DOF Preview Button; what am I seeing?

[ajmcdo]

I've been shooting with my 10d, 16-35 2.8, 24-70 2.8 and 70-200 2.8 L lenses this afternoon (all at f22), a sunny Australian Autumn with a yard full of trees. I'm trying to get a handle on DOF, hyperfocal length and realistic landscapes. After reading our forum's stuff and Vivid Light's explanations of best Hyperfocal/DOF shooting I thought I'd have a go at capturing landscapes with DOF that reflected the reality of what I was shooting.

Some shots were great some not so. The really good ones seemed to come from the 70-200 f2.8L at about 100mm. Sorry I can't post shots yet, I'm still trying to get a broadband connection.

One thing puzzles me greatly. When I press the DOF Preview button I don't know what I should be taking on board. Mostly the viewer screen darkens and that's it. What should the DOF preview be telling me? How do you guys deal with this in practical terms?

Tony McDonogh

[G3]

OK, here's what happens. When you set the aperture, you are setting how large you want the opening in the lens to be at the time the shutter is fired. The aperture stays wide open no matter how you have it set until you press the shutter button, then the mirror flops up out of the way (blocking your view through the finder), the lens stops down to the selected aperture, the shutter fires and the the mirror flops back down so you can see through the finder again. The reason the aperture stays wide open all the time (until you press the shutter button) is to let more light in to make it easier to focus..so the finder will be brighter. What the Depth of Field preview button does is to stop the lens down to your selected aperture so that you can see what will be in focus and what won't. That's why the finder darkens. What you should be looking for is what is in focus and what is out of focus at that aperture setting. When the lens is stopped down like that and you are looking through the finder, it's pretty much wysiwyg (what you see is what you get).

Depth of Field is (in large part) a product of the size of the aperture. With a small aperture (large f number), more will be in focus. With a large aperture (smaller f number) less will be in focus. So, if you want the subject in focus and the background blurred out, you would select a large aperture (small f number). This effect is also dependent in part on distance to subject, distance from subject to background and the focal length of the lens. In general, you can get a much greater depth of field with a short lens, such as a wide angle lens, where it is possible to have everything from 3 feet to infinity in sharp focus. The more magnification, the shallower the depth of field.

[timmyquest]

I'm already aware of what the button does, and if i hadnt been i would be now ;). But seriously, does anyone find it of any use. On every canon that i've owned this thing has been here, and on all of them it's too dark to see anything.

[G3]

I'm already aware of what the button does, and if i hadnt been i would be now ;). But seriously, does anyone find it of any use. On every canon that i've owned this thing has been here, and on all of them it's too dark to see anything.

Yes. I use it extensively when doing Macro work. The depth of field when doing Macro is about as generous as the IRS. I have to see what's in focus and what isn't. You just have to keep a lot of light on the subject so the finder will be bright enough to see what's going on. You can use the modeling flash for that, or sometimes I use photofloods just for that purpose, then turn them off and use the strobes I have set up to make the photo.

I won't buy a camera that doesn't have DOF preview and Mirror Lockup (MLU).

[ajmcdo]

Question answered, thanks.
i do agree with timmyquest that what I see is dark enough to be hard to work with in the field.
Tony McDonogh

[robertwgross]

If the DOF Preview button shows you a very dark image, then what does that tell you about your lens aperture?

To put it differently, if an open aperture still makes the DOF Preview look too dark, then maybe you want a lens with a wider aperture.

I learned DOF with a Canon film camera that had no DOF Preview, so back then, I only considered three cases: (1) wide open aperture, minimum depth of field, (2) closed down aperture, maximum depth of field, and (3) intermediate aperture, compromise depth of field. With this limitation, I could never get very good with DOF.

Then I got a Canon digital camera with DOF Preview and learned how to use it. It is too easy to stick the camera into a close-up mode and then not worry about DOF, but that is when we need DOF Preview the most.

---Bob Gross---

[G3]

If the DOF Preview button shows you a very dark image, then what does that tell you about your lens aperture?

To put it differently, if an open aperture still makes the DOF Preview look too dark, then maybe you want a lens with a wider aperture.

