paul Posted April 18, 2021 Share Posted April 18, 2021 I've had easy success using a ZWO EAF on my refractor, but the results I am getting with an EAF on my 150mm newt are disappointing so far with double diffraction spikes resulting. I've tried APT and NINA. Rather than investigate further with tweaking parameters I revert to the bhatinov mask, but I would like to automate it as I need some sleep for work.🙂 I'm finding that during the night the focus moves off from its sharpest and I would like APT or NINA to tweak it periodically. I've searched for tips and apart from people commenting on how the central obstruction can confuse the process (doughnut holes make it difficult) I don't see anyone stating they have it working. I suspect I need to improve my estimate of backlash, but it would be good to hear other people experience before I waste my time! Can anyone offer tips or a focusing package that they know works? (FYI I'm using the latest ZWO 7 filter set and I don't see significant filter offsets on the newt at all.) Quote Link to comment Share on other sites More sharing options...
AstronomyUkraine Posted April 18, 2021 Share Posted April 18, 2021 5 hours ago, paul said: I've had easy success using a ZWO EAF on my refractor, but the results I am getting with an EAF on my 150mm newt are disappointing so far with double diffraction spikes resulting. I've tried APT and NINA. Rather than investigate further with tweaking parameters I revert to the bhatinov mask, but I would like to automate it as I need some sleep for work.🙂 I'm finding that during the night the focus moves off from its sharpest and I would like APT or NINA to tweak it periodically. I've searched for tips and apart from people commenting on how the central obstruction can confuse the process (doughnut holes make it difficult) I don't see anyone stating they have it working. I suspect I need to improve my estimate of backlash, but it would be good to hear other people experience before I waste my time! Can anyone offer tips or a focusing package that they know works? (FYI I'm using the latest ZWO 7 filter set and I don't see significant filter offsets on the newt at all.) The best way to determine backlash in the EAF, is to clear any backlash numbers you have entered in NINA, if any, make sure you have no basklash entered in the driver too. Move the focuser in a 1000 steps, then move it out 10 steps at a time until you see the fine adjustment knob move. Count the number of time you moved the focuser in, then multiply by 10, that is your focuser backlash. My EAF has a backlash of 110, meaning I moved the focuser in 11 times in increments of 10 steps. 1 Quote Link to comment Share on other sites More sharing options...
MarkAR Posted April 18, 2021 Share Posted April 18, 2021 Sounds a bit like your focuser is slipping. Quote Link to comment Share on other sites More sharing options...
paul Posted April 18, 2021 Author Share Posted April 18, 2021 2 minutes ago, MarkAR said: Sounds a bit like your focuser is slipping. Its a rack-n-pinion focuser and I'm not discounting anything as the scope tracks that sky. There is a also a temperature change over the period of about 5 degrees that will account for a small change too. I'm just trying to get the auto-focus routines to zero in so I can adjust for any slippage automatically. 5 hours ago, AstronomyUkraine said: The best way to determine backlash in the EAF, is to clear any backlash numbers you have entered in NINA, if any, make sure you have no basklash entered in the driver too. Move the focuser in a 1000 steps, then move it out 10 steps at a time until you see the fine adjustment knob move. Count the number of time you moved the focuser in, then multiply by 10, that is your focuser backlash. My EAF has a backlash of 110, meaning I moved the focuser in 11 times in increments of 10 steps. The focuser doesn't have a 1:10 but I attached a large paper pointer to the knob on the opposite side and estimated the backlash to be <> 33 steps. That seems low compared to yours so I'll double check the numbers. I put these values in the driver and in APT/NINA perhaps I'm double accounting? Quote Link to comment Share on other sites More sharing options...
MarkAR Posted April 18, 2021 Share Posted April 18, 2021 Best way to detect when the focuser actually moves when checking backlash is if you can mount a dial indicator. If temperature is an issue can you set APT or NINA to auto focus every 30 to 60 minutes ? 1 Quote Link to comment Share on other sites More sharing options...
