DoF preview button. How does it work?

[bernards]

Hey guys I have tried depressing this DoF button a couple of times. It doesn't actually do any thing for me. How do I go about using this feature? Does it only work certain lenses?

[student]

Originally Posted by bernards Hey guys I have tried depressing this DoF button a couple of times. It doesn't actually do any thing for me. How do I go about using this feature? Does it only work certain lenses?

This is how I use the DOF preview. When you look through the viewfinder, the view is at the widest of the aperture of the lens you are using irrespective of the aperture you intend to use.(don't ask me about the mechanics of this! have not got to this yet! but it is! This is also the reason why a lens with a maximun aperture of f2 will be brighter than one with f4. So many people buy a "faster", meaning a wider aperture lens, in order to have a brighter viewfinder). When you press the DOF preview, the viewfinder takes on the view of the aperture you have set. So, if your lens has a maximun aperture of f2, the viewfinder will show you the picture and illumination of a f2 aperture. But if you decide to shoot at f22 and set your lens to f22, and you press the DOF button, the viewfinder will be very dark, because you are now looking through f22! The advantage is that, with a darkened state, you can check the depth of field, meaning how much of the scene is actually in focus. Another advantage is that if there is flare, it will light up like a star!

If you have the camera in front of you, try it now and see for yourself.

[bernards]

Ah! Thanks Student.

That figures. I was trying to use that button while composing with a rather large aperture. It probably didn't make a much difference from my max aperture, that was why I couldn't see any difference.

[jumbocrab]

You might want to refer to this:
http://forums.clubsnap.org/showthread.php?t=84146

[denizenx]

as long as ur VF turns slightly darker u know it's working LOL... but of cos f/4 lens dof preview at f/4 is ptless

[obviousdude]

Originally Posted by student This is how I use the DOF preview. When you look through the viewfinder, the view is at the widest of the aperture of the lens you are using irrespective of the aperture you intend to use.(don't ask me about the mechanics of this! have not got to this yet! but it is! This is also the reason why a lens with a maximun aperture of f2 will be brighter than one with f4. So many people buy a "faster", meaning a wider aperture lens, in order to have a brighter viewfinder). When you press the DOF preview, the viewfinder takes on the view of the aperture you have set. So, if your lens has a maximun aperture of f2, the viewfinder will show you the picture and illumination of a f2 aperture. But if you decide to shoot at f22 and set your lens to f22, and you press the DOF button, the viewfinder will be very dark, because you are now looking through f22! The advantage is that, with a darkened state, you can check the depth of field, meaning how much of the scene is actually in focus. Another advantage is that if there is flare, it will light up like a star! If you have the camera in front of you, try it now and see for yourself.

great clarification..

many thanx. very helpful of you.

[rainman]

Originally Posted by student This is how I use the DOF preview. When you look through the viewfinder, the view is at the widest of the aperture of the lens you are using irrespective of the aperture you intend to use.(don't ask me about the mechanics of this! have not got to this yet! but it is! This is also the reason why a lens with a maximun aperture of f2 will be brighter than one with f4. So many people buy a "faster", meaning a wider aperture lens, in order to have a brighter viewfinder). When you press the DOF preview, the viewfinder takes on the view of the aperture you have set. So, if your lens has a maximun aperture of f2, the viewfinder will show you the picture and illumination of a f2 aperture. But if you decide to shoot at f22 and set your lens to f22, and you press the DOF button, the viewfinder will be very dark, because you are now looking through f22! The advantage is that, with a darkened state, you can check the depth of field, meaning how much of the scene is actually in focus. Another advantage is that if there is flare, it will light up like a star! If you have the camera in front of you, try it now and see for yourself.

Hmm..I understand that by pressing the DOF button, the viewfinder will do the "state" of the aperture setting.

I do not understand by looking at a dark viewfinder I'm able to check how much of the scene is in focus. Any1 clarify this?

Thanks.

[jumbocrab]

A darker viewfinder is only incidental - don't get distracted by it - you should concentrate on what objects are in focus and what's not in focus.

To convince yourselve, get hold of a fast lens, say f1.8 or f1.4. Find a bright scene. Set desired aperture to f8 or smaller. Before pressing the DOF button, look through the viewfinder for objects that are just a little bit out of focus. Press DOF button and suddenly, the object will become better focused!

Not many can "see" the difference and that's because the image at the viewfinder is very small. You really need good eyesight. It's also difficult when you use a slow lens (those with small apertures). The difference is even more minute. I personally don't use the DOF because my eyesight is not too good.

[justarius]

Originally Posted by rainman Hmm..I understand that by pressing the DOF button, the viewfinder will do the "state" of the aperture setting. I do not understand by looking at a dark viewfinder I'm able to check how much of the scene is in focus. Any1 clarify this? Thanks.

Try stopping down gradually to let your eyes adjust to the darker image. So if you want to shoot at f16, try stopping down to f4, f8, f11 then f16 to let your eyes adjust.

The gauge for sharpness is a very rough one though, as jumbocrab has pointed. I use it more to ensure that there isn't any distracting foreground elements present (a tree branch close to your lens might not be visible at f1.8 but will surly jump out at you at f8.. )

[bernards]

Thanks guys. I did understand when to apply this feature now. Not as useful as I initally thought, but still a great feature.

[rainman]

Originally Posted by jumbocrab A darker viewfinder is only incidental - don't get distracted by it - you should concentrate on what objects are in focus and what's not in focus. To convince yourselve, get hold of a fast lens, say f1.8 or f1.4. Find a bright scene. Set desired aperture to f8 or smaller. Before pressing the DOF button, look through the viewfinder for objects that are just a little bit out of focus. Press DOF button and suddenly, the object will become better focused! Not many can "see" the difference and that's because the image at the viewfinder is very small. You really need good eyesight. It's also difficult when you use a slow lens (those with small apertures). The difference is even more minute. I personally don't use the DOF because my eyesight is not too good.

Hmm..finally understand...probably its good for checking flare (mayb) but totally defeat its purpose of checking DOF because I believe no1 can check for focus when the viewfinder turns dark

Anyway good explaination. Thanks!

[student]

I do not use the DOF as a sole guide to check for what is in or out of focus.

My habits were formed by the use of a rangefinder camera, where the depth of field is indicated in the markings in the lens. With some exceptions where the lens maker is too optimistic of the accuracy of the depth of field indicator, most of these are actually quite accurate.

When I use an SLR with a fixed focus lens, there is also a depth of field indicator on the lens barrel (at least in my lenses). So I combine the use of the lens marking and the DOF preview. Perhaps not necessary. Life is not always logical.

But I think using the DOF preview to check for flare is indeed very useful.