[grimmy2016]

So I posted earlier today about getting a Vivitar 75-205 lens only to find out its for Olympus. (Orig thread with pics https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/156715-olympus...x-adapter.html)

From reading above it seems as though I should NOT try to do the modification because its too long and heavy of a lens? Is that what RioRico was implying or did I take it wrong.

I really want to use the lens and dont want to modify it at all unless I am sure it will work properly on my KR.

Thanks

[ripit]

From what I gather he doesn't trust modifying the olympus mount with a really heavy lens but he can clarify that. From my measurements, I don't see why it wouldn't take it (maybe its not rotating in far enough) but I haven't actually done it and could have easily missed something that he has seen doing it. As far as replacing the mount, if done right I think it could take the weight of any lens as well as a proper mount.

[RioRico]

Very well, I shall clarify: I have had no problems mounting modded lenses. BUT... I am VERY nervous with lenses weighing more than 500g-600g. Lenses that heavy and more just don't FEEL safe for me on my K20D. I have had no disastrous failures (yet) to verify that fear, and I don't want any! You COULD possibly get away with mounting a heavy lens. But I'm too queasy.

Why? Because the mod involves shaving away some of the lens' bayonet flags. The leading edges are tapered down to a level where there just isn't a lot of material left. Again, I haven't experienced a failure, but I just don't know how strong those flags are.

If you want to go ahead with the mod, I'll again STRONGLY recommend using a cheap macro tube set to see what how the lens and mount interact, and to use as a test mount. Good luck!

[ripit]

I think I missed that part before about the flags being thin. That would make me nervous with a very heavy lens too. Thanks for the clarification. I had primarily looked at how deep the flag engaged which looked good. Nikon on the other hand which some lenses apparently will go (I haven't had any fit yet) doesn't have deep enough engagement so I think that is what my mind was comparing it too. You haven't ever modified a nikon mount to fit have you? I started on one but it was looking like a lot of material was going to have to be removed. I was removing mostly from the base to avoid thinning the flags too much (what a giant pain' I still havent got it to fit yet and have temporarilly given up).

[RioRico]

I think I missed that part before about the flags being thin. That would make me nervous with a very heavy lens too. Thanks for the clarification. I had primarily looked at how deep the flag engaged which looked good. Nikon on the other hand which some lenses apparently will go (I haven't had any fit yet) doesn't have deep enough engagement so I think that is what my mind was comparing it too. You haven't ever modified a nikon mount to fit have you? I started on one but it was looking like a lot of material was going to have to be removed. I was removing mostly from the base to avoid thinning the flags too much (what a giant pain' I still havent got it to fit yet and have temporarilly given up).

Yes, I have modded Nikon-mount lenses, and have also mounted non-modded lenses. I have seen 4 basic mount types:

1) Some pre-AI mounts with smooth aperture rings will force-fit directly and closely to PK cameras with no modification -- but also with no security. It's not hard to just cut a slot for the PK lens-locking pin to engage.

2) Some non-AI mounts have an extended aperture ring all the way 'round. Such can be force-fit to PK but then changing apertures is hard. I've put 1mm thick washers or spacers under the base to allow free movement.

3) AI mounts have what I call "nub and arc" protrusions on the aperture ring. This was my first mod: remove those with the Dremel metal-cutting blade, and lightly sand the ring base to de-burr it. And I cut a security slot.

4) AI-AF mounts. I've only had one, and I sold it (for a good price!) rather than mod it because I wasn't sure a mod would work. I DO NOT recommend trying to mod an AF base. Do so at your own risk. Don't blame me!

I've not had to thin|taper Nikon flags -- they fit smoothly under PK mount lugs. But I still apply my 500-600g limit to Nikon-mount lenses, modded or not. Call me paranoid...

[Squier]

I've been looking at Nikon Telephoto lenses - 300mm f2.8 ED for instance - but some sellers dont say whether the lens is Al or Pre/Non Al. How can you tell by looking at the photos of a Nikon Lens ?

