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Image Transfer Lenses

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Posted by Tom Stokes on December 15, 2000 03:16:04 UTC

I once built an 8" F/4 Newtonian that used an image transfer lens system. The diagonal was placed very close to the primary's focal plane and then the focal plane was transferred to where an eypiece could reach it, a total distance of about 10". The advantage of doing this is that the diagonal size can be quite small, about that needed for an F/8. For the lenses, I used two plano convex achromats of about 1" dia. and 5" F.L. mounted in the eyepiece holder. They were mounted symmetically with crowns facing. I used a simple knife-edge null test in selecting the lenses. Unfortunately, all the lenses I found had some degree of spherical aberration. This was probably because they were fairly fast, F/4 to F/5, and surplus. Just the same, it was one nice scope and viewing the milky way in an 8" at 32X (or less) is awesome. Now I am thinking of resurrecting the project. Does anyone know where I might start looking for lenses? I'm even conidering grinding my own. Where can I purchase suitable flint and crown glass?

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