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02-21-2014, 01:45 PM   #1
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M42 lens not tight fit on pentax body

I have a small problem with my "new" Pentacon 300/4 lens. Or rather it is a big problem because the lens is not usable as it is. The lens in question is an old pentacon six lens but with an adapter for M42. And this is where the problem starts.

This M42 adaptor is just a cone with threads. So there is no plate that sits against the camera. This is a problem because the M42 to Pentax-K adapter wobbles quite a bit in the mount. it needs a backplate on the lens to push against the body. and since this adaptor does not have this I need to come up with a simple solution to create a back plate on the lens.

You can see how it looks here https://www.dropbox.com/sc/a4ryorpr3vrlujo/mLLMY1biBw#/

I've been thinking for a few hours now and basically I've come up with two different ideas.

1. Making some sort of outer casing that would be about 1cm thick that would sit snug against the adapter on one end and the camera body on the other.

2. use a washer and glue it onto the adapter.

But do anyone else have any good ideas?

02-21-2014, 02:00 PM   #2
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See this thread:

https://www.pentaxforums.com/forums/120-general-technical-troubleshooting/216...s-turning.html

Scroll down to my post.

If you can adjust infinity or if by chance your lens already focuses past infinity or if you don't mind losing the ability to focus to infinity, using a "non-infinity m42 adapter" which has its own plate built-in will also make it stable.
02-21-2014, 02:00 PM   #3
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You can get a Pentacon 6 to K mount adapter for $20, that is by far the most trouble free solution.
02-21-2014, 02:01 PM   #4
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How about inserting something over the lens body cone such that one end would snug up against the cone and the other end would snug up against the camera body? Maybe you could use a larger diameter, somewhat deep rubber plug or stopper. Use a hole saw cutter with a rotary drill to cut a hole for the lens body cone to slip through.

I would avoid putting something directly in between the adapter and what little surface area you have on the lens mount threads. That would push the lens out and mess with your infinity focus point.

02-21-2014, 02:02 PM   #5
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QuoteOriginally posted by elliott Quote
You can get a Pentacon 6 to K mount adapter for $20, that is by far the most trouble free solution.
That sounds even easier.
02-21-2014, 03:14 PM   #6
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Well, the bayonet mount of the pentacon six is not there, it is replaced with a M42 mount instead. There is a thread mount on the base of the lens where you attach the mount you want to use.

here you see a lens with the pentacon mount: Orestegor 300 4 300mm Meyer Pentacon German Tele Lens Pentacon 6 M42 Exakta CLA | eBay

I do not have the pentacon six mount, I only have the M42 mount. So the pentacon six to pentax K is no viable solution.

The rubber plug or whatever would work great, But I have to find a ~30mm wide rubber washer, Or several... Unless the rubber can create a mount firm enough on the cone.
02-21-2014, 03:40 PM   #7
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QuoteOriginally posted by discharged Quote
But I have to find a ~30mm wide rubber washer, Or several... Unless the rubber can create a mount firm enough on the cone.
I just get them from the hardware store for a buck or two -- they are slightly too small (seemingly, but that's what you want) and I force/stretch them on. If they ever come off, they are too stretched to work again so I have spares around. But I couldn't use my Meyer's without them easily, and I love those lenses.
02-21-2014, 04:03 PM   #8
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QuoteOriginally posted by discharged Quote
Well, the bayonet mount of the pentacon six is not there, it is replaced with a M42 mount instead. There is a thread mount on the base of the lens where you attach the mount you want to use.

here you see a lens with the pentacon mount: Orestegor 300 4 300mm Meyer Pentacon German Tele Lens Pentacon 6 M42 Exakta CLA | eBay

I do not have the pentacon six mount, I only have the M42 mount. So the pentacon six to pentax K is no viable solution.

The rubber plug or whatever would work great, But I have to find a ~30mm wide rubber washer, Or several... Unless the rubber can create a mount firm enough on the cone.
Long, cylindrical rubber plugs and dowels are easy to find. Some are tapered to be used as stoppers and plugs for plugs and pipes. They come in all sorts of diameters and lengths. You could get one with a 3" outside diameter and cut/drill a hole through the center for the lens to slip through.

As you screw the lens into the adapter the lens body should butt into one end of the rubber and squish it gently. Likewise, the camera body will gently squish the other end. You may have to trim the length of the rubber a bit. Compressing the rubber will create a little bit of tension that should hold the lens.

Here are some examples of plugs on McMaster-Carr. That store is expensive but you pay for the price of "easy to get" and "quick to deliver". Your local hardware store should be much cheaper.

McMaster-Carr

02-21-2014, 04:54 PM   #9
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I actually solved this quite easy. I used some vulcanizing tape, wrapped 15 or 20 times around the mount and then let it set before i trimmed it down with a sharp knife.

I threaded on the adapter (with the lock removed, that lock is just plain stupid!! They should just have made them work with the normal lock instead) and tried it on the camera again. Now it is working great, I have a tight seal and no wobble at all. Focus at infinity and everything aswell.

This lens is awesome, focuses down to about 3,5 meters and with 450mm equv, that means a small bird would cover the entire sensor. I got sharp images and no CA at all. I will have to do more extensive testing tomorrow ofc, but initial tests show great promise! However it is a heavy beast, weighing in at around 6 pounds it is not something I wanna go around with handheld!

The build quality seems to be everything you would expect from a german lens, solid and distinct. The focus is smooth and with that high quality feel that some mf lenses have, hard to explain but the initial kinda reluctance to change if you understand what I mean.

The aperture is stepless, thats a bit weird and will take some time to get used to... and the 19 aperture blades it will without doubt create amazing bokeh
02-21-2014, 06:12 PM   #10
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QuoteOriginally posted by discharged Quote
I actually solved this quite easy. I used some vulcanizing tape, wrapped 15 or 20 times around the mount and then let it set before i trimmed it down with a sharp knife.

I threaded on the adapter (with the lock removed, that lock is just plain stupid!! They should just have made them work with the normal lock instead) and tried it on the camera again. Now it is working great, I have a tight seal and no wobble at all. Focus at infinity and everything aswell.

This lens is awesome, focuses down to about 3,5 meters and with 450mm equv, that means a small bird would cover the entire sensor. I got sharp images and no CA at all. I will have to do more extensive testing tomorrow ofc, but initial tests show great promise! However it is a heavy beast, weighing in at around 6 pounds it is not something I wanna go around with handheld!

The build quality seems to be everything you would expect from a german lens, solid and distinct. The focus is smooth and with that high quality feel that some mf lenses have, hard to explain but the initial kinda reluctance to change if you understand what I mean.

The aperture is stepless, thats a bit weird and will take some time to get used to... and the 19 aperture blades it will without doubt create amazing bokeh
The aperture is probably a preset and is just set at smallest f-stop (Does it have a little dot or mark? Probably a spring-loaded ring -- push it and set it to the desired aperture and then it will be free moving from wide-open to that setting).
02-24-2014, 06:29 PM   #11
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I think you want a "flanged adapter" - one with a collar. It might cost you infinity focus, but it depends on the lens. Just make sure its high quality - we had lots of threads with scares due to cheapo adapters getting stuck
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