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12-02-2015, 11:42 AM   #1
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M42-Bayonette converter for 500mm Pentax-K?

Would it be feasible to use a converter so that I can use a Pentax-K 500mm M42 lens on my K-50? Would the converter effect the focusing at all?
Thanks for any advice.

12-02-2015, 11:51 AM   #2
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If it's a Pentax K isn't it K-mount already?

If it is M42 it would be a Takumar.
12-02-2015, 11:51 AM   #3
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QuoteOriginally posted by Dewman Quote
Would it be feasible to use a converter so that I can use a Pentax-K 500mm M42 lens on my K-50? Would the converter effect the focusing at all?
Thanks for any advice.
The m42 to k adapter should take care of everything, and infinity focusing will be possible. Good luck!

For such a long/heavy lens I would recommend getting the OEM adapter:
Pentax Mount Adapter K 30120 B&H Photo Video

There is otherwise no significant difference between the M42 and the K version of the 500mm, by the way.

Adam
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12-02-2015, 12:08 PM   #4
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I used a 400mm M42 Takumar on my k-x and k-5 with good results. I would suggest using an adapter that is fixed to the lens in this case. It is difficult to screw such a long lens to the camera. I used the OEM adapter for all other lenses, putting the adapter on the camera then screwing in the lens. But the 400mm was too big so I got a third party adapter (took several tries until I got a good one) removed the spring and then attached it tightly to the lens using a k-mount lens cap for leverage.

Always use the tripod foot on the lens not the camera if you are mounting to a tripod.

12-02-2015, 12:10 PM   #5
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You may find a rimmed M42 - PK adapter gives a more stable and tighter fit. With a 500mm lens the effect on infinity focus will be negligible - only an issue for eg moon shots.
12-02-2015, 12:31 PM   #6
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QuoteOriginally posted by jatrax Quote
I would suggest using an adapter that is fixed to the lens in this case. It is difficult to screw such a long lens to the camera.
I was reading the MX manual the other day, and even with more mundane lenses it recommends threading the adapter onto the lens first and then fitting it as if it were a K-mount lens. So that's the official recommendation from Asahi Optical Co.
12-02-2015, 12:42 PM   #7
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QuoteOriginally posted by pathdoc Quote
I was reading the MX manual the other day, and even with more mundane lenses it recommends threading the adapter onto the lens first and then fitting it as if it were a K-mount lens. So that's the official recommendation from Asahi Optical Co.
But to remove the lens you have to unscrew it...

12-02-2015, 12:56 PM   #8
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The M42 to K adapters all lock onto the camera body with a spring so neither the adapter nor the lens utilizes the lens lock pin on the camera body.

BUT IF YOU ARE REALLY BRAVE (maybe foolish).

Get an adapter, remove the spring, mount adapter + lens and mark the position where the lock pin on the camera body hits the back of the lens*. Remove the lens, drill a hole** of appropriate size at the precise location, remount to make sure the pin sits into the hole and locks the lens in place. If not, remove, drill hole one tiny drill size larger. remount & test, repeat until the lock pin slips in (if the hole is a little oversize it wont matter so long as it just slips into the edge of the hole).
NOW: remove the lens & separate the adapter. Put a little Thread Lock around the inside threads of the adapter and screw onto the lens using a rear lens cap, removing the the cap as soon as the adapter is tightly seated. Allow the Thread Lock to dry and set completely, and if done right, you now have a converted K mount 500mm that will go on/off just like any other K mount lens.

*alternative: Use a rear lens cap to determine the position of the hole on the back of a K mount lens. Drill it, check the alignment of the hole, then fit the rear cap to the lens + adapter as a template to guide drilling the back of the lens. The cap will cover the rear lens opening & prevent metal from getting inside.

**Easiest if you have a drill press to make the hole (obviously: cover the rear lens opening when drilling).
12-02-2015, 01:07 PM   #9
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QuoteOriginally posted by boriscleto Quote
But to remove the lens you have to unscrew it...
Yes, but I was just repeating the advice for mounting it in the first place. (Subsequent M42 lenses would of course be screwed in, and the usual rules applied for removing the adapter when you were done.)
12-02-2015, 01:23 PM   #10
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Thanks for all the good advice. I've never had a lens THIS big before! Holy cow.... 7 1/2 lbs! But, it should be fun.
12-02-2015, 01:23 PM   #11
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The way the last one I used was done was to put a cheap M42 adapter on - drilled as mentioned above - no springs. The adapter was silicone caulked in place. The lens was used like a K mount. Worked great.
12-02-2015, 01:25 PM   #12
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QuoteOriginally posted by boriscleto Quote
If it's a Pentax K isn't it K-mount already?

If it is M42 it would be a Takumar.

My bad. On the rim of the lens, it says Asahi Optical, but on the lens cap, it says Takumar. However, it is a coated lens. It has yet to arrive, so I'll know more about it soon. Looking forward to playing with it. Ordered an adapter.
12-02-2015, 01:53 PM   #13
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QuoteOriginally posted by Dewman Quote
My bad. On the rim of the lens, it says Asahi Optical, but on the lens cap, it says Takumar. However, it is a coated lens. It has yet to arrive, so I'll know more about it soon. Looking forward to playing with it. Ordered an adapter.
You're going to need a very sturdy tripod. Probably a gimbal too.
12-02-2015, 02:19 PM   #14
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Note the 500/4.5 has a removable camera mount which would be interchangeable between the Takumar and K Series version. If you are using a Pentax M42 adapter you can attach it to either the camera body or camera mount and then mount the body/camera mount to the to the lens. This removable mount is where the filters are attached.

Phil.
12-02-2015, 03:23 PM   #15
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QuoteOriginally posted by gofour3 Quote
Note the 500/4.5 has a removable camera mount which would be interchangeable between the Takumar and K Series version. If you are using a Pentax M42 adapter you can attach it to either the camera body or camera mount and then mount the body/camera mount to the to the lens. This removable mount is where the filters are attached.

Phil.
This is one of the best ways to attach your lens to the camera, but be aware that it can be very fiddling for the filter mount to lock on. i have two 500/4.5 and i personally attach the camera to the lens and not vice-versa. Have fun with your takumar!
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