35mm by 35mm Sensors

[CJD]

Would it be posible to develop a DSLR with a 35mm by 35mm sensor using existing 35mm lenses?

Just a thought.

[CJD]

OK

So I have now engaged brain.  Of course you can't

Its been a long week.

Sometimes I'm really thick.

[Tim Gray]

Nope.

Without going into the geometry in detail, it should be easy to see that the image circle in a traditional 35mm format is going to be the diamater equal to the corner to corner diagonal of a 24x35 rectangle.  The diagonal of a 35 x 35 mm rectangle is clearly going to be larger, and thus extend outside the image circle.

[Tim Gray]

posts crossing in the night.

[BernardLanguillier]

A 24*36 mm sensor has a diagonal of 43.3 mm,
a 35*35 mm sensor has a diagonal of 49.5 mm.

There is therefore a 6 mm gap only.

It depends on the lens of course, but most lenses stopped down even a little bit should have an image circle of 49.5 mm.

The sensor would probably be usable with all long lenses, and shorter ones stopped down a little bit.

Regards,
Bernard

[Ray]

It depends on the lens of course, but most lenses stopped down even a little bit should have an image circle of 49.5 mm.
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I imagine that's true, but I think it would be very inconvenient with the shorter focal lengths. As it is, I see a significant reduction in resolution in the corners (and some vignetting) with my 24-105 zoom at 50mm and f6.3. By f11 it's gone. If the diagonal of the sensor were increased by 6mm, the vignetting and resolution fall-off would probably still be there in the corners at f11 and at f4 would be really bad.

However, in circumstances and at f stops where such degradation were unacceptable, one could always crop the image to the standard 35mm fomat. One could probable soon learn what lenses were particularly bad in this respect, so I see a square 35mm format as an an advantage. One could even have an in-camera, user adjustable program which would automatically throw up a 36x24 matte in the viewfinder with certain lenses at certain f stops.

[phila]

There is also the physical factor (in many existing Canon lenses, at least) that to limit stray light bouncing around, there are rectangular "24x36" shaped apertures built into the optical path. So the image falling on the sensor is not circular.

[Ray]

There is also the physical factor (in many existing Canon lenses, at least) that to limit stray light bouncing around, there are rectangular "24x36" shaped apertures built into the optical path. So the image falling on the sensor is not circular.
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I wondered if someone would mention this. I'm not sure what effect these 'frames' have, which are sometimes positioned at the exit pupil on some lenses. On my Sigma 15-30 there are tiny screws indicating the the frames can be removed. On my Canon 24-105 there is also a frame behind the exit pupil which has no screws so perhaps it cannot be removed. But oddly enough, it's not a 36x24mm frame, but approx. 29mmx24mm.

If you imagine the typical diagrams showing how light from the target (scene) passes through the lens and arrives at the film plane or sensor, then a blocking aperture of 35mm format dimensions is not necessarily going to prevent an image of at least 50mm in diameter reaching the sensor, and especially not at large f stops (small entrance pupil apertures).

Since I find the 5D very usable at f16, a 17mp 35mm square format 5D of the same pixel density would actually be quite a useful tool.

[CJD]

Phew !

Cheers guys, thought I had made an idoit of myself with the OP, but looks like there might be something in it.

The original musing was around the fact that as we are no longer confined by film stock, the sensor can be any shape/size within the confines of the useable image circle.

Thought it might be an interesting avenue for the 35mm system to increase sensor size beyond FF and get a bit more real estate without making those pixels too small

....so what size sensor could MF lenses accomadate?  And how about a 3:2 format MF camera?

[jani]

I wondered if someone would mention this. I'm not sure what effect these 'frames' have, which are sometimes positioned at the exit pupil on some lenses. On my Sigma 15-30 there are tiny screws indicating the the frames can be removed. On my Canon 24-105 there is also a frame behind the exit pupil which has no screws so perhaps it cannot be removed. But oddly enough, it's not a 36x24mm frame, but approx. 29mmx24mm.

That's not so odd. The image circle is smaller there.

[Ray]

That's not so odd. The image circle is smaller there.
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Indeed! The oddness is in the fact that these frames at the exit pupil, which are presumably there to block out stray light and reduce flare, are not the same proportions as the 35mm format. They are closer to being square.

[samirkharusi]

It's really a question of what is the most sellable aspect ratio. 1:1.5 seems restricted to 35mm and personally I find it too tall when used in portrait mode. Consumers seem content with 1:1.33 (most of those P&S digicams, also matches most computer monitors), but personally I would prefer an aspect ratio that needs no cropping to print on A5, A4, A3, A2, A1, etc, similar to 5x7", or 1:1.414. So my preferred sensor would be 25x35mm, rather than a square 30.6x30.6mm.

[Ray]

So my preferred sensor would be 25x35mm, rather than a square 30.6x30.6mm.
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Samir,
Long time no see!  

Preferred aspect ratios will not only vary from individual to individual but from subject to subject. One could do a lot of market research analyzing millions of photos throughout the ages, and paintings too, and come up with a single preferred aspect ratio, for marketing purposes.

But the best solution of all, would be for the manufacturer to offer the flexibility so the user can choose a preferred aspect ratio (by means of a matte appearing in the viewfinder) for each individual shot, which might also take into consideration vignetting and resolution fall-off in the corners with certain lenses at certain f stops, and at the same time maximize the pixel count.

Currently, if you want a square aspect ratio for a particular shot using 35mm, you have no choice of anything bigger than 24x24mm.

[jani]

Indeed! The oddness is in the fact that these frames at the exit pupil, which are presumably there to block out stray light and reduce flare, are not the same proportions as the 35mm format. They are closer to being square.

Good point, I didn't notice that the second number was the same.

Perhaps someone has had some foresight in predicting different formats.