Hello
I am planning to build a 500mm lens out of two close up +1 positive meniscus, and maybe interchange the elements to build different focal distances... could someone tell me the distance that the two elments should be from eachother, or from the stop? i am planning to build the lens out of 77mm +1 close up lenses using rings (removing the glass from skylights and uvīs) so the spacing is easier. I have found that this way is a lot easy than alanīs green do it yourself barrel...
so spacing... is there any formula? and for a rapid rectilinear (achromats instead of positive meniscus)? or a double gauss design (two positive meniscus instead of one in each side of the stop)?
i am chasing a relatively cheap relatively bright long lens for collodion... and maybe something else...
Thanks
Rui Lourosa
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