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06-08-2013, 04:39 AM   #1
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Help pls - M Lens beginners question

Just bought my 1st Pentax, a K100D & have been having a grand time test driving the kit lens & a fab SMC-M 50mm f1.7. I've just got a SMC-M 80-200mm f4.5 too. At 1st glance in good condition but the front optic (no uv filter) has what appears to be tiny bubbles in/on it, on the inaccessible side. I can only see them in a certain position & am unsure if they are part of the glass itself. Anyone shed any light on this pls?

06-08-2013, 05:15 AM   #2
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Hard to tell without seeing it but it could be in the cement that joins elements together in a group. A group is a number of glass elements joined together as a single unit. If they are very small, will most likely have little effect on image quality.
Other problems include the dreaded fungus, dust specs and coating delamination but it doesn't sound like any of those.

Thanks,
06-08-2013, 05:31 AM   #3
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You don't want a UV filter on your lenses anyhow. Hoods, yes, UV no. Hoods offer more physical protection than UV filters and actually do something to improve your photos. Your digital camera already has a UV (and IR) filter applied directly to the sensor. Adding another optical surface will only degrade your image.
06-08-2013, 05:42 AM   #4
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QuoteOriginally posted by ismaelg Quote
Hard to tell without seeing it but it could be in the cement that joins elements together in a group. A group is a number of glass elements joined together as a single unit. If they are very small, will most likely have little effect on image quality.
Other problems include the dreaded fungus, dust specs and coating delamination but it doesn't sound like any of those.

Thanks,
I don't think it's any of those things either - there are probably hundreds of them absolutely tiny - imagine the tiniest fat droplets. Best description I can manage, sorry! Anyway the proof will be in the photos - just thought someone must have seen this before.

Thanks somuch for the response though

06-08-2013, 05:49 AM   #5
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QuoteOriginally posted by JimJohnson Quote
You don't want a UV filter on your lenses anyhow. Hoods, yes, UV no. Hoods offer more physical protection than UV filters and actually do something to improve your photos. Your digital camera already has a UV (and IR) filter applied directly to the sensor. Adding another optical surface will only degrade your image.
Well that's useful info - and there was I about to rush out & get a filter for the 50mm f1.7 - would prevent direct physical damage to the optics through airborn pollutants (eg. fat droplets, acrid rain) though?
06-08-2013, 06:57 AM   #6
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The SMC coating is pretty darn durable and will stand up to proper cleaning probably better than any but the most expensive filter. A lens hood actually blocks a lot of pollutants too because the lens is recessed. About the only two filters for a dSLR that cannot be easily duplicated in software are polarizers or neutral density. Putting an extra layer of unnecessary glass in front of your lens will always degrade your image some as the light will bounce around between the filter and the lens. Really good filters are of course better than cheaper filters, but it is still there, and really good filters are not inexpensive. Proper sized hoods on the other hand never degrade your image - in most cases they improve it - and with few exceptions offer as much if not more front element lens protection.
06-08-2013, 07:40 AM   #7
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Think I may have found it - on this forum of course! It sounds like lens separation

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/227086-whats-stuff-my-lens.html

Bought it on ebay for a princely 10 so not worth sending it back. Shame as it otherwise looks & feels great.
06-08-2013, 12:19 PM   #8
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I would go ahead and try the lens I have the same lens I bought it knowing it had oily blades. I wanted to try tearing a lens apart and didn't want to sacrafice a good lens so for $2.00 I bought it. I ended up geting most of the oil off but Then decided to send it to a repairman just to be on the safe side and make sure it was done right. It is one of my favorite lenses. The spots on the front element may not effect a photo or only cause a problem shooting straight into a light source. It is worth a try at any rate.

06-09-2013, 04:38 AM   #9
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Well good news folks - the lens takes great photos, no lens creep, smoooth & sharp!

Just got to hone my manual skills!

So pleased I switched to Pentax - all this lovely old glass with built in shake reduction - perfect for amateurs like me!

Thanks for all your help!
06-09-2013, 05:40 PM   #10
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QuoteOriginally posted by GBNeil Quote
Well good news folks - the lens takes great photos, no lens creep, smoooth & sharp!

Just got to hone my manual skills!

So pleased I switched to Pentax - all this lovely old glass with built in shake reduction - perfect for amateurs like me!

Thanks for all your help!
Good news! My M50 f2 is also full of fungi but can still produce reasonably sharp images. Don't ever get put down but rusty old lenses.
06-10-2013, 08:51 AM   #11
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I have the older Pentax 50mm f1.4 with 52mm filter ring instead of the usual 49mm used in the M series lenses. It had fungus. I took it apart and cleaned pout all of I could, put it back together and it gets excellent pictures. I still need to open it up again and see if I Can finish the cleanup, but what's left doesn't seem to be having an adverse affect.

This shot was taken a few days ago with it, wide open at f1.4. I usually don't shoot wide open but wanted to see what it would deo.



This was taken with the same lens at f4



And I can still see a bit of fungus around the outside edge of an internal rear element...getting shots like that I'm tempted to leave it alone, but I'd like to try and remove the rest. I missed it last time I opened it up...

So if your lens is still getting good shots, use it while you can...
06-10-2013, 09:07 AM   #12
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Thanks for that mythguy9 (are there really 8 others & Paleo Pete. Actually I have lens separation I think, so what I'm seeing is tiny air bubbles in melted glue. I got the impression I can't remedy this myself, so I'll leave things be. I've just bought a Ricoh Rikenon P 70-210mm f3.9 Macro Zoom - reckon I'll keep the better of the two.

This old Pentax glass is a bit obsessive
06-11-2013, 07:04 AM   #13
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If it's lens separation, no you can't fix it. Lenses are cemented together and have to be perfectly aligned. Years ago in binocular repair I had to learn to do it, canadian balsam was used. Same glue used for fishing rod tips. Both lenses are heated on a hotplate, some canadian balsam in the one with a convex surface. The other one matches that surface. Once the glue melts they are put together very carefully to avoid bubbles, (almost impossible) and the bubbles are worked out by moving it around, then you try to center it. After cooling it's put in an optical machine that tells you if they are aligned properly, probably not, and you reheat it and do it again...My first one took me 6 tries I think till I got the alignment within tolerance...

Without some specialized equipment, lens separation can't be fixed because you can't realign the lens properly. If it's done with canadian balsam, regluing would not be difficult, it just takes a little heat. Somewhere around180-220F I think, it's been a while, I'm not sure any more. Well above car trunk in Texas temperature anyway, that won't melt it...(but it will melt the hide glue used in guitar assembly, that takes about 140F) But realignment would be impossible without some expensive equipment. It looks easy...but once I tried it I found out just how difficult it is to actually get it aligned right...If it's not aligned right, the lens is looking off to one side. Not good...
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