---Bob Gross---

I don't understand what you are saying, Bob....but, it's late and my brain fades a little at this hour, too. :)

When you press the DOF preview button, you are stopping the lens down to the selected aperture. That has nothing to do with the maximum aperture of the lens. The finder is naturally going to go darker, if the selected aperture is smaller than the the max aperture of the lens. The smaller the selected aperture, the darker the finder will get when you press the button. Just because the finder goes dark doesn't mean that you have selected an aperture that is too small either, because the exposure you get is going to be dependent on the shutter speed as well as the selected aperture.

Did I misunderstand what you were getting at?

[ron chappel]

Personally i have only ever used the DOF button a few times in my life-i hate the whole concept and just go by experience as to what i want included in the focus zone
That said,i did see a great article on the web...named something like "10 good uses for the DOF button" or somesuch.It really did have some usefull ideas

I'm going to try finding it again.....

[RonR]

Here's a chart that you can fill out with your lens specifics and it will give you the DOF - I can't figure out the DOF button either and when I tried it didn't really see what it did or was suppose to do - I'm sure it's me. :roll:
http://www.johnhendry.com/gadget/dof.php

[Belmondo]

I think the DOF preview button is one of those SLR 'traditions' that Canon feels they have to include for old time's sake. If they really intended for us to use it, they would have made it a lot more convenient than it is. If you hold the camera like most people, it's impossible to press it without removing the left hand from its grip altogether. DOF charts are much easier and more accurate.

Thos.

[ShutteringFocus]

What are you seeing? A darker image of what you see without it pressed down... :roll:

haha...no, these guys are right, (imaging that :shock: )

[Tom W]

I've not found a great deal of use out of the DOF preview when shooting landscapes and such outdoors, but when getting in close, I've found it to be useful. Macro is a little deceiving - experience might tell you that f/11 or so will give you adequate DOF, but it often isn't a small enough aperture. The DOF button is quite helpful in those situations provided there is enough light to see.

[G3]

I've not found a great deal of use out of the DOF preview when shooting landscapes and such outdoors, but when getting in close, I've found it to be useful. Macro is a little deceiving - experience might tell you that f/11 or so will give you adequate DOF, but it often isn't a small enough aperture. The DOF button is quite helpful in those situations provided there is enough light to see.

Right. Plus, when shooting Macro, it's important to be able to precisely see where your plane of critical focus is. You do have to get a lot of light on the subject for it to be useful. That's why I use photo floods for focusing on Macro, then turn them off when I'm ready to shoot. The finder on the 10D leaves a little to be desired as far as magnification and brightness, so most of the time I use the Angle Finder-C for the extra magnification. That's one of the things I love about Medium Format. You have that big, bright focusing screen and finder to work with.

[Tapeman]

I use it frequently.

Most of the time is when the camera is tripod mounted and I am fussing about, thinking about expoure, composition, DOF, light & stuff like that.

It is a less usefull if you don't have a bright viewfinder or you are shooting in low light.

[robertwgross]

I don't understand what you are saying, Bob....but, it's late and my brain fades a little at this hour, too. :)


The selected aperture must be a number the same or larger than the widest aperture that the lens is capable of.

If you are going to compare two lenses, and the faster one can go to f/1.4 and the slower one can go to f/3.5, then when you get to the wide open situation and push the DOF Preview button, you will "see" major differences between what the faster lens is doing as compared to the slower lens.

Getting DOF "right" is more difficult with the faster lens. But then, the faster lens allows you to shoot in dimmer light.

---Bob Gross---

[G3]

I don't understand what you are saying, Bob....but, it's late and my brain fades a little at this hour, too. :)


The selected aperture must be a number the same or larger than the widest aperture that the lens is capable of.

If you are going to compare two lenses, and the faster one can go to f/1.4 and the slower one can go to f/3.5, then when you get to the wide open situation and push the DOF Preview button, you will "see" major differences between what the faster lens is doing as compared to the slower lens.

Getting DOF "right" is more difficult with the faster lens. But then, the faster lens allows you to shoot in dimmer light.

---Bob Gross---


OK. I gotcha...I DID misunderstand what you were trying to say. What you were saying is, if at the wide-open setting of your lens, it is still too dark, then you need a faster lens.

