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10-15-2010, 07:43 AM   #1
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Why are camera sensors still rectangular?

Just wondering, as our lenses seem to be staying round (outside the compact category), why our camera bodies still use such a small fraction of the imaging circle.

I know packing the shapes on a circular platter will reduce production efficiency, but imagine a sensor that is cross shaped; a 3:2 rectangle overlayed on a 2:3 rectangle, possibly with the outside corners connected to make a octagon. Now you go from landscape to portrait with the flick of a switch, touch of a button, or even in post! Well not for the average user, it seems like the added cost would be offset for the high-end crowd; they'd no longer need a vertical grip or an L-plate.

Also, as I understand it, the outer edges of the sensor are occupied by processing elements (at least on CCDs) If you could move these into the triangles that turn the cross into an octagon, you could still reduce the maximum dimension of the sensor.

Just food for thought.

EDIT:
Please note that below I make the switch to proposing a bigger, 24mm square sensor, as it really probably make more sense than any exotic shape.

Also, while we're breaking conventions, how about adding a hole for an anti-twist pin like those found on camcorders. It'd greatly simplify our support purchases, leaving more money to spend on the products the camera manufacturers provide.



Last edited by m88k; 10-15-2010 at 01:13 PM. Reason: added updates to streamline further responses and propose another change
10-15-2010, 08:24 AM   #2
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Interesting. The only problem with that is that there would be no legacy "Full Frame" film version of it, so people wouldn't be able to complain about not having a FF version of the new sensor.
10-15-2010, 09:25 AM   #3
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I've been wondering the same thing for a while, and I bet part of the reason is the SLR form-factor itself. Currently, everything from the chassis, shutter, mirror, prism, viewfinder, finder screen, etc., is optimized for that rectangular image. Of course, APS-C and 4/3 sensors are smaller, but they achieve it by simply reducing the size of everything by a certain factor.

Think what would happen when they have to suddenly allow for a square sensor (which is really what you're proposing). Everything has to be redesigned to be a square. Square mirror, square prism, square focus screen, square shutter, square corridor. The biggest problem is, obviously, going to be the mirror, since by increasing the depth by 1.5x (assuming the rectangle ratio is 2:3), you will have to increase depth of the camera body, hence increasing the minimum distance between the mount and the sensor plane, which is equal to the flange focal distance. Suddenly, none of your lenses will focus to infinity any more. You have to redesign all your lenses.

An EVIL camera will be without most of these problems. I think that such a sensor that makes more sense in the digital age has *some* chance of showing up during this transition to EVIL. But not as long as we're doing it the SLR way.
10-15-2010, 10:42 AM   #4
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being square

Parallax, I don't quite see the issue you're putting forth. Are you just saying the FF purists will whine that it's not traditional? The square sensor I move to below would, I imagine, make the FF enthusiasts happier than they are with aps-c; you're gaining sensor size, and at least SOME advantage to carrying 35mm lenses.

Rawhead, you replied while I was typing this up, and discussing going square. You're right, it would require a bigger focusing screen, mirror, and prism. You'd also likely need to increase the size of the shutter. However, you're incorrect on the requirement of changing the registration distance. A square based off the aps-c width would have a height of approximately 24mm (less in practice) This actually puts it at the same height as the 35mm film bodies, but with the same 2/3s of the width that aps-c cameras already produce. Pentax, along with Nikon, Canon, and Sony/Minolta, has kept the same registration distance from the 35mm days, so Olympus and Sigma are the only two I can imagine not being capable of this. Though is it Canon where the aps-c lenses break FF mirrors? Anyway, for the purpose of this forum (pentax), registration distance is a non-issue.

Body size will increase, but probably not enough to offset the bulk removed in accessories. While you're at it, drop the onboard flash to compensate a bit; most buyers will probably barely miss it.



Well, I was thinking about this instead of chiral and achiral molecules during class, and tried to do some quick calculations for the number of shapes that would fit on a 200mm wafer. (Standard for CMOS imager production according to DALSA) Unfortunately, rectangle packing is a hell of a lot more complicated than I initially thought (or didn't think).

