Messing with lens element spacing for over-correctPosted By Tom Mengel |
Hi all,
I have a old 4 element (in two groups of two) 96mm F5 (480mm) lens mage in Germany under the brand of Rollenstok that I’ve made into a cheap “copy-scope”. It actually works very well (particularly for the color correction and field flatness – those 4 elements do make a difference!) but it’s noticeably over correct at infinity due to it’s primary role as a copy type lens. Even with that said it gives pretty good images up to about 10X/inch but then the in/out focus reveals the correction problem. I can make out Cassini’s division on Saturn and 4/5 bands on Jupiter but there is a “focus haze” that is real annoying at higher powers and if I could zero that out it would actually be a pretty good scope.
My question for the lens gurus: Can re-spacing the front and rear groups in a lens of this type help the correction when focused at infinity? Is it as simple as taking off the front retaining ring and putting in a spacer? Or am I going to just mess the whole thing up, in which case I’ll just keep it as a RFT.
Thanks!
I have a old 4 element (in two groups of two) 96mm F5 (480mm) lens mage in Germany under the brand of Rollenstok that I’ve made into a cheap “copy-scope”. It actually works very well (particularly for the color correction and field flatness – those 4 elements do make a difference!) but it’s noticeably over correct at infinity due to it’s primary role as a copy type lens. Even with that said it gives pretty good images up to about 10X/inch but then the in/out focus reveals the correction problem. I can make out Cassini’s division on Saturn and 4/5 bands on Jupiter but there is a “focus haze” that is real annoying at higher powers and if I could zero that out it would actually be a pretty good scope.
My question for the lens gurus: Can re-spacing the front and rear groups in a lens of this type help the correction when focused at infinity? Is it as simple as taking off the front retaining ring and putting in a spacer? Or am I going to just mess the whole thing up, in which case I’ll just keep it as a RFT.
Thanks!