That's true, to an extent. However, if you are using flash, that will not apply. Since you are going to flood the subject with light at the time of exposure, you can still get the exposure even if the finder is too dark to see what you are focusing on. A faster lens might help you focus in low light situations, but has little to do with actually exposing the frame. That's why I was saying I use photo floods while focusing.

[robertwgross]

The only problem that I have on my D60 is the DOF Preview button itself. It seems to be in an awkward location, and it is a tiny button. I can never seem to find it automatically when I am in a normal shooting position. I always seem to back off from the camera, find the button, get one fingertip on it, then move back onto the camera. That discourages me from using it much. Yet, I just got through editing on 750 digital images that I shot over two weeks, and the first weakness I saw in some of them was poor control of the DOF.

---Bob Gross---

[MarkH]

If you are going to compare two lenses, and the faster one can go to f/1.4 and the slower one can go to f/3.5, then when you get to the wide open situation and push the DOF Preview button, you will "see" major differences between what the faster lens is doing as compared to the slower lens.


I don't quite understand what you mean here Bob. You seem to be suggesting setting the aperture to the widest setting (smallest number) and pressing the DoF button? But on my 10D the DoF button does nothing when I do that!

Surely the DoF button stops down the aperture to the selected setting, at widest setting there wont be any stopping down at all!

My experience is that when I fit my 50 f1.8 and look through the viewfinder, it is brighter then when I fit my 28-135 f3.5-5.6 IS lens and look through the viewfinder, no need to use the DoF button to see that.

[paul162brown]

This might sound like an obvious one, but I'll throw it in anyway.............

When I first learned how to use DOF preview, (not on a Canon EOS as it happens, but it worked in exactly the same way), I shared some of the concerns posted by some members on this thread about darkness etc etc

However, one solution, if you have the time, is to slow down, take your time, and just be patient. You will be suprised how much your eye will adjust to poor light conditions if you just keep your eye against the viewfinder. Same theory with seeing in the dark. If you come out of your brightly lit house into the dark outside, you will not see much. However, if you stay in the dark and do not look at anything bright for a few minutes, your eyes will adjust and you will see quite well. Just keep your eye against the viewfinder, wait for your eye to adjust, and you will see more than you think!

Of course, it all depends on how much time you have.
:)

[G3]

If you are going to compare two lenses, and the faster one can go to f/1.4 and the slower one can go to f/3.5, then when you get to the wide open situation and push the DOF Preview button, you will "see" major differences between what the faster lens is doing as compared to the slower lens.


I don't quite understand what you mean here Bob. You seem to be suggesting setting the aperture to the widest setting (smallest number) and pressing the DoF button? But on my 10D the DoF button does nothing when I do that!

Surely the DoF button stops down the aperture to the selected setting, at widest setting there wont be any stopping down at all!

My experience is that when I fit my 50 f1.8 and look through the viewfinder, it is brighter then when I fit my 28-135 f3.5-5.6 IS lens and look through the viewfinder, no need to use the DoF button to see that.


I'm not entirely positive, but I think what Bob was saying is that if you have 2 lenses of the same focal length, but different max apertures, such as a 50mm f2.8 and a 50mm f1.4 and you set both of them to, say f11 and press the DOF preview on each, you will see a bigger change in the finder brightness with the 50mm f.4. Which makes sense because there is a bigger difference between f1.4 and f11 than between f2.8 and f11.

If that's not what he was saying, then I guess I don't understand either.

[robertwgross]

G3, yes, I think that is the idea that I was trying to get across.

In a normal consumer camera lens, there is not a very large aperture available. So, with f/5.6 to f/11 in play, it isn't too hard for the normal consumer user to get some reasonable depth of field for just about anything that the camera decides to set. And that is OK, because the normal consumer user isn't trying to do anything very artsy with depth of field.

A serious flower photographer, on the other hand, often wants to control the depth of field down to tiny amounts, from the front of the flower to the back of the flower, and that's all. With a normal consumer lens, this could be quite frustrating. With a very fast lens, like f/1.4, the serious shooter can get just control just about as fine as necessary. But that makes the serious shooter (with the fast lens) more dependent on a depth of field preview button.

