What does this mean: "flattening the depth of field"?

Question

Someone just described "flattening the depth of field" as a wide range of distances being almost equally in focus. I'm not sure I understand.

I'm thinking in a prescription glasses sense. Does this mean a wide range of distances being almost equally in focus in such a way that focus at 5 ft is as clear as focus at 20 ft? Or does this mean that focus is almost equal in the sense of a single measurement used across a wide range of distance, such as 5 ft being less clear in focus because of 20 ft focus measurement being used at 5 ft?

Also, does "flattening the depth of field" make objects appear smaller/bigger or closer/further wearing glasses than with the unaided eye?

Sorry for the hard question. Your help is appreciated.

Answer 1

Depth of field, simply put is, how far past the `subject` will remain in focus when you take a picture.

A large depth of field means that most of what is in the viewing area will remain focused.

The term you used; flattening makes me think the depth of field is lessening, not increasing. I have not heard this term, but going by how I'd take that term, that's what I think it means......decreasing the depth of field (dof).

If it does mean increasing the dof then it's a poor way to describe it in my opinion.

Changing the dof doesn't change the magnification at all. It simply means how much of what you see remains in focus. If you take a picture of someone standing on a panaroramic hillside with trees and green pastures and so on in the background, and your friend took your picture with a shallow dof then you (the subject) and maybe a little bit behind you would be in focus, and the rest would be out of focus.

However, if your friend took your picture with a wise dof then you, and a long ways behind you would remain in focus.

Part of this is the amount of light available for the picture. The more light you can get into the lens the better your dof will be. It's not the only thing, but for our discussion I think that suffices.

Does this `shed any light` on this for you??? lol

Answer 2

This is used in cameras for photography, so that focussing is avoided and a fixed focus lens does the job. Also used in microscopy since the object being observed may not have a true flat surface and if the depth of field is less, a lot of adjustment is needed for focusing as you move over the object.

Depth of field is affected by the focal length of the lens and also the aperture of the lens. In prescription glasses, the focal length is fixed for the upper portion and lower portion so that near vision (throuh the lower portion) and distant vision (through the upper portion) is clear. Such glasses are called bifocal glasses. Varaible focal lenses are also available to eliminate the sharp transition between the near and the far objects, but these lenses are much more expensive.

I feel that depth of field is not a factor in prescription glasses since the glasses are prescribed taking into account the power of the eye lens and the accommodation etc.

Answer 3

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