Quote:
Originally Posted by Camelopardalis
The main reason I threw the temperature thing out there is because I'd spoken to a few others at AF who were using temperature-sensing motorised focusers to solve exactly the same problem...and mine was the only Esprit on the field 
Yeah looks like the blue is usually sacrificed on a doublet, probably not the greatest if you want to capture some OIII  |
Quote:
Originally Posted by Somnium
thanks for your first impressions, i look forward to more details. i am not sure how big the focussing issues were, but is it possible this is due to changes in temperature. I am not sure how much this affects refractors but it may be a component of the issue. when you get a chance i would love to see a colour image to see how well the CA is corrected. congratulations again on your new scope, you have to be very happy with the results.
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Yeah, I'm not sure. I have been imaging for a couple of years now from this location and I've never seen any measurable focus shift on any other scope due to temperature. I've been able to image for hours on end, always starting from the early evening, with the FWHM fluctuating but ultimately maintaining a horizontal trend.
Now it's possible that triplets are different in this regard, I've only ever used my other triplet once for real imaging, but I do use my GT-81 triplet as a guide scope and I've not noticed significant focus shift with that in the same conditions.
The other option is that this is a big beast, and maybe it hadn't fully cooled. I'm not sure if that would affect focus, but maybe? I would also expect the non-insulated aluminium composite panel box that I like to call an "observatory" probably doesn't have great insulative properties so I would expect the scope to be pretty close to ambient to begin with. I've never validated that theory with measurements though.
Anyway, probably seems like I'm saying with certainty that it wasn't temperature related, but I'm not actually ruling it out, I'm just leaning towards other causes based off previous experience (with different scopes!). I could be wrong, and time will tell :-)
I've contacted both SkyWatcher in the US and Tasco in Australia regarding my focuser issues and hopefully I'll have some helpful advice soon.