DOF and Cropping take 2

Started 5 months ago | Discussions thread
falconeyes
Contributing MemberPosts: 773
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Re: Awaldram
In reply to awaldram, 5 months ago

I think I have no reason to argue with anyone here, so let me pick two points where I think I can contribute.

Pin-hole cameras: they are covered by the equivalence principle if you drop the assumption/approximation of neglegible magnification. In every equivalence class, there are indeed pin hole cameras (need to specify MP resolution to quantify its properties). However, their focal lengths and hyperfocal distances are similiar which means they can't do closer focus (can't focus inside the lens). So, if you add focus distance besides FoV to an equivalence class, then there are many which don't include pin hole cameras indeed. Almost had this paragraph in my white paper but decided against. As I dropped treatment of finite magnification. Magnification creates confusion as it isn't an image property. Magnification wrt. (printed) image size is, wrt sensor size isn't. Which is why I replaced it by FoV and use the neglegible magnification approximation where applicable.

DoF would have a similiar problem but it is easily treated. Just specify the permissable circle of confusion to be a constant fraction of image size, like 1/1730 or 1/1500 or 1/2300. Doesn't matter as long as you stick to your definition.

As you say, the real beauty of the equivalence theoreme is that as soon as any of the three properties "depth of field", "image noise", "diffraction" becomes equal in two images (for a given field of view, shutter speed, camera position, focus distance, focus direction, number pixels and brightest pixel normalized to 100%), the other two properties do automatically become equal too (holds true w/o the neglegible magnification aporoximation too).

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Falk Lumo

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