Rebel XT question - DPChallenge Forums

Canon EF 24-70mm f/2.8L USM

03/22/2006 02:58:47 AM · #1

What exactly does that depth of field preview button under the lens do?
I've read the manual but it's not really clear on this.

gloda

Canon EOS-5D Mark II

03/22/2006 03:01:46 AM · #2

The lens is usually set to maximal aperture when you look through the viewfinder. When you push the button, you see the DOF as it will be on the picture. However, this means that your picture will become very dark in the viewfinder at apertures like 32.

Message edited by author 2006-03-22 03:02:06.

Tamron AF 28-300mm f/3.5-6.3 XR Di LD Aspherical IF for Canon

03/22/2006 03:04:23 AM · #3

Press the DOF preview button to stop down to the current aperture setting. By doing so the diaphragm in the lens will close to the current aperture and you can check the DOF through the viewfinder. Known as viewing range of acceptable focus.

Message edited by author 2006-03-22 03:05:06.

crayon

03/22/2006 03:14:24 AM · #4

is this feature available on all dSLRs? Thanks

03/22/2006 03:15:35 AM · #5

Originally posted by southern_exposure:

I'm really not being an ass when I say this Scott but I know what it says in manual. I guess I don't really understand what it's for. I understand what it does but I don't get what type of situation you would want use this in? Do you use it ever? I guess give me an example, maybe that would help.

Bear_Music

Sony 24-70mm F4 Vario-Tessar T* FE OSS

03/22/2006 03:29:48 AM · #6

Originally posted by dsmeth:

Originally posted by southern_exposure:
Press the DOF preview button to stop down to the current aperture setting. By doing so the diaphragm in the lens will close to the current aperture and you can check the DOF through the viewfinder. Known as viewing range of acceptable focus.

I'm really not being an ass when I say this Scott but I know what it says in manual. I guess I don't really understand what it's for. I understand what it does but I don't get what type of situation you would want use this in? Do you use it ever? I guess give me an example, maybe that would help.

When you have the camera on a tripod and you are photographing close-ups where DOF is critical, the DOF preview allows you to judge whether you are focused on the correct spot and stopped down enough to have everything in focus that you wish. Or, conversely, if you are after shallow DOF, it allows you to check and see that you don't have too MUCH.

The problem is that dSLR viewfinders are very small and they get very dark when you stop the lens down like this. It can be helpful to have an additional, VERY bright light up close to your setup that you turn on for focusing, and then turn off when you are actually shooting. And it should go without saying that DOF preview is only useful in manual focus mode.

Robt.

edit to add; for an example of a shot made with DOF preview see my footwear entry:

The focus was on the eyes, and I wanted a middling-shallow DOF here. What I ended up with is exactly what I was after. I had a 500-watt flood a foot from the setup for focusing, and turned it off for the shooting.

Message edited by author 2006-03-22 03:33:41.

Tamron AF 28-300mm f/3.5-6.3 XR Di LD Aspherical IF for Canon

03/22/2006 03:32:05 AM · #7

Originally posted by dsmeth:

Yes I use it sometimes when DOF is important - shallow or deep. When you are looking through a dSLR viewfinder and it says you have a f/2.8 AV and you have a lens that has a max. aperture of f/2.8 then you will see the same thing if you look through the view finder without pressing the button or pressing the button because most if not all lens are open to it max. aperture until you press the shutter.

Now lets say you have your AV set to f/22 and you are using the same lens with a max. aperture of f/2.8. When you are looking through the viewfinder without pushing the DOF button you are seeing things a aperture f/2.8 but when you take the picture it will close the diaphragm to f/22. So what you seen before you press the shutter is not what you will have in the image. But if you press the DOF button it will close the diaphragm down to f/22 letting you see what the picture should look like. Release the button and you will see it wide open again.
Hope that helps.

Message edited by author 2006-03-22 03:33:16.

03/22/2006 03:40:33 AM · #8

Thanks for the help guys. I'll play with and see what happens. I think I've only ever pressed it once before, didn't get the purpose of it, and never pressed it again.

sir_bazz

Pentax K-5

Pentax FA 50mm f/1.4 AF

03/22/2006 03:43:41 AM · #9

I find it the most redundant feature on my dslr.

I find confirming dof is much easier by taking a test pic and reviewing it on the LCD. But I guess thats one of the advantages of a good sized/high-res LCD.

cheers,
bazz.

Message edited by author 2006-03-22 03:44:12.

Tamron AF 28-300mm f/3.5-6.3 XR Di LD Aspherical IF for Canon

03/22/2006 03:44:47 AM · #10

Originally posted by dsmeth:

Thanks for the help guys. I'll play with and see what happens. I think I've only ever pressed it once before, didn't get the purpose of it, and never pressed it again.

Good luck and bear offer some great advice with lighting for focus, etc.

Tamron AF 28-300mm f/3.5-6.3 XR Di LD Aspherical IF for Canon

03/22/2006 03:47:48 AM · #11

Originally posted by sir_bazz:

You are right about that. That is one issue of two I have with the 350XT. The LCD is small and dark even with the brightness upped. Plus I wish they would of put a preview LCD on the camera.

Bear_Music

Sony 24-70mm F4 Vario-Tessar T* FE OSS

03/22/2006 03:48:46 AM · #12

Originally posted by sir_bazz:

We old film guys are used to doing it this way :-) It's all we had, back in the day.

R.

Canon EF 100-400mm f/4.5-5.6L IS

03/22/2006 03:55:24 AM · #13

Originally posted by Bear_Music:

Originally posted by sir_bazz:
I find it the most redundant feature on my dslr.

I find confirming dof is much easier by taking a test pic and reviewing it on the LCD. But I guess thats one of the advantages of a good sized/high-res LCD.

cheers,
bazz.

We old film guys are used to doing it this way :-) It's all we had, back in the day.

R.

How far back "in the day" are you going Robert. Don't remember seeing to many 35mm with LCD's LOL

Kaizer

Canon EOS-350D Rebel XT

03/22/2006 05:42:24 AM · #14

Lets see... DOF button

Know what it is, know how to work it.... Never used it....

smilebig4me1x

Canon EOS-400D Rebel XTi

Canon EF-S 18-55mm f/3.5-5.6

03/22/2006 06:06:53 AM · #15

Originally posted by dsmeth:

Thanks for the help guys. I'll play with and see what happens. I think I've only ever pressed it once before, didn't get the purpose of it, and never pressed it again.

This reply WAS me. Now that i understand what it actually does i will be pushing that little button a bit more!

Bear_Music

Sony 24-70mm F4 Vario-Tessar T* FE OSS

03/22/2006 01:17:48 PM · #16

Originally posted by dsmeth:

Originally posted by Bear_Music:

Originally posted by sir_bazz:
I find it the most redundant feature on my dslr.

I find confirming dof is much easier by taking a test pic and reviewing it on the LCD. But I guess thats one of the advantages of a good sized/high-res LCD.

cheers,
bazz.

We old film guys are used to doing it this way :-) It's all we had, back in the day.

R.

How far back "in the day" are you going Robert. Don't remember seeing to many 35mm with LCD's LOL

Huh? What I meant is we didn't have LCDs, and we didn't have instant feedback of any kind, so we HAD to use the DOF preview button...

R.

crayon