Quote:

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Take the lens and place it under monochrome light if you have it or if you don't use an Engery Saver type bulb. You should see interference rings between the two elements. They should appear perfectly round when viewed from looking straight down on the elements. If the rings are off center, then that usually indictates that one of the spacers in thicker then the others.

- Dave

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I don't mean to hi-jack this great thread, but this quote caught my eye.

My 80mm lens came without index marks, so I marked them as they sat in the box and try to keep them aligned when I fit them to the cell. Can I assume this technique works for smaller lens sets also? I am almost ready to mount the lens permanently and it would be nice to have everything aligned as close as possible before hand.