400mm prime

I have a 400 Tamron 1-6.3 32 M42 Mount Lens which I brought for the 2x mc7 attached to it quite a few years ago,not having a tripod I didnt worry about using it but now I would like to, it has been sitting in my cupboard and apears to be OK, no dust or any thing that I can see.

Could any body tell me what the ring next to the apture ring is for it has OPEN CLOSE on the ring. thank you

It's probably a "pre-set" lens - in other words you select the aperture you want to use with the first ring, and then open and close it with the second (open to focus, close to meter and take the shot).

All the aperture ring does on lenses of this design is move a "stop" around to prevent the closing action going beyond a specified point. On later lenses both actions would be combined into the single ring.

Thank you hefty, your knowledge of lenses amazes me thank you for that.

ps have you used any thing like this.

I've used several pre-set lenses, but not the particular one you're referring to. Once you get used to their way of working though you'll find they're quite straightforward in operation.

You'll find most lenses benefit from being stopped down a little to improve sharpness; in the case of yours (and with a max aperture of f/6.3) I'd imagine it would be best at around the f/8-f/11 mark - at least in Australia you get enough sunshine to make that possible!

Nice of you to say that,but today it rained for 6 hrs non stop, it gave me time to catch up on macro. thanks again

M42 mount didn't originally incorporate the ability for cameras to automatically stop down the lens, so you have to do it manually. Later lenses have an "Auto/Manual" switch which essentially does the same thing, except that in "Auto" mode the lens stays open until a little pin on the mount is pressed by the camera to stop it down.

Oddly, this property if anything makes them easier to use on current DSLRs since you can stick the camera in Av mode and control the aperture with the switch.

Hmm...

I recently acquired a Super Tak 35mm f3.5 along with a genuine adapter (it came attached to a gorgeous KM). I put the lens and adapter on my K-m in Av mode with the lens set to M, but the shots mostly seem very underexposed - only one of the test shots was ok. I did try exposure compensation but the problem is outside the range of adjustment.

All my K mount lenses are fine, with the well-known caveat about apertures smaller than f8 on pre-A series lenses. I don't think it's a camera or lens fault, but they just don't seem to work together for some reason.

Could it be that you're hitting the limit of the metering, it can only meter so dark you know.

It might be, but with a K series lens in the same conditions it's absolutely fine which is why I'm finding this odd.