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02-28-2014, 09:28 AM   #1
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About to modify a nice Tak 300mm... am I nuts?

As per my other thread...

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/252774-300m...focus-m42.html

I am sending my 300MM F4 Takumar in for service... and it suddenly occured to me that I have some options.

How evil of me do you think it would be, that as long as it is in for service and will be apart to have the loose element dealt with and infinity focus set, that I have them set infinity based on the non-flush mount M42 to K-Mount adapter?

I would like to do this because that style adapter has a flange with the hole that would allow me to use the lens release button for quick mount/dismount of the lens.

I don't know how many of you have held a 300MM f4 Tak, but it is a heafty beast, and it's no small amount of work, not to mention wear and tear on the M42 mount screwing/unscrewing into the adapter on the camera.

It's not like I'm worried about re-sale value, this one is a keeper, and it's not doing any irreversable damage to the lens. I'll leave the flanged M42 to K adapter on the lens pretty much permenantly.

So... anyone else done this sort of thing? Any regrets? I'm already leaning 90% towards going for it... comments welcome.

02-28-2014, 09:44 AM   #2
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I wonder if they could actually change the mount while they are at it. Still, I'd go for it!
02-28-2014, 09:49 AM   #3
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That's actually a good idea. I've never had issues with taking the locking part of the M42-K flush adapters apart, but even with my 200mm f/4 I'm sometimes worried about the lack of locking. With the flange adapter, you'd get a bit sturdier of a mount that would lock on!
02-28-2014, 10:38 AM   #4
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QuoteOriginally posted by Erictator Quote
. . . that style adapter has a flange with the hole that would allow me to use the lens release button for quick mount/dismount of the lens.
There's a practical alternative using a non-flanged adapter: Simply drill a shallow hole at the appropriate location on the lens base to accept the latch pin. There's many ways to accurately locate the hole - using a salvaged PK mount plate is one - and radial location isn't especially critical as there's no data pin positions to match.

Optimum hole size is 2mm/0.08". Since radial registration isn't critical a slightly oversize hole causes no problem.

I prefer to index the latch hole so the aperture scale is at the 10 or 2-o'clock position so it isn't hidden under that @#$#@ built-in flash bump. Radial position of the M42 adapter isn't critical since the lens registration distance is based on the face of the lens-to-body surface regardless of where the threads snug up tight. Once positioned, a drop of acrylic fingernail polish or super glue fixes the adapter in place.

I've used both the OEM style and flanged adapters in this manner. The flanged adapters were modified for infinity focus by removing the "hat brim" flange on a lathe. (That can also be accomplished using a flat surface, sand paper and a lot of elbow grease and patience.) The adapter may be shimmed against the lens base to position the aperture scale as desired.

I've modified three M42 lenses in that manner (one was a SupTak 300/4) but unfortunately don't have one to photograph at this time.

H2

[ Keep in mind that the M42 adapters were originally intended to be semi-permanently attached to the then new K-mount bodies to allow continued use of an expensive collection of screw-mount lenses. Thanks, Pentax - that was a thoughtful allowance for working pros that couldn't afford to replace an entire lens collection but wanted the newer PK/A bodies. ]


Last edited by pacerr; 02-28-2014 at 10:49 AM.
02-28-2014, 10:42 AM   #5
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Could you use the flange adapter as a drilling guide? Drill where the hole in the flange is, into the lens mount?

I have one laying around, and have thought about drilling my Helios since the focus is so stiff.
02-28-2014, 10:54 AM   #6
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QuoteOriginally posted by fretlessdavis Quote
Could you use the flange adapter as a drilling guide? Drill where the hole in the flange is, into the lens mount?
Not necessarily - if the flange is present the infinity position is doubtful. Pencil mark indexes on the lens and mount should proof the location. It really isn't difficult to locate the hole by trial and error using index marks.
02-28-2014, 10:56 AM   #7
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QuoteOriginally posted by pacerr Quote
Not necessarily - if the flange is present the infinity position is doubtful. Pencil mark indexes on the lens and mount should proof the location. It really isn't difficult to locate the hole by trial and error using index marks.
Ah, damn. I was about to run and get the drill!
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