Changing lens mounts.

[Mike Kennedy]

Can it be done? I have an Auto Sears 135mm f2.8 lens with a mount stamped U. It will fit a Pentax K1000 but will not stay in place when adjusted.I would like to replace the present mount with an HM42 from one of my cruddy lenses.
Any suggestions?
Thanks,
Mike

 

[Mike Kennedy]

OOPS! It should of read M42.
JMK

 

[Nick Zentena]

Are you sure it's not M42 now? From memory Sears used M42 and then K mount. If it doesn't fit the K mount then my first guess is M42. U could stand for Universal mount.

Unless you're attached to the Sears lens I wouldn't spend money on a M42 mount. Very good M42 mount 135mm lenses tend to be fairly cheap.

When you hold it on the camera does it make infinity focus?

 

[titrisol]

Those used to be sekor lenses, good but not outstanding.
I guess it'll be cheaper to buy a (new) one

 

[gma]

As cheap as all used photo equipment is these days I think you would be better off to buy one that fits rather than paying big bucks to have a used lens mount modified.

 

[Dave Parker]

Far easier to purchase a new one that fits the camera correctly, there were many number of Universal mount lenses made, but not all of them worked the same, various companies changed small things to suit their brands,

This website contains a wealth of information about various lens mounts, how they were developed and what can be done to what types of lenses, in additon to some information on homebrew stuff.

Dead Link Removed

In additon, they have registration distances and just about anything else you can think of!

Dave

 

[Mike Kennedy]

Thanks Dave. APUG is the first place I turn to when a fly gets in the ointment

 

[benjiboy]

Pentax K to M42

Can it be done? I have an Auto Sears 135mm f2.8 lens with a mount stamped U. It will fit a Pentax K1000 but will not stay in place when adjusted.I would like to replace the present mount with an HM42 from one of my cruddy lenses.
Any suggestions?
Thanks,
Mike

Hi, Mike,
There used to be an adaptor made by Pentax and several accessory manufacturers that fitted in to the K mount ,and was spring loaded so it stayed in and it adapted to fit M42 screw lenses , it was just a little silver ring you should be able to get hold of one still. If you do locate one make sure it comes with the little tommy bar to remove it otherwise you will have problems. As far as I remember the adaptor may effect a lenses ability to focus on infinity but at least it will be usable to some degree

 

[Seele]

There used to be an adaptor made by Pentax and several accessory manufacturers that fitted in to the K mount ,and was spring loaded so it stayed in and it adapted to fit M42 screw lenses , it was just a little silver ring you should be able to get hold of one still. If you do locate one make sure it comes with the little tommy bar to remove it otherwise you will have problems. As far as I remember the adaptor may effect a lenses ability to focus on infinity but at least it will be usable to some degree

Bentley,

The K-mount, although designed by Zeiss, took into account of backwards compatibility with M42 lenses via that adapter, so full focussing range is preserved. The original adapter by Pentax was not supplied with a tool for removal; the original instruction manual indicated that you use something like the top of a ball-point pen for the purpose.

While the K-mount throat is a little larger than M42 screw mount, the body thickness is the same, hence the adapter sits inside the throat, which also makes it necessary to take the lens off before removing the adapter. In addition to that, the lens itself needs to have facilities to stop down the diaphragm externally, as the striker pin cannot be pushed in when mounted. When Praktica introduced the B-mount system, the camera body was designed to be a little thinner so the adapter sits on top of the body bayonet, and at the same time has an inner flange which forces any automatic diaphragm lens to work as manual, eliminating the danger of over-exposure which afflicts the Pentax system. Of course, you can fit a Praktica adapter to each M42 lens to make it bayonet mount if you so wish, but with the Pentax arrangement, it was probably designed to frustrate you enough to get K-mount lenses instead.

 

[benjiboy]

Thanks Seele,I had forgotten it's more than twenty years since we sold them in the camera store I had. It must have been the independant ones I remember that a sort of flat piece of metal with two notches in it was supplied with them to remove them with.

 

[Seele]

Bentley,

I have a feeling that the Pentax adapter cannot be removed by a spanner as you described; even those third-party ones have to use some appropriate object to poke into the slot so as to push the spring back; if a spanner was indeed supplied, it would need three hands to remove it.

There might be a chance that you were thinking of Minolta adapters for M42 (and other) lenses; the Minolta mount locks the lens in a different way and the spanner makes it much easier for installation and removal.