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06-03-2020, 07:13 AM   #1
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Thrift Risk...Fail for Fungus. Disassembly? Pentax SMC-F 70-210mm

All,

I got a Pentax SMC-F 70-210mm lens from a thrift buy. I spent $35 for the lens and an old SF1 (which I will re-sell, if possible). The lens focuses fine, and the zoom is stiff, but workable. However, it has a good case (read "bad") of fungus inside, making everything blurry. My thought is to disassemble the lens and attempt to clean it. Has anyone done this? Is it worth sending to anyone to have it professionally cleaned? Who would do that service? Thank you!

06-03-2020, 08:14 AM - 1 Like   #2
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I have one but it's in my wife's work-from-home office so I'll go from memory. The front elements are in one carrier so they all come out in a piece. There's a small grub screw on the side of the front barrel that locks them in place. Then the group unscrews using the filter threads. I think this is three elements, including two cemented ones. This pair often gets element separation, looking like gasoline on a puddle. The group is difficult to separate.

At the back, I think there is a tube containing a few more elements that comes out in one piece. Look for spanner slots around the rear element. I remember the mount contains many individual parts for the electrical contacts. I found it very difficult to reassemble. There is either a trick to it I don't know or it was all done with robots. I believe you have to disassemble the mount to get anything else apart. There used to be disassembly photos on a web site but the link is bad.
06-03-2020, 08:30 AM   #3
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QuoteOriginally posted by Just1MoreDave Quote
I have one but it's in my wife's work-from-home office so I'll go from memory. The front elements are in one carrier so they all come out in a piece. There's a small grub screw on the side of the front barrel that locks them in place. Then the group unscrews using the filter threads. I think this is three elements, including two cemented ones. This pair often gets element separation, looking like gasoline on a puddle. The group is difficult to separate.

At the back, I think there is a tube containing a few more elements that comes out in one piece. Look for spanner slots around the rear element. I remember the mount contains many individual parts for the electrical contacts. I found it very difficult to reassemble. There is either a trick to it I don't know or it was all done with robots. I believe you have to disassemble the mount to get anything else apart. There used to be disassembly photos on a web site but the link is bad.
Thank you! Can you shoot me the link so I can search for it?
06-03-2020, 08:38 AM - 1 Like   #4
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Considering the general price of this lens, ($40 to $75) in good used condition on auction sites, taking the time to try and clean one with "bad" fungus does not seem to be worth the effort to me. Those F zooms are not easy to take apart and if you do not have the knowledge and tools there is a good chance you will not get it back together correctly.

If you have the time and want to have a go it is certainly possible but I would just dump it and move on. I've repaired or cleaned fungus from a number of lenses but some you have to just let go.

06-03-2020, 08:48 AM   #5
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QuoteOriginally posted by jatrax Quote
Considering the general price of this lens, ($40 to $75) in good used condition on auction sites, taking the time to try and clean one with "bad" fungus does not seem to be worth the effort to me. Those F zooms are not easy to take apart and if you do not have the knowledge and tools there is a good chance you will not get it back together correctly.

If you have the time and want to have a go it is certainly possible but I would just dump it and move on. I've repaired or cleaned fungus from a number of lenses but some you have to just let go.
If nothing else, I would disassemble just for the experience.
06-03-2020, 09:05 AM - 1 Like   #6
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QuoteOriginally posted by jawats Quote
If nothing else, I would disassemble just for the experience.
And if you have the time that is a very worthwhile endeavor! It is quite amazing what they pack into those lenses.

Make sure you have all the tools needed and a clean work area. In some cases its best to dissemble inside a large plastic bag so that when the parts go 'sprong' they are contained and not lost.

Good luck and don't hesitate to ask questions there are a number of people on this forum that regularly do lens work. I've done quite a few but almost all were Takumars so quite different than what you are attempting.
06-03-2020, 09:14 AM   #7
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QuoteOriginally posted by jatrax Quote
And if you have the time that is a very worthwhile endeavor! It is quite amazing what they pack into those lenses.

