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Repair manual for Pentax - A 645 Lens


ynnek

Link Posted 05/12/2018 - 15:59
I acquired a Pentax - A 645 100mm f4 Macro has fungus. Does anyone here have a service manual or other resource about the disassembly of these lenses? Or should I wing it?

Kim C

Link Posted 05/12/2018 - 16:18
ynnek wrote:
I acquired a Pentax - A 645 100mm f4 Macro has fungus. Does anyone here have a service manual or other resource about the disassembly of these lenses? Or should I wing it?

I wasn't aware the was a 100mm macro in the 645 range.

Looking at my 120mm Macro, not sure where to start.

JAK

Link Posted 05/12/2018 - 16:26
Take it or send it back?
I've investigated having fungus infected lenses cleaned professionally but was told there is no guarantee that the fungus won't come back.
One thing puzzles me, to my knowledge the only Pentax 645 macro lenses are:
HD PENTAX-D FA 645 Macro 90 mm F2.8 ED AW SR (current)
smc PENTAX-A 645 Macro 120 mm F4.0
smc PENTAX-FA 645 Macro 120 mm F4.0 (current)
But no 100mm ones!
If it is what you say, 100mm, it might be a very rare prototype or something in which case it would almost certainly be worth restoration.
As to help with disassembly, difficult with an unrecognised lens!
Are you sure it isn't this one: https://www.pentaxforums.com/lensreviews/SMC-Pentax-A-100mm-F4-Macro-Lens.html ? But that isn't a 645 lens.
John K

ynnek

Link Posted 06/12/2018 - 12:52
My apologies, the correct lens is a Pentax - A 645 120mm f4 Macro. I cannot send it back. It was bought with a kit. I am waiting to get my film back. I shot a roll with it to see how it affects the image. Thanks form all of the replies.

JAK

Link Posted 06/12/2018 - 13:48
I'd be careful using fungus infected lenses. You wouldn't want the spores jumping ship to wreck another lens.
Someone on the USA forum has described how to deal with an A 50mm F1.7 lens here. I'd presume the process would be comparable for your 120. I gather the 120 has 9 elements in 7 groups (with floating elements.)
Maybe Kim may offer further guidance. At least it isn't an FA one. Are you used to dealing with lens disassembly? In any event good luck if you attempt it.
John K
Last Edited by JAK on 06/12/2018 - 13:57

Kim C

Link Posted 06/12/2018 - 14:43
JAK wrote:
I'd be careful using fungus infected lenses. You wouldn't want the spores jumping ship to wreck another lens.
Someone on the USA forum has described how to deal with an A 50mm F1.7 lens here. I'd presume the process would be comparable for your 120. I gather the 120 has 9 elements in 7 groups (with floating elements.)
Maybe Kim may offer further guidance. At least it isn't an FA one. Are you used to dealing with lens disassembly? In any event good luck if you attempt it.

The A series lenses are very easy the clean. 2 problems. There are many types of fungus. It's not so much a problem of the spores jumping ship. They are all around us all the time. But they won't germinate unless they have the right conditions. It is more the type of fungus. A few of them produce acid as a by product of their growth. This acid attacks glass and etches it. If this has happened the lens is a write off. The cost of having the elements re polished is far more than the lens is worth. If it is a more normal fungus, Once clean you do need to kill anything left using alcohol or something else.

But looking at the 120 macro, It will be difficult to remove the groups. On the 35mm lens, it is usually relatively easy the remove the rear baffle and then unscrew the rear froup without dismantling the mount. In a similar way, It is usually easy to remove the trim at the front to remove the front group. But floating elements are a problem. Also there is very little room around the rear mount and no baffle so the whole mount might have to come off.

Helpful

ynnek

Link Posted 06/12/2018 - 17:45
Kim C wrote:
JAK wrote:
I'd be careful using fungus infected lenses. You wouldn't want the spores jumping ship to wreck another lens.
Someone on the USA forum has described how to deal with an A 50mm F1.7 lens here. I'd presume the process would be comparable for your 120. I gather the 120 has 9 elements in 7 groups (with floating elements.)
Maybe Kim may offer further guidance. At least it isn't an FA one. Are you used to dealing with lens disassembly? In any event good luck if you attempt it.

The A series lenses are very easy the clean. 2 problems. There are many types of fungus. It's not so much a problem of the spores jumping ship. They are all around us all the time. But they won't germinate unless they have the right conditions. It is more the type of fungus. A few of them produce acid as a by product of their growth. This acid attacks glass and etches it. If this has happened the lens is a write off. The cost of having the elements re polished is far more than the lens is worth. If it is a more normal fungus, Once clean you do need to kill anything left using alcohol or something else.

But looking at the 120 macro, It will be difficult to remove the groups. On the 35mm lens, it is usually relatively easy the remove the rear baffle and then unscrew the rear froup without dismantling the mount. In a similar way, It is usually easy to remove the trim at the front to remove the front group. But floating elements are a problem. Also there is very little room around the rear mount and no baffle so the whole mount might have to come off.

JAK & Kim thanks for the responses. And no JAK, I have never attempted to disassemble a lens. I am though a machinist, so I understand the complexity of the issue. But I look at it this way, If it works good. If not, then all I lost was a compromised lens.

ynnek

Link Posted 06/12/2018 - 17:46
BTW, The other two lenses that came with the kit are fine.

Kim C

Link Posted 06/12/2018 - 18:00
ynnek wrote:
BTW, The other two lenses that came with the kit are fine.

It will not be the easiest lens to start on. But then again the early MF ones are not expensive. Generally most find the make mistakes with the first lens they do.
Last Edited by Kim C on 06/12/2018 - 18:00
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