Newbie DOF Preview Question

[Civilian]

I just got a Rebel Xti. First Digital SLR. Had a first Generation Maxxum for years, but I'm coming into the modern era.

The DOF preview button is new to me. If the Maxxum had one, I never noticed it. The instruction booklet suggests that you can hold down the DOF and change the fstop and watch the change it makes. I tried that and, as I was changing the fstop and hearing it make a weird little noise, I stopped and immediately I wondered if I had done/was doing damage to the camera or lens by holding down the DOF preview button while changing the ap.

Am I being paranoid? If it really is harmful, is it likely doing this only once would have done any harm?

[KevC]

The noise is the aperture blades snapping into place.

It's not harmful at all. Your lens does this automatically when you press the shutter, you just can't hear it cos of the mirror slapping =)

[Zohar]

Well I just changed the f stop and yeah it made a noise but a quiet one and it got a little darker, that is what is supposed to happen. Don't worry bud :) Have fun with the XTi and welcome to POTN!

[Civilian]

Ok. Cool. Thanks guys. What worried me was that I was holding down the button while changing the fstop instead of changing the fstop -- pressing it/releasing it -- change again -- press/release -- change, etc..

I don't know why, but it seemed like that could hurt it, pressing the DOF preview at the same time as changing the fstop.

But you've put me at ease. Back to playing with the camera.

[dkangel]

Why is it that it gets darker. I would have thought the DOF button should show you the blur you will see. All I have ever noticed is it gets a bit darker. What am I doing wrong?

[AirBrontosaurus]

Why is it that it gets darker. I would have thought the DOF button should show you the blur you will see. All I have ever noticed is it gets a bit darker. What am I doing wrong?

It is closing the aperture blades, which is making less light reach the view finder. Thus, the image darkens.

DOF preview is a little tough to use because of the tiny size of the viewfinder. You won't notice a night/day difference between, say, f/4 and f/5.6. If you try wide open to something like f/32, you may see a more noticeable effect.

[dkangel]

It is closing the aperture blades, which is making less leght reach the sensor. Thus, the image darkens.

DOF preview is a little tough to use because of the tiny size of the viewfinder. You won't notice a night/day difference between, say, f/4 and f/5.6. If you try wide open to something like f/32, you may see a more noticeable effect.


Thanks for that explanation. I guess I dont see much use in it is all. Maybe there is but I have yet to see how it helps.

[LBaldwin]

Thanks for that explanation. I guess I dont see much use in it is all. Maybe there is but I have yet to see how it helps.

When you start doing portraiture you can use it to check and see if yucky backgrounds are going to be a problem. When shooting flowers you can use it to check and see if the entire flower will be in focus. In WA shots you can use to check for flair off of the aperture blades. It is one of the most useful tools that Canon has on their gear. If your camera has one learn to use it.

Les

[AirBrontosaurus]

Yes, I didn't mean to say it was useless. But, I shoot mostly macro, where DOF preview isn't that helpful. Other than that I just use DOF calculators or get used to my lenses. I probably should use the DOF preview, but I'm lazy.

[dkangel]

LBaldwin - ok will do, I will start practicing with it more.

[Madweasel]

Yes, I didn't mean to say it was useless. But, I shoot mostly macro, where DOF preview isn't that helpful.
I'm surprised to hear you say that. DOF is critical in macro work, so I would think you'd be keen to see how much you get.

[nicksan]

Perfectly normal methinks...

[AirBrontosaurus]

I'm surprised to hear you say that. DOF is critical in macro work, so I would think you'd be keen to see how much you get.

Well, I do most of it by feel. Since I always shoot at either 1:1 or 2:1 and keep a constant aperture, I have a pretty good idea of what the DOF for a given shot will be. Also, with a full set of extension tubes, stopped down to f/9 or f/11, the viewfinder gets really, really dark. It's tough to see much of anything. let alone make good judgments of DOF.

However, I shoot hand held, and my subjects are insects that move a lot. If I was shooting something stationary on a tripod with lighting, then the DOF preview would be more useful.

[Bob_A]

It is closing the aperture blades, which is making less leght reach the sensor. Thus, the image darkens.

DOF preview is a little tough to use because of the tiny size of the viewfinder. You won't notice a night/day difference between, say, f/4 and f/5.6. If you try wide open to something like f/32, you may see a more noticeable effect.

Just a tiny correction ... less light reaches the viewfinder, not the sensor when you press the DOF preview button (the mirror is still down). :)

[AirBrontosaurus]

Just a tiny correction ... less light reaches the viewfinder, not the sensor when you press the DOF preview button (the mirror is still down). :)

Bah, ya got me. Noted and corrected. Thanks!

[Madweasel]

Well, I do most of it by feel. Since I always shoot at either 1:1 or 2:1 and keep a constant aperture, I have a pretty good idea of what the DOF for a given shot will be. Also, with a full set of extension tubes, stopped down to f/9 or f/11, the viewfinder gets really, really dark. It's tough to see much of anything. let alone make good judgments of DOF.

However, I shoot hand held, and my subjects are insects that move a lot. If I was shooting something stationary on a tripod with lighting, then the DOF preview would be more useful.
Yes, both good points. I guess I was mainly thinking of tripod-mounted macro work.

[Madweasel]

With my old manual Tamron macro lens I don't have a choice as I have to manually stop down before taking the shot. That gives me a DOF preview whether I want one or not! My next lens will definitely be the Canon 100mm macro.