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02-18-2010, 11:19 AM   #1
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Used lenses, Dust ok?

I'm looking at a used 100mm 2.8 macro pentax smcp-d lens it says;

"Glass is clean with no fungus or scratch. Might have some dust inside, which does not affect final photo. Body is clean. No visible deep scratch."


Does this sound right ... can the dust be cleaned out somehow via repair if it affectes image quality. Do allot of used lenses have dust inside them?

02-18-2010, 11:39 AM   #2
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QuoteOriginally posted by cannabiscurescancer Quote
I'm looking at a used 100mm 2.8 macro pentax smcp-d lens it says;

"Glass is clean with no fungus or scratch. Might have some dust inside, which does not affect final photo. Body is clean. No visible deep scratch."


Does this sound right ... can the dust be cleaned out somehow via repair if it affectes image quality. Do allot of used lenses have dust inside them?
Dust inside the lens should make absolutely no difference in the IQ of the lens. Even small scratches won't make a difference.

Take a look a this....


http://www.lensrentals.com/news/2008.10.30/front-element-scratches
02-18-2010, 11:41 AM   #3
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Most lenses will have some dust inside. It's easy to see but not a big problem. It can be cleaned, but it's not that easy to avoid introducing more dust in the process.

Here's a dust demonstration I did for someone else. The first photo has a clean lens, f8, about 50mm, tripod, 2s delay, ISO200:


Some "dust" on the front element:


Some "dust" on the rear element - I had to unmount the lens for this, so the photos don't quite line up:


Now let's see how much dust that was. The front element "dust", a dot of paper cut from a Post-it note:


The same dot applied to the rear element:


Comparing the full-size images, I can easily see the contrast is reduced, with maybe some color tint. The dot takes up a considerable percentage of the rear element, and the effect is more obvious. I have never seen a lens with that much internal dust.
02-18-2010, 11:48 AM   #4
Igilligan
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Hey Dave

I would love to see that same test at F18-22 ish... on the rear element especially

I have a macro lens with dust on inside of the rear element. If I am trying to stop way down for DOF in my macro shots I can definately see some effects at in the macro shots especially if I crop.

do you still have your test dot?

02-18-2010, 12:05 PM   #5
emr
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There's also an interesting article about how much "dust" a lens can have before it really starts showing. The "dust" in this case is on the external surface, but quite eye-opening anyhow.

Dirty lens article
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