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Old 09-07-2020, 11:13 PM
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Stonius (Markus)
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Temperature and filter offsets.

Is it worth it?


Sure you can take your nominal focus and subtract the temperature compensation and adjust for filter offsets, or you could just you know, run a v-curve and actually look at what's going on.


Put it this way. I would feel uncomfortable relying only on temp and filter offsets to determine critical focus. And if you're going to do a V-curve anyway, why bother calculatng the offsets in the first place?


Am I missing something here?


Markus
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Old 10-07-2020, 08:15 AM
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Atmos (Colin)
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Filter offsets are a good safe idea as they allow you to focus with the luminance filter and still have accurate focus with your narrowband.
Temperature compensation isn’t something I’ve used but it could be used to extend the time between refocus rather than stopping them altogether.
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Old 10-07-2020, 12:44 PM
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Quote:
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Filter offsets are a good safe idea as they allow you to focus with the luminance filter and still have accurate focus with your narrowband.

Ah, yes, that would make sense, because the offset would be constant.
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Old 10-07-2020, 01:03 PM
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I’ve always wondered about this...I largely take it for granted that my filters are parfocal, but a lot depends on the filter wheel and how they’re fixed in, etc.

At f/4, I re-run the autofocus routine as the scope is suitably twitchy (narrow CFZ) and it takes less than a minute to run, but wonder about the slower f/ratios...I wonder how much it is visible

Needless to say, the faster the scope, the more sensitive it will be to temperature dependent focus shift.
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Old 10-07-2020, 01:59 PM
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I am leery of temperature compensation. I ran it for a little while early on but found that firstly, you need a really good focuser if you are going to allow it to move mid sub, and second, it was hard to get the response of the system to match the response of the telescope. By that I mean, if 2 degrees temperature change means 100 steps of focus change, you can't just decide that the temp has changed by 2 degrees over a sub (Early in the night in the summer for instance) and allow temp compensation to move the focuser by 100 steps between subs in response as it might take another two subs for the telescope to catch up to the focuser as it stabilises.

I use temperature delta to trigger an auto focus run. I am just working to set up Voyager on a friends gear and hopefully once that is up and running I can see how it handles focusing though NB filters, it handles focus very reliably with my OSC setup.
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Old 10-07-2020, 02:18 PM
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Ah, Paul, I like your thinking. Of course there will be a lag between the ambient temperature and the expansion / contraction of the scope.


I'm in the middle of transitioning to Voyager too. Lots of parameters to master / reading to be done, though this time I want to master some of the stuff I never got around to with SGP, like filter offsets and automated meridian flips.


Cheers


Markus
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Old 10-07-2020, 06:16 PM
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Quote:
Originally Posted by Stonius View Post
I'm in the middle of transitioning to Voyager too. Lots of parameters to master / reading to be done, though this time I want to master some of the stuff I never got around to with SGP, like filter offsets and automated meridian flips.
Automated meridian flips in SGP is as easy as checking a box...no mastering necessary
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Old 10-07-2020, 08:05 PM
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Voyager was not much more than that either. The only hassle I had was related to using a CCM (Cheap Chinese Mount) and the way EQMOD and Voyager interacted with each other. Possibly also a difference in the way Voyager handles plate solved pointing compared to SGP as well.

Long story short, Voyager does one thing I like more than SGP, it images right up to flip time (Which is AFTER the meridian) so you don't loose imaging time in the best part of the sky. But you need your mount to be set up to track well past the meridian and you need to delay the flip long enough to be 100% certain that the scope will end up pointed west of the meridian after the flip (Cone error etc) or EQMOD will reject the sync after the flip and you land in trouble. After sorting that I have had about 20 flawless flips while I have been in bed. The only thing that has stopped one since was cloud.
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Old 10-07-2020, 08:48 PM
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Not sure when you last used SGP, Paul, but itís had all these options for as long as Iíve been using it...Worked first time with my CCM (NEQ6)

My flips take less than 3 minutes - the majority of which is slewing time.
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Old 10-07-2020, 09:34 PM
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I didn't have any issues with flips in SGP either after the first couple of tries at it, they were mount settings related too as the default mount limits in EQMOD kept on stopping the show mid flip. The difference is that Voyager then exposed errors in the mount pointing and made me do something about it where SGP tolerated them. The only thing I can think of that may be different between the two is I think SGP points, plate solves, calculates and applies an offset, plate solves etc and when you get within your defined pointing accuracy, syncs the mount. Voyager points, plate solves and syncs then points again if required. The pointing errors on the flip meant the after flip pointing was east of the before flip position by about 12 minutes, and was about 30 seconds before the meridian. If you try to sync EQMOD to a position east of the meridian when it thinks it is east side of the pier, pointing west, it rejects the sync.

All I had to do was allow it to image further past the meridian before flipping. From memory SGP stops imaging if the next sub will go past the flip time? Voyager by default will start a new sub right up to the scheduled flip time and delay the flip to finish the sub, there is a separate config to abort the sub and flip to prevent a crash if that is required.

I did have some oddball crashes (Software) with SGP which is what made me look at Voyager, which has only ever got itself tied in knots when I was fiddling with spacing and constantly connecting and disconnecting the gear to be able to unplug the camera. It focused my SCT much more effectively than SGP which was my other reason for moving, effectively focusing an SCT seems a bit of a bugbear in SGP which a delay in the focus shot after the focuser reports it has stopped moving would fix but when asked for that the SGP devs more or less say "Make your telescope work properly" when the issue is more or less built in to the SCT design. There are a lot of things I like about it more than SGP to be honest, but the learning curve is steeper.

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Old 11-07-2020, 08:28 AM
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Weird! Yeah I’ve never had that problem

From my settings, I allow it to image for 3 minutes past the meridian before it executed a flip, and I usually take 60 second subs, but it’s happy to keep taking them. It’ll even start a new sub with only a few seconds left on the countdown timer.

A mate of mine had problems with SGP crashing whereas I didn’t...and we run almost identical hardware (Intel NUC, SW mount, ZWO camera).

My general sentiment is that software is written by humans, and no software is immune from problems!
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Old 11-07-2020, 09:51 AM
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Reinforcing that, you could be talking about my gear there, NUC, SW mount, ZWO cams.

The focus setup on the SCT was the big driver for me to change as SGP would never really do it right, the focus curve would always have dog ears on it and it would impact the calculated position. If you do multiple focus runs one after the other, you have to expect the final position to move around a bit, but the Voyager runs produced a tighter group of results.
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Old 12-07-2020, 08:43 AM
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Yeah SCTs are a bit of a problem child with focusing. I’m sure it’d work OK if you had an R&P hanging off the back, but then you’ve got the whole back focus thing to worry about

To be somewhat on topic (), even SCTs experience significant focus shift with temperature. I was trying to bag some Jupiter last night (trying being the operative word) and over the course of a few hours I had to refocus 3 times. And being winter up here, it had dropped from all of 16 degrees at 8pm to a chilly 12 at 1am.
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Old 12-07-2020, 01:36 PM
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You are lucky, I found my C925 required focus runs about every 15 minutes in the summer, at the start of the night anyway.
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