Is there a particular Nikon model that is the best for modification ? EG any pre A1 model ?

[ripit]

I'm feeling pretty stupid about the one nikon mod I have done. I just took it back out and it does rotate about 45 degrees in so maybe that is all I am going to get and it goes smooth enough that far. Measuring the lugs and the camera though, the lugs are .050" but are only engaging by .025 because the mount is a little bit smaller in diameter. That means that if you were to slide the lens all the way to the side under a little force, the lugs could just disengage and slip out on one side (in theory anyway and if my measurements are right). When twisted on though, something is pushing the lens to one side, so I can only guess that on one side the lugs are wedged in but just holding on by the very edge of the lug. I have been using a pentax p3 to trial fit (it was a little beat up and I'm not sure it works, free with a lens so that my test mount).

What really makes me feel stupid though, it that it is a nikon t4 adapter. The t4 and tx lenses I have are all tanks (probably in the 800-900+ gram range). I probably could have sold the adapter for a few bucks before I trashed it. And the grand finale of stupidity in hind site, I got a tx-pk adapter on a lens shortly after. I guess its a learning experience about fitting a nikon mount though. Personally I would trust a lot more weight on an olympus mount that a nikon mount.
Out of curiosity, have you ever tried to take material off the mount side of the lens on an olympus instead of the lugs? I'm guessing that it would be a giant pain if a lot of material had to be removed but I was just curious if you had tried it?

[RioRico]

I've been looking at Nikon Telephoto lenses - 300mm f2.8 ED for instance - but some sellers dont say whether the lens is Al or Pre/Non Al. How can you tell by looking at the photos of a Nikon Lens ?

I don't know all the details of the different N/AI mount versions. AI's have the "nub and arc" protrusions at the bottom of the aperture ring. I *think* the pre-AI's are those with an extension all around the aperture ring, requiring the lens-base spacers I mentioned above, and the non-AI's are those without that extension, that can just force-fit in a PK mount with no problem (but no security -- see my SECURITY note below).

Is there a particular Nikon model that is the best for modification ? EG any pre A1 model ?

I don't know enough about Nikon-mount lenses to answer that. I got some lenses cheap; I was lucky; and I hack away merrily on lenses that aren't too costly nor heavy. Beyond that, I'm just wandering in the wilderness.

Measuring the lugs and the camera though, the lugs are .050" but are only engaging by .025 because the mount is a little bit smaller in diameter. That means that if you were to slide the lens all the way to the side under a little force, the lugs could just disengage and slip out on one side (in theory anyway and if my measurements are right).

SECURITY: And that's why I cut a notch about 1mm deep and wide and 5mm long for the PK locking pin to engage, to keep the lens from sliding away. Haven't lost one yet!

Out of curiosity, have you ever tried to take material off the mount side of the lens on an olympus instead of the lugs? I'm guessing that it would be a giant pain if a lot of material had to be removed but I was just curious if you had tried it?

I'm not sure what you mean. The problem with OM and C/Y lenses is that their bayonet flags are just a bit too thick to fit under the PK mount lugs. I don't really want to trim my K20D so I attack the lens flags instead. Again, sticking a lens into a cheap PK macro tube set clearly shows what obstructs what, and where.

[ripit]

I hadn't tried it with an olympus and was thinking about what I found on the nikon (the lugs don't seem to be too thick but the space from the lug to the lens face is too short so far as I can tell). If the lug is too thick then obviously you would have to take it off the lug. I was referring to taking material off the lens mount face though, not off the camera face. thats how I got the nikon tx adapter to free up. I would never sugest trashing your camera to get an old cheap lens to fit.

[Squier]

Thanks Rico !

One thing - Pre AI and Non AI ..... are they not the same ?

[RioRico]

One thing - Pre AI and Non AI ..... are they not the same ?

I'm not sure. I do know that the differences I described are real -- some have the lip all the way around the aperture ring, some don't.

[Squier]

If Ken Rockwell is to be be believed, the first series 300/2.8 Nikon was rubbish