DOF Question

jwhphoto · Sep 21, 2008

What settings are generally used to create DOF? is it a larger aperture? I really am not sure how this works and would like some more information so i can try this out. Currently i only have a 18-135 mm lens, so is this lens able to do good DOF?

Thanks

jwhphoto

Early · Sep 21, 2008

jwhphoto said:
What settings are generally used to create DOF? is it a larger aperture? I really am not sure how this works and would like some more information so i can try this out. Currently i only have a 18-135 mm lens, so is this lens able to do good DOF?

Thanks

jwhphoto

As you close down the lens, the more DOF you will get. Also, wide angle lenses will give you more DOF then telephotos.

kundalini · Sep 21, 2008

Each lens at each aperture setting has DOF. Wiki definition.

What are you trying to accomplish?

jwhphoto · Sep 21, 2008

Heres a pic i took today in downtown Sacramento. It was taken at 18mm, f/4.0, 1/200 sec. I was able to blur the background some, but i would like less detail than this in some of the other ones i shoot. (getting the blur in this pic was luck for me, i still dont know how to do it exactly) What i want to do most is if i take a close up of a flower, and there are other flowers 2-3 feet behind it, i want those quite out of focus.

Also feel free to C&C this photo please.

Josh66 · Sep 21, 2008

For that you'll need a large aperture (small f/#). The larger the aperture, the more out of focus the background will be.

Overread · Sep 21, 2008

Well the wider the aperture you use (the smaller the f number) the smaller your depth of field gets (the area in a shot which is in focus). Once you are at the widest your lens will go then the only other way to increase the blur is by distance - from you to subjcet and from subject to background.
In the case of the shot you show above you have done the right method - the subject (in focus) is close to the lens - whilst the background if much further off. Couple that with a wide aperture to get your background blur.

I think to get more blur - unless you add blur in editing - then you need a wider lens - f2.8/1.8 area

kundalini · Sep 21, 2008

If that 18-135mm lens is the Nikon version, then f/3.5 is your maximum aperture. You are likely to get better image quality at f/4 to f/5.6 than at f/3.5, however you'll need to check reviews at photozone.de or somewhere for actual results.

Another factor to achieving the blurred effect (bokeh) you're after is focal length in addition to what Overread stated with regard to subject-to-background. I'm fairly confident that the wider the field of view, the less bokeh effect you will get.

Try this at you leisure, set up an inanimate subject, anything... a can of soup, set of bongos, your ex-girlfriend.... Have the background a minimum of at least 5 feet from the subject. With camera-to-subject and subject-to-background remaining constant, take test shots at varying, but precise, focal lengths.... say 18mm, 50mm, 85mm, 100mm, 135mm. All at the same aperture. So if your maximum aperture at 135mm is f/5.6, set all shots at f/5.6. This should give you an idea of what part focal length plays with the blurred background. Of course the next excercise will be to keep the maximum aperture at those same focal lengths and that will tell you what your lens is capable of.

Just a thought. Someone else will come along and have a better idea. :biggrin:

Overread · Sep 21, 2008

hmm you reminded me Kundalini - out of interest when you say wide field of view do you mean a shorter focal length?

I think its the greater the focal lengths that lead to increased background blur

Resin42 · Sep 21, 2008

jwhphoto said:

Is this the world's tallest Dalek?

kundalini · Sep 21, 2008

Overread said:
hmm you reminded me Kundalini - out of interest when you say wide field of view do you mean a shorter focal length?

I think its the greater the focal lengths that lead to increased background blur

Maybe I screwed the terminology up, but 18mm is a wider field of view than 135mm.

Also when going more towards the telephoto end of focal lengths, you also get compression which aids in achieving bokeh with a wide aperture and isolating subject from background, provided there is a distance of subject-to-background.

Correct me if I'm wrong, please.

Overread · Sep 22, 2008

ahh no you were right = it was late and I read your point backwards!

manaheim · Sep 22, 2008

Not sure if this was said, but the closer to your subject you are the more shallow your depth of field. (less in focus)

This is in addition to the effect of aperature.

This also works in reverse, so the further away you are the more that is in focus. This is handy because it allows you to use very wide aperatures when shooting landscapes, which tends to give you sharper images up to the point closest to you where the focus will fall off. (which can be adjusted by hyperfocal focusing)

Some valuable links:

http://www.thephotoforum.com/forum/showthread.php?t=130556
http://www.great-landscape-photography.com/hyperfocal.html
http://www.dofmaster.com/hyperfocal.html

Turnerea · Sep 22, 2008

manaheim: thanks for those links- I learned alot about the hyperfocal focusing there, and think I could really use that when shooting landscapes. I'm in the market for a wide lens, and would hope to get DOF markings on it.... but I don't see many zooms with it, only prime lenses. Do any companies make zoom lenses for Canons that have DOF markings?

manaheim · Sep 22, 2008

My pleasure. Don't know about your specific question on lenses with the rangefinder marks, but I can tell you that generally the practice of printing these on lenses has died off quite a bit. Very annoying actually.