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02-22-2016, 10:38 PM - 4 Likes   #1
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I saved a Asahi m42 200mm f/3.5 preset with a dented screwmount... using a dremel

I was reading the "The "Keeper" Lens Club -- You'll regret it if you sell it" thread when I saw this post: https://www.pentaxforums.com/forums/122-lens-clubs/94353-keeper-lens-club-you...tml#post975006 and realized, that a) I had a (seemingly) mint copy downstairs, and b) It has 18 aperture blades! c) I needed to shoot with this lens immediately after storing it without use for so long.
You can imagine my disappointment when I tried to put an extension tube on the lens and it wouldn't mount straight. At first I thought I had somehow crossthreaded the extension tube onto the mount, but then I discovered the dent in the screwthread... taking up about 1/5th the circumference of the mount.

My first thought was disassembly and sourcing the mount from an example with fungus or a cracked front element or the like. Unfortunately, this lens doesn't have any screws accessible externally, and only two internally which are for the focusing elements and not the mount. Then I had a much more radical idea... to just excise the dented portion of the mount... leaving the other 4/5ths to carry the load. But first I took the tripod collar off... that required two flathead screwdrivers, one in the gap that is tightened shut with the knob, and one 180 degrees from the tripod mount on the top of the collar, where there is a small pin that secures the collar. Then I put a tissue (probably should have done something that would generate less dust) on top of the rear element to protect it from metal shavings. Then I took my rotary tool (actually a black & decker, but dremel is more pithy) and made cuts to the screwmount on each end of the dent. After that, I just shaved down the middle portion. I did this on 4/6th power with a carbide cutting blade. This was the result:
Fortunately I was then able to attach an extension tube properly and mount it to my K-50 using my m42 adapter. As much as I hated carving up a lens in such beautiful shape, a dented screwmount is pretty much a fatal injury to a lens without radical intervention. Here are those beautiful aperture blades:

All previous shots taken with a K-50 and Super Takumar 135mm f/3.5 with extension tubes.
Here is the 200mm back in action, taking a macro shot (with extension tubes) of one of my SVs:


Just thought I'd share... if you have any telephoto lenses with a dented screwmount, this might be a solution.

Cheers.

02-23-2016, 12:39 AM   #2
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Seems like not the most refined, but very practical surgery you did to your lens, which by the way looks great, just as this beautiful SV. What counts is that you can take photos again! Congrats!
02-23-2016, 12:45 AM   #3
Tas
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I thought you were nuts, however comma...

Mate, you're right about the surgery being radical, but kudos to you. The bokeh from that beastie looks excellent. And those 18 blades look stunning. Like marble to look at.

Hope you post lots of images and make plenty of people envious of what you have in your hand to use.

Tas
02-23-2016, 09:45 AM   #4
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You could mill a custom part from an internet company. Sometimes the 3D printing companies offer milling in metal as well. All you need is a 3D model, that can be done in freeware software, like sketchup, or a trial version of rhinoceros (free for 90 days and not for commercial use).

02-23-2016, 09:41 PM   #5
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Wonderful!

The Tak 200/3.5 is my favorite Tak and my favorite tele. Glad you were able to save this one.
02-23-2016, 09:52 PM   #6
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This is one of my favorite Taks as well. I picked up a gorgeous copy from an estate sale last year. Seeing the 18 blades in it blew my mind!
02-24-2016, 04:49 AM   #7
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If you can keep using it then the mod works, what the hell, the mount was shot anyway, so you didn't do anything that hurt the value, but please, don't just use this as a macro lens on extension tubes.

It is a fantastic lens for short wildlife shots, and for outdoor portraits. It has less CA than any of the Tak 200/4's or the SMC Pentax 200/4
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200mm 3.5, asahi m42 200mm, collar, dent, dented screwmount, diy, extension, fix, k-50, k-mount, lens, m42 200mm f/3.5, mount, pentax lens, preset, screwmount, slr lens, tripod, tube
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