DOF preview: the other worthless button?

When using the DOF button for maximum DOF, you are changing focus to obtain sharp edges in both the near and far fields. The point of focus is not necessarily at the main subject to obtain maximum DOF.

DOF button is useful in my landscape shooting. I use it when I'm sliding in my GNDs for correct placement.

Just curious...

Does the 40D adjust (i.e. amplify light with ISO change etc.) when you use the DOF preview in live-view mode?

photobitz wrote in post #4305017
Just curious...

Does the 40D adjust (i.e. amplify light with ISO change etc.) when you use the DOF preview in live-view mode?

Yup, it does. Very useful feature. Now you can preview your DOF without darkening the frame using LiveView. Great for macro. There's probably a limit of how much it can amplify the image brightness before it gets too noisy or gives up.. but I haven't tested this out yet (just got my 40D yesterday ).

Update: just tested... If the incoming light gets too dark and u use DOF preview, Live-view might be unable to simulate the exposure... in that case it will be unable to amplify the brightness to match what you'd expect your exposure to be. The "Exp Sim" logo will flash if this is the case... This is probably in the manual... will have to read.

I am an old time film shooter recently converted to digital. My main film camera was a T90 with a DOF lock mode. This allowed me to lock down the depth of field preview button and adjust the aperture on the lens. As I did, the shutter speed was automatically adjusted. This was particularly great when shooting wildflowers and macro. Once you learn to look beyond the basic darkening of the screen as you change the f-stop, you can actually SEE exactly what will and won't be in focus in the final image. Damn I miss this. The DOF preview does a similar task but is less elegant. Without a DOF preview button I would dump my Canon equipment. It is that essential.

I use it... works better with the bigger viewfinders of the 1D bodies, not so well on the 10D/20/etc. I think my main use is to check that things in the background won't be too visible when stopped down.

The DOF scale is useful too, for me mainly for wide angle lenses when I want to have very deep DOF though.

mikechong wrote in post #4305477
Yup, it does. Very useful feature. Now you can preview your DOF without darkening the frame using LiveView. Great for macro. There's probably a limit of how much it can amplify the image brightness before it gets too noisy or gives up.. but I haven't tested this out yet (just got my 40D yesterday ).

Update: just tested... If the incoming light gets too dark and u use DOF preview, Live-view might be unable to simulate the exposure... in that case it will be unable to amplify the brightness to match what you'd expect your exposure to be. The "Exp Sim" logo will flash if this is the case... This is probably in the manual... will have to read.

Wow, I didn't know it could do that! Great! Now I really can't wait for mine to arrive.

Finally playing with the DOF button, I can see some use but overall I don't think I'd use it. Can be fun though to know if F2.8 is too much maybe you should go to F4 or F5.6. I see it's use, just for certain situations and times you have more...time.

From what I am hearing pressing DOF button will trigger the flash?

I did not know that, what purpose would that serve??

I do use DOF to visualize depth of field.

I use the DOF preview button fairly often.... I find myself still struggling with getting the DOF I want on some shots and the preview lets me figure out what looks best dynamically. I hold the button down, then change the aperture with the wheel, and you can see the DOF change in the viewfinder.

You could do the same by taking shots I guess, but I like to do it this way.

It'll trigger the modelling light by default.

I can think of two uses:
1) Easy access to the ML function,
2) Enough light to actually see something in dark surroundings when pressing the DoF preview button

It's a great flashlight...er...it's a great way to see if your lights will fall where you hope they will. Granted, the Strobist method is "hey <subject>, can you see the flash head through the snoot from where you are", so modeling flashes aren't necessary, but not all of your subjects can call an audible, and it's also beneficial to know if an un-snooted flash is aimed right.

Madweasel wrote in post #4308052
Wow, I didn't know it could do that! Great! Now I really can't wait for mine to arrive.

I can't wait for my 30D to get stolen so I can replace it new for old under my insurance policy! LOL

I've been watching 40D demos on youtube and there is just so much extra packed into it. I am really lusting for one now.

flying_rph wrote in post #4273917
I use it all the time. Also, with the live view function on the 40D and Mark III, you are able to see the results on the LCD when you use the DOF preview button.

I am looking forward to using it with my 40D for macro work. The 30D viewfinder is a bit small to make good focus adjustments, but the live view will make the DOF preview truly useful.