Make sure you have all the tools needed and a clean work area. In some cases its best to dissemble inside a large plastic bag so that when the parts go 'sprong' they are contained and not lost.

Good luck and don't hesitate to ask questions there are a number of people on this forum that regularly do lens work. I've done quite a few but almost all were Takumars so quite different than what you are attempting.
The plastic bag is not a bad idea. I have the workspace and a magnetized dish for small screws, as well.

Apparently, this 70-210 is not so different from the 70-210 Tak, but I suppose you mean older ones. Thanks again!
06-03-2020, 09:21 AM - 1 Like   #8
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You will need a lens spanner and possibly JIS screwdrivers. On the Takumars you also needed a lens ring removal tool which you can make. Not sure if the F series needs that though, maybe the spanner will work for them. Keep track of which screw goes where, they generally used a bunch of different sizes.
And yes, I mean the actual Takumars not the later lenses that just used the name like the 70-210. Those are quite different and internally more like the F series than a Takumar.

06-03-2020, 09:24 AM   #9
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QuoteOriginally posted by jatrax Quote
You will need a lens spanner and possibly JIS screwdrivers. On the Takumars you also needed a lens ring removal tool which you can make. Not sure if the F series needs that though, maybe the spanner will work for them. Keep track of which screw goes where, they generally used a bunch of different sizes.
And yes, I mean the actual Takumars not the later lenses that just used the name like the 70-210. Those are quite different and internally more like the F series than a Takumar.
looks like you can get a Tak-F for about 1/2 of the 70-210, and it's equally well rated.
06-03-2020, 09:51 AM - 1 Like   #10
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QuoteOriginally posted by jawats Quote
looks like you can get a Tak-F for about 1/2 of the 70-210, and it's equally well rated.
I am not sure if it is consistent on all models but I believe that the difference was in the coatings. The Pentax-F series had SMC but the psuedo Takumar versions did not. I had the opportunity to test side by side the Pentax-F (orange writing) and Takumar versions (white writing) of the 28-80. I greatly preferred the images from the Pentax-F version. That could be sample variation but I think my tests bear out the difference in price. I just looked and the Takumar version has 8 elements in 8 groups and the F version has 12 elements in 9 groups so not the same optically either. But I'm not sure about the 70-210.


The ratings on those older lenses are suspect as lots of the ratings are 5 star with a comment "great lens for the price". That doesn't make it a great lens optically though.
06-03-2020, 10:05 AM   #11
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QuoteOriginally posted by jatrax Quote
I am not sure if it is consistent on all models but I believe that the difference was in the coatings. The Pentax-F series had SMC but the psuedo Takumar versions did not. I had the opportunity to test side by side the Pentax-F (orange writing) and Takumar versions (white writing) of the 28-80. I greatly preferred the images from the Pentax-F version. That could be sample variation but I think my tests bear out the difference in price. I just looked and the Takumar version has 8 elements in 8 groups and the F version has 12 elements in 9 groups so not the same optically either. But I'm not sure about the 70-210.


The ratings on those older lenses are suspect as lots of the ratings are 5 star with a comment "great lens for the price". That doesn't make it a great lens optically though.
Thank you, jatrax!
06-03-2020, 10:22 AM - 1 Like   #12
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QuoteOriginally posted by jawats Quote
If nothing else, I would disassemble just for the experience.
FYI, here is a short article on lens spanners: Lens Spanners -- Using the right tool for the job - PentaxForums.com

- Craig
06-03-2020, 11:25 AM - 1 Like   #13
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disassembling pentax lens - Google Search
06-03-2020, 02:41 PM - 2 Likes   #14
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I got a fungus infested lens from E-Bay a few years back. It never made it to my camera closet; directly into the bin it went. I've got way too much good gear in my closet to risk 'infecting it'. For $35, buy another copy.
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