dslr sensor aspect ratio

Discussion in 'Canon EOS' started by joe_piano, Apr 23, 2012.

  1. I'm posting this here but it really applies to all dslr full frame and apsc frame sensors.
    It's my understanding that when Leica first introduced the 35mm format it was based on the existing 35mm movie film stock. Hence, we have the 1:1.5 aspect ratio of the 35mm format. I've always found this format to be too wide for my personal taste and prefer the 1:1.25 of 4x5 film or the 1:1.17 of 6x7 film. These formats are both less wide than 35mm, and are formats that I prefer.
    The 35mm format has always been a little odd in that it doesn't match the standard aspect ratio of most stock printing papers which are available as 8x10, 8.5x11, 11x14, etc.all of which are less wide than 35mm but, since 35mm was designed to use the existing movie film stock size, it was a compromise we adapted to.
    My question is why 35mm digital sensors still use the same old 1:1.5 aspect ratio? There is no need to. A much more economical aspect ratio would be 1:1.25 to match stock printing paper sizes and, is also a ratio I find much more pleasing and workable than 1:1.5. My personal taste I admit.
    If 35mm sensors were about 33 x 26 they would have about the same surface area as the current 35mm size (36x24) and fit in the same image circle as existing 35mm lenses. It seems odd to me that the old format has been adopted to new technology when there is no reason to do so. Just wondering.
     
  2. Full frame lenses are made with a 43mm circle of coverage, which is the diagonal of the 24x36mm frame. You have to stay within that so it does put some limits on what you can do, though 33x26 may be possible (I haven't done the calculation).
    Also photographers had been shooting 35mm for 50 years or more when digital came in. They were used to the 35mm format. Olympus went with 4:3 rather than 3:2 for their cropped sensor forma and P&S uses 4:3. Why? I've no idea.
    24 x 36 wan't pre-ordained. They could have made it 24x24 or 24x30 or 24 x 40. There was no technical reason to chose 36mm wide. The only limit was on the 24mm width.
    24x36mm works. The old saying about not messing with something that isn't broken applies. Why should 33x26 be better than 24x36? Just because you like it doesn't count!
    I suppose you could pick a format that matched 8.5"x11" paper (1:1.3), but in Europe they use 8.3" x 11.7" paper, which is a 1:1.4 ratio. In neither the US nor Europe is the aspect ratio of standard paper formats fixed. You could equally well as why not make printing paper match the 3:2 ratio of standard 35mm?
     
  3. Any old format is still good if it gets the job done :)

    In defense of 1:1.5, it's closer to the "golden ratio" than the other ratios mentioned by you. As for printing, we can still
    print 4x6, 8x12, 16x24 without any cropping.

    35mm has a good solid history and support too
     
  4. Lenses are circular. To keep image quality at the edges, larger aspect ratios demand, for the same quality, unnaturally higher lens performance toward the edges that are further from the lens center. Might we not get better image quality at the edges of our frames if they were a square inscribed in the image circle of the lens? This ignores the paper size issue, but it would seem to make the best use of the lens.
     
  5. Mr. Smith,
    In re your question: "Might we not get better image quality at the edges of our frames if they were a square inscribed in the image circle of the lens?"
    No.
     
  6. Maybe the sensor ought to be round.
     
  7. My question is why 35mm digital sensors still use the same old 1:1.5 aspect ratio? There is no need to. A much more economical aspect ratio would be 1:1.25 to match stock printing paper sizes and, is also a ratio I find much more pleasing and workable than 1:1.5. My personal taste I admit.​
    I suspect there's more to it than the image circle and the sensor. An SLR is a very complex mechanical device. If they wanted to maintain the same lens mount system going from film to digital, that means the flange to sensor distance is a value that they can't deviate from. which means that the "box" that includes the lens flange, mirror and sensor is a fixed size, and that limits their options on the size of the mirror. The mirror can't be made taller to accommodate that ratio at the same 36mm width (assuming full frame, of course...) because it would hit things, and narrowing the ratio would put off a lot of pros who were all used to working in the standard ratio. Of course, they could have chosen a different ratio for the crop cameras, but then pros (and amateurs alike) would be put off by the fact that their crop camera isn't the same ratio as their full frame...
    Olympus went with 4:3 rather than 3:2 for their cropped sensor forma and P&S uses 4:3. Why? I've no idea.​
    The "standard" CRT/LCD screen size for computers up to 1024x768 (and some larger) was 4:3. Also, most digital cameras that aren't SLRs use(d) a 4:3 ratio. And, they were starting from scratch with micro 4/3, so they really could have done anything they wanted to, like 16:9, or 1:1...
    From a technical standpoint, 4:3 makes better use of the image circle of a lens, and from a marketing standpoint, you can say you have more megapixels, since a 3:2 ratio sensor with the same lens, same sensor width, and with the same pixel size would have to have fewer MP...
    Personally, I'm warming to the idea that they should all just have a square sensor, since I usually crop my images in post anyway, and have been using a square format rather a lot. It also eliminates 95% of the need for L-brackets, rotating tripod collars, extra buttons on the camera or battery grip (for operating the camera in"portrait" mode), and even the deep cutout in ballheads...
     
