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01-31-2010, 12:56 PM   #1
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Whats the best lens test ?

We just got a new Tamron 17-50 and Sigma 105 macro and was wondering what's the best way to test the lens to make sure they are right. Never have done anything like this before so figured there must be easier way, well to a degree anyways. Seems the Tammy isn't as sharp as I thought it should be. But it could be my K20D as I am still learning the fine tuning part of it. Any and all help would be much appreciated.

01-31-2010, 02:54 PM   #2
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Go out and take some pictures.
Look at the pictures.
If they look OK, odds are the equipment is also OK.
01-31-2010, 06:44 PM   #3
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And if they aren't OK, ask yourself if you've done everything within the power of the photographer to improve the pictures. Posting images here for critique can help, but do realize that many if not most problems with pictures are related to technique, not equipment.
01-31-2010, 08:12 PM   #4
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With older lenses, I like to check for exposure problems. Meter a scene with constant light, take an exposure, and using the same exposure value, choose different apertures. So if your first exposure is at f8 and 1/60 sec., you should get about the same brightness from f2.8 and 1/500, or f22 and 1/8. It's probably not necessary with new lenses but it only takes a few shots.

You can check for decentered elements by seeing if one side of a photo is in focus while the opposite side is not, when the subjects on each side are the same distance away. A brick wall or fence will be a good subject.

All lenses are going to be a bit soft and low contrast wide open, better stopped down. You could compare to the kit lens for the Tamron. If it's not better at equal settings, there might be an issue.

Autofocus requires more rigorous testing than some people seem to think. Obviously a lens that doesn't focus at all is broken, but lenses are rarely that bad. More likely, the lens may not appear to focus where you want it. To test this, you have to make sure there's only one place that the lens could choose to focus; everywhere else is wrong. That's why people use focus test charts and follow the instructions for them.

That's probably enough to make sure you don't have a bad lens out of the box.

01-31-2010, 11:51 PM   #5
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There are a number of approaches to testing lenses. Wheatfield's test is the probably the most useful and the most pragmatic. As Dave noted, there are several aspects to evaluating lens function. The only thing I might add to his suggestions is to perform any evaluation for decentering using a sturdy tripod. Care should be taken to ensure that the lens axis is perpendicular to the target on both x and y axises.

Ultimately, if you are concerned that your Tamron is defective, you can always send it back on warranty and ask that they adjust or replace.

On last thing to consider....

Your Tamron is relatively fast at f/2.8. Wide open, both contrast and sharpness will be reduced somewhat while any tendency to exhibit flare will be increased. Depth of field is also much reduced, even at shorter focal lengths. Any of the above will yield "soft" results.

Steve
02-01-2010, 06:29 AM   #6
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I perform a couple of tests when I add a new lens to my collection.

I check exposure 2 ways, one as Just1MoreDave suggests, to check the accuracy of each aperture, the other is to run through the aperture stops in Av mode (for A lenses) or manual with green button and see where the camera metering drifts with thelens as a pair. it is useful to know if a specific lens tends to drift over the range of esposure. My Tamron 28-75F2.8 for example drifts slightly up in exposure by about 1/2 stop from wide open to stopped down. Not much but useful to know.

Aside from exposure performance. as others say, I go out and shoot, Try all focusing distances and / or focal lengths. If the pictures are satisfying, the lens is OK.

You may also wish to try some shots with bright lights not in the field of view, but close, to check the effectiveness of the hood and coatings. With only 1 exception, all my lenses are full frame, and the hoods could actually be bigger since I am shooting on an ASP-C sensor. I receintly got a ricoh screw mount 135mm lens, and although sharp and contrasty indoors, the flair outdoors is incredible, and the hood that comes with the lens is totally useless.
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