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09-22-2016, 08:14 PM   #1
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Problem on disassembling SMC Pentax 400mm F5.6

I just bought this lens and decided to clean the fungus in it.

First I removed the name ring, and took out the front element.



Then I removed the mount.



And, I'm stuck at here. I tried to twist the front with a spanner wrench, and I tried my best but it just won't even move a bit.



So, I looked at somewhere else, and I saw some screws inside the back of the lens but I can't get to there.



Then, I noticed a gap at here so I was wondering if i can twist it open so I can get to the screws.



Well, everything is holding still even I used my full strength.



So, I'm stuck at here. Can someone help me? Thanks.

09-22-2016, 11:41 PM   #2
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I believe the person you'd want to talk to is forum member dcshooter. Contact him and see what he says.
09-23-2016, 02:51 AM   #3
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Could it be that the ring on the front has a left thread?
09-23-2016, 04:22 AM   #4
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Apply a little solvent to the front retainer ring - I use a 50 unit disposable needle to apply the tiniest amount of acetone imaginable (delivery is precise). If there is any gunk/ glue, the acetone is just enough to release the ring. Then you can remove (and no it is not left hand thread).

09-23-2016, 04:30 AM - 2 Likes   #5
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Mark's advice is good. Another alternative to acetone is MEK which has better wetting action and tends to be a bit more effective than acetone, though a bit more nasty to work with.

I would also advise getting a new spanner from SK Grimes. The Grimes spanners are much more robust and can be vise mounted and will be much more effective than the dinky one in the picture at removing larger rings.

Also, to confirm, the ring is standard threaded, although turning it clockwise a bit might actually loosen the threadlock up a bit.

If all else fails, try hitting the front of the lens for a few minutes with a blast of hot air from a hair dryer and removing the ring while still hot. The heat expands the metal and often can loosen even the most stubborn rings.

Last edited by dcshooter; 09-23-2016 at 12:48 PM.
09-25-2016, 03:41 AM   #6
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Thanks for the replys guys. I've figured out how to open the back of the lens. But still no luck with the front, even after I heated it with hair dryer for 10mins. Maybe I should try some acetone.
09-25-2016, 07:06 AM - 1 Like   #7
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QuoteOriginally posted by nats_ji Quote
Thanks for the replys guys. I've figured out how to open the back of the lens. But still no luck with the front, even after I heated it with hair dryer for 10mins. Maybe I should try some acetone.
I am going to suggest you something, but be aware that I've never handled this lens. I think that you will have to disassemble the lens from the middle (remove rubber, unscrew three screws), all until the point when helicoid can be unscrewed (maybe it's possible without the rubber grip removal, from the back of the lens), then you slide back the hood and there will probably be three screws holding the front group in place. After they've been removed, unscrewing the front group should be easy.

Do these steps at your own risk, as I could be completely wrong.

Edit: Take a look on the site, I think somebody posted SMC M 200 disassembly, that might give you some ideas.

Regards,

Marko
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