Refractor Lens Question

Hi, I have a friend of mine with a 90mm Meade Refractor with a doublet. He did something stupid, he took the cell apart and isn't sure how to put the lenses back properly. Can anyone let me know which way the lenses go back together. There was a thick and thin lens. I don't have the guts to take one apart to check. Thanks in advance for any help.

Clear, Dark and Steady Skies,

Spaced-Out Bob

Bob,
Generaly speaking the front element will have two convex surfaces. We will call the element surface closest to space, surface 1, and the other convex surface, surface 2. Usually surface 2 will be curved more than surface 1. The second element will have one concave surface, surface 3, and one flat to convex surface, surface 4.

Convex surface 2 should match concave surface three pretty close depending on the lens design.

When the objective is re-assembled, the order would be surface 1, surface 2, a circular spacer or tab spacers that were removed, then surface 3, and surface 4 at the rear of the objective.

Next do a star test to see what it looks like. If everything was put back together properly it should be acceptable. If it looks like garbage, take the objective apart and turn the first element over, re-assemble. Star test again, and if it still looks like garbage you have a problem. You could then make some changes to spacing and try all over again.

I would recomend taking careful notes on what is done incase the process gets involved.

I guess if you would like to avoid the frustration Meade would probably put it together again for whatever their service rate is.
Dale