DOF Preview

[chrisk]

given i will be spending more time in using my macro lens i'd like to learn how to use the DOF Preview button properly. to be honest i have absolutely no clue whatsoever on what it does and how to effectively use it. all i know is that when pressed it darkens the image...then what ? i don;t get it.

can y'all pls lend a hand on what exactly it does and how to use it correctly.

[phillipb]

Macro.... forget it.
Typically you will be using very small apertures for macro shots, which means that the viewfinder would be too dark for you to be able to see anything.

[chrisk]

i normally use between f2.8-f8, that shouldn;t be too dark. on the occasion i use up to f16 say, but not so often.

regardless, what exactly does it do ?

[phillipb]

Sorry, I didn't address your original question very well.

What you normally see in the viewfinder is a view with the lens fully open. Basically what happens when you use the DOF preview button is that the lens is stopped down to the aperture that you have chosen. so that you can see what effect it has to the DOF. Problem is, if you use say f11, the amount of light going to the viewfinder is very little and you can't really see the DOF anyway.

[young_einstein]

regardless, what exactly does it do ?

Looking through the viewfinder 'normally' the lens aperture is always wide open, regardless of what settings you're actually shooting with.

That's to let the most light through the lens and give you the brightest [read: easiest to see through] viewfinder.

Pressing the DoF preview button stops down the aperture iris to whatever setting you're shooting with, so you can actually see how it's going to turn out.

That obviously restricts light though, and dims your viewfinder quite a bit [depending on the aperture setting you're actually using], so what it's supposed to be trying to show you becomes too dark to see properly.

Kind of a catch-22 really.

I shoot an awful lot of macro, and personally I don't bother with it at all. I find it vastly easier to just check the results on the LCD, and then adjust from there.

DoF preview is a waste of time!

[chrisk]

thanx for the info. so am i supposed to be seeing what is in and out of focus is that what you mean ? it's obviously not the exposure how good do your eyes have to be for that !

i agree with you, wouldn't it just be easier to just check the LCD ?? seems an almost redundant feature in DSLR's. does anyone here use it that can explain why they would use this instead of the LCD ?

[young_einstein]

thanx for the info. so am i supposed to be seeing what is in and out of focus is that what you mean ?

Yes.

[digitor]

Unfortunately on DSLRs with less than optimum viewfinder brightness and small mirrors the DOF preview doesn't work very well at all. The small mirror means that you don't get to see the effect of any aperture larger than about 2.8 anyway, and the dimness makes it hard to see the effect of the aperture change when the lens is stopped down.

If you can get hold of a film SLR with a 50/1.4 lens on it, set it to f8 and check the DOF preview - that is how it's supposed to work!

Cheers

[gstark]

i normally use between f2.8-f8,

Not for macro, you won't be.

The issue here is that as you get closer to your subject (and that includes this move into macro distances) the range of your DoF decreases dramatically. At f/2.8 at 1 metre you may have DoF of several millimeters (depending upon which lens you're using), but as your subject to focal plane distance decreases, so too does the DoF range for that aperture, for that focal length.

When you're in macro-land, you often find it's best to achieve focus by rocking backwards and forwards slightly, rather than trying to adjust your focus ring. There's a good reason why you can buy accessories such as macro focusing rails ....

And yes, autofocus is often left by the wayside when you're shooting macro.

Often, even at apertures of f/16 or greater, you may find that the head of an insect like an ant may be in focus, but its legs are not.

So you find yourself wanting to add light (look at ring flash and other macro lighting solutions) and use even higher aperture values to get even more of your subject into focus.

So, unless you're shooting detail of stamps (or other flat objects) you will find that you need to shoot with high f-stop numbers in order to simply get an acceptable amount of your subject matter into clear focus.

Now consider going outside to shoot that grasshopper or bee on the leaf of a plant .... in a slight breeze. Even the slightest breeze will move your subject, and any attempt by you to achieve good focus will be thwarted by the ambient conditions. It's not impossible .... but it can be frustrating.

Look at issue 2 of Chimp, and the article on BlacknStormy's work. Look at her images ...

Now, getting back to your original question .. as you've surmised, your viewfinder gets dark when you use the DoF Preview button, and it becomes difficult to see anything, let alone which part of your subject matter is in or out of focus.

In pre-digital days it was all we had, but with the advent of chimping, it is far easier to shoot and chimp, and then assess where your shooting is going, than to use the DoF preview.

[chrisk]

ok...i;ll ask the stupid question...what is chimping ?

[gstark]

The only stupid question is the one that you fail to ask.

Chimping

[Ivanerrol]

Chimping.

[gstark]

Beautiful!

[Ivanerrol]

Is this chimping or Katting?

[the foto fanatic]

Those Canon cameras ARE good for something!
Pet food!!

(Important disclaimer: That was an attempt at humour! I will duck any personal attacks that may come my way. )