Anyway, If your goal is to produce a sensor capable of both the 3:2 and 2:3 formats, the simplest shape would be a 1:1 square sensor with side length of the longer side of the base imager, approximately 24mm in this case. A square with side length equal to the long side of a 3:2 rectangle is going to have 50% more area than the rectangle.
For simplicities sake, we'll go ahead and assume that area=cost. Technically speaking, with increasing area, cost increases in jumps; according to the great wiki, aps-h is about as big as you can go without making a huge jump in cost, with 28.7x19mm dimensions, totaling 548mm^2 area it's only slightly smaller than the 23.6mm square based off of aps-c, which would have a total area of 556.96mm^2. So I would imagine that this sensor could be produced without making the leap to the multi-mask methods that make FF sensors so extraordinarily expensive.

Unfortunately, I've got no clue what the cost breakdown of a modern dslr is, so I can't really continue with a good estimate of the added cost. However, the rise of the bottom end dslr market, where users seem more apt to replace bodies than collect lenses, would suggest that the manufacturers are no longer pulling most of their profit from lenses as was rumored in the past. In other words; dslrs are cheaper to produce than we think, and the cost has little bearing on what we pay for them.
I'd call this camera a win if it could be made for less than 400 USD more than the K-5, seeing as it eliminates the vertical grip and L-plate, the two of which come to a similar sum. Admittedly, I've never used a vertical grip or an L-plate, but I'd imagine the plate interferes with using the grip comfortably, whereas you'd never need to remove the plate from the proposed body.

Ok, so our square sensor will produce some major vignetting on in the corners with dedicated aps-c lenses. However, you'll still get at least 3:2 formats perfectly, and it'd be an excuse to start selling higher priced FF lenses again. Pentax may not view this as an advantage, seeing as they're currently selling aps-c lenses at FF prices. But with lenses with a big enough image circle, you'd have the option of a square output with oh so many more crop options. It'd also make it possible to get 8x10's of subjects that just barely fit in the frame, something that's been annoying me lately.


Last edited by m88k; 10-15-2010 at 10:47 AM. Reason: fixed indents
10-15-2010, 10:48 AM   #5
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QuoteOriginally posted by m88k Quote
Parallax, I don't quite see the issue you're putting forth. Are you just saying the FF purists will whine that it's not traditional? ...........
Something like that.
10-15-2010, 11:27 AM   #6
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CMOS sensor silicon wafer:

10-15-2010, 11:55 AM   #7
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Sensors are still rectangular because people still insist on pictures being rectangular.

10-15-2010, 12:19 PM   #8
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Fascinating picture Jogiba, I find it interesting that they pack in several sizes of sensor on a plate, but the layout doesn't seem to be focused on optimized yield. Maybe it makes more sense to be able to cut straight lines rather than packing them in and requiring jigsaw cutting patterns. It also seems wasteful to etch those outer sensors running off the edge of the wafer...

Wheatfield, I think you missed the point of the post. I'm not looking for circular or interesting polygon based photos. I'm suggesting a sensor that would allow the camera to grab both portrait and landscape photos while held in the standard position. Specifically, a 24mm square sensor, which would get the most out of aps-c lenses and gain some benefits from full frame lenses, which are still quite common among pentax users.
10-15-2010, 12:27 PM   #9
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There were medium format film cameras that shot a square photo. I think this is mostly tradition. It's easy enough to crop a digital image to a square. If sensors were square, there would be a thread about why they aren't rectangular.
10-15-2010, 01:12 PM   #10
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Again, part of the point is getting missed. The idea is a BIGGER square sensor would maximize use of aps-c lenses and add functionality for 35mm lenses, while, in theory, not significantly changing the body cost, particularly when you remove the accessories it would eliminate.

I know my second post was massive, but the biggest point was a 24mm square sensor would be offer the same area as an APS-H sensor, which is allegedly the biggest you can go while maintaining the cost structure of APS-C production.
10-15-2010, 01:48 PM   #11
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QuoteOriginally posted by m88k Quote
The idea is a BIGGER square sensor would maximize use of aps-c lenses and add functionality for 35mm lenses, while, in theory, not significantly changing the body cost...
Well, i think the problem is mirror box redesign BUT. Since APS-C is 24x16 and FF is 36x24, you could simply use FF mirror box. Just narrow it down a bit. This means no need to change flange distance.

QuoteOriginally posted by m88k Quote
...particularly when you remove the accessories it would eliminate.
Only from user POV.
Manufacturer is not interested in dropping very useful and required accessories (almost guaranteed additional sales with every dslr). What economical sense makes investing money in complex, non standard camera and chip design and dropping some income sources.
I don't think such custom design would cost less than a grip. And there would not be huge additional sales just for this feature.

