So why is it that ...

[cyrus]

So why is it that the image seem from a viewfinder is always in focus, where as the camera lens has to be focused?

[jb7]

You focus with your eye-
The image from the viewfinder is a virtual image; it does not form an image at a plane, without the aid of another lens, such as your eye-

[BrianShaw]

... also, the eye/brain can variably and continuously selective focus but a camera lens can't.

[Gene McCluney]

A SLR VIEWFINDER would (in general) go in and out of focus with the lens,as you are using the lens to image the view. A rangefinder viewfinder is totally separate from the taking lens and is only designed to show you field of view. A view camera ground glass uses the taking lens, so it shows focus.

[cyrus]

You focus with your eye-
The image from the viewfinder is a virtual image; it does not form an image at a plane, without the aid of another lens, such as your eye-

Ah this makes sense. I noticed that the lens in viewfinders are concave so I guess it combines with the convex iris to form an image in the eye

[ic-racer]

If the viewfinder is, say, a pair of binoculars, then it is not so that it is in focus.

The viewfinders that give a wide angle of view will give more depth of field than your eye already has. So it seems like everything is in focus. A 'telephoto' type viewfinder will give less depth of field than your eye's normal state and may need to be focused (like binoculars).


A ground glass image follows the physics of the camera's lens, and has nothing to do with your eye.