Depth of field help please

mtnman2888 · Jul 7, 2008

First off, I want to say that i am new to the forum although i have been lurking for awhile. I have already learned alot just from looking and i'm sure it won't stop. I recently purchased a canon rebel xsi with two lenses: the 18-55mm ef-s (came with the kit) and a 70-300 mm 1:4-5.6 is usm.

I played with the camera a little and it's taking some great pictures. One thing i wanted to do is take a picture where the subject is in focus but everything else is blurry. Reading the manual, it says simply to lower the aperture to 5.6 and you will get the desired blurred background effect. I've tried this several times with no luck at all. I'm sure there is more to it but i'm not sure what i'm doing wrong or if the lens is simply not suited for that type of picture. Any help would be appreciated, thanks!

Bryant · Jul 7, 2008

It's called bokeh. Read this, it should help:

http://en.wikipedia.org/wiki/Bokeh

manaheim · Jul 7, 2008

Do you have an example picture where you felt it didn't work that you could post?

By and large, the aperature is really what controls focus depth. A larger aperature would toss the background more out of focus.

Mike_E · Jul 7, 2008

You are going to have a little trouble getting good bokeh way down at f/5.6.

Try getting as close to your subject as you can and have the background as far away as possible.

The smaller the aperture the larger the DOF. You have to get the background out of the DOF.

You could also read this site top to bottom. http://www.cambridgeincolour.com/tutorials.htm

HTH

lockwood81 · Jul 7, 2008

Since the lens that you are working with doesn't have a very large aperture, you can do something else to achieve the DOF you are looking for.

Using your 70-300 at f/4 place the subject you want to capture a good distance away, then zoom in with your lens. This will blur the background...as long as the background is quite aways back from the subject. Or use the 18-55 at f/4 and get as close to the subject as you can while still in focus with the background a good distance away.

Give it a try.

manaheim · Jul 7, 2008

Bryant said:
It's called bokeh. Read this, it should help:

http://en.wikipedia.org/wiki/Bokeh

I really think this term should be banned from existence. :lmao:

Mike_E · Jul 7, 2008

What have you got against wikipedia?

mtnman2888 · Jul 7, 2008

Thanks for the suggestions, i will give these tips a try tomorrow evening. I don't really have any pics to post right now but i will try it tomorrow and post the results. From what i gather, a wide angle lens has a large depth of field, correct? I am thinking about getting one of those also but am still shopping around trying to find the best one. Thanks again.

table1349 · Jul 7, 2008

manaheim said:
I really think this term should be banned from existence. :lmao:

Still having trouble spelling and pronouncing bokeh, huh? :smileys:

WDodd · Jul 7, 2008

mtnman2888 said:
Thanks for the suggestions, i will give these tips a try tomorrow evening. I don't really have any pics to post right now but i will try it tomorrow and post the results. From what i gather, a wide angle lens has a large depth of field, correct? I am thinking about getting one of those also but am still shopping around trying to find the best one. Thanks again.

Focal length is one of the factors but it isn't the biggest one. If you want the most control over bokeh get a lens with a very large maximum aperture (low f/number) like f/1.8 or f/1.4. Canon and Nikon both make a very affordable 50mm f/1.8 if I am not mistaken.

Aperture controls the amount of light that is entering the lens by closing down or opening up a hole in the lens. It works like this:
Large F# (i.e. F/22) = small opening = large depth of field
Small F# (i.e. F/1.8) = large opening = small depth of field

Focal length has an effect on DOF because the light will have different amounts of time to disperse depending on how far the hole we talked about is from your sensor.
A larger focal length = less DOF.
Shorter focal length = more DOF.

Lots of opposites making it as confusing as possible

BTW: Wikipedia just taught me that bokeh was derived from a Japanese word!

Mav · Jul 8, 2008

I took this photo at 140mm and f/8

The key is to zoom in as much as possible, while placing the background as far away as you can. In this case I'm only about 6 feet from the camera, but the background is probably more like 50 feet or more away. That's still far enough in this case to get some nice out of focus area blur.

Mike_E · Jul 8, 2008

Nice F. Why are the PC covers so easy to lose?

Steph · Jul 8, 2008

Bryant said:
It's called bokeh. Read this, it should help:

http://en.wikipedia.org/wiki/Bokeh

Not really. It is called shallow depth of field (which depends on the aperture, the focal length, the subject to background distance and camera to subject distance). Bokeh is more about describing the quality of out of focus areas (which may result from shallow depth of field and depends mainly on the lens design).