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Old Sep 14, 2007, 5:19 AM   #1
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Quick question, presumable Dawg would know.

Is the K-mount fitting on Pentax lenses removable? the reason I ask is I have some niceM42 lenses and an old pentax lens that I don't use (SMC 28mm with a scratch on the rear element) and wondered if the bayonet mount plate just comes off with a few screws. Screw-mount adaptors cost about £15-20 even for the rubbish HK ones that lose infinity focus, but I can pick up a few mouldy K-Mount lenses for a few quid if I can remove the fitting easy.

I am making a make-shift one now from an old body cap that will be useless for all but the closest of shots, but would like something more useable without spending a lot.

One of the screws is stuck on the 28mm lens (actually broke one screwdriver tip) so would need to drill it out if I can take the plate off.

Thanks in advance
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Old Sep 14, 2007, 9:51 AM   #2
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Tachikoma wrote:
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Quick question, presumable Dawg would know.

Is the K-mount fitting on Pentax lenses removable? the reason I ask is I have some niceM42 lenses and an old pentax lens that I don't use (SMC 28mm with a scratch on the rear element) and wondered if the bayonet mount plate just comes off with a few screws. Screw-mount adaptors cost about £15-20 even for the rubbish HK ones that lose infinity focus, but I can pick up a few mouldy K-Mount lenses for a few quid if I can remove the fitting easy.

I am making a make-shift one now from an old body cap that will be useless for all but the closest of shots, but would like something more useable without spending a lot.

One of the screws is stuck on the 28mm lens (actually broke one screwdriver tip) so would need to drill it out if I can take the plate off.

Thanks in advance
With three to four screws removed it should come right off. The ones with contacts and a few others have the coupling lever attached deeper down and sometimes have a very tiny spring attached that can be removed. The screw mount is much smaller in diameter to the K/mount base plate so attaching it may be a problem. Epoxy glue should hold it well if you scuff the surface of both plate and screw mount before applying it. You may have to remove things from the middle of the K/mount plate too as there is usually a filler of some sort there to close in around the small bottom lens.
Some of these lens have steps or other things protruding below the base plate. These would have to be ground off to make it flat enough to not affect infinity focus. Be careful here as the base is usually chrome plated brass and grinding brass on a bench grinder can cause the grind rock to explode. Serious here now...I've seen it happen and blind a man. I use a Bridgeport mil to flatten mine and you can use a rotary sanding disk or a belt sander...But if you use a bench grinder you're on you're on.

To align the K/mount plate...Put the red dot in line with the distance legend and line . This way the f/stop readings and adjustment along with the Focus distance legend will be on top. Hope this helps. But remember that anything you do to your lens is on your head!! LOL

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Old Sep 14, 2007, 10:11 AM   #3
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Just what I needed, thanks dawg!

Not too worried about losing the infinity focus, most of my shots are close-ups and this one M42 58mm f.2 lens (not sure what it is, it's all in Russian) appears to be very good at them.
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Old Sep 14, 2007, 1:57 PM   #4
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Tachikoma wrote:
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Just what I needed, thanks dawg!

Not too worried about losing the infinity focus, most of my shots are close-ups and this one M42 58mm f.2 lens (not sure what it is, it's all in Russian) appears to be very good at them.
Hope things work out with it...Donh't forget to post photos of what you did and the resulting photos using it!

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Old Sep 14, 2007, 2:56 PM   #5
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Will do!

Sadly I couldn't get the mount off the 28mm lens, the screws must be corroded and fused to the frame or something under the surface, chewed up 2 other screwdriver heads...

However, I did get the mount off the Sigma 70-210 lens, couldn't get the damn thing back together, but it's no big loss. So I now have a nice stainless steel mount, that I just need to file down by about 2mm and it should fit perfectly. However I don't have anything strong enough to file down steel, so I may have to outsource the work to a workmate on Monday who is better equipped than I.
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Old Sep 14, 2007, 8:59 PM   #6
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Tachikoma wrote:
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Will do!

Sadly I couldn't get the mount off the 28mm lens, the screws must be corroded and fused to the frame or something under the surface, chewed up 2 other screwdriver heads...

However, I did get the mount off the Sigma 70-210 lens, couldn't get the darn thing back together, but it's no big loss. So I now have a nice stainless steel mount, that I just need to file down by about 2mm and it should fit perfectly. However I don't have anything strong enough to file down steel, so I may have to outsource the work to a workmate on Monday who is better equipped than I.
Just keep trying and don't give up.



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Old Sep 15, 2007, 9:06 AM   #7
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Hi tachikoma, stainless steel is tough stuff to file,is it is posible to grind it with a small angle grinder ?( if it is a flat surface, you can keep the grinder v steady and if it is securely clamped, as if the grinder picks up it will hurle it across the room!). Or, if I was back at work use a small bench grinder, but this is fiddly work and difficult/dangerous for the non engineer to attempt.Time to sound out any contacts in engineering/model engineering club,( I'd be happier and quicker doing this sort of job than trying to get PC software to work !) best of luck, SS

Oh, just remembered, tight screws; ways to remove:- gently in this case,(it's a lens!) apply screwdriver to screw and tap handle a few times (with small hammer!). Apply heat, bit difficult but solder iron might do it. Try tuning screw at same time hitting handle as above, probably need three hands for this or an assitant. If all else fails drill out screw! best of luck SS
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Old Sep 15, 2007, 9:57 AM   #8
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Hi silversurfer, it's the inside flange (for want of a better word) that needs filing, only by 1mm or so to allow the m42 thread to fit inside. It's not going to be a "proper" mount as infinity focus won't work, but it should make a nice macro/portrait lens. I won't be able to get anything in there unless it's mounted to a lathe (which I don't have) or file it by hand. Hopefully my workmate will have something that can do the job, and I can ask them to do it in return for a few beers!

Here's the mount:
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Old Sep 15, 2007, 12:01 PM   #9
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You'll find most of these are not stainless steel but chrome plated Bras or bronze. They file pretty easy!

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Old Sep 15, 2007, 12:15 PM   #10
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Ah right, it has machining marks on it, so I assumed that wouldn't show if it had been plated. I will pop into a hardware store tomorrow and pick up a few cheap files, the Mrs won't let me touch her tools...
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