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Author Topic: Sensor aspect ratio  (Read 2757 times)
elgenper
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« on: May 05, 2004, 06:35:18 AM »
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Why indeed?  For myself, I never liked the long, narrow 35 mm format, and moved on to use Rollei and Hasselblad with their square frames (there were other reasons too, of course).  My first digicam had a ratio of 1.33 instead of 1.5, and while not my beloved square, it was far nicer than 35 mm.  Of the 6 digis I´ve owned since, only one (the D60) had that nasty 1.5 ratio, meaning I had to crop away 1 of the 6 megapixels in most pictures, like I had to with 35 mm. UGH!  My present camera has 1.33 ratio and 5 megapixels, and I seldom have to crop.

When Oscar Barnack designed his Ur-Leica in 1914, he had to adapt to existing cine films, where a lot of the film width was used for perforations.  He chose to make one frame length equal to eight sprocket holes; since he could not make the frame wider than 24 mm, that gave him a decent total area of the frame.

This decision stuck; instead of making unperforated or singly perforated 35 mm film for still cameras (a few tried, but it didn´t sell), the world kept using cine film with that oddly shaped frame crammed inside the perforations.

Now, with digital sensors, one would think we might at last leave the constraints imposed in 1914, and make these sensors optimal in esthetic proportions and utilization of the image circle of the lenses.  And what happens?  All manufacturers of DSLR:s (except Olympus; kudos to them!) stick with these obsolete proportions.  And the buyers and reviewers?  They all yell for "full frame" sensors!  Full frame of what?  Of a constrained compromise made 90 years ago, that´s what.  Come on, try to be innovative, make use of what´s available today, just like Barnack was innovative in 1914!

(Phew, I´m heating up....  But it´s all so STUPID!

Per
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Aaron Bredon
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« Reply #1 on: May 05, 2004, 03:00:31 PM »
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I guess it depends on what one likes.  Personally, I like the frame shape of my 1Ds and do NOT wish it were 1.33:1.

And there are also some good arguments for square images.
One is that you don't need a vertical handgrip - just crop vertically rather than horizontally. Another is that you actually get more usable capture area out of the light circle.

Perhaps the ideal digital sensor would be a circular sensor covering the entire light circle, so you could pick the aspect ratio you wanted, and get maximal resolution for all aspect ratios. (of course this is unlikely to happen, as rectangles make more efficient use of the silicon wafer)
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BJL
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« Reply #2 on: May 05, 2004, 05:55:27 PM »
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I have also wondered about how the 3:2 ratio became entrenched some decades ago, despite the fact that most or all standard print shapes were less elongated than that (even "snapshot" sized prints used to be shapes like 4"x5", 3.5"x5", 9x12cm before the standard moved to 4"x6"/10x15cm).

Part of the story is the original Leica design, doubling up the 35mm movie frame of 18mmx24mm to get 36mmx24mm. But a few other shapes were experimented with, none catching on (except for a bit of "half-frame" 18x24mm).

My new speculation is that 24x36mm is in fact an excellent format for use within the constraint of using the widely available, very economical, 35mm film and its 24mm maximum width, because
a) the smallness of 35mm film makes it desirable to be able to use that full 24mm width of the film when printing at all the common shapes
 the commonly used print shapes all lie in the range from about 1.25:1 to 1.5:1 (3 1/2"x5", 4"x5", 4"x6", 5"x7", 8"x10", 11"x14", 16"x20", etc., and in some European countries 9x12cm, 18x24cm used to be common).

Making the frame shape the widest of these, 3:2 or 24mmx36mm, allows every common print shape to be achieved by cropping only at the sides, still using the maximum possible 24mm height; any narrower frame (like 24x32mm for 4:3 shape) would require cropping to less than 24m height to get 3:2 print shapes (about 22x32mm for 3:2 shape from a 24x32mm negative.)

That is, I suspect that the success of the 24x36mm frame is not that it is the "ideal" shape (no single ideal print shape exists), but that it is minimizes loss of resolution when cropping by being at the wide end of the range of commonly used print shapes.


P. S. I see a good reason why the 4:3 (1.33...:1) shape is used by every current digital camera model with sensor size of up to 4/3" format, and by the new 22MP digital backs, and by most current scanning backs for large format. This shape is close to the middle of the common print shape range and so for photographers who use shapes scattered over this range, this sensor shape minimizes the average "pixel wastage". However, for people who mostly prefer the more panoramic shapes like 3:2 and up (this is meant to be a landscape oriented forum after all), 3:2 sensor shape makes more sense.
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Tim Gray
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« Reply #3 on: May 04, 2004, 03:48:21 PM »
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If the standard presentation formats are 1.25:1 - 8x10 or 16x20 why are the sensors (Canon SLR) 1.5:1?

A rectangular 1.5:1 sensor fits into a circle with a radius of 1.803 "units".  A rectangular sensor with a 1.25:1 aspect ratio fitting into the same circle (if my math is correct - 1.1265x1.4081 = 1.5862 sq units) would have an area almost 6% larger than the 1.5:1 sensor - so rather than cropping good pixels to fit a 1.5:1 presentation format, I'd have 6% more (assuming the same size/density pixels).

Why are we stuck with a 35mm aspect ratio?
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jeffreybehr
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« Reply #4 on: May 05, 2004, 11:37:39 AM »
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(Phew, I´m heating up...)

THAT I agree with.

Actually, boys, some of us LIKE the rectangular formats and find 1.25:1-ratio pics too close to square.  Certainly that ratio is more appropriate (than 1.5:1) for portraits, but I've not shot one of those in 20,000 frames.  When I crop my 1.5-ratio images, sometimes they get squarer and sometimes they get more rectangular.  

I guess it depends on what one likes.  Personally, I like the frame shape of my 1Ds and do NOT wish it were 1.33:1.
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boku
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« Reply #5 on: May 05, 2004, 03:05:26 PM »
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More than a few medium format cameras were bought because 1::1.5 aspect ratio with horizontal orientation is un-natural for most studio applications.
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Bob Kulon

Oh, one more thing...
Play it Straight and Play it True, my Brother.
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