to say Sony A7r#, but that may be more related to the GFX lenses vs. the Sony lenses than GFX being MFD.
On the other hand, the point you make that it is easier to make f/2 or f/2.8 lenses of high quality than f/1.4 lenses is very valid.
Excellent article, BTW!
I’ve always believed the “MF look” is a holdover from film days where the only way to capture such high detail was to use MF. You could also capture it using LF cameras, but I’m sure MF was more common or accessible, or more closely associated with those subjects with an audience that might be interested in replicating a “MF look.”
R Cone says
Thank you for your interesting summary.
Yes, linear “perspective is determined by camera location (to be precise, the location of the entrance node of the lens)” as you note.
No, it is not determined by “the field of view.”
This is illustrated elegantly in Jacobson, Ray, & Attridge, The Manual of Photography on p 46 in 8th Ed., pp 57-60 in 9th Ed. adding Axford to author list.
You’re right, with the conventional mathematical definition of perspective. But my definition included the location of objects in the image.
Gerd Peters says
I really enjoyed your article. Thank you for writing ….
Nat Young says
An interesting read. However, I do have a quibble about the section on Dynamic Range. Conventionally, we compare DR at its maximum (which varies from camera to camera, but is often at the same ISO setting for different formats) or specifically at the same ISO setting (in which case the larger sensor camera’s image is made with more light, and is likely to have more DR for the reasons you give).
On the other hand, this is dealing with ‘unequivalent’ settings, where the larger sensor receives more light. When a smaller and larger sensor camera are at equivalent settings, the smaller sensor camera will be made with the same amount of light (in the normal case, at a lower ISO setting). That means that smaller sensor cameras often have the same DR as larger sensor cameras at equivalent settings.
Yes, indeed. Equivalence works fine as long as you stay in the area where it applies.
Dan Wells says
Equivalent images often require impractical settings… I often shoot my Z7 at ISO 64, with an f4 lens around f4 – f5.6. Yes, a 46 MP Micro 43 camera with an f2-f2.8 lens of half the focal length is equivalent – at ISO 16!
Practically, any existing Micro 43 camera is far inferior for that particular image (a high detail landscape) – I’d rather have 46 MP than 20 or fewer, and no existing Micro 43 camera is >20 MP, plus I’m shooting ISO 64 while the smaller sensor not only won’t let me get to the ISO 16 I’d need for equivalence, it’s stuck at ISO 200 (or occasionally 100).
Of course, for a sports image, give me the E-M1 mk II over a much slower Z7…
There are a number of hardware capabilities that influence practical image-making (in no particular order)…
1..) How are you going to display/print it? A 4K display is only 8 MP, the highest resolution common computer monitor (the Retina iMac) is 14 MP, and 8K TVs are around 33 MP (due to aspect ratio, it takes a 40+ MP camera to get enough pixels on the long axis).
For printing, my Z7 makes extremely sharp prints (even viewed closely) up to 24×36″ (and likely beyond, but my printer is a 24″ Canon Pro-2000 – I’ve printed a cropped 24×48″ with excellent results, which would have been 32×48″ without the crop ). I was surprised at how big a difference the 46 MP made over a 24 MP camera. Anything with more resolution would need a 44″ printer (and a big display space) to show it off. 44″ printers are huge beasts, and that may be more of a barrier than building a higher resolving camera.
2.) Lenses. It’s possible to build a great lens for any format… Olympus PRO, Fujinon X, Nikon, Sony and Canon 24×36, Fujinon GFX, Schneider for Phase… On the other hand, some systems tend to have lenses that don’t do the sensors justice.
Only Fuji makes a full line of excellent APS-C lenses. Nikon, Sony and Canon all have a couple of really nice lenses, but, beyond that you either use FF lenses (and lose the size/weight advantage, which is really in the lenses) OR accept low-quality lenses made for $400 cameras.
The Fuji X-T2 shares a sensor with the Nikon D3300, but the Fujinon 18-55 f2.8-4 is a beauty while the Nikkor 18-55 f3.5-5.6 is made from the bottom of a Coke bottle (as are all $100 kit zooms – the little Sony collapsing lens doesn’t even bother using glass Coke bottles).
Micro 43 has some junk lenses, but they also have some real gems, especially the Olympus PRO line…
All the full-frame lineups have some excellent lenses – some years ago, Sony was weaker, but the G-Masters and some others are great. Nikon deserves some kudos for the size/quality of the Z lenses – they tend to have modest apertures, but they look and carry more like APS-C lenses than FF lenses as sharp as they are (now how about a 70-300mm PF to go with them?).
