Where can I get hold of a threaded reducer for filters?

[Kaptain Klevtsov]

I have a Sigma 600mm Nikon fit telephoto lens and it takes filters but not the right size. The filter drawer is threaded 30.5mm which is too big for my filters. The thing that I need will be threaded externally to fit the drawer and internally to take the filters. The length should be around 3mm.

I had wondered about trying to make one myself, but firstly I can't find the thread size for the EP fit filters and secondly I think my lathe is a bit big and rough for such a delicate thing.

If I get hold of one I can stick the CLS filter in the drawer and I have a 75mm f/8 'scope for widefield stuff. And all for cheap!

Any clues?

Captain Chaos

[Ambermile]

Any help?...

[Kaptain Klevtsov]

I don't do German.

The dimensions are very useful though!

I got it sorted out anyway, it turns out that the CLS filter OD slips into a counterbore in the filter drawer, unlike the filter I tried first. This holds it in place until I slide it in, then it can't come out so it works so far. I tried it for daylight snaps and it works, just messes up the colour a bit as expected. Now I need to hoover up the clouds and test it for real.

Piggyback time next time the sky turns black with dots.

Thanks for the drawing Arthur.

Captain Chaos

[FLO]

I am guessing that you have the Sigma 600mm catadioptric?

If so, I think the filter is part of the optical design which makes it very fussy when using filters other than those supplied with it.

You can test this by taking a picture without a filter in the holder - does it work?

[radioactive]

CC you may want to have a look here they maybe some help now or in the future

http://www.observatory.org/vpacs.htm

[Kaptain Klevtsov]

Steve, yes its the Cat lens and it doesn't like the no filter option as you suspect, I had tried taking the filter out (Antares LPR) of the holder and fixing it to the clear lens, that didn't work. The CLS filter and holder can be gently forced into the filter holder and that will focus on the cricket score shed out of the back. Waiting for something small and white to aim at next.

Radio - nice link, thanks.

Captain Chaos

[Kaptain Klevtsov]

Quick test

Conditions were rubbish, the window had rain on it and there was slight drizzle between the target and me.

The target was my old friend the pylon which is somewhere close to a mile away so to test the focus ability at infinity ish here are the results:-

And a close up at 100% image size

So all I need now is some clean dark sky.

Captain Chaos

[FLO]

Looks pretty bad from here CC