Nick,
A couple of things come to mind if you are not getting HFR low enough:
-Double check your sampling. If you are far less than one this could cause bloating. If you have a mono cam try binning 2X2 or 3X3 and see if the HFR changes.
-Try an object or area where no large stars are present. A bright star can alter the average HFR for the whole image and affect your V-curve.??
-With the ZWO EAF (what you have?) I have never found auto-focus to work that well (in SGPro) and the V-curves are pretty bumpy. My MoonLite CHL produces very symmetrical curves all the time. With the ZWO I usually just try to move in and out with the position controls and check the HFR number after each click and check where the lowest HFR is.
All the best,
John?
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This is a link also to a 10 min test sub (NEF format) - no processing done on it
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Good point. I have a couple of "normal" looking ones and the first one thats a bit odd - I think because I had changed the exposure time to 4 seconds which is not enough
HFR of my subis is around 3.2-3.6 pixels at a scale of 2.2
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You might also post a picture of the AF curve you are getting.?
Definitely do your experiment with Bahtinov mask and have NINA measure all of the image HFR values.?
Goal here is to see whether there is a limit to what focus you can get or whether NINA is going back to a poor focal position due to backlash.
--
Edward
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OK so I measured 1000 steps = ~4mm (no calipers but I have a set on order since I need them only)
= 4/1000 mm per step = 4um/step
My scope is an AT60ED so f/6 = 6 x 6 x 2.2 = 79.2um
Width of zone = 79.2/4 = 19.8 steps
So my step size starting point should be 19.8 * 1.5 = 30, so I am not far off at 25
Thanks again! I am going to run a few tests if the weather holds tonight.
I fail to believe 6a/sec is the best I can do here
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Thank you Edward, this is amazing info! Yes, the ZWO has some backlash and I am hoping the NINA "Overshoot" method will minimize this
I am going to do the calculations you present above and see what I come up with, this is super interesting and helpful !
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Recommending settings as absolute numbers is meaningless. I still suggest you start by?computing:
(1) how many microns your focuser moves per stepper motor step. You can command the focuser to move a large number of steps and measure this physically how far the focal plane moves. Alternatively, knowing the gear ratios and stepper motor specs you can compute this from first principles. For my scope, it is about 3.98 um/step
(2) the width of your critical focus zone in microns. The formula is f * f * 2.2.? ?So, for my f/7 scope, this is 7.0 * 7.0 * 2.2 = 108 um. The faster the scope, the smaller the window.
(3) width of the CFZ in steps by taking the ratio of the above. For my scope, it is? 108 um / 3.98 um/step = 27.1 steps.
Two observations from this:?
First, the focuser system? has at least 10 or so motor steps in the CFZ so the AF system is not "under-sampled".
Second, a good starting point for the NINA AF step size is 1.5x this value. For my system, that is about 40 motor steps. This ensures that NINA will not jump completely over the CFZ yet not waste time "over-sampling" the parabolic portion.?I then choose an initial move of 5 AF steps.? Unlikely you have to change this if you get the AF step size right. This heuristic will get you out on the "arms" of the hyperbola.
Once you have this, you have to deal with focuser backlash. It is my understanding that ZWO AF can have substantial backlash. In Cuiv's video, he found something like 100 or 150 steps of backlash. On my DIY focuser, I have 8 steps of backlash which is less then halve the CFZ. You may need to enable and tune some form of backlash compensation. Conflicting recommendations out there about whether to measure the backlash physically (motion of draw tube) or optically (changes to HFR). The new NINA mode for overshoot-based compensation looks very promising .... I don't use either because I programmed backlash compensation in the focuser controller itself, not in NINA, and do not have much backlash to start with.
Finally, I have had good success with the nominal choice of Trend and Hyperbola, but that is my system. The choices are all work-arounds when your focuser measurements do not trace out a decent hyperbola, either due to mechanical issues like backlash or due to lousy seeing.?
The rest of the settings look fine. Don't bother with enabling more exposures per AF step. I found a good presentation on why this is not as effective as sampling the curve in more places.
--
Edward
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I am using 1.10 HF3 - I have had enough to worry about so far without being on nightlies :)
I also use overshoot with 300 as the backlash, which seems to work - I dont get flat curves, just ... not low enough in the middle
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Yeah I may turn off the trend part - I read that over on Cloudy nights this morning
My scope is small so I am actually not flipping -- if there were no cables I dont think it would ever hit the tripod physically
I am using ASTAP but I think I used to use ASPS or PS2 with similar results
The duo-band filter kills a LOT of light, but I am basically getting the same results as before I added it
I do only have a doublet scope which I suppose could be impacting me a bit, but I should ope to do a bit better
Going to turn off trends later, slew to a bright star and put the mask on to see where we are
Thanks for the suggestions !