Nobody bothers to make a weak lens for medium format (unless it’s something deliberate like a Lensbaby)!
3.) Sensor generation. Right now, everything but Micro 43 is on the same sensor generation , with the Sony A9 arguably a generation ahead with its stacked sensor. The newest APS-C sensor (presently just the X-T3?), the 100 MP 33x44mm sensor and the 150 MP Phase One sensor are actually exactly the same pixel size in different sensor size slices – they may very well be the same pixels. The 24 MP and 40+ MP Sony FF sensors (which includes Nikon and others using Sony sensors) are very similar technology, but with different pixel sizes.
Micro 43 is a major generation behind right now – the 20 MP sensor is from 2016, and isn’t BSI – some cameras use the even older (2012?) 16 MP sensor.
The old 50 MP small medium format sensor is also a generation behind, but it compensates with size…
If I were making higher-end bodies around any sensor size other than 24x36mm, I’d have at least some concerns about sensor supply, even though most sizes look good right now.
Micro 43 has always had trouble getting sensors, except when the 16 MP sensor was new (it was a similar generation to then-current APS-C sensors).
APS-C is a very popular size, and there will continue to be sensors for the foreseeable future – except that Fuji wants high-end sensors to go with nice bodies and lenses, and everybody else is using it mainly for $400 cameras and is extremely price-conscious. Will there continue to be innovative sensors for Fuji, or will Sony insist that their $1200 cameras share sensors with other makers’ $400 models (sensors that may not get features as quickly)?
24x36mm shouldn’t be a problem – everybody’s moving toward the upper end of the camera market, and this seems to be the size the upper end has settled on.
Sony has presently decided to supply niche markets like 33x44mm (and even the tiny market for even larger sensors) with current sensors – but this could change. For years, the only big sensors available were CCDs, many years behind in image quality above base ISO (they were spectacular at their very low base ISOs, but degraded very quickly as ISO rose). The 50 MP CMOS sensor also hung around for a very long time, and is still by far the most affordable sensor above 24x36mm.
4.) Ability to get the shot. The best sensor and lens in the world don’t do any good if they can’t get to where the image is, and they can’t focus on the subject. The Z7 is a nearly revolutionary camera for the particular sort of photography I do, because it’s a LOT of image quality in a compact, rugged package (the A7r series have the image quality, but not the sealing). I shoot landscape on very long hikes – my relatively new Z7 has already done a 15 mile day, while I took an X-T2 450 miles on the Pacific Crest Trail… I could find even higher image quality, but I couldn’t carry it (has anyone ever backpacked with a Phase?)
On the other hand, if I shot sports, I’d far rather give up all those pixels for an E-M1 mk II’s focus system and long lenses.
Chuck Davis says
Great article, Jim — I really enjoyed it. Just a brief comment here regarding your observation regarding anamorphic cinematography lenses. I agree — there is something amazing (some may say odd or unnatural or downright magical) about anamorphic bokeh and lens flare and I think the biggest factor here is that anamorphic lenses have two focal lengths, so each lens has a vertical focal length and a horizontal focal length— and the two variables render two different depths of field which has always seemed unnatural to me, albeit it can be very aesthetically powerful. Here is a link to an interesting article (from Cooke Optics) that addresses this phenomenon pretty well, I think:
As an underwater cinematographer, I know shooting in-water with anamorphic lenses can be a challenge, vs. spherical lenses, and that is one of the reasons the Super 35mm cine process became popular (i.e., the technique of shooting wide screen 2.35:1 with a spherical lens, on a cropped four-perf pull down 35mm negative — using the full width of the negative, but not the height), with a full-aperture cine frame with the same aspect ratio of the “projected” anamorphic format — but that is a whole other conversation for another time! The thing is, though — the Super 35 cine elements when edited in with anamorphic elements seem seamless at first, but they do indeed have a different “feel and look” IMHO, which you spoke of — but it works for the movies!
Excellent article, Jim. I learned a lot new from this, and I will also use this as one of my reference articles (when I talk to people).
I don’t think this conversation is ever going to die. It’s like Sony vs. Canon vs. Nikon, which never dies despite all of them producing excellent 35mm digital cameras.
But, now I gotta get into film medium format to experience it. I use film 35mm often, and it’s good.