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12-24-2008, 11:03 AM   #1
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Best way to test a lens

Hi. I'm a new forum member and this is my first post. I'm hoping for some advice concerning the best way to test a new lens to make sure you got a good copy.

I have a Pentax K10D and have been using the kit lens all this time. Yesterday, I finally bought some new lenses - a Tamron SP AF28-75 f /2.8 and the Pentax DA 55-300mm f/4-5.8. I did a lot of research and both seem like good lenses and good value for the money.

I'm concerned though because I've been reading about people getting bad copies of lenses. It's one of those instances of ignorance is bliss - yikes, front-focus problems, back-focus problems, etc. I'm pretty new to photography and I didn't realize those were even concerns. To make matters worse, it seems like it's sometimes a camera problem and sometimes a lens problem. To be honest, it makes my own eyes kind of blurry, especially seeing the focus test charts people use to test their lenses. Can someone recommend a basic battery of testing, preferably not using the focus charts (partly because it seems difficult to tell if the problem is simply that you didn't focus on the right part of the chart), but some type of more "real world" testing. I bought the lenses from B&H so I have 14 days to return them if something is off.

Thank you very much for your time and help.

Peace, Christopher

12-24-2008, 11:53 AM   #2
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Just shoot what you'd normally shoot and see if you like the results. IMHO people get waaaaay too hung up on machine test data (largely irrelevant unless that machine is shooting your pictures) and photos of brick walls and focus charts. If you take shots and like them, be happy. If you take shots and don't, then ponder pixel peeping and some basic focus tests (though even when I do that I shoot things I know, not charts.

Photography is a human endeavor and machines only assist. Trust your eyes.
12-24-2008, 11:56 AM   #3
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QuoteOriginally posted by nostatic Quote
Just shoot what you'd normally shoot and see if you like the results. IMHO people get waaaaay too hung up on machine test data (largely irrelevant unless that machine is shooting your pictures) and photos of brick walls and focus charts. If you take shots and like them, be happy. If you take shots and don't, then ponder pixel peeping and some basic focus tests (though even when I do that I shoot things I know, not charts.

Photography is a human endeavor and machines only assist. Trust your eyes.
I agree


you will soon see if its not up to standard with day to day shooting.

Go out and shoot and run the lens through its capablilities.


Neil
12-24-2008, 12:00 PM   #4
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That's two great replies, many folk get hung up on brick walls and newspaper to test their lenses, just take pictures, enjoy and look at the results.

Seasons Greetings to you.

12-24-2008, 11:24 PM   #5
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The funny thing is I have a lens that I think has some back-focusing problems in real life. However, whenever I shoot a focus chart, it seems to be all right (I tried newspaper, but couldn't guarantee I was really focusing on the right line of type. A focus chart where there's a single bar that you focus on and nothing else close to it is much easier). I even went so far as to shoot a wall with raised letters - it focused properly on the part of the letter I chose to focus on. However, when I was shooting some real-world comparison shots with another lens, it consistently focused behind the other one, and behind what I was trying to focus on. I keep thinking that the problem is me, not the lens, and it could be but I'm not sure.

I agree with the others - go out and take real-world pictures. If they look fine to you forget about problems others might have - otherwise you'll be forever second-guessing your equipment. That's not good because then you'll start seeing things that aren't there and worrying about it (like my example above).
12-24-2008, 11:58 PM   #6
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here's a link to an article about subjectively testing a lens http://theonlinephotographer.typepad.com/the_online_photographer/how-to-stress-a-camera-le.html
and these principles applied to the DA35 http://photo.net/columns/mjohnston/pentax-35mm-lens/optical-discussion/
12-25-2008, 02:44 AM   #7
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go and take the pictures. If they come out as you want them to (supposing you shooting and PPing techniques are OK) then they are good lenses...
BR
12-26-2008, 03:00 PM   #8
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we should really take a poll.

i would be willing to bet go out and shoot what you normally shoot is the best way, at least for focusing and overall image.

you should, however, do an exposure check. I find on some lenses, they slightly drift to over esposure as you stop down (error in apature)

Both my K50 F1.4 and my tamron 28-75 F2.8 have a very slight but noticeable drift up in exposure by 1/2 stop from wide open to minimum apature.

My test is using the green button for manual lenses and Av for A series lenses, to shoot a block wall or paved surface and then using the histogram check the value in the center 10%

12-26-2008, 03:10 PM   #9
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For the Tamron, I checked w/ a tripod/ballhead and MLU for BF at various ranges, but not using a test chart. One of my bad ones was also obviously weird at 75mm at portrait distances.
So I'd say try a few regular photos, but if things get weird, break out the testing gear and document it. That's what you should do if you send it back anyways...just so Tamron knows you tested it and can see your results...
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