Depth of Field button on DSLR

I"m curious about what the Depth of Field button really does..

I understand that when you focus for a shot, then depress the D of F button, its first gets darker and then what?

Do you turn the "aperture" dial to see if you can get a better photos while still holding the D of F button?

I can do that by just looking at my live lcd monitor on the camera, no?..

Any suggestions?

Thanks....

Supposed to help you preview the shot, i guess. for what it's worth i use it never.

Normally the lens stays wide open while you are viewing, whatever aperture is selected for the shot. When you press the DOF button, the lens stops down to what is selected for the shot, so you can see the depth of field (will both the subject and background be in focus? etc.) And yes, since the lens is stopping down the view gets darker.

Tiger's got it as to how it's supposed to work...

I think think it's efficacy is debatable. I rarely use it, if ever.

On fast lenses, especially if your subject is close, you will see the difference in DOF as you change aperture values. But, the darker part does make it tough to actually see this change. The feature works better on FF or 1.3 cameras than crop bodies where the viewfinder is kinda small. I never use it.

mypoppy31 wrote in post #10181665
I"m curious about what the Depth of Field button really does..

Does teh exact same thing that it does on a film SLR.

Get's darker? I'm getting the impression that instead of worrying about the DOF preview button you should be reviewing the basics, such as what the aperture is, what DOF field is, and how these two things are related. Once you know those, the function of the DOF button will be obvious.

No, you cannot.

However, Live View automatically increases brightness so that you can see what changes in the relative depth of field that the aperture creates. Another boon for Live View, whenever it's feasible to use it.

I think that button is useless, map it to turn on/off ALservo.

It actually doesn't do anything useful on a digital SLR. It does stop down the set aperture, but the problem is that with digital's brightness optimized viewfinders, you still cannot accurately preview the DOF wider than f4. And if you are stopped down past f4, it will likely be too dark to preview the DOF.

So, yeah, useless button other than for seeing your aperture blades.

tolyD wrote in post #10181785
I think that button is useless, map it to turn on/off ALservo.

Unfortunately it can't be remapped on most bodies.

tkbslc wrote in post #10181807
It actually doesn't do anything useful on a digital SLR. It does stop down the set aperture, but the problem is that with digital's brightness optimized viewfinders, you still cannot accurately preview the DOF wider than f4. And if you are stopped down past f4, it will likely be too dark to preview the DOF.

So, yeah, useless button other than for seeing your aperture blades.

Unfortunately it can't be remapped on most bodies.

oh that sucks, it works on 7D

When you look through your VF, you're looking through the lens wide open since the camera doesn't stop the lens down to your selected aperture until the moment you take the shot.

Pressing the DOF Preview button stops the lens down to the aperture you've selected so you can preview the DOF. It's quite useful if you need to check your DOF.

The viewfinder on the 7D has the same size as the one on a 1D Mark III, so it's not always the APS-C bodies have smaller viewfinders.

The DOF button is actually more useful on digital cameras than it was on film. Thanks to the rear LCD's capability to compensate for the darkness when you stop down, it's easier to see the effect of the depth of field in live view than it has even been in the viewfinder, even on a camera like my manual focus EF from 1975.
The image on the display doesn't have any brightness optmizations which precludes seeing the effect of the depth of field either.

Honestly it isn't very useful on the 7D so you might as well map it to something else as the 7D's special LCD enabled viewfinder only shows you the depth of field down to f/4 or so while the 1D shows you to f/2.8. It isn't just about the size or brightness of the viewfinder, it affects the apparent DOF in other ways as well. On other cameras (1D, 40D, 50D) you can change the focus screen which also aid in showing you the depth of field and accurate focus. The EF-S and EC-S screens work with f/2.8 and faster lenses for this purpose. The 7D can't change the screen as it has an LCD in it.

That's why I wrote that using the DOF button in live view is a good idea.

One other use of the DOF preview button is it allows you to set the aperture when using reversing rings and cheap extension tubes.