: Has anyone ever replaced the three spacers in an air-spaced achromat? If you have some experience with this, I have some questions: : 1. How critical is the thickness of the spacers? : 2. What are the best materials to use as spacers? : 3. What is the best way to make sure the spacers do not shift when the retaining ring is screwed back on.

: A second issue relating to the air-space distance, has anyone experimented with the seperation and/or rotating the doublet for better color correction and alinement. Excuse my spelling.

I have found most air-spaced lenses are intended to have a .01" space but you should measure what you take out. I am glad to hear about the source for the aluminized self-adhesive dots. I use aluminum foil sprayed with Scotch 77. Aluminum foil is stable and laminated as such can give a little. It is water and fungial resistant whereas paper is not and can actually wick moisture into the optic. Plastic should work well too. Be sure it has a high melt temperature because if it gets hot it might draw and shatter the elements. Teflon would be excellent. There should be some Opticians marks on the element that line up for optimum correction. All good primaries will be marked. To be safe use a permanent felt tip and draw two lines on one side across the edge of all the elements. For added measure, place one ink dot on the first element next to the two lines, two dots on the second etc..

Good Luck, -Rick