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05-13-2009, 10:27 AM   #1
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How to inspect used lens?

From time to time I see decent local deals on used lens. But I am not confident enough in determining the quality besides checking for the visual dings and scratches. Can someone shed some light on how to check for fungus? sharpness? and any other things to look for... thanks in advance.

05-13-2009, 10:54 AM   #2
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Fungus usually looks like crystalline spiderwebs on an inner element (at least from what little I've seen up close).

Sharpness is not easy to determine without taking test shots.

Other things to look out for are oil on the aperture blades - sometimes that means the lens got too hot and the lubricating grease melted and migrated onto the blades. It can cause them to become sticky and slow. Set the aperture ring to the smallest aperture (biggest number) and wiggle the aperture lever back and forth to make sure the blades open/close snappily. Once in a while you'll see blades with rust on them - avoid those.

You should also check the smoothness of the focus and/or zoom rings - any rougness or catching could indicate problems and may get worse over time.

Also, shake the lens and listen for rattles - sometimes an element comes loose and can cause image quality/focus issues.
05-13-2009, 12:47 PM   #3
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Look in the lens, from the camera end of it, at a bright light. You can push the lever to open the aperture. On an older lens you will see dust, fluff & fungus you don't notice when you look down the front.

Dan.
05-13-2009, 02:16 PM   #4
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To check for fungus and other internal defects:
  • Dim the room lights
  • Look through the rear element while shining a small penlight (torch) at an oblique angle through the front element
  • Move the light around a bit to allow close examination of all visible structures
  • Change your viewing angle as well
  • Repeat viewing through the front element
This technique will show fungus, cracked or broken elements, dust, bubbles, scratches, internal fingerprints, haze, and element separation.
  • Fungus looks like fine filaments or a cloudy "puff". Fungus may also "eat" into the cement between grouped elements causing the elements to separate.
  • Separated elements look like a fine crystalline pattern (failure of the glue bond) or a discontinuity
  • Haze looks like a cloudy film

Steve

05-13-2009, 04:57 PM   #5
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There was a very good guide put together maybe a month back.

https://www.pentaxforums.com/forums/pentax-lens-articles/59245-pawnshop-lense...ers-guide.html
05-13-2009, 07:34 PM   #6
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Thanks for all wonderful tips, I will be practicing them on a lens shortly.
05-20-2009, 05:19 PM   #7
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QuoteOriginally posted by tvfd911 Quote
This is actually a very good read and advice specially if you have more pawnshops in your place rather than stores that actually sell camera gear or lenses.
As in my case, no camera shops for probably 30miles or so, but a lotsa-lotsa pawnshops.
I should make it a point to visit most of the pawnshops once a month, now that I got to thinking.
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