Wow, I can't say I've ever seen one that was melted. That melted part seems so pinpoint accurate almost like the return beam was focused there. That sort of seems impossible with the optics in the path but I know that Lunt rear blocking filters are way differently built than Coronado and that a Coronado will work on a Lunt scope but I don't think its design will safely work the other way around. I could be wrong though as I'm not very savvy on how they design or test these things. Just by looking at them though, it appears that the first element in a Coronado BF seems to reflect back the beam while Lunt's blocking filters use something like a KG glass to absorb it. If you've ever had both a Coronado and Lunt scope you know that on a Lunt system they usually put an ERF (red glass with strong IR blocking coating on it) way up in front prior to the etalon. Coronado does not do this, they only have redglass, #29 red I think, so it passes a lot of IR through the etalon. As your scope is setup in the image I would expect the IR to reach the blocking filter and be absorbed by it but it would put a tremendous amount of stress on your Lunt BF as they are designed to have ERF's further up in the system to remove some of that IR. It seems impossible but its a hard arguement when you see the image. The only thing it could be is IR being reflected back from one of the internal elements.
Larry, you are correct about stress on the Lunt, sometime later I had a friend and Lunt owner looking at my blocking filter. He said you have a cracked blocking filter and on close inspection, he was correct. I had to send to Lunt where it was repaired. Lesson learned , don't mismatch Solar equipment. Your sure know the operations of Solar equipment and the pitfalls and problems that can happen when you don't use equipment properly, or know what you are doing.
Edited by Bill Cowles, 13 August 2014 - 10:52 PM.