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12-09-2009, 09:49 PM   #1
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Question regarding 35mm vs APS-C

Do full frame 35mm sensors absorb more light [thereby giving you better low light shots / faster shutter speeds] given equal exposure time and aperture as the APS-C?

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12-10-2009, 01:12 AM   #2
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In theory, yes but it also depends on the sensor.
12-10-2009, 02:34 AM   #3
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If an APS-C and a FF sensor use the same design: yes.
The larger sensor has larger pixel surfaces to capture photons, and will create a higher electrical signal.
However, there is more than factor that influences the signal/noise ratio; temperature, cross talk, the sensor photo diode technology, the quality of the microlenses etc.
12-10-2009, 07:33 AM   #4
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I'm not an expert by any means, but I tend to think that no, FF doesn't necessarily provide better f-stop performance.

If we consider resolution, FF will have a greater ability to resolve the image than an APS-C sensor (given equal pixel density), but the intensity of recorded light will be the same (at equal apertures).

This however, depends on the lens being used. The above assertion assumes that the respective sensors are using lenses designed for their given sensor size.

The advantage of FF over APS-C in terms of f-stops would only really become aparent if one were using a lens designed for FF on an APS-C sensor (FA, DFA, M, A, K, etc.) Since the lens is designed for a larger sensor (or film frame) the smaller APS-C sensor will not be able to capture all of the light. The intensity of the light it does capture will therefore be lower than with a lens made for it since the available light (light entering the lens) will be the same for both types of lenses.

Not sure if that makes sense to you or is even right. Again, I'm not an expert, but this is how it makes sense to me.

12-10-2009, 07:51 AM   #5
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QuoteOriginally posted by boodiespost Quote
Do full frame 35mm sensors absorb more light [thereby giving you better low light shots / faster shutter speeds] given equal exposure time and aperture as the APS-C?
The 35mm sensors have 864mm˛ of surface vs 370 for APS-C. Thus yes it gathers more light (if the light intensity is the same, ex: lenses using the same f/stop). In theory this gives about 1-1/3 stop advantage to 35mm for noise over APS-C. In practice because of many other variables (lens used, DOF needed, sensor technology) this does not always translate into a clear advantage.
12-10-2009, 08:50 AM   #6
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QuoteOriginally posted by boodiespost Quote
Do full frame 35mm sensors absorb more light [thereby giving you better low light shots / faster shutter speeds] given equal exposure time and aperture as the APS-C?

Thanks

How can you have faster shutter speeds AND equal exposure time?

Assuming the SAME scene, ISO, and f-stop, you would need the same shutter speed (to keep the same exposure value) regardless of sensor size.

There would be differences in noise levels though (especially in the higher ISO range)
12-10-2009, 09:31 AM   #7
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QuoteOriginally posted by egordon99 Quote
How can you have faster shutter speeds AND equal exposure time?

Assuming the SAME scene, ISO, and f-stop, you would need the same shutter speed (to keep the same exposure value) regardless of sensor size.

There would be differences in noise levels though (especially in the higher ISO range)
I think the correct way to compare two images involves comparing noise levels, especially at higher ISO's as you suggest.

On this basis you'd expect the FF image to have 2/3 the noise of the APS-C image for the same exposure.
12-10-2009, 11:02 AM   #8
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Does a large bucket collect more water than a small one if you leave them out in the rain for the same period of time? Answer: yes, if you count the total volume of water collected, no if you measure the *depth* of the water in each bucket. That's why we can say "it snowed three inches last night" without havng to specify how big a bucket we used to measure that. We don't even need a bucket when measuring snow - we can just stick a ruler on the ground.

What this means in photographic terms is, the *exposure* will be exactly the same whether 35mm or APS-C, because exposure is basically the depth of the water in the analogy above. But the overall perceived *noise* levels will be lower for 35mm, because perceived noise is more or less *inversely* proportional to the total amount of light collected.

So if you shoot with exactly the same aperture, ISO, and shutter speed, you'll get exactly the same exposure on both FF and APS-C, but less noise in the FF shot. You could also, then, choose to shoot a hgher ISO on FF, thus giving you the same noise as APS-C, but a faster shutter speed for the same exposure (or a brighter exposure for the same shutter speed).

That' all assuming we keep aperture the same. Of course, in order to get the same aperture (and same field of view) between FF and APS-C, you'll often need a physically larger lens to do it: a 200/2.8 is a lot bigger than a 135/2.8.

Sometimes, we might say a 200/4 for FF is "equivalent" to a 135/2.8 for APS-C, because if your shoot the 200/4 on FF at higher ISO, you'll get exactly the same shutter speed *and* the same noise as APS-C. That is, while it is true that the FF sensor can collect more light overall (just as the larger bucket collects more water), it needs a much larger lens to allow it to do so. If you use lenses that are "equivalent" (meaning, 1.5X the focal length and one stop smaller aperture for FF), you'll actually end up collecting the same amount of light (water) on both sensors.

This was the subject of a very long thread a few months ago that I don't really recommend reading as there was a lot of confusion and argument generated along the way.

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