DOF in EOS 300 : LUSENET : Canon EOS FAQ forum : One Thread

HI, I just got an EOS 300 also my first SLR camera (total beginner). I've have been fiddling around with it trying to get accustomed to it. I am confused about the DOF preview function. When I press the button, I don't see anything happening? What am I supposed to look for? Do I make adjustments? Thanks so much.


-- Jeanette Teo (, September 05, 2001


DOF preview stops the lens down to it's shooting aperture. Normally when you look through the viewfinder you are seeing the view with the aperture wide open regardless of what the aperture is set at. When you set the lens from it's largest aperture (for example f/3.5) to a smaller aperture (for example f/16) you will see no change in the viewfinder. The lens doesn't stop down until you actually shoot the picture.

However, since stopping down increases depth of field (that is, the range within which objects are sharp) it is advantageous to be able to preview that subsequent effect. DOF preview stops the lens down to the set aperture. Be aware that 1) if you have the camera set to the widest aperture, the image in the viewfinder isn't going to change because there is nothing for it to change to, and 2) at much smaller apertures the image darkens a great deal, so you may need to press the DOF preview on and off several times to gauge the effect.

-- Peter Phan (, September 05, 2001.

A good way to learn about the effects of DoF Preview is to use the camera in Aperture priority program mode, or in full manual. As you change the aperture and press the DoF Preview button, you will be able to see the viewfinder darken, and should see an effect on the zone that is in focus.

A simple & fun test is to lay out a number of objects at different distances on a counter or table. Focus on an object in the middle. As you "stop-down" or increase the f-stop number, you can see more and more objects coming into focus in front and behind of the original subject. A tripod helps.

Have fun!

-- Hung James Wasson (, September 06, 2001.

Hi Jeanette, in my experience, not much light comes through the view finder on the 300 anyway & trying to utilise the DOF feature at an aperture small enough to get any DOF is futile. Try getting some DOF data charts for your lens from the canon museum or do a search on and obtain the formula to calculate them for yourself. Jason.

-- Jason Eadie (, September 07, 2001.

DOF stands for depth of view preview.If u press the button,the aperture will close/stop down to the value set by the slr.It is particularly useful when u want to know the 'range' within which objects will be clear. There are 3 reasons why it shows nothing as u described 1.malfunctioning of slr (take it for repair) 2.the command dial is at basic zone 3.the aperture u or the slr set is the largest setting,eg,the lens has a max aperture of 5.6 and u set this value,u will see nothing,since TTL metering require full-open aperture

-- Tokamak (, September 08, 2001.

Hi, I have the same camera since a month, so, DOF works only when a 'creative mode' is choosen!! Try it eg. in the AV or M mode! Gabor

-- Gabor Apati Nagy (, September 10, 2001.

Jeanette - I see no-one has explained what depth-of-field is, so I'm going to jump in. Let's get practical - if you focus your lens on something 10 feet away everything 10 feet from your lens will be in focus. What about the stuff 8 feet away, or 15? That depends on the f/stop you choose. The smaller the f/stop the more in-focus things will be either side of your focussed distance. But the smaller the f/stop means that less light gets in, so you have to use lower shutter speeds. I'd have a little trouble describing what you should see in the viewfinder but I'd suggest an experiment so you can see the difference. Shoot someone standing on grass, maybe at a park. Shoot their whole body, trying to focus on the eyes. Do one shot wide open (f/3.5 maybe?) and another at f/22, both in the aperture- priority mode. When you get back the pictures you'll see in one that the grass gets fuzzy (out of focus) almost immediately in front and behind the person - the other picture will have sharply focussed grass from well in front to well behind the person, and THAT is the depth of field. Maybe we should call it the depth-of-field-in- focus. Once you've seen it in your pictures maybe you'll find it easier to see in the viewfinder.

-- Zave Shapiro (, September 12, 2001.

Moderation questions? read the FAQ