  8. zml

    zml

    Joe: as already said - lenses do cover 24x36 mm and lenses are expensive to compute, design and make.
    The chief reason for having that particular frame size was then, ca. 1920-1925, image quality (IQ as we call it now...) The most used fim frame size for large screens then was 18x24 mm (there were many, many other formats used throughout the history of moving pictures) and, although it was OK for moving pictures, film stock was not good enough for stills, not even when modestly enlarged. Oscar Barnack put the film in the camera horizontally and doubled the frame dimensions which made the resulting negatives suitable for modest enlargements (6x9 cm or postcard size 9x12 cm was the norm then.) But not even then the aspect ratio of "traditionally" produced paper sizes changed to accomodate the new format.
    Much later, 6x7 cm negative was called "ideal format" and fits with (almost...) no cropping on some paper sizes, ironically, mostly on those sized in inches. Somehow there are still papers 18x24 cm but not metric 18x21 cm...
    As an aside, what's wrong with cropping your "negatives" to the desired aspect ratio/dimensions?
     
  9. Obviously there are numerous reasons we still use the 'same old' AR, but I, for one, am an advocate of the 'circular sensor' approach. We (now) have the processing power to simply 'crop' the circle (though the VF might be a challenge ;-) ), and w/ adequate resolution.
    Unfortunately that would be a prohibitively expensive sensor (at least 3 - 4 x the cost of existing 'FF' sensors)... sigh.
     
  10. Optically, I don't think a circular sensor would be an issue, though, there are other issues. First is the "yield" of sensors on a single silicon wafer. They don't make sensors one at a time, they cram as many as they can on a single silicon disc, and cut them apart later. Circular sensors would leave large areas of nothing, though I'm sure they'd find a way to solve that. The second problem is storing the image. The current use is for rows and columns of pixels. With a circular sensor, you'd be wasting a lot of space. The area of a circle is only 79% of the area of a square where the side of the square is equal to the diameter of the circle. For efficiency in storage, they'd need to change to a different method of storage, perhaps using vector notation (angle & distance), but that would necessitate a wholesale rework of any application that touched the image...
     
  11. zml

    zml

    > circular sensor
    The main issue is that unless one designs an "ideal lens", i.e. aberation and light fall off free optics, the image circle projected by the lens must be significantly larger than the image circle of such "circular" sensor, which dramatically increases the cost of optics. Say, your basic 2000 dollars 85/1.2 L would become a $5000 lens.
    IMO the times are the best ever in photography: we have high res "35 mm format" cameras with significant cropping possibilities in all kind of formats and ratios, and larger sensors, if needed, too.
    Try cropping a 24x36 mm film frame: unless one used Tech Pan in a camera fitted with the best possible lens and mounted on a very sturdy tripod, cropping more than 10-15% of the frame led to significantly lower IQ. Nowadays, I routinely crop 50% of the frame from 21 mpixels with great results...
     
  12. Larry West, I too would love to see square sensors but, I suppose it would add considerably to the cost of manufacture. Speaking of cost, I wish I could justify the cost of a medium format back but my print sales just won't support it. As a work around, with my 35mm equipment, I stitch 3 frames together by shifting my camera while using a tilt-shift lens. It's a bit cumbersome and slow but gives me large files (at 46x36mm) with an approximate aspect ratio of 1:1.25. My favorite format, when I shot mostly film was 6x7, close to ideal in my opinion (and I do realize this very subjective). If someone were to manufacture a modestly sized digital medium format rangefinder (ie. less expensive than current medium format sensors), similar to the Mamiya 67 or the older Fuji rangefinders, I would find a way to afford it. I can always dream, in the meantime I'll make do with stitching. BTW, I know I can always just crop my 35mm frame to match a 1:1.25 aspect ratio but I just hate throwing pixels away.
     
  13. zml

    zml

    Square sensors? Too big image circle required hence the cost of optics. Ain't gonna hapen soon in a "budget friendly" digital format. Besides, if you "hate to throw pixels away" from a 24x36 mm frame think of all the pixels you'd be "throwing away" from a square sensor. There are good "square format" pictures but most look better in a rectangular format and the, really, only two raisons d'être for square film frame/sensor are that the camera with a square format doesn't need to be turned sideways, and the ease of cropping: many DA/editors wanted a square 6x6 image so they could crop it in landscape and/or portrait format without excessive loss of quality. I've been using 6x6 since the beginning of my adventure with photography (circa 1968) and have maybe 10 prints to show in a "square" format: the rest was croped to the 6x4.5 cm equivalent.
    The first and only photo club I belonged to was called '6x6', BTW, and yes we wuz square :)
     
  14. Personally, I like the aspect ratio of standard DSLR's and 35 mm film. But that's just me. It fits most of my compositions fine--except for people, where I often prefer the format that produces 8 x 10's.
     
