20D DOF Preview Button Question

Richard · March 9, 2006

My understanding is that pressing the DOF preview button closes the aperture while you are looking through the view finder to what it will be when you release the shutter. What I don't understand is what this is telling me or how to use it. :scratch:scratch Overall, it just seems to darken what I see according to the f stop I have set--no surprise there. I would appreciate it if someone could explain to me how they use this feature. Must be good for something...:dunno

Cheers,

Shay Stephens · March 9, 2006

rsinmadrid wrote:

My understanding is that pressing the DOF preview button closes the aperture while you are looking through the view finder to what it will be when you release the shutter. What I don't understand is what this is telling me or how to use it. scratch Overall, it just seems to darken what I see according to the f stop I have set--no surprise there. I would appreciate it if someone could explain to me how they use this feature. Must be good for something...

Cheers,

As you have noticed, the image in the view finder gets darker. In addition to the decrease in the amount of light reaching the eye/sensor with a small aperture, the depth of field gets changes too. However, it can sometimes be hard to see that with the darkened screen, especially when hand holding the camera. So extra care must be taken to note the areas that are/are not sharp, and then toggle the button on and off to see the (sometimes) subtle changes.

If you really want to test this feature systematically, I recommend putting the camera on a tripod and setting up a scene with subjects that range from close to far. Focus midway, and then start testing the DOF preview button. It will be a lot easier to see the changes. Once you see them and recognize what is going on, it may be easier to spot in the field.

HeldDown · March 9, 2006

Essentially how it's useful is this: If you compose a shot, focus on your subject, and fire it at f/1.8, and then look at the screen and go "Crap, way too much OOF background" or "I needed more DOF" so you go back and shoot the frame at f/16. Look at the screen and you realize your DOF is far too deep? IF you press the DOFP button and look, it represents what your ACTUALLY DOF will be at the given aperture, instead of what you're seeing on your mirror.

God I hope that helped. Shay's right about sitting up a tripod in a well lit room, and try focusing on something like a flower or a standing cordless phone in front of a pile of junk. Then it'll be obvious.

pathfinder · March 9, 2006

The secret to the depth of field preview button is that you cannot be in a hurry like most folks are today.

You must press the button, look through the viewfinder and wait - some times 15-30 seconds - for your eye to dark adapt before you begin to inspect the image for areas in and out of focus.

Think of a view camera shooter with his head underneath that black cape looking at the ground glass that will hold his film - he does not just take a quick glance, but slowly, studiously studies the image before he loads the film and opens the shutter on his $8.00 piece of film.

To use the preview button, you must emulate the view camera shooter - slow down and take the time to really LOOK through the viewfinder AFTER your eye has dark adapted. That's why Shay's suggestion to do this with the camera on a tripod is so apt.

I find the Preview button hard to use handheld.

Bob&Glennie · March 9, 2006

pathfinder wrote:

The secret to the depth of field preview button is that you cannot be in a hurry like most folks are today.

You must press the button, look through the viewfinder and wait - some times 15-30 seconds - for your eye to dark adapt before you begin to inspect the image for areas in and out of focus.

Think of a view camera shooter with his head underneath that black cape looking at the ground glass that will hold his film - he does not just take a quick glance, but slowly, studiously studies the image before he loads the film and opens the shutter on his $8.00 piece of film.

To use the preview button, you must emulate the view camera shooter - slow down and take the time to really LOOK through the viewfinder AFTER your eye had dark adapted. That's why Shay's suggestion to do this with the camera on a tripod is so apt.

I find the Preview button hard to use handheld.

That Sir, is really good information and good advice for all of us. "Slow down" and take the time to really see what you are looking at. Thank you

MainFragger · March 9, 2006

DoF button..
Whose brilliant idea was it to put a button on the lower left portion of the front casing? Its almost unoticeable, highly unintuitive (to me at least) and pretty much a pain to use.

I think the guy that designed that button is the same dude that insisted to the end that the Titanic was unsinkable.. The worse part of that, is that as someone who worked in the electronics industry, I can almost guarantee that if I worked for Canon and asked them this internally, they would reply, "According to our test groups, that was the best place for it..."

MainFragger/Brian

David_S85 · March 9, 2006

The idea of that DOF preview button is an old one, as well as the choice of placement. So old in fact, that the person who made the decision on placement is probably long since dead. It's been there for about 50 years or so. They used to be a lever, then a push bar thing, and now its a button.

The up front location is related to how one used to hold a camera and stop down the lens with aperture ring. The button is then just a thumb motion away from there.

Those used to the traditional SLR's will go there naturally. I am one of those who likes it where it is.

But could it be in a better place now that the aperture ring has been
replaced by a control dial?

MainFragger wrote:

Whose brilliant idea was it to put a button on the lower left portion of the front casing? Its almost unoticeable, highly unintuitive (to me at least) and pretty much a pain to use.

I think the guy that designed that button is the same dude that insisted to the end that the Titanic was unsinkable.. The worse part of that, is that as someone who worked in the electronics industry, I can almost guarantee that if I worked for Canon and asked them this internally, they would reply, "According to our test groups, that was the best place for it..."

MainFragger/Brian

DoctorIt · March 9, 2006

what's a DOF preview button?

(that's a winger joke, nevermind)

I must say, I find the DOF preview on my nice bright D2H viewfinder much more useful than on all the little Canon's I had.

Good advice from PF though. Slow and steady

Richard · March 10, 2006

I followed your advice, using a tripod and taking my time. I just didn't understand what to look for before. I think I get it now.

Thanks for taking the trouble to explain it to me.

thumb I may be a bit slow but I am persistent.

Cheers,

Shay Stephens · March 10, 2006

Now that you know what to look for, it should work for you even hand holding now

:

rsinmadrid wrote:

I followed your advice, using a tripod and taking my time. I just didn't understand to look for before. I think I get it now.

Thanks for taking the trouble to explain it to me. thumb I may be a bit slow but I am persistent.

Cheers,

Antonio Correia · March 10, 2006

DOF preview button
I think this can be also usefull

:

Quotation from http://www.cambridgeincolour.com/tutorials/lens-flare.htm :

"VISUALIZING FLARE WITH THE DEPTH OF FIELD PREVIEW
The appearance and position of lens flare changes depending on the aperture setting of the photo. The viewfinder image in a SLR camera represents how the scene appears only when the aperture is wide open (to create the brightest image), and so this may not be representative of how the flare will appear after the exposure. The depth of field preview button can be used to simulate what the flare will look like for other apertures, but beware that this will also darken the viewfinder image significantly.
The depth of field preview button is usually found at the base of the lens mount, and can be pressed to simulate the streaks and polygonal flare shapes. This button is still inadequate for simulating how "washed out" the final image will appear, as this flare artifact also depends on the length of the exposure (more on this later)."

Best regards and a nice week-end.

chrisjlee · March 10, 2006

Antonio Correia wrote:

I think this can be also usefull :

Very useful!

Antonio Correia · March 10, 2006

Good. This as meant to be so.

chrisjlee wrote:

Very useful!

Useful and not usefull

20D DOF Preview Button Question

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