DOF preview button

Hey guys, this is my first posting here. Had been lurking around this forum for sometime

Most EOS DSLRS have this DOF preview button. According to the manual, it says press the button to stop down the aperture to check the DOF.

It does not really show the actual DOF, rather the overall picture darkens when the button.

in fact, by setting the focal zoom length and f-stop correctly, i'm able to see the actual DOF in the VF, w/o the need to pressing the button.

so my question is, is the preview button really useful, or its just redundant?

it closes the aperture to the shot setting, rather than leaving it wide open as normal (for a/f & lightest view). You should be able to see foreground/background becoming sharper as you close down the aperture (and of course the light level drops). Without pressing it you won't get the correct DOF. Try focusing on something close up in Av mode at your lowest f stop, and check the background as you spin the dial up to the highest.

ok, i think i got it.

i think what happened is that if i were to set to, say, f/8, after the AF is locked, i'm able to see the blurred background w/o pressing the preview button, but to determine the extent of blur-ness, the preview button is there to tell me.

am I right to say that?

You won't notice it so much with a large aperture like f8, bump it up to f22 and put something at 1' and 6' and you'll definitely notice the difference.

ok, i just tried that, indeed the background looks more sharper (but still blurred) although it looked much dimmer.

but then again, what the human eyes perceive as such a dark-picture at f/22, the imaging sensor is still able to capture the picture with sufficient brightness....

I use it when I have time and am thinking about blurring the background or making sure everything I want in focus is in focus. I used it a lot more when I was shooting film. Now I'll just bracket.

bokehed wrote:
=bokeh'ed]Hey guys, this is my first posting here. Had been lurking around this forum for sometime

Most EOS DSLRS have this DOF preview button. According to the manual, it says press the button to stop down the aperture to check the DOF.

It does not really show the actual DOF, rather the overall picture darkens when the button.

in fact, by setting the focal zoom length and f-stop correctly, i'm able to see the actual DOF in the VF, w/o the need to pressing the button.

so my question is, is the preview button really useful, or its just redundant?

actually you don't see it through VF, your aperture always wide open, untill you take a shot, only then is closes to value you set. DOF allow you to see what it will look (kinda close) closing aperture to the value you set.

I'm finding your language a little confusing so i'll explain what it does.

When you're looking through the viewfinder and no buttons pressed the lens is always open to it maximum aperture, regardless of what you've set on the camera. The aperture stays wide open because AF is much faster, and framing your shot is easier.

When you press the DOF preview button the lens changes its aperture to what you've set in the camera. This reduces the aperture so you can see what the depth of field will be in your taken photo. The image in the viewfinder gets dimmer because when you stop the lens down less light gets in.

Hope that helps.

Thanks all for ur valuable zippy responses! Really appreciated.

Put your camera in av mode, hold down the depth of field preview button and dial through all the apertures, step by step. Do this twice, once looking through the viewfinder, and again looking into the front of the lens.

As you look into the front of the lens, you notice the lens diaphragm (which is fully open and thus not visible without the DOF preview button pressed or when a "wide open" aperture is selected) closing down as you select smaller apertures. It will thus be obvious why the viewfinder gets darker. But this smaller aperture opening also yields broader depth of field (more stuff is in focus), and you'll also see that through the viewfinder with the preview button pressed.

Ordinarily (when the preview button isn't pressed), the diaphragm is wide open, and only shuts down for a brief second as you take a photo, then opens back up again. This gives you the brightest view in the viewfinder, and also the shallowest depth of field, which is useful for accurate focusing.
-harry

DOF buttons are VERY important to have on a camera!
If they weren't there we would be inundated with forum posts from old timer whingers that insist a camera is useless without one ...and nobody should learn photography without struggling with the super dim viewfinder

Here's a hint...take a pic and look at the screen. DOH!

Thanks for the posts, this should be very useful shooting my modeling photos. I guess I should give it a try.

Scuse my random burst of sarcastic humour there

There was a great site on the net somewhere about ten good uses for the DOF button.It really was mostly pretty usefull stuff,like using it to easily recognise hot spots and such.
Sadly i have never been able to find the site again

bokehed wrote:
=bokeh'ed]Hey guys, this is my first posting here. Had been lurking around this forum for sometime

Most EOS DSLRS have this DOF preview button. According to the manual, it says press the button to stop down the aperture to check the DOF.

It does not really show the actual DOF, rather the overall picture darkens when the button.

in fact, by setting the focal zoom length and f-stop correctly, i'm able to see the actual DOF in the VF, w/o the need to pressing the button.

so my question is, is the preview button really useful, or its just redundant?

You will see the efffect more easily if you are using a lens of 50mm or more, like 85 or 135, focus on something with the aperture wide open (like f1.4) and notice what else is in focus in front and behind it. Not much!

Now stop the lens down to f11 focus on the same thing and press the DOF button, see how much more is in focus infront of , and behind, the point you focsuused on?

That's the point of that button to let you see the DOF before you shoot. Yes the screen goes darker, but that can't be helped, what the button does is let you see whether the depth of field you have, at the aperture you have, is enough for everything to be in focus that you actually want to be in focus.

So it's not redundant because there are many occcasions where you might want to calculate DOF carefully before taking the pic