[7.62lew]

Ok, so I bought a sigma 400mm tele macro lens in k-mount. When I try to mount the lens to my K5IIs it drops into the bayonet and sits flush as normal. However, when I try to rotate to engage the bayonet to lock the lens in place, it hits a hard stop. It doesnt even try to start. At first i thought it must be the wrong mount but side by side with my pentax lenses everything matches up exactly. Tried mounting it to film camera also. No luck. Any ideas?

[aslyfox]

can you identify the lens you are talking about ?

Sigma Lenses - Pentax Lens Review Database

[pepperberry farm]

can you show us a photo of the lens mount?

[7.62lew]

This is the lens...

Sigma 400mm F5.6 APO (AF) v3: 1995 > Lens Reviews - Sigma Lenses - Pentax Lens Review Database

---------- Post added 06-06-2019 at 07:17 PM ----------

Looking at the lens mount the edges looked really sharp, like they were just machined and not cleaned up? After messing with it on an old film camera i managed to get it installed and after working it back and forth 8-9 times it will mount, just snug. Maybe the mount was replaced and its not worn in (wishful thinking?)? I have till the 12th to return it, so maybe I will try it for a few days.

What do you think?

[jatrax]

Some older third party lenses had a larger bayonet shield than Pentax OEM lenses had. This was not an issue on film cameras but on digital the SDM contacts come into contact with the longer bayonet shield and the lens will not mount.

I have not heard that this is an issue on this lens, but the 400mm is not as common as others. So it might be the problem, or not. Something to look into.

[aslyfox]

Some older third party lenses had a larger bayonet shield than Pentax OEM lenses had. This was not an issue on film cameras but on digital the SDM contacts come into contact with the longer bayonet shield and the lens will not mount.. . . .

the OP might want to look at this:

The Evolution of the Pentax K-mount - Articles and Tips | PentaxForums.com

especially the section under " third party variants "

"he other trap is the shield that protects the aperture stop down lever. The image to the left shows what the shield should look like and does look like on a genuine Pentax lens. Some older third party lenses have a much larger shield which prevents mounting the lens on a Pentax DSLR. Current third party lenses (Sigma, Tamron, Rokinon, etc.) have correctly shaped shields (or no shields) and pose no problem. "

[bdery]

Look at the flange on the lens mount. There is an aperture lever there (rectangle sticking out of the mount, towards the camera) with a machined lip protecting it. Compare the length of that lip with that of a more recent Pentax lens, and you'll see if the length (around the barel) is different. I'm guessnig it is, I've had that problem with older Vivitar and Sigma lenses.

Normally it's very easy to solve. There should be probably three tiny screws holding the "lip" section in place, simply remove it and use a grinding tool to remove the extra material so the lip looks like that of a "regular" lens. Then use a Sharpie or permanent market to color the exposed metal, screw everything back, and shoot away.

first time I did it it took me longer because I was wary, second time took me 5 minutes all told.

[7.62lew]

Thanks for the help. I checked the lip against my FA* 300/4.5 and the are they same length.

It seems to be mounting fine now. I honestly think there must have been a burr or something on the lens mount right where the groove on the camera mount and the lip on the lens mount meet. The lens seems to be functioning as it should.

I will use it as much as I can over the weekend see how it does.