[StepOne]

I got this weird fish-eye lens, but i have a mount problem. I guess is a T mount and i took it off the lens, was not for Pentax. I suppose the inner ring from the mount adapter was supposed to unscrew, but it got stacked there.
Am i right, do i need T-P/k adapter?
If i buy one adapter, will i be able to remove the inner ring ? (i guess is easier to unscrew the one on the adapter). Here is how it looks:

Attached Images

   

[gp1806]

Unless you can find a T mount adapter that fits the inner ring, you will need to unscrew that inner ring to mount the new adapter.

[RioRico]

That looks like my bothersome Vemar 12/8, also branded as Spiratone, Lentar, whatever. Yours looks like version 1 with the single rounded lens cap; I have version 2 with the 2-piece cap system. Yes, it's T-mount. Yes, you must unscrew the inner ring. Don't worry, it's easy and pretty foolproof.

The only problem is... I've tried various T2-M42 and -PK adapters, even ground down the inner T2 ring for a closer fit, and mine won't reach infinity focus. I can get up to maybe 2m of DOF at f/16 but that's it -- mine is a fishy closeup lens. I posted the problem over at ManualFocusLenses forum but got no usable help. If you get yours to reach infinity, let me know, OK?

[StepOne]

That looks like my bothersome Vemar 12/8, also branded as Spiratone, Lentar, whatever. Yours looks like version 1 with the single rounded lens cap; I have version 2 with the 2-piece cap system. Yes, it's T-mount. Yes, you must unscrew the inner ring. Don't worry, it's easy and pretty foolproof.

The only problem is... I've tried various T2-M42 and -PK adapters, even ground down the inner T2 ring for a closer fit, and mine won't reach infinity focus. I can get up to maybe 2m of DOF at f/16 but that's it -- mine is a fishy closeup lens. I posted the problem over at ManualFocusLenses forum but got no usable help. If you get yours to reach infinity, let me know, OK?

Thanks, i'll let you know how it works as soon as i will have this "mushroom" mounted

[Lowell Goudge]

I have the following observations

the adaptor you got looks like a nikon adaptor, which you may be able to modify to pentax with a little grinding.

the "thread on ring, need not come off, this ring is standard size and will fit any T mount base you get that is meant for pentax. get a pentax K or M42 T mount and you are set. each T mount has a ring like this and 3 set screws that engage it.

You may need to look at infinity focus, and I think between nikonand pentax you can correct this by removing the ring (that I said you didn't need to remove, and flipping it over. I had to do this on one of my T mounts)

good lick, and OH, By The Way, I think you need to lock the mirror up to use this lens, due to the rear element location

[RioRico]

You may need to look at infinity focus, and I think between nikonand pentax you can correct this by removing the ring (that I said you didn't need to remove, and flipping it over. I had to do this on one of my T mounts)

Hmmm, I'll have to try that. Yeah, a T2-NI adapter should be ~1mm thinner, which could make all the difference. Good idea, thanks!

good lick, and OH, By The Way, I think you need to lock the mirror up to use this lens, due to the rear element location

Mirror-up isn't necessary. The pictured rear element seems to protrude because the T-adapter outer ring isn't on it. With my shaved mount, the Vemar rear element extends ~7mm beyond the lens base. With an NI mount, that would be ~8mm. I measured the mirror clearance on my K1000, ZX-M and K20D as being >12mm. So there is plenty of room in there.

[Lowell Goudge]

I have the following observations

the adaptor you got looks like a nikon adaptor, which you may be able to modify to pentax with a little grinding.

You may need to look at infinity focus, and I think between nikon and pentax you can correct this by removing the ring (that I said you didn't need to remove, and flipping it over. I had to do this on one of my T mounts)

Hmmm, I'll have to try that. Yeah, a T2-NI adapter should be ~1mm thinner, which could make all the difference. Good idea, thanks!

I think yuou should be able to get the lens to focus to infinity unless it is either a canon lens origonally or someone has played with it. but good luck on adjustments

[Nick Siebers]

I know at least some Tmount adapters have a similar inner and outer ring, you could remove the inner and just screw the outer on to what is on the lens. That is what I did for my single T mount lens.