  15. I suspect that they used this format because it was familiar to those in the target market for these cameras. There is nothing sacred or more or less right about any particular format and some of us will use various aspect ratios depending upon the content of the image. (I happen to like a 4:3 ratio.)
    Dan
     
  16. Some images I crop wider to the 4:5 aspect ratio. Occasionally, I'll go all the way to 1:1 (square). In other cases, I go narrower to 9:16 (wide-screen movie format).
    2:3 isn't perfect, but it's a nice middle of the road choice that offers a lot of cropping options. And it's pretty firmly entrenched.
     
  17. Maybe the sensor ought to be round.​
    This was the first thing that popped into my mind when I first started considering maximizing the yield from the image circle.
    I am not sure that the "keyhole [peephole?] effect" from round images would not make me feel more like a voyeur than I already do. Maybe we should stay with 3:2. I like it better every day.
    Why, then, do I keep cropping and resizing to 4:3 for display on the screen? I think that it is because I feel that the image should fill the screen, without light borders on top and bottom.
    Movie aspect ratios have often been chosen to produce more panoramic effects, and there are many who lament cropping movies and DVDs to fit the TV screen. (Lawrence of Arabia in 4:3 come to mind: the desert just disappears.)
    I am daily in awe at what the denizens of the EOS forum (among others) find to talk about. I could be out preparing for the sunrise and its long landscape shadows. . . .
    --Lannie
     
  18. @Mr. Gregory,
    Would you care to elaborate on your response?
     
  19. I do a lot of printing (Home printer European format paper ratio 1:1.4 and commercial which is either 1:1.5 or 1:1.4) but mostly I view my photos on a monitor that nowadays has a ratio of 16:9 or 1:1.78. I like to fill my monitor so I nearly always crop the image to suit.
    So for me the actual image ratio depends very much on how I am going to finally view it. The 1:1.5 format suits me fine.
     
  20. ... fall off free optics, the image circle projected by the lens must be significantly larger than the image circle of such "circular" sensor, which dramatically increases the cost of optics​
    Current (EF) optics already must produce fine quality and detail (varying of course w/ lens) over a circle w/ a radius of almost 22mm to project that onto a rectangular surface 24x36mm. Why would using a hypothetical cicrular sensor w/ r=21mm be any different? I don't really see much need for a revision of current lenses to facilitate this... Of course you would always see some vignetting (depending on aperture and lens), and some lenses (whose contacts obscure part of the image circle) wouldn't be able to fully utilize a circle.
    The advantage I see is NOT in a natively circular sensor, but in the ability to change aspect ratios WITHOUT cropping (since the camera could simply read from the appropriate pixels, a 16:9 natively would be able to be wider than 36mm (~38.4mm), and a 4:5 or 1:1 AR would be much taller) The effect to field of view could be dramatic - using the same lenses...
    And of course I do absolutely agree NOW is the best time... we just want more ;-)
     
  21. zml

    zml

    > Why would using a hypothetical cicrular sensor w/ r=21mm be any different?
    Assuming decent optics, when you carve a square/rectangle from a circle, the light fall off (and some other aberrations) are visible only in the corners. With a round sensor, many people would like to use the entire circle ("it is there so why crop...") hence the image circle would need to be much larger than the actual sensor diameter to avoid light fall off and such. Small thing but otherwise there would be a lot of kvetching. OTOH the chances for a round sensor are nil, although there were some round image formats in the early stages of film/plates.
     
  22. The 3:2 aspect ratio was not exclusive to 35mm cameras. It's the same as that of the old 6x9 medium format folders. Aside from being very close to the golden mean (which is not exclusive to photography, by the way), its wider format lends itself better to many, if not most outdoor and street-like compositions because the ground (or the horizon) is essentially one big ever-present horizontal line... while at the same time not having the squished-down look of 16:9.
    Given that, if you had to carve 3:2 out of a square, circle or whatever every time you take a picture, you would have to haul around more camera and lens size than you need since such a sensor would have to be large enough to accommodate all the standard aspect ratios. It's for the same reason that the 645 format evolved to make medium format cameras smaller, since many people always cropped the square to a rectangular format anyway.
     
  23. Your sizing information is US Centered.
    Ilford offers papers in 7x9 1/2, 9 1/2 x 12 and 12x16 which seem to work well for the 35mm frame in my printing.
    If you want other proportions in your camera then build one, modify the opening in one you have or shoot larger formate where you can easily modify film holders for whatever format you like.
    If you are like most who shoot and print your crop relatively often. Why not just make an easel opening of the size you like to print, use paper larger so you have clear and clean edges with the image centered/wighted and centered and live with that?
     

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