Depth of Field Preview Button

I have owned a Canon A2E and more recently a 350XT.
both those like most SLR have a DOF preview button.

I never quite found this very useful, for the simple fact that it's too dark, so it's pretty hard to really distinguish what's in or out of focus.

A lot of photography technique literature mentions checking the DOF using this button, but I can't say that worked for me (using A-DEP made for it, but it's not all that great on the DSLR..nto sure why Canon changed how they were doing it...was great on A2E...another topic..)

Does anybody have a good example (type of picture, etc...) that I could use to really observe the DOF when using the preview button feature?

Thanks

Vincent

I agree with you that the depth of field preview button has limited use. It's nearly impossible to truly assess subtle changes in depth of field using the preview on a 35 mm or smaller viewfinder-- particularly because it gets very dark. In those situations I think that having a better intuition for changes in aperture (or using a depth of field calculator) is perhaps much more productive and consistent. On the other hand, here's my top 4 examples where I feel the DoF preview button is still quite helpful:

(1) Cameras that have the new "Live View" feature
Note: the viewfinder also gets darker in these cameras, but this can be somewhat compensated for by either increasing the rear LCD brightness or temporarily adding exposure compensation (but making sure to turn this exposure compensation back off for the actual shot). There's a little more on this topic in the thread on the pros/cons of Live View.

(2) Visualizing changes in background blur (bokeh)
This can be very helpful when you want to avoid or carefully place the location of a specular highlight in the background.

(3) Visualizing depth of field with a tilt/shift lens
Often times the location of the DoF is very counter-intuitive when using a tilt shift lens to reposition depth of field. Although not perfect, even a dark viewfinder can help for this...

(4) Visualizing the impact of lens flare
This is admittedly a much less common use, but on occasion it can prove helpful. This is because the size and location of camera lens flare can change pretty dramatically depending on your lens's aperture setting.

Overall, what I find funny is that until the advent of Live View, most of the above top uses serve to tell us anything about the depth of field...

Yes, the A-DEP can be annoying in some cases, but helps out in others.
Yes, the DOP preview is often not too useful for me (XTi camera).

I will share some tips/techniques that have helped me. Mind you I am still learning about all this.

1) What I typically do when shooting portraits or close subjects against a (busier) background, is I take my eyes off of the viewfinder and try to frame the scene with the naked eye. As you might know, we see things through a wide open lens through an SLR and that might hide/blur distracting objects.

<i>Example: The pole coming out of Jenny's head wasn't really there when looking through the viewfinder. But when I looked at Jenny without a camera, I clearly saw the pole coming out of her head.</i> Simple, seems obvious, but helps me a lot.

2) I do use A-DEP now in situations such as: <i>A tree branch with flowers framing a historical wall at a distance</i>

3) If you can manage to have a DOP calculator tool on you, it might serve you very well. Be it on paper, plastic, or digital.

Hope that helps a bit.

Elie