Help with a sigma lens


Link Posted 18/04/2012 - 16:38
Hi - I'm fairly new to dslr ownership, so excuse any daft questions!

I recently purchased a Sigma 28-70mm f3.5/4.5 from ebay, advertised as a PK mount lens. However I tried fitting it to my K-x and I can't get it to lock into place. I was fairly sure that all K-mount lenses should work with a k-x body. I have no other 'old' lenses to compare it with, only the 18-55mm and 50-200mm kit lenses (which work perfectly as expected). I've had a look online but can't find any helpful info, so if anyone can help me out it'd be greatly appreciated.



Link Posted 18/04/2012 - 16:58
Can you provide some photos of the lens, in particular showing the mount and any lettering on the lens.

If it's a K mount lens, it should fit, but don't force it.

The mount mechanics, lug spacing etc. should be almost identical to your other lenses. it's only the electrical contacts and aperture mechanism that will be different.
Peter E Smith

My flickr Photostream


Link Posted 18/04/2012 - 17:06
Does the fitting look any different in any way?

If it is PK then it should fit.

Just a thought. Is it too small, because a Minolta MD fitting is very similar but smaller diameter



Link Posted 18/04/2012 - 17:07
Good point about the Minolta fitting.

Also, check the mount. There is a small hole where the locking pin goes in. Check there is no debris in it.
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Link Posted 18/04/2012 - 19:28
Also could be a Praktica PB bayonet mount.

Looks very similar to PK but just does not fit and the aperture lever is in different position. Possibly would be marked PB.



Link Posted 18/04/2012 - 19:42
I have a link to some photos of the lens:


Hope these help.




Link Posted 18/04/2012 - 20:57
I have an old Sigma 70-210 which fits my kr with no problems and the mount looks different to yours, it looks like yours has lugs on the outer ring which mine dont.
All the best

And come him slow or come him fast it is but death who comes at last.


Link Posted 18/04/2012 - 21:42
Having looked at your images of the lens mount, I don't know what mount it is, but it doesn't look like a Pentax mount.

Look at any of your other Pentax lens mounts. If you compare the three lugs that form the bayonet on the lens, on the Pentax lens you will notice that two of those bayonet legs have one rounded end and one squared end with the two squared ends facing each other.

Your Sigma lens appears not to have those squared ends to the bayonet lugs.

My terminology may not be perfect but if you look at the Pentax lens you should see what I'm referring to.

If I'm right, the lens was incorrectly described as "Pentax fit".
Peter E Smith

My flickr Photostream
Last Edited by Mannesty on 18/04/2012 - 21:42


Link Posted 18/04/2012 - 22:32
Here is a link to pictures of various SLR mounts,


May be of some use to you or others.



Link Posted 18/04/2012 - 23:25
From the images on the web site linked to above, I'd say that your lens mount looks most like an Olympus OM mount.
Peter E Smith

My flickr Photostream
Last Edited by Mannesty on 18/04/2012 - 23:26


Link Posted 18/04/2012 - 23:36
It is certainly not a Pentax Mount.
I crossed referred it to one of my lenses.
The red dot should be at the top of the left hand "flange". the Aperture control lever should be slightly in on the right hand "flange" and the AF link should be about 5% off centre anti-clockwise from the bottom point of the lens.

So no, it's not a PK mount.
Some Cameras


Link Posted 19/04/2012 - 08:23
I agree it's not Pentax fit (at least not a version I've ever seen)

I'm intrigued by the "sticky out pin" on the mounting ring (about 7 oclock in imgp0992), I've not seen that before.

I assume by now you've registered your disatisfaction with the seller.

Incidentally, without prying, what town are you nearest to. It's quite likely there is someone on the forum local to you. We Pentaxians may not be many but we are a friendly bunch of brothers (& sisters)

Last Edited by Frogherder on 19/04/2012 - 08:35


Link Posted 19/04/2012 - 08:35
I agree, definitely not a Pentax mount
“We must avoid however, snapping away, shooting quickly and without thought, overloading ourselves with unnecessary images that clutter our memory and diminish the clarity of the whole.” - Henri Cartier-Bresson -


Link Posted 19/04/2012 - 09:08
It's not an Olympus... that has the release and stopdown buttons 180deg

Could it be Sigma's own mount?
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff



Link Posted 19/04/2012 - 15:00
I have been in touch with the seller, and he has since admitted to it being an Olympus OM mount. He has also agreed to a full refund and even the return postage costs, what a nice fella! So congratulations to anyone who guessed correctly, and thanks to all of you for the help/advice.


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