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01-11-2021, 01:12 AM   #1
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Problem: can't loosen screws to clean dust and fungus

Hi,
I came across a Pentagon 50mm f1.8. Although I already have the Pentax-M 50mm f1.7, I decided to clean it. However, I haven't got very far. There are three screws holding the rear element to the rest of the lens. And - that's the bad part - I could loosen only one of them.
Anyone any idea how I could get rid of the other two?
They look pretty bad. (Image)
Thanks,
J


Last edited by ShutterPro; 05-10-2021 at 06:12 AM.
01-11-2021, 03:21 AM - 2 Likes   #2
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use acetone or mek, also try shocking it with a screw drive ans a small hammer. or use a soldering iron and heat it up. THESE are suggestions and to be done at your own RISK
01-11-2021, 06:48 AM - 2 Likes   #3
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Are you using a JIS driver on cross-head screws rather than a Phillips screwdriver? JIS drivers and much less prone to strip the heads of JIS screws.

Heating the screws with a soldering iron is usually a good bet. The only f/1.8 normal lens is the K 55mm f/1.8 so I'm assuming this is the lens in question.

SMC Pentax 55mm F1.8 Reviews - K Prime Lenses - Pentax Lens Reviews & Lens Database

There shouldn't be anything near by that heat would damage and enough "thermal soaking" that it would take quite a long time for the heat to spread to somewhere where it might cause damage. Heating would soften any thread lock and possibly get the metal to expand and contract enough to loosen the screw.

Worse comes to worse you can get a micro-screw extractor but then you would have to find replacement screws of the proper size.

Normal lenses in f/2.0, 1.8 and 1.7 are quite numerous so finding a copy free of fungus is not difficult.
01-11-2021, 07:08 AM - 2 Likes   #4
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QuoteOriginally posted by Not a Number Quote
Are you using a JIS driver on cross-head screws rather than a Phillips screwdriver? JIS drivers and much less prone to strip the heads of JIS screws.

Heating the screws with a soldering iron is usually a good bet. The only f/1.8 normal lens is the K 55mm f/1.8 so I'm assuming this is the lens in question.

SMC Pentax 55mm F1.8 Reviews - K Prime Lenses - Pentax Lens Reviews & Lens Database

There shouldn't be anything near by that heat would damage and enough "thermal soaking" that it would take quite a long time for the heat to spread to somewhere where it might cause damage. Heating would soften any thread lock and possibly get the metal to expand and contract enough to loosen the screw.

Worse comes to worse you can get a micro-screw extractor but then you would have to find replacement screws of the proper size.

Normal lenses in f/2.0, 1.8 and 1.7 are quite numerous so finding a copy free of fungus is not difficult.
'Pentagon' = 'Pentacon'

Pentacon 50 1.8 | Vintage Camera Lenses.

01-11-2021, 09:15 AM - 1 Like   #5
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QuoteOriginally posted by Not a Number Quote
Are you using a JIS driver on cross-head screws rather than a Phillips screwdriver?
German lens with slot-head screws.


Steve
01-11-2021, 05:52 PM - 3 Likes   #6
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Slotted screws are sometimes easy because you can grind a new slot with a Dremel, and make it fit your screwdriver. That screw looks pretty small and I'd worry about creating an unwanted slot in the surrounding part.

Look at the other screws to see if you can find replacements. If you can, consider drilling out the problem screws and replacing them. Use a center punch to keep the drill on the screw.
01-12-2021, 02:51 AM   #7
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QuoteOriginally posted by Not a Number Quote
Are you using a JIS driver on cross-head screws rather than a Phillips screwdriver? JIS drivers and much less prone to strip the heads of JIS screws.

Heating the screws with a soldering iron is usually a good bet. The only f/1.8 normal lens is the K 55mm f/1.8 so I'm assuming this is the lens in question.

SMC Pentax 55mm F1.8 Reviews - K Prime Lenses - Pentax Lens Reviews & Lens Database

There shouldn't be anything near by that heat would damage and enough "thermal soaking" that it would take quite a long time for the heat to spread to somewhere where it might cause damage. Heating would soften any thread lock and possibly get the metal to expand and contract enough to loosen the screw.

Worse comes to worse you can get a micro-screw extractor but then you would have to find replacement screws of the proper size.

Normal lenses in f/2.0, 1.8 and 1.7 are quite numerous so finding a copy free of fungus is not difficult.
Thank you for your tips I'll try them out. I really mean the Pentacon 50mm, my spellcheck changed it.

---------- Post added 01-12-21 at 02:51 AM ----------

QuoteOriginally posted by niceshot Quote
use acetone or mek, also try shocking it with a screw drive ans a small hammer. or use a soldering iron and heat it up. THESE are suggestions and to be done at your own RISK
Thank you

---------- Post added 01-12-21 at 02:54 AM ----------

QuoteOriginally posted by Just1MoreDave Quote
Slotted screws are sometimes easy because you can grind a new slot with a Dremel, and make it fit your screwdriver. That screw looks pretty small and I'd worry about creating an unwanted slot in the surrounding part.

Look at the other screws to see if you can find replacements. If you can, consider drilling out the problem screws and replacing them. Use a center punch to keep the drill on the screw.
Thank you. I managed to remive one, but the rest is stuck. But I'll try again. The screw looks strange. It isn't very regular in shape. Wonder if I can find a substitute.

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