AstronomyUkraine Posted April 18, 2021 Share Posted April 18, 2021 13 minutes ago, paul said: The focuser doesn't have a 1:10 but I attached a large paper pointer to the knob on the opposite side and estimated the backlash to be <> 33 steps. That seems low compared to yours so I'll double check the numbers. I put these values in the driver and in APT/NINA perhaps I'm double accounting? Yes you are double accounting. ZWO recommend to leave the backlash at zero in the driver, if you are using backlash compensation in the software. Not sure about temperature control in APT, but NINA you can. 1 Quote Link to comment Share on other sites More sharing options...
TerryMcK Posted April 19, 2021 Share Posted April 19, 2021 7 hours ago, MarkAR said: Best way to detect when the focuser actually moves when checking backlash is if you can mount a dial indicator. That's a great idea. I have a dial indicator and magnetic base but never thought of doing that. I have the Lakeside focusers on my scopes and never really got to grips with the backlash. EKOS of course can do it but I seem to have randomly set parameters and not really got the autofocusing in EKOS to work. So I have been using the Bahtinov to do the initial manual focus and if there is a filter change I have an offset dialled in per filter but not 100% sure if they are correct. Quote Link to comment Share on other sites More sharing options...
paul Posted April 23, 2021 Author Share Posted April 23, 2021 It was focuser slip and double accounting! I ran the backlash estimator in APT and it quoted backlash figures had grown to 900. I disassembled the focuser and found that the rack was loose and moved independently! I tightened that back down and refitted the draw tube. I adjusted the tension of the hexafoc to reduce some friction but that introduced slop as the draw tube moves. I decided to live with that for the moment as I'm not imaging planets with that scope. Running the APT auto-focus routine gave me a new backlash figure of just 17 😀 I removed the backlash figure from the ZWO driver and set backlash to 17 in APT with a 200 step final move out. In NINA I used the overshoot method and used 200 steps. Both NINA and APT achieve good results with my current settings with NINA giving the best at the moment. I ran a sequence last night with NINA doing Auto focus at meridian flip and every hour over 4hrs and the results were good. I should now be able to to investigate if I really do need filter offsets. Thanks for your help @MarkAR @AstronomyUkraine 2 Quote Link to comment Share on other sites More sharing options...
AstronomyUkraine Posted April 23, 2021 Share Posted April 23, 2021 (edited) 1 hour ago, paul said: I removed the backlash figure from the ZWO driver and set backlash to 17 in APT with a 200 step final move out. In NINA I used the overshoot method and used 200 steps. Both NINA and APT achieve good results with my current settings with NINA giving the best at the moment. I ran a sequence last night with NINA doing Auto focus at meridian flip and every hour over 4hrs and the results were good. I should now be able to to investigate if I really do need filter offsets. Sounds like you got a good result there. As for filter offsets, I have never used them, if you refocus 2 or 3 times a night, which set of figures do you use to calculate the offset? My refractor can have a difference of up to 100 in focus position over a night, so I never touch filter offsets. My LRGB are parfocal, so I never refocus when changing from one to the other. My NB filters may need a slight adjustment. If your focus position doesn't change much during the night, filter offsets might work for you. Edited April 23, 2021 by AstronomyUkraine Quote Link to comment Share on other sites More sharing options...
paul Posted April 24, 2021 Author Share Posted April 24, 2021 22 hours ago, AstronomyUkraine said: Sounds like you got a good result there. As for filter offsets, I have never used them, if you refocus 2 or 3 times a night, which set of figures do you use to calculate the offset? My refractor can have a difference of up to 100 in focus position over a night, so I never touch filter offsets. My LRGB are parfocal, so I never refocus when changing from one to the other. My NB filters may need a slight adjustment. If your focus position doesn't change much during the night, filter offsets might work for you. That's a good point. I need to check the logs but I don't think the focus shifted much (it was LRGB for that session). Quote Link to comment Share on other sites More sharing options...
AstronomyUkraine Posted April 24, 2021 Share Posted April 24, 2021 1 hour ago, paul said: That's a good point. I need to check the logs but I don't think the focus shifted much (it was LRGB for that session). If your capture software has the option, you can put the focus point in the image file name. That's what I do in SGP. 2 Quote Link to comment Share on other sites More sharing options...
MarkAR Posted April 24, 2021 Share Posted April 24, 2021 Well done for getting it sorted, backlash of 17 is excellent. Quote Link to comment Share on other sites More sharing options...
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