astrojohnarthur

Judging by my experience with the 480mm, no. It’s only 1/8 of a turn. The 480 has been great ever since - still In use at about 8 years old now. My trouble is I live near the western coast of N Ireland and it could be quite a while before I get out again to check the Esprit 120. I’ve included “before” and “after” pics with the 480mm. Different cameras and total integration times but same target. Iron cross stars on the before.

Sorry to come late to the party but I’ve just bought an Esprit 120. The first night I used it, I didn’t notice a problem with pinched optics but on the second night, when it was -2 outside, it was very obvious with hexagonal defocused stars during focusing routine. Looking back at my previous images, the problem was just visible there too. Fortunately, I’ve experience of pinched optics from my Altair Astro 480mm f6 triplet which gave “iron cross” stars from the 4 screws holding the lens elements. Backing off each of the 4 screws by 1/8 turn fixed the problem completely. This morning, I’ve accessed the 6 (x3) hex screws holding the Esprit 120 lens elements by unscrewing the dew shield and then removing the sticky backed black felt strip overlying the screws. I’ve backed all 18 off by 1/8 turn and then put everything back in place. I live in very cloudy Northern Ireland so it will be a while before I can see if this has worked but I’m hopeful. The image is from my 480mm f6 triplet prior to backing off the 4 screws -“Iron cross” stars.