SQA55 Temperature sensitivity

Thanks for sharing this! Will test this out once I get the AF installed.

That really seems like alot of shift.   Have you ruled out the focuser slipping?

Check your autofocus history throughout multiple nights, look for the focus point consistently drifting in one direction.  

Also, the Roki barely needs to autofocus more than once in a night.  Even on nights with big temp swings, I've only ever refocused once using HFR as a trigger, the HFRs drifted about 0.01 over 6 hours.

Travis McGeehan:
@Brian Puhl thanks I'll check that too - what would I do for the focuser slipping, would it need to be tightened?

​​​​​​I'd just check for it first.  You shouldn't be able to move the focuser by hand.  Something this drastic would be obvious.  You can also try moving the focuser by the opposite knob from the autofocuser.  The autofocuser should stop you from going anywhere, aside from the usual backlash.  

Im not saying this is what it is, but I'd be looking towards mechanical issues.  Seems like alot more than normal temperature drift.

Brian Puhl:
You can also try moving the focuser by the opposite knob from the autofocuser.  The autofocuser should stop you from going anywhere, aside from the usual backlash.

*Not if it is direct drive, only if you have reduction gears within the EAF.

Ok, so here is all I've discovered with this APN objective. It's important to mention this is an APN objective as the focus consist to move the objective inside de tube here...

-To reduce backlash you have to put the "fine focuser" ring in one of its course limit. Only one side is working to reduce backlash

-if you have a medium to heavy camera (like me with the QHY600 + filter wheel), then the weight of the imaging train will make the objective to move in the tube which will make mandatory to guide with OAG instead of piggy back.

-I've tried to build a lot of model with the 10micron 1000 and 2000 and all of them was catastrophic (30 to 60 arcs RMS), this was definitely  showing lot of flexure in the tube which make guiding mandatory

-you need to be sure the last movement of your focusing is against gravity when you are autofocusing

-I've swapped the rotating ring by a simple ring CNC and it's a game changer (not for the flexure but more because I consider that the rotating ring is an anomaly for many reason)...

-if you play with the extremity of the objective with your finger (when focused) you will see you can move the objective first  up and next down and also  rotate it.... Yes.. there is some play internally, you have to live with that (I'm suspecting some shitty plastic part not well adjusted inside the objective

I'm talking about that on CN here
https://www.cloudynights.com/topic/929708-askar-sqa55-55mm-f48-petzval-astrograph/?p=14030829
https://www.cloudynights.com/topic/929708-askar-sqa55-55mm-f48-petzval-astrograph/?p=13907345

Last but not least: sharpstar support is useless and pathetic. I've give up in the ticket I've raised with them....

cheers

I have the SQA55 as well with a ZWO EAF. I don't seem to be having the problem you are but I am running NINA with 3 focus triggers 1) HFR 10% 2) Temperature 3C and 3) Time 60mins. Below is part of the image history of my run last night spanning from around 7:30 pm to midnight and one of the focus runs:

Travis McGeehan:
Ah ok thank you. I'm using an ASIAir plus to run everything, don't know if it has that option for the EAF.

Your backlash with a ZWO EAF on the A.A. is automatically zero.

Welcome to the world of longer refractors. I have noticed that our short FL rigs like Redcats and lenses seldom go out of focus and only set them to refocus every 2hrs. The Medium FL units (300-600) every 1-2hrs especially early in the evening when temp change is greater and our longer refractors (1000mm or more) every 30min for the first 3hrs and then once an hour. All aluminium tubes tube assy's are pretty similar, even Taks. There's a good reason many high end scopes utilise carbon fibre or some form of low expansion material. Another things is the better and faster the optics, the easier it is to notice the change in focus. Your SQA55 is both of these so refocus regularly (assuming other factors mentioned by others are all sorted) and enjoy the results. Your follow up image is a beauty btw Travis!