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09-02-2010, 04:13 PM   #1
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How can I evaluate a used lens?

I'm a DSLR newbie, had my K-x (with 2 lens kit including the 55-300mm) for around a month.

I'm interested in several lenses but figure firstly I'll get an 18-250mm, both because of it's versatility (I'll attack IQ later), and the fact that it's no longer in production. I think it's been OOP since at least January 2010. AFAIK, it doesn't matter if I get the Tamron or the Pentax version. I saw a post saying the lens is really the same, including the coatings (said the coatings on the Pentax version look different from the other Pentax SMC lenses, so the coatings are probably the same as for the Tamron version).

Well, I found a listing for a used Pentax 18-250mm and the seller says he's selling it because he's returned his camera to Amazon. Says he bought the lens used on ebay (in "like new condition", quotes by current seller). How can I evaluate the lens to make sure it's OK? I could bring my K-x and a laptop to view photos (the seller lives ~15 miles from me). What can I do to put the lens through the necessary paces? The seller is asking $369, says it has the hood.

09-02-2010, 04:30 PM - 1 Like   #2
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Most problems are found by examining the lens. You'll want to check the glass and shine light through the lens. Smudges, dust, haze, or fungus are what you're looking for, and of course shouldn't be there. You'll also want to smell the lens- some lenses come from homes where people smoked, and as a result, lenses can get irreversibly smelly.

Most importantly, you'll want to check that all moving parts on the lens are in good working order. This includes the focusing ring, the zoom ring, and the aperture ring, if available. Also, make sure that nothing else outside on the barrel is loose, and that the lens makes no rattling sounds when shaken.

Like-new lenses are typically in quite good condition, so I'm sure the one you're looking for will be a nice copy!

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09-12-2010, 06:47 AM   #3
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Thanks for the information. I printed a copy, highlighted the basic points and brought it with me to the sale. The lens looked, felt, sounded and smelled "as-new" and I paid the asking price of $369. It did have the lens creep evidently typical of the great majority of copies of this lens, but I wasn't going to let that be a show stopper or try to use that as a reason to try to bargain the price down. I took a few shots once I got the lens home, but nothing I'd call methodical testing. I'm looking for suggestions on how to properly test a lens (I now have this and my two kit lenses, and my new K-x). Ideas, suggestions appreciated.
09-13-2010, 04:15 AM   #4
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There are focus charts you can download or purchase if you'd like....you can also just take pictures and inspect. Pick a subject with some detail. There is the much used "brick wall" but any flat surface with detail works well. Set the camera up on a tripod, then take a series of pictures at different focal lengths, and fstops. Examine. This particular lens has been reviewed at various places, you can compare your test shots to theirs and get an idea of what you have.

But don't over analyze it. Don't expect razor sharp images at 200% crops while at 5.6 250mm You could also take pics, make a few prints. If you are happy with the outcome, then its a good lens.

That said, I have the same lens. Its not razor sharp, but if you're looking to carry only 1 lens, and you need versatility, you can't go wrong. It is a fine lens....

Best of luck with your new purchase,

09-13-2010, 04:26 AM   #5
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Here's a great post from the Articles Forum.

https://www.pentaxforums.com/forums/pentax-lens-articles/59245-pawnshop-lense...ers-guide.html

Tim
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