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 Post subject: Filter thread size
PostPosted: Tue Jan 29, 2013 2:52 pm 
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I have a couple of filters which attach to my 2" diameter Barlow. I'd like to use them on my 200 mm camera lens which has a 67 mm filter thread. I can't find the filter thread quoted in mm but it seems to measure 48 mm. Stop down rings I've found are 67 mm to 49 mm. Would this be the correct size? Bill C


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 Post subject: Re: Filter thread size
PostPosted: Tue Jan 29, 2013 3:01 pm 
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Bill,
You are correct a 2-inch filter has 48mm threads. You will need a step up 48-67 (or is it a step down 67-48?) ring for your lens. They are available on ebay but make sure you get it the right way around - the terminology used is far from obvious. You may need to do it in 2 steps if the precise step ring is not available. There will be vignetting at full aperture but lenses usually need stopping down anyway.
David
PS if that's your L lens then it won't need stopping down! The alternative is an Astronomik clip filter that fits inside the camera and then your lens can run at full aperture


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 Post subject: Re: Filter thread size
PostPosted: Tue Jan 29, 2013 4:26 pm 
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I think that the 48mm threads are used almost exclusively on 2" eyepiece fittings - I've only seen 49mm and 46mm on cameras - so ready-made 48mm stepping rings may be hard to come by.
But I have here a custom 62>48mm step-down ring which Brian made for me out of black Delrin (or something similar) so if you can get a 67>62 step-down ring you may borrow it to try.


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 Post subject: Re: Filter thread size
PostPosted: Tue Jan 29, 2013 8:15 pm 
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David and Ross. Thanks for your comments. I now know the thread size for sure. I may take you up on your kind offer Ross rather than go to the added expense of clip filters. Bill C


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