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09-11-2011, 08:52 PM   #1
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Dropped lens - What should I check for?

I accidentally dropped another lens yesterday, after dropping my Sigma 17-70 into sand a few months ago.

The victim this time was my Pentax-M 28mm f2.8.. fell out of my pocket.

Heard quite a loud thud. But, upon checking the lens, no dents or scratches found (fortunately the front & rear caps were still on). The aperture and focusing looks fine and moves as it should. Images look ok, but I haven't done detailed testing yet.

What else should I check for? Can a drop cause disalignment of the optical elements?

09-11-2011, 10:32 PM   #2
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The M 28/2.8 may go out of alignment inside where the cup portion that holds the aperture blades. Check to see if there is any hesitation in the action of these blade and set to the smallest (f22) to see if a neat polygon is there. Check for wobble in any direction from the barrel compared to the base... grip, but not hard, the part that moves in and out and gently twist... if none out of the ordinary is good. Check for odd rattlings by shaking the lens as you would mix a drink. Listen and feel if anything is moving... if nothing from any of these then you might have come off very luck?
09-11-2011, 10:58 PM   #3
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Done all of your suggested tests. Everything seems fine.

How about images? How do I check the optical alignment?
09-11-2011, 11:40 PM - 2 Likes   #4
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If you would like to try this primitive test...
Fill a sheet of paper via a word processor the letters 'E' '%' 'X" or any character that give left-right, up-down, diagonals. A size that small, but not too small that the viewing for details would be too rough... maybe 8 to 12 point size. Print out five and tape to a wall about 5 feet/1.5 meter mark and arrange the sheets center, corners and in the far enough apart to fill the frame (film or digital). Mount the camera in a flat accurate to the wall as possible, measure with a rigid tape gauge form corner to lens. The lighting should be daylight if possible. Check at aperture 2.8 to 22 if possible to compare normal corner drop off to issues. Inspect the images. You are looking for signs of poor detail, increase of chromatic aberrations or if the mark of the distance is way off the actual.

... Oh, and the '%' helps because you can see issues as the little zeros loose the clarity.


Last edited by MysteryOnion; 09-12-2011 at 05:23 AM.
09-12-2011, 11:46 AM   #5
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QuoteOriginally posted by hagiri_11 Quote
I accidentally dropped another lens yesterday, after dropping my Sigma 17-70 into sand a few months ago.

The victim this time was my Pentax-M 28mm f2.8.. fell out of my pocket.

Heard quite a loud thud. But, upon checking the lens, no dents or scratches found (fortunately the front & rear caps were still on). The aperture and focusing looks fine and moves as it should. Images look ok, but I haven't done detailed testing yet.

What else should I check for? Can a drop cause disalignment of the optical elements?
Dude, to dis-align optical elements in an M lens, you'd have to smash it with a hammer, don't worry your lens is fine. I think the biggest hazard when these lenses fall is that their front is a bit heavier and the filter ring and focus ring tend to bend. But if your lens looks ok, I'm sure its fine.
09-13-2011, 12:32 PM   #6
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QuoteOriginally posted by VaSA Quote
Dude, to dis-align optical elements in an M lens, you'd have to smash it with a hammer, don't worry your lens is fine...


Zooms are also more vulnerable to damage and misalignment, because they have concentric barrels supported at only a few points. The elements in a prime lens are much more securely mounted.

The last time I dropped a lens, I got a terrific excuse to buy a DSLR.
09-19-2011, 10:33 AM   #7
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QuoteOriginally posted by Just1MoreDave Quote


The last time I dropped a lens, I got a terrific excuse to buy a DSLR.
Please do tell!
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