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07-16-2014, 01:48 PM   #1
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Damaged Rear Element Coating

I was using my 77 limited in the field and, while off the camera, something blew in my face that made me sneeze quite suddenly. The result was a small amount of spittle that landed on the rear element. I immediately dried it but there are now visible spots in the coating.

So far I haven't noticed any issues when I use it, but it makes me bat-sh_t crazy every time I look at it. KEH says they can replace the rear element for $130, which is worth it to me provided I'm not doing more harm than good. Does anyone have experience with KEH, or anyone else for that matter, doing this kind of replacement?

07-16-2014, 01:54 PM   #2
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QuoteOriginally posted by jrpower10 Quote
I was using my 77 limited in the field and, while off the camera, something blew in my face that made me sneeze quite suddenly. The result was a small amount of spittle that landed on the rear element. I immediately dried it but there are now visible spots in the coating.

So far I haven't noticed any issues when I use it, but it makes me bat-sh_t crazy every time I look at it. KEH says they can replace the rear element for $130, which is worth it to me provided I'm not doing more harm than good. Does anyone have experience with KEH, or anyone else for that matter, doing this kind of replacement?
Have you tried cleaning it with anything, other than drying it? (So, are the visible spots "in" the coating, or "on" the coating?) Dirty rear elements have very little affect on photo quality, so if you don;t want to use some sort of cleaner, you may simply leave it as is. It would drive me batshit too, so I'd be inclined to clean it using a bit of lens cleaner. Lots of posts here about cleaning.
07-16-2014, 02:51 PM   #3
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QuoteOriginally posted by MarkJerling Quote
Dirty rear elements have very little affect on photo quality
Mark, I hesitate to directly contradict you, but contamination or scratches on the rear element do effect image quality and are one of the key things to look for when purchasing a used lens. OTOH, a front element can be pretty ugly and still take a decent photo.

To the OP...You can clean your rear element using lens cleaner and a clean soft cotton cloth. Apply the cleaner to a corner of the cloth, gently swab the contaminated area, and finish with a dry portion of the cloth. Take care to not apply direct pressure or any sort of scrubbing and you will be fine. My practice is to use regular glass cleaner (Windex) and either a white cotton rag or shred of high quality paper towel. Purists might use a Kim Wipe or Tec Pad.


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07-16-2014, 02:54 PM   #4
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No need to be paranoid. Wet clean it first. I've cleaned the front and rear elements my FA31 many times with isopropyl alcohol, no harm done.

Some are disturbed by alcohol, I guess they fear it seeping into the lens barrel. It's never happened to me. Anyhow, I'm not suggesting you use alcohol, just try cleaning the darn thing with something, before you freak out and replace the element ... seriously ...

07-16-2014, 03:07 PM   #5
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QuoteOriginally posted by stevebrot Quote
Mark, I hesitate to directly contradict you, but contamination or scratches on the rear element do effect image quality and are one of the key things to look for when purchasing a used lens. OTOH, a front element can be pretty ugly and still take a decent photo.

To the OP...You can clean your rear element using lens cleaner and a clean soft cotton cloth. Apply the cleaner to a corner of the cloth, gently swab the contaminated area, and finish with a dry portion of the cloth. Take care to not apply direct pressure or any sort of scrubbing and you will be fine. My practice is to use regular glass cleaner (Windex) and either a white cotton rag or shred of high quality paper towel. Purists might use a Kim Wipe or Tec Pad.


Steve
Hi Steve. I think you'll find that I stated "very little". I did not say none. Certainly, a scratch would affect image quality but a few small spots probably will have a minor effect, if at all. I have also recommended cleaning it, so I think we're singing off the same song sheet here, if perhaps in a slightly different register.
07-16-2014, 03:26 PM   #6
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Tried a lenspen when it happened to no effect. I'll try again tonight with cleaner and post the results.
07-16-2014, 03:29 PM   #7
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QuoteOriginally posted by jrpower10 Quote
Tried a lenspen when it happened to no effect. I'll try again tonight with cleaner and post the results.
See this thread too.
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/268091-got-...-remove-2.html
07-16-2014, 03:29 PM   #8
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I've cleaned the rear elements of my lenses dozens of times, especially after being in wet environs like the waterfalls I like to shoot. it's no different than cleaning the front element - use care, a soft cloth and a gentle cleaner.

on top of that, should the coating actually get scratched, which happened to me when I drop kicked a lens and it skidded across some sand, it cost me like 75 at CRIS to have it recoated. replacing the element is a drastic last resort that I don't think is warranted in this case.

07-16-2014, 06:57 PM   #9
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I use these to clean lenses all the time. Use them on my multi-coated glasses pretty much every day without ill effect. I've cleaned my front and rear elements on all my lenses with them too.

07-16-2014, 11:17 PM   #10
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Wow, OK it cleaned up perfectly. Guess I just learned the value (or lack of) of the lenspen cleaning. I couple drops of eyeglass cleaner and a soft clean t-shirt and it looks brand new. Thanks all.
07-17-2014, 05:09 AM   #11
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If you drip the lens cleaner on the cloth first instead of the lens, then you don't risk it puddling and running into other parts of the lens, especially around the edges of the element which may not be hermetically sealed.
07-17-2014, 08:53 AM   #12
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QuoteOriginally posted by MarkJerling Quote
Hi Steve. I think you'll find that I stated "very little". I did not say none.
...and I would suggest that "very little" is an understatement. You can test this of course by doing a set of photos of a test target both before/after applying some mucous to the rear element. The effect should be about the same as applying petroleum jelly to the front element of a projector lens.

You are correct, however, in that there is no harm done in doing a little clean-up!


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07-17-2014, 09:01 AM   #13
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Why is everyone so paranoid about cleaning lenses? It is incredibly hard to scratch these modern coatings. If it has got gunk on it, clean it off, good as new.
07-17-2014, 09:32 AM   #14
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QuoteOriginally posted by vonBaloney Quote
Why is everyone so paranoid about cleaning lenses?
Very good question! I have noticed that things come in bursts on this site and this must be the week for lens cleaning angst.

That being said and all sarcasm aside, I can sympathize with the OP and others who really don't want to damage or ruin an expensive tool. These things are learned, sometimes by sad experience. It is a good thing that resources like the Pentax Forums exist so that we can all help each other along.


Steve
07-17-2014, 01:37 PM   #15
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For me it wasn' concern about cleaning it (as I posted, I tried cleaning it with a lenspen before I posted and that did nothing, so I assumed the coating was damaged). The lesson for me was lenspens, while handy, aren't a substitute for lens cleaning fluid. Sprayed some on a cotton t-shirt and gently wiped the spots off, and all was well.

Thanks again for suggesting I try again. Worked out perfectly.
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