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Originally Posted by casstony
The good news is that the focuser can almost certainly be made serviceable with adjustments similar to those I described above - most crayfords (excepting FT) have a somewhat similar construction and operate on the same principles. If you can get some info/pictures about how to adjust that particular focuser that's great, otherwise I'd suggest getting permission from the retailer to disassemble and adjust the focuser yourself - once it's apart you can see which screws do what. Failing that send the focuser only in to the retailer or Skywatcher for adjustment and ask them to adjust it to suit a heavy load - no need to ship the whole scope.
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Cheers Tony :-) I've hit up Skywatcher to see if they'll provide some details. I think all other crayfords that I've seen diagrams of usually have one clear grub screw that you adjust for tension, but these ones only have four symmetrically-placed bolts underneath so without opening it up fully or being provided with documentation, I'm not sure what to do.
Quote:
Originally Posted by Camelopardalis
Nice one Lee. My Esprit has been giving me nice round stars with no halos, which is what I was looking for in an imaging apo.
Lee, what was happening with the ambient temperature while your subs were getting softer / going out of focus?
I've noticed that I need to refocus regularly during the first half of the night at AstroFest, and I suspected thermals. After midnight when the temperature became more stable I didnt need to touch it much. If the tube is contracting with dropping temperature, it surely can't be unique to this scope.
The focus lock is a bit quirky, but as you say there's no shift. My focused doesn't slip, but then my DSLR only weighs about 500g.
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Cheers Dunk :-)
Not sure about ambient temps, I wasn't measuring them. They were presumably dropping due to it being early evening, but I don't know by how much.
It's possible it was temperature related, but I have
never seen such a shift on any one of my scopes, and I doubt the temperature shift was that much different. Given the other issues with the focuser, I think that's the likely culprit.
The main thing with buying a triplet for me is once you use parfocal LRGB filters with a doublet and a bhatinov mask, you'll see how out of focus the blue (probably, I guess that depends on your scope) light is. From there you think about how it's a spectrum rather than a discrete block and a significant amount of light in the spectrum isn't being brought to focus every time you're shooting L. This of course could cause colour halos, but I imagine other things could cause those.