If the f/1.4 lens were all the way open, then I suppose that you don't see any change when you hit the preview button. If the f/1.4 lens were selected to f/3.5, then you might see a lot of change. If the similar f/3.5 lens were set to f/3.5 then again you won't see a lot of change.

In other words, the faster the lens, the more important the preview button.

---Bob Gross---

[G3]

G3, yes, I think that is the idea that I was trying to get across.

In a normal consumer camera lens, there is not a very large aperture available. So, with f/5.6 to f/11 in play, it isn't too hard for the normal consumer user to get some reasonable depth of field for just about anything that the camera decides to set. And that is OK, because the normal consumer user isn't trying to do anything very artsy with depth of field.

A serious flower photographer, on the other hand, often wants to control the depth of field down to tiny amounts, from the front of the flower to the back of the flower, and that's all. With a normal consumer lens, this could be quite frustrating. With a very fast lens, like f/1.4, the serious shooter can get just control just about as fine as necessary. But that makes the serious shooter (with the fast lens) more dependent on a depth of field preview button.

If the f/1.4 lens were all the way open, then I suppose that you don't see any change when you hit the preview button. If the f/1.4 lens were selected to f/3.5, then you might see a lot of change. If the similar f/3.5 lens were set to f/3.5 then again you won't see a lot of change.

In other words, the faster the lens, the more important the preview button.

---Bob Gross---

OK..I gotcha. I agree with what you are saying. Sometimes, when shooting high magnification macro, I have to really stop down to pretty small apertures to get everything in focus that I need. That's when you really see the effect of the DOF preview, and it's also when you really need some sort of auxilliary lighting to be able to see what's going on with the DOF.

[PacAce]

Has anybody tried using the DOF preview with the 420EX or the 550EX? When the flash is on, pressing the DOF preview button will fire a burst of flash for a couple of seconds so that you can check the DOF. I've used it to check DOF indoors a couple of times but the duration isn't long enough to really assess DOF so I have to fire off a couple more bursts to be sure. It does solve the "everything going dark" syndrome.

[G3]

Has anybody tried using the DOF preview with the 420EX or the 550EX? When the flash is on, pressing the DOF preview button will fire a burst of flash for a couple of seconds so that you can check the DOF. I've used it to check DOF indoors a couple of times but the duration isn't long enough to really assess DOF so I have to fire off a couple more bursts to be sure. It does solve the "everything going dark" syndrome.

Yep...that's called "Modeling Flash". I mentioned that near the top of this thread. :)

[manncer]

8) 8) 8)

AJMCDO you sure started a good thread. It would be nice if Canon could give us a DOF view that was illuminated. That can't be that hard.

manncer

[G3]

8) 8) 8)

AJMCDO you sure started a good thread. It would be nice if Canon could give us a DOF view that was illuminated. That can't be that hard.

manncer

They do. It's called "Modeling Flash".

The only way to illuminate the focusing screen and viewfinder is to illuminate the subject. What you are looking at in the viewfinder is light reflected off the subject. How bright the finder is going to be is dependent on how much light is coming through the lens. The size ond surface of the focusing screen will affect brightness also, but not to the degree that the size of the aperture will. The idea of DOF preview is to show you how much will be in focus in the image that results from firing the shutter at whatever aperture the photographer (or camera) has chosen. The only possible way to do that is to stop the lens down to the chosen aperture and look through the lens as it will be when the shutter is fired. Since you are looking through a smaller aperture, not as much light is allowed to pass through the lens and to the finder.

The only other thing they could really do is provide a larger focusing screen. The problem with that is that the size of the focusing screen is directly related to the size of the image sensor or negative. That's why the Drebel and 10D's finder view is smaller and somewhat dimmer than a 35mm EOS camera....the image sensor is smaller, so the focusing screen is smaller. That's also why my 6x4.5 camera has such a big bright finder. SLR cameras are the only cameras that have this issue because they are the only ones in which you focus through the same lens that takes the picture. But..they are also the only ones that offer a DOF preview, for the same reason.

[Lamplight]

Hmm...After reading this thread I'm going to test out the DOF preview a little more. Like others, everytime I've tried it the view is too dark for me to see anything, regardless of what apature I have set. However, my eyesight isn't the best. In fact, if I try to manually focus the image will be blurry every time. :oops: