Hah, looks like WO made an error with the backfocus. It is really around 57.5mm (see Agena page on the Pleiades 68), and people have been using the 55mm (remember I didn't believe that number?) and complaining about coma.
Definitely proves that no one at that company even test their products under the night sky.
They are simply issuing new spacers to reduce the backfocus to 55mm. But, heck, I am sticking with the original spacers to get an extra 2.5mm of backfocus to play with. Or get PreciseParts to make me a spacer to get 56.2mm backfocus to match the FSQ stuff.
I suspect the Pleiades 68 that is coming tomorrow from CloudBreak is from the first manufacturing run, so it will likey come with 57.5mm backfocus.
Nothing changes with the optics. Just a different metal spacer so the unwashed who don't know how to find proper backfocus can stay with their 55mm (its not even 55mm once you add a filter glass anyway. I suspect that the precision needed for a f/3.8 is nothing to sneeze at). Draw a curve with EAF ∆ vs backfocus ∆ (like using filter glass thicknesses), and the curve should cross zero at 57.5mm or so :-) :-).
But if there is coma at APS-C, the Pleiades goes into the trash. If it works at APS-C, I would be tempted to try my ASI6200MC to see how wide it can go. I think the WO glass will be lucky to work at APS-C; all that I am expecting from such a cheap scope.
BTW, Pleiades name is because of the 7 glass elements. (I would have called it Artemis :-) :-). They should have just call it Subaru :-). For those who don't know what I am refering to, take a look a Subaru car's logo to see what the name refers to. The unaided eyes today can at best see six stars, not seven. The Greeks have good eyes, or something about the missing sister. :-). I wonder if WO knows that one of the glass elements is missing :-):-). I don't think they teach Greek classics in Taiwan.
I really like the fact that there is no external drawtube. That thing should take all kinds of instrumentation weight.
Chen
