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Question about achromat
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PostPosted: Mon Nov 30, 2015 8:48 pm    Post subject: Question about achromat Reply with quote

hello folks , i have a question about achromat closeup lenses , i have a elnikkor 50 /2.8 enlarger which i bought in "as is" condition and found out that the 1st optical doublet block is missing , it has the the first elelmnt ,2nd cemented doublet and the last element , now my question is can i use the cemented doublet as high quality achromatic closeup filter ??My main intention is to get a achromatic close up lens for free Twisted Evil Twisted Evil


PostPosted: Tue Dec 01, 2015 2:29 am    Post subject: Reply with quote

The remaining doublet looks as if it has quite small radius curve and so may be quite powerful.

You can roughly estimate its focal length by holding it up to a bright window some distance away and then measuring the distance to a piece of paper with the image of the window focussed on it as sharp as you can get it.

The diameter seems quite small, so using it as a close up lens might be a problem


PostPosted: Tue Dec 01, 2015 3:42 am    Post subject: Reply with quote

Not always a good idea. Not every doublet is an achromat. IMO the front and rear lens groups are supposed to corect each other (allmost symetric lens) and therefore the dublet alone may not be an achromat. Anyway, you should actually test it to see if it's O.K. for you.


PostPosted: Tue Dec 01, 2015 5:44 am    Post subject: Reply with quote

That's a cheap and very enlarger lens, just get another one... Wink


PostPosted: Tue Dec 01, 2015 10:53 am    Post subject: Reply with quote

In a double-Gass lens, the menisci have negative optical power. They have no use as close-up lens.