Need help fitting a filter on a lens

[Andy Perrin]

I bought a Asahi Super-Takumar 50mm f/1.4 for NIR and visible use, but I can't get my R72 filter to fit on it using my 52-49mm step-down ring. I'm not sure what the matter is, because allegedly 49mm is the correct diameter for that lens? If my information is wrong, does anyone know what the diameter really is? This could be a problem with tolerances. My step-down ring is of the $3 variety.

[Andrea B.]

I think it must be a tolerances problem. That lens should have 49mm front diameter for step rings.

Do you have any other 49mm lenses you could try this ring on? Or any other 49mm step rings you could try on this lens?

 

Does there appear to be any dents or other distortions in the front of the lens?

 

I like Fotodiox step rings. They seem well made. In case you want to order up a new one.

 

ADDED: Does it seem to be a diameter problem? Or a thread pitch problem?

Sometimes I have used some silicone lubricant on step rings. Have to use it sparingly because it can migrate a bit.

[OlDoinyo]

Some stepper rings are temperamental in this regard, as they may be made inexpensively. If you have a 49mm filter you could use it to test the lens and adapter threads separately to see which is to blame. Or is the problem on the 52mm side? You do not make that clear.

[Andy Perrin]

No, it goes lens->49-52mm adapter->filter. I don't have any 49mm filters because I decided to standardize on 52mm, but maybe I should invest in a higher quality adapter.

 

Andrea, the adapter ring has worked fine on everything else I own! It could be the thread pitch, I guess? Or maybe the tolerance is JUST a hair too small on the lens side and a hair too big on the adapter side.

[Andrea B.]

Well, it seems kind of odd that this stepper worked well on other lenses but not this one. But it happens.

 

I don't recall running into any thread pitch problems on the filter side of lenses.. And I can't say I've yet encountered any particular problems with Takumars. Trying to think how many I have - 6 or 7 Taks I think - all older. But maybe too small of a sample for generalization. "-)

 

I have encountered some cheap T2 mount adapters where the maker got the wrong thread pitch.

 

But anything is possible. And it doesn't take too much for the less expensive step rings or filter mounts to get out of round or become somewhat worn. It is probably best to order up a new one. If a new one does not work, then you will confirm that something is awry with the front filter thread on the lens. Do try a little cleaning and light lube-ing first though. Maybe there's just grit in the threads or something?

 

Clark's observation is spot on - these gadgets can be a bit tempermental.

[enricosavazzi]

In my experience, tolerances of cheap threaded adapter rings can be off by up to a couple of mm. See example at

http://savazzi.net/photography/wrong_ring.htm

[Andy Perrin]

I bought a better quality ring and it fit this time, but VERY tightly, even with some light lubrication. (Klaus suggested the lens may be dinged. I couldn't see anything, but it could be just slightly out of true and my eye would not catch it.)

[Andrea B.]

Makes sense that we can have a ring out-of-round or a lens front end out-of-round, but not both at the same time! :D

Anyway, I'm happy that the new step ring worked out for you. Now you can take that Tak out for a spin.

 

Check that lube for a few days and make sure it doesn't migrate onto the glass to ooze inside the lens.

[Andy Perrin]

I don't think the lube will migrate far. I applied it to a paper towel and then wiped the towel around the threads of the adapter. There is very little to migrate.

[Andrea B.]

oh good! I sound a little obsess-y about that, don't I? Sorry!! :D Had it happen once with a silicone lube stick thingie.