Road Train !!!!!!!!!!

by Russell McMahon

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People keep inventing different form factors and formats for cameras, but none seems to have hit on what seems (to me) like an obvious one. Why doesn't somebody build a camera with a sensor that has a 4x5 aspect ratio, but the diagonal size of the sensor the same as an APS-C and/or full-frame (35mm) sensor (and a mount compatible with their existing lens line)?

Maintaining the same diagonal size means this would remain compatible with (most?) existing lenses for the same mount. Since typical use would no longer involve cropping, a sensor with exactly the same number of sensels (and therefore, the same pitch/density/well size) as a current one would still have higher usable resolution.

Just FWIW, the sensor sizes seem to work out to around 18x23mm to work with APS-C lenses, and 27x34mm to work with full-frame lenses. Does anybody see a major downside to this idea?

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why not 1x1 aspect ratio then? –  asalamon74 Feb 3 '11 at 15:29
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Because most frames, albums, etc., are 4x5, 8x10, etc. Hassleblad has been pushing square format for decades, but I've never found most arguments for it (or pictures taken with it) particularly compelling. –  Jerry Coffin Feb 3 '11 at 15:35
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@Jerry - The MOST common printing and photo album format is actually 4x6, which corresponds to exactly the format of most DSLRs. Those who use 4/3 or m4/3 cameras (4:3 aspect) have to crop or letter-box their images to fit those. –  Itai Feb 3 '11 at 15:57
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We have circular lenses... we should just move to circular sensors and be done with it. ;-) –  Craig Walker Feb 3 '11 at 17:11
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@Craig: circular probably isn't very practical -- although it makes maximum use of the lens, it would waste lots of space on the wafer when being fabricated. –  Jerry Coffin Feb 3 '11 at 17:28

7 Answers 7

up vote 22 down vote accepted

The mirror has to be a lot bigger for 4x5, particularly at 90 degrees to the axis the mirror flips about. The shutter also gets bigger in the direction it has to move (there's a reason the shutter moves up and down not left to right). This means a slower moving mirror and shutter.

Another consequence of the bigger mirror is the lens mount has to be further away (greater registration distance), which gives you less space for the rear element and so you have to use a retrofocus design for normal lenses. You would also break compatibility with current lenses - despite the fact that the image circle is big enough, the mirror would hit the rear element!

Squarer formats are more common in medium and large format photography where more time is taken over a shot so a slow mirror/shutter can be tolerated (many use leaf shutters anyway) but anywhere where speed dominates, such as sports smaller and more elongated formats allow a little extra speed.

Another area where you tend to find 4:3 sensors is in compacts where you have no mirror to move. The only mass market 4:3 DSLR I can think of were the Olympus 43rds, and they're moving away from having mirrors...

Look at the full frame Canon 5D, it has a slower max shooting rate and a slower sync speed (a measure of how fast the shutter curtains move) than the equivalent APS-c model. Although Nikon have a high speed FF camera, it's extremely expensive, and I bet it would go faster with a smaller mirror.

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The 5D is slow, but the 1ds.III isn't. Nobody's really pushing the limits of shutter design anymore though -- the Minolta 9xi did 1/12000th max and 1/350th x-sync in 1992 (on full frame). This also only really affects the FF version -- the mirror and shutter for the APS-ish one are still smaller than a current full-frame version. –  Jerry Coffin Feb 3 '11 at 17:24
    
The mirror size increase would be ~4mm for the full screen version. There have been horizontal shutters too (old Leicas) -- though, of course, their maximum speed was quite low. –  Jerry Coffin Feb 3 '11 at 17:58
    
The speed issue clearly isn't insurmountable, but at 5:4 APS-c camera would lose compatibility with APS-c only lenses (such as Canons EF-s) meaning you'd be selling a FF camera with a narrower sensor. At which point you might as well get FF sensor and crop... –  Matt Grum Feb 3 '11 at 17:59
    
@Matt Grum: I don't see it losing compatibility with (at least most) APS-C lenses. Sony certainly supports mounting APS-C only lenses on their FF bodies. It crops to APS size, but the mirror still works fine. They do use a more complex mirror mechanism than others, but I'm not at all sure it'd be necessary for this small a change. –  Jerry Coffin Feb 3 '11 at 18:18
    
@Jerry You'd be fine with Nikon, Sony etc. but not Canon, M43. Still it's not really a 5:4 oversize APS-c it's more like a FF with the sides chopped off... A 5:4 FF sensor would be worth it, but then you'd fall into lens incompatibility again with all manufacturers. –  Matt Grum Feb 3 '11 at 19:12

I think, basically, there's not enough of a difference. These give you about 12% greater height in exchange for about 5% in the other direction. That's not worth the risk of putting something "weird" into the market.

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To address the OP's question about why these other aspect ratios not used in the small format line of cameras, all I can say is that they tried that already. There have been several attempts at squeezing more pictures on a roll of 35mm film over the years from your square format (24x24mm) to a slightly compressed frame (somewhere between a 4:3 and a 4:5). In all of these cases, the width of the film remained constant, as they were simply using the 35mm film.

For whatever reasons, those alternative formats just never took off like the ubiquitous 2:3 aspect ratio on almost every consumer and prosumer camera now. It really had little to do with the mirror mechanics or shutter design. That was a solved problem, since all they had to do was make it less wide. In fact, because it wasn't as wide they could probably support faster frame rates for burst mode.