Btw, with cross or octagonal shaped sensor you will get in readout problems. Normal column/row structure would loose it efficiency. Rows/columns near the corners would have to work as output shift registers etc. With CMOS, how would you wire addressing for such sensor? Wouldn't this introduce uneven and hard to deal with noise characteristics? Uneven readout speed for video?

Many many problems, but very limited usefulness.
10-15-2010, 03:28 PM   #12
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Ah... the 5D MK2 currently being my only DSLR, I wasn't thinking about strictly with APS-C cameras.

And I think I have the answer there. If we're talking strictly about APS-C cameras, then we're talking about a complete redesign of everything, and using a sensor that is 67% of the size of FF (instead of 44% for APS-C), everything is gonna add up (R&D as well as actual manufacture) that by the end, you're going to have a camera that is just as expensive as a FF cam.

Then, the question becomes, will people be willing to shell out that much money for the absolute best APS-C system possible, when the alternative is to have a FF camera? I think that would be an even smaller niche.

Again, I think the only timing that such a radical paradigm shift could occur is with the development of a completely new system: mount, flange, lenses, body.

For example, people have pointed out that Sony's Emount is large enough to accommodate an FF sensor/lenses. One possibility is that they're thinking about a FF sensor NEX PRO. Another possibility may be they're thinking about a square sensor. But I just don't think it's a viable thing to pursue with an SLR.
10-15-2010, 07:00 PM   #13
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Theoretically speaking though, the 24mm square ought to avoid the exorbitant increase in costs when producing larger sensors.

The rest of this post kinda goes off topic, just giving fair warning here.

Realistically speaking, I question how much of the price of our cameras is in the sensor, especially considering the price difference between top end p&s models and bottom end dslrs. Or how about the fact EVILs are all more expensive still than the bottom model SLR kits? The camera market is at best an oligopoly, and outside mass market cameras, is relatively uncompetitive price wise.

Quick example I believe demonstrates that the camera manufacturers get us to pay for more innovations/ R&D than we receive; Olympus 4/3 format 300mm f 2.8 vs the Canon 300mm f2.8 IS. Despite the FAR smaller image circle the Olympus cameras require, the Olympus lens weighs in at an extra 740g over the Canon according to manufacturer specs.
10-15-2010, 09:59 PM   #14
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look at around 42 secs... i think this is kinda doing what you talk about... sorta... I understand the difference... but thoughts?
10-20-2010, 01:02 AM   #15
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Jord, the Mamiya system actually gave me the idea. However, I'd imagine as long as you're still in the APS-C sensor price range, a square sensor is likely cheaper than a rotatable one.

I just found proof, I'm not the first guy to think this is a good idea. DPreview's pentax forums had some lunatic suggest this square format would be Pentax's big release at PMA 2009. Several of the responders also liked the idea of a square format.

As far as removing accessory profits, the grip is the only accessory Pentax makes that would be effected. And I'd be willing to bet they could still sell a battery grip to a lot of the regular grip buyers, seeing as the camera wouldn't feel right to them without it. However, if such a format was offered and took off, it'd be the third party accessories that'd take the real hit. No more need for rotating flash brackets, L-Brackets, nodal systems that put the camera on it's side, camera rotators, and whatever other portrait format accessories I'm missing. These third party accessories consume photographic gear budgets that might otherwise be pointed at more first party toys, like bodies, flashes, and lenses. Added bonus to Pentax; they can sell new square flashes, without third party manufacturers to compete with.

Manufacturing costs; I can't speak for Pentax, but Canon, in their 2009 whitepaper on full frame sensors, claims that all costs are trivial compared to the sensor. According to the paper, the increase in mechanical component sizes does little to change pricing between Canon's APS-C (smaller than their Pentax cousins) cameras and they're FF models. Even more interestingly, the R&D costs are identical. To quote; "Research, development, manufacturing and distribution costs are all independent of camera size, so a smaller camera will not cost appreciably less than a larger one for any of these reasons."

The cost ought to be similar to APS-H sensors, seeing as the size is the same. The sensor doesn't have any truly special specifications other than the somewhat unique shape, so there shouldn't be any R&D, just a custom redesign. The real issue is probably that the manufacturers are afraid we won't embrace the format and they'll get stuck with a load of cameras they can't sell at a profit. However, a square sensor, pentaprism camera built to compliment the k7/k5 would definitely be the camera that convinced me to make my k100d a bag-dweller. A nice, round 16MP would be plenty for my tastes, all I need is a manufacture daring enough to make it. (Hopefully Pentax, unless some third party wants to start making K-mount dSLRs :-D)
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