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Old Oct 15, 2003, 9:18 PM   #1
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Default How do I test the accuracy of my autofocus mechanism?

Anybody heard of a way of testing the focus of a digital camera?
I swear my Toshiba PDR 3310 has somehow lost much of its ability to focus...quickly, if at all, in many circumstances.
I'd like to find some way (other than shipping it to Kingdom Come) to determine whether or not it is in need of "serious" repairs.
Tips? Thanks.
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Old Oct 15, 2003, 10:49 PM   #2
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Find something with large font words on a wall, with horizontal and vertical lines, zoom out, and take a picture of it a few feet away, then move back a bit and take another shot, and see if the pictures are in focus.

Is it in specific situations that you are having trouble focusing? There are limits on the focusing mechanism:
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Old Oct 16, 2003, 7:00 AM   #3
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and see if the pictures are in focus.
You will probably have to do this afterwards using a photo editor zoom to be absolutely sure unless your camera has a postview zoom option. Use the widest aperture and fastest shutter speed. But don't get fooled into thinking your pics are out of focus when they may just be soft due to lack of edge contrast. Since I turned off sharpening, to the uninitiated pics might look out of focus - but apply unsharp mask and sharpen and they spring to life!

The other relevant issue, is given a strong vertical and horizontal edge your camera should do a good job, but a more likely problem I've experienced is that in some scenes, the electronic focus point does not match the point of interest - and zooming in to focus and back out doesn't work with these lenses. I sometimes think it's a pity the AF doesn't highlight the part of the image in the EVF it used or even gave a distance measurement. VOX
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Old Oct 16, 2003, 8:30 AM   #4
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Use an eye chart at your optomerist office.
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Old Oct 16, 2003, 9:17 AM   #5
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Testing an AF system is not easy. To do it properly (i.e. eliminate outside influences) you really need to do some of these things:

use a tripod. Hand holding is not nearly good enough.

use a remote shutter release (or time release)

don't test it near vibrating equipment like your fridge

test it at various zoom setting and f-stops.

Test at varying distances to the subject.

make sure there is a very well lit, constraty subject (some use news print, but that isn't exactly a very sharp subject.)

Put several things that that are within the picture (but not the subject that is focued on) that are infront of and behind the focus plain. Somewhere is always in focus (assuming the optics are not just really bad.) It is usually much easier to see that focus is off by seeing that it's focusing at a different point in space.

Use single shot mode.

Make sure the target being focused on is perpendicular to the camera (if its flat.)

do the test several times.

There are other things, search around on the web for AF tests. (Or even here, I've written about how to do this in other posts.)

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Old Oct 19, 2003, 9:39 PM   #6
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Thanks very much for all your kind contributions, guys. Eric, your tips were especially comprehensive........and, VOX, I think you may have 'hit another nail on the head': I believe I HAVE been relying on the old "half-depress-the-shutter-while-pointing-at-your-subject" method, then moving OFF the subject to "centre up" the shot (most often when shooting two people who are two feet apart and you typically end up being focused on the wall, ten feet behind!) I wasn't aware that this method doesn't work with digital autofocus. (Or maybe just not with the Toshiba PDR). Whatever.
You guys have given me lots of ideas for testing the little darling.....(I really like that eye chart idea!) and I'll try them all before tossing out what has otherwise been a little gem of a camera.
(Still wish it would focus FASTER though. I'm just now reading all the reviews that say it IS slower than most. Oh well, this can be my 'scenery' camer and I'll have to use something else for candids and sports!)
Thanks again fellas for your great, fast and comprehensive response.
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