About 60 years ago, they played around with the different aspect ratios. The negatives I inherited from my grandfather proves this as I have everything from 1:1 to 4:2 represented in 127 film (4cm wide). I wish I could point to the place in history where the common 2:3 format became the defacto standard. Now the big companies just don't want to repeat history and risk losing money on something that didn't work in the past.


The shape and proportion of the DSLR sensor format is legacy from 35mm film, which is also 3:2 format. There are medium format digital cameras which use a larger and different proportioned sensors. One example would be Hasselblad H4D-31 with a 4:3 sensor. Another would be Hasselblad 503CWD with a 1:1 sensor. In case you were wondering, the mirrors on the Hassy's are huge, and mirror slap can be a real problem.

Your treasured 4:5 perspective is the realm of large format photographers. There are digital scanner backs for your 4x5 view camera, and these things need a lot of light. It's not quite 4"x5" like the film you would normally use, but it is the same perspective.

On both medium and large format cameras, they use leaf shutters at the lens rather than the curtain shutters near the film you see in almost all (D)SLR cameras. The shear mass of moving a curtain 6cm (medium format) or 11in (really large format) doesn't make sense. The leaf shutters just have to cover the aperture of the lens which is smaller than your 24x36mm curtain in the back of your SLR.

For the folks who like trivia, Kodak's first consumer camera took circular pictures. Getting the pictures developed required sending the whole camera in, and they would develop the used film and replace it with a new roll. The format didn't catch on, as it was very difficult to use artistically. Besides, most paper is rectangular.

One of the advantages of a square format is that you can make it any format you want. You know you will be cropping and will shoot accordingly--but you won't ever have to tilt your camera. Since the square format is currently the realm of medium format shooters, that's a real bonus (those cameras are big).

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Focal plane shutters are certainly not unknown in either the medium or large-format worlds. 4x5 press cameras often used focal plane shutters (have you ever wondered why vintage race car pictures have tilted elliptical wheels?). Okay, you had to manually wind 'em up before you could use 'em, and the traverse time was about 1/20s, but they gave shorter exposures than the Copal #0 you'd have to use otherwise. The Pentax 67 (the "Texas Nikon") used a focal plane shutter, as did most 645-format film MFs. Often the ability to use one or two leaf shutter lenses with flash was a selling point. –  user2719 Mar 2 '12 at 22:14

Why doesn't somebody build a camera with a sensor that has a 4x5 aspect ratio, but the diagonal size of the sensor the same as an APS-C and/or full-frame (35mm) sensor

Because:

  1. It's cheaper to build one manufacturing line / format instead of two.
  2. Consumers generally expect things to match history / preexisting standards.

Because of the reduced sales from #2, the costs of #1 are usually not worth it unless there's a VERY good reason to switch.

So, even though there was no technical reason why digital sensors had to be a certain aspect ratio (at least not to my knowledge), they quickly settled on the 35mm film 3:2 standard, because that's what people were used to.

The existing sensor sizes and ratios are "good enough" so there's little incentive to build a new one.

The good news, when it comes to aspect ratio: today's DSLRs have so much resolution that you can crop the photo to whatever size you like. You don't have to wait for hardware to evolve to your liking; you can do it in software. You're wasting pixels, yes, but there's so many to lose that it's not worth worrying about.

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Canon have three DSLR formats and numerous compact and bridge formats so I don't think that's the problem, there are however compelling technical reasons to do with mirror size and registration distance. –  Matt Grum Feb 3 '11 at 15:51
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@Matt, Canon is a special case because they make their own sensors and even the least popular ones sell in great volumes, just because they're Canon. The other sensor makers concentrate on the ones that are a sure thing. –  Mark Ransom Feb 3 '11 at 20:47

On the presumption (I'm still pondering) of essentially agreeing with other answers here (the problems of splitting a line up, possible mirror issues, etc.), what I personally would love to see is a set of viewfinder overlays (similar to the focus-point squares already extant) that can be turned on and off, and show cropping guides - which perhaps even crop (in camera) the file for you. These guides could just be lines (a la what's in the viewfinder of a Mamiya RB67), or they could be black bands, a la letterboxing. You could then have guides for 4:5, 1:1, 11:14, 5:7, etc., with the only changes being viewfinder overlay hardware, and UI, crop, etc. software. You do lose the advantage of more imaging sites, but perhaps once this is implemented, they could do that too, and just make 2:3 an overlay.

Another possible concern: where do you then put all the readouts, if you go towards square? Currently, they take advantage of the space made available at the bottom of the frame. :)

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+1 for comment about the readout cells –  user1207217 May 1 '13 at 12:39

I don't know about the other DSLR's on the market, but my Olumpus E-5 has multiple formats ie: 4/3 16/9 3/2 6/6 5/4 7/6 6/5 7.5 and 3/4. In my opinion that is just about enough for everybody.

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I'm glad square format (or closer to square - 5:4) hasn't become mainstream because honestly it doesn't fit well with me as a human being with horizontally panoramic vision.

A square format sensor may be useful from an editing point of view, but I would still rather photos end up in 3:2 as it's ergonomic, you might say.

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Two thoughts on this answer: On the one hand, I think in ways it's a red herring - while it's quite easy to argue that human vision is oriented more towards wide than tall (based on the shape of our eyelids, eyebrows, etc.), our field of view is hardly a straight-edged rectangle, and anyway, that's irrelevant to an individual's aesthetic preferences for their own creations. On the other hand, I do think it makes sense to pay attention to human biological factors when considering standards for things like cameras, which will be used by many people in many circumstances, so... good to mention. –  lindes May 1 '13 at 22:45

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