Depth of field??

[alice21]

Hey all,

I am new to the board and have a question that I am hoping one of you may have an answer to. I own an A85 which I bought due to the fact that it was more than just a point and shoot. I was told that I would be able to take portrait shots keeping the subject in sharp focus and everything else blurred. I am not having much success and the only time that it works is in macro focus. I can achieve the desired look but only on subjects such as flowers where the picture is very up close.

I realize that a simple solution would be to buy a better camera but it's just not in the budget right now. I have tried all of the settings that are supposed to make portrait possible but I am wondering if the lens is the problem. If so is there one that I can purchase for this camera?

Thanks :) :)

Alice

[hapm]

Sorry to say that you were misled. My wife is a portrait photographer and her typical shot is a head shot with a blurred backround. She has always used slr's. First film, then the D30 and now the 10D and sometimes a barrowed 20D. There are three factors that determine DOF and as you have discovered focus distance is one of them. The other two are aperture and focal length. Larger apertures (smaller numbers like f/2.8) will produce less DOF. The problem with getting shallow DOF out of a small sensor camera like yours has to do with lens focal length and sensor size. The zoom lens on a camera like yours might produce the 35mm film equivalents of something like 35-100mm but if you look on the end of the lens you see numbers like 7-21mm. The sensor is much smaller than a 35mm negative and it takes wider angle focal lengths to compensate for this. Unfortunately for you, wide angle focal lengths have an abudance of DOF. Here is a link to a DOF calculator: http://www.dofmaster.com/dofjs.html
You can select your camera in the format box. Next put in the telephoto focal length off the end of your lens. Notice it says to use actual focal lengths. You can next put in your biggest aperture at telephoto probably f/5 or so. Then put in a typical shooting distance for portraits 10-15'. The DOF that the calculator indicates may not seem that large, but now switch the format to 35mm or a dslr and change the focal length to say 100mm. See how much smaller DOF becomes? My wife uses a 70-200mm f/4 zoom on her 10D for headshots. A cheaper setup would be one of the digital Rebels with a portrait lens like the 85mm f/1.8 or 100mm f/2. A prime lens is cheaper than a good zoom and will have a larger max aperture and be lighter.
Good luck,
Hap Mullenneaux

[etaf]

use the calculator - use the 16.2mm end full telephoto - make the aperture the minimum so F4.8
shot at around 10ft then you will have 13.8 ft behing make sure you subject is much further away from the background say 20+ ft and it should start to work, but hapm has provided a very comprehensive answer.
also try using portrait setting on the camera that should use a minimum aperture

[Bodryn]

If you haven't yet done so, try using the largest possible aperture you can set manually, and try varying the telephoto to maximum advantage. If that doesn't work well enough, I suppose it means either getting a better camera or else using some software that can be used to artificially blur the background areas of each photo. I can do this with JASC Paint Shop Pro v.9. However it is a pain to have to use software to do this and it takes time to do it reasonablly well.

Ditto on that DOFmaster calculator mentioned above. I've been using the Palm version of that and it is a very clever and fun program to use. It instantly gives you the depth of field under varying circumstances and can be customized to your camera.