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How do I disassemble an Osawa 28mm f2.8 P/K lens?
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PostPosted: Sun Jun 19, 2011 10:23 pm    Post subject: How do I disassemble an Osawa 28mm f2.8 P/K lens? Reply with quote
I have an Osawa 28mm f2.8 P/K lens and the focus ring keeps on slipping. I'd also like to see if I can adjust the infinity focus as it doesn't reach infinity on my Canon 400D.

I've tried pressing the face of the lens on the rubber sole of a shoe to see if it will unscrew, but it won't budge either clockwise or anti-clockwise.

What is the best way to get into this lens to check the focus ring and if it has screws to adjust infinity?

Here is the lens:






Thank you in advance Smile


PostPosted: Mon Jun 20, 2011 12:10 am    Post subject: Reply with quote
From behind. Here is my tip from taking apart a number of PK lenses: get a little point-n-click or cell phone camera and photograph every step. Use a sharpie to put tiny alignment marks on internal components. This will help you reassemble it correctly.


PostPosted: Mon Jun 20, 2011 1:21 am    Post subject: Re: How do I disassemble an Osawa 28mm f2.8 P/K lens? Reply with quote
-halli- wrote:
I have an Osawa 28mm f2.8 P/K lens and the focus ring keeps on slipping. I'd also like to see if I can adjust the infinity focus as it doesn't reach infinity on my Canon 400D.


Is it just the rubber portion that slips? If so, you should be able to pry the grip back just a bit, and dab some contact cement on the backside of the rubber to hold it in place.

For the infinity focus issue, are you using a quality adapter that can reach infinity with other lenses? The infinity focus adjustments should be via externally accessible screws... not anything that would require taking the lens apart.


The reason for both questions - there are a lot of risks involved with opening lenses. Many people try to fix seemingly minor problems, and end up with much more serious issues - decentered lens elements, internal dust or smudges, an offset on the focus helicoid, or even damage from slipped tools. If the issues aren't significant, it often isn't worth the risk to take a lens apart. Wink


PostPosted: Mon Jun 20, 2011 6:13 am    Post subject: Reply with quote
It is the whole ring that slips, not just the rubber grip. Other lenses do reach infinity with the adapter.

By "from behind" do you mean I have to disassemble from the mount?

Thanks


PostPosted: Mon Jun 20, 2011 6:26 am    Post subject: Reply with quote
Well don't worry if you can't fix it as my Osawa 28mm is 2nd from bottom, up from the Yashica 28mm DSB for quality of results compared with my fifteen other 28mm lenses.


PostPosted: Mon Jun 20, 2011 3:55 pm    Post subject: Reply with quote
Excalibur wrote:
Well don't worry if you can't fix it as my Osawa 28mm is 2nd from bottom, up from the Yashica 28mm DSB for quality of results compared with my fifteen other 28mm lenses.


Rats, I was hoping that the lens would be better than that. Sad


PostPosted: Mon Jun 20, 2011 5:01 pm    Post subject: Reply with quote
-halli- wrote:
Excalibur wrote:
Well don't worry if you can't fix it as my Osawa 28mm is 2nd from bottom, up from the Yashica 28mm DSB for quality of results compared with my fifteen other 28mm lenses.


Rats, I was hoping that the lens would be better than that. Sad


Well it's all relative and I only noticed the difference because of having better lenses e.g Hexanon, Canon FD, Vivitar close focus, CZJ etc 28mms ...but you never know, with manufacturing tolerances, I might have a bad M42 Osawa and you have a great one Wink


PostPosted: Mon Jun 20, 2011 5:13 pm    Post subject: Reply with quote
Excalibur wrote:

Well it's all relative and I only noticed the difference because of having better lenses e.g Hexanon, Canon FD, Vivitar close focus, CZJ etc 28mms ...but you never know, with manufacturing tolerances, I might have a bad M42 Osawa and you have a great one Wink


Here's hoping!

I've got three 28mm lenses and none of them reach infinity.

My Prinzflex Auto Reflex (M42) is adjustable and I'm in the process of faffing with that one.

The Pentacon Prakticar (PB mount) needs a lens tool to open the front but I believe is adjustable.

The Osawa seems OK with the little fiddle I've had with it, but I haven't used it properly due to the infinity issue.


PostPosted: Mon Jun 20, 2011 5:27 pm    Post subject: Reply with quote
-halli- wrote:


I've got three 28mm lenses and none of them reach infinity.

My Prinzflex Auto Reflex (M42) is adjustable and I'm in the process of faffing with that one.

The Pentacon Prakticar (PB mount) needs a lens tool to open the front but I believe is adjustable.

The Osawa seems OK with the little fiddle I've had with it, but I haven't used it properly due to the infinity issue.


That Pentacon Praktica might be interesting, I've two 28mm PB mount lenses one is the very good CZJ and the other is a Sigma mini wide.


PostPosted: Mon Jun 20, 2011 5:50 pm    Post subject: Reply with quote
Excalibur wrote:

That Pentacon Praktica might be interesting, I've two 28mm PB mount lenses one is the very good CZJ and the other is a Sigma mini wide.


How do I tell the difference?


PostPosted: Mon Jun 20, 2011 7:36 pm    Post subject: Reply with quote
-halli- wrote:
Excalibur wrote:

That Pentacon Praktica might be interesting, I've two 28mm PB mount lenses one is the very good CZJ and the other is a Sigma mini wide.


How do I tell the difference?


http://www.praktica-users.com/lens/blenses.html


PostPosted: Mon Jun 20, 2011 8:09 pm    Post subject: Reply with quote
Excalibur wrote:
-halli- wrote:
Excalibur wrote:

That Pentacon Praktica might be interesting, I've two 28mm PB mount lenses one is the very good CZJ and the other is a Sigma mini wide.


How do I tell the difference?


http://www.praktica-users.com/lens/blenses.html


Cheers, looks like mine is the second version with plastic barrel.


PostPosted: Mon Jun 20, 2011 8:46 pm    Post subject: Reply with quote
Yes, through the mount. I have yet to be able to take apart a K Mount lens through the front. It can be done (as the 500mm Samyang tutorial from this weekend showed), but it's much easier to just gut them through the mount.


PostPosted: Mon Jun 20, 2011 8:50 pm    Post subject: Reply with quote
David wrote:
Yes, through the mount. I have yet to be able to take apart a K Mount lens through the front. It can be done (as the 500mm Samyang tutorial from this weekend showed), but it's much easier to just gut them through the mount.


Cheers, perhaps a job for when I've got a bit more time then Smile
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