Why won't a 86mm filter will not screw into my Rodenstock Sironar-N?

[AtlantaTerry]

I bought an 86mm filter for my 300mm f5.6 Rodenstock Sironar-N lens but it only screws in about 1/2 of a turn then stops.

The lens threads are pristine, there are no dings, dents or bends. So what is going on?

Did Rodenstock use some sort of non-standard threading on the lens? If so how do I get filters, step rings, etc. to properly work?

Thanks.

Terry

[Jim C.]

Two guesses, you bought a wrong filter size or it's a chinese no name brand filter, similar story is I bought some step rings off the Bay for cheap
and ... welll, they were cheap, a few of the step ring's were either badly threaded, or they were overzealous with the anodizing. Had the same
issue you have, they threaded on 1 or 2 turns then stopped.
Using those as a key ring now.

[Corran]

Jim, it sounds like what your problem may have been is thread pitch. I know all of the cheap step-rings are 0.75mm thread pitch, while many older filters/lenses are 0.5mm thread pitch. Also problematic is that larger lenses sometimes have 1mm thread pitch.

I use some step rings on older lenses and they only screw in about one half turn, but I just use them that way with no problems.

Terry, since you've got a larger 86mm filter, it may be 1mm, I don't know. If so, you'll probably need to make sure the filter you buy is also 1mm pitch.

[Jim C.]

Corran, it was not a thread pitch issue, it was a set of 8 step rings and I was screwing them into each other.

[Lachlan 717]

It can also be mixing metals.

Often, the rings are aluminium, whilst the threads are often brass. Different expansion rates caused differences in thread/groove.

I have had this happen with metal lens caps. Good design in principle; PITA in practice!!

[pasiasty]

86mm filter threads are either fine (M86x0.75) or coarse (M86x1.0); the latter pitch is more common, and your Sironar should have it (see catalogue).

Buy a cheap step-up ring on eBay, e.g. 86-95, and try if it screws in. And another with internal thread 86 (e.g. 77-86) and try if the filter screws in. The cheap, Chinese rings are available only with common pitches. Or use a (metric) pitch gauge.