Continuation: Sensor Size, Present & Possibilities

Started Apr 10, 2013 | Discussions thread
olliess
Contributing MemberPosts: 922
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Re: On DOF
In reply to EinsteinsGhost, Apr 10, 2013

EinsteinsGhost wrote:

olliess wrote:

EinsteinsGhost wrote:

2- Exposing part of a full frame sensor (FF in APS-C mode)

Unless there's a special shutter or a black mask for DX crop mode, I'm guessing you "expose" the whole sensor regardless. You just don't record all the data from the FF sensor.

You have only the image circle projected through the lens in DX crop mode.

Supposing you really want to argue about this, do you think that no light shines on the FF sensor outside of the APS-C frame when DX crop mode is activated? Even allowing for a dedicated DX lens?

3- Digital cropping

In #1 and #2, you compose accordingly, and likely expose for the composition. And #3 can be done to either, or to any sensor size. The question is, why would you prefer #3 over #1 or #2?

That's like asking, "Why crop at all?" The answer is that you like the picture better after trimming away off some of it.

No, that is asking: Why would you prefer #3 over using a longer FL lens?

Two obvious cases come to mind: 1) you don't have a longer lens with you, and 2) you get to make the final decision later.

EinsteinsGhost wrote:

olliess wrote:

EinsteinsGhost wrote:

There is no need for that. This was taken with NEX-3 and 35mm f/1.8 lens (wide open):

Why exactly would you need 50mm f/1.4 on FF?

A) To increase the subject isolation while keeping the same subject-background distance

B) To keep the same subject isolation while decreasing subject-background distance

C) To increase the exposure to reduce noise

D) To increase the shutter speed in case the subject suddenly jumps at the camera.

Do we need to continue?

You didn't use an objective analysis, but went with a theoretical one.

What kind of "objective" analysis is possible? I gave you a list of possible objectives one could accomplish with a wider aperture. The same would apply to a 35 mm f/1.2 on the APS-C sensor.

Have you never encountered a situation where your DoF is too shallow for good isolation? With my APS-C bodies, I see that often and feel the need to stop down to have sufficient DoF. After all, I wouldn't want portraits with eyes in sharp focus but blurred out nose.

When I need more DOF, I can always stop down a fast lens. I can't open up that 35/1.8 wider than f/1.8. The same reasoning applies to all fast lenses, even though you don't always (maybe even rarely) shoot wide open.

But you knew this, and it's been repeated in thread after thread after thread.

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