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For me Trends and Hyperbolic caused issues.? I use Hyperbolic.??
Which Plate Solver are you using?? ?What are your Losmandy and NINA meridian flip settings?
------------------------
Jim W
Phoenix, AZ. USA
Losmandy GM811G, NINA 1.11, ASI2600MC Pro, Sky-Watcher Scopes
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I have the ZWO focuser and thinking my step size is too big (although the NINA folks told me to increase it even higher than I have now)
Initial step size: 4, Step size: 25, Exposure 10 secs, Method: Star HFR, Curve fitting: Trends and Hyperbolic
Just manually going through the steps the other day, it seemed like it took very few to change the focus quite a bit
the NINA AF bot told me to increase my step and the developers suggested to make it 40 !
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That¡¯s great news. What autofocuser hardware? I put together a DIY system called ¡°myFocuserPro2¡±. The documentation has good explanations of critical focus zone and backlash that helped me tune NINA AF settings. I am reliably hitting 1.5¡± HFR on an f/7 scope using NINA. Aim for about 1.5 CFZ per AF step, 4 or 5 AF steps on either side of focus, and compensate for backlash. Cuiv The Lazy Geek has a good YouTube video on backlash settings.
--
Edward
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Great news Nick.? What release of NINA are you using and which plate solver?
------------------------
Jim W
Phoenix, AZ. USA
Losmandy GM811G, NINA 1.11, ASI2600MC Pro, Sky-Watcher Scopes
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Re: New G11 Question Concerning Stiction
Hi all,
Good discussion on balancing.?? To recap:
1. Slew or position your counterweight rod to be horizontal.
2. At that position, there is zero weight on the DEC clutch pad, so carefully release the DEC clutch knob (watch for the scope to flip over!) and test for balance.? Reposition your scope or scope weights or dovetail until you are fairly in balance.? Perfect balance is not required as the motor, gearbox, and clutches have good strength.?
3. At this same position, if you have a amp-meter (ammeter) on your Gemini power input, you can slew the RA to East and to West and compare the Gemini (mostly RA) motor current.? If the slew current in both directions closely matches, your RA is in balance. If you use this, you do not need to release the RA clutch at all.? So this is the best general approach if you use high friction clutches.
4. If you don't have an electronic measurement of motor current, then still with counterweight horizontal, you can release the RA clutch and gently push the RA axis East then West.? Try to use the same force in both directions and try to judge the angle it takes to stop again.? These should be about the same.? You adjust your counterweights until it is about equal response.
5. If your RA axis clutch area has a machined groove for the "wavy washer" (an alternative form of the Belleville spring washer,) then adding one of these springs in will help push up your scope load, and it will reduce the outer area torque hold of your 4.25 inch OD clutch pad down to about 2.5 inch (the OD of the wavy spring).? All the scope load that was on the 4.25 inch clutch disk will now be on the 3 spokes of the same clutch pad at the diameter of the wavy spring.? It does not eliminate the clutching completely.? It just reduces the torque of the clutch disk.??
6. If you lower your RA angle to zero using the back ELevation knob (putting the CWD shaft totally vertical) then rotate the counterweight shaft horizontal, then release the RA clutch, ( like the DEC at horizontal ) there will be zero weight on the RA clutch pad.? This adjustment of EL to zero means having to re-polar align your RA axis, and exhaust your wrist by manually turning the back Elevation knob.? Not fun, but it works of course.??
So...DEC is very easy to balance on all mounts, but the easiest and most accurate way to balance RA is to go electronic....use a power supply that shows the amps of the Gemini (mostly the motors).? This works with or without a wavy washer, for all mount versions new and old, and all Geminis new and old.??
Best regards, Michael
On Sun, Jul 4, 2021, 5:17 PM Brian Valente < bvalente@...> wrote: Yes - this is covered in detail in the wavy washer video
?
Question..
Doesn¡¯t the Wavy Washer require a machined groove that not all mounts
have??
?
Not
positive, but I don¡¯t believe my mount will accept one..
?
Derek
?
?
There is no drawback to using the wavy washer.
Nobody who got the washer wishes they hadn't and would rather do the alt=0
trick.
The Losmandy mounts are already front-heavy, and I don't want the thing to tip
over while trying to balance the scope.
Someday, when you man up and get a BIG scope, you will enjoy not having to
crank it to zero for every little change in setup.
--
Brian?
Brian Valente portfolio
|
Re: New G11 Question Concerning Stiction
Yes - this is covered in detail in the wavy washer video
?
Question..
Doesn¡¯t the Wavy Washer require a machined groove that not all mounts
have??
?
Not
positive, but I don¡¯t believe my mount will accept one..
?
Derek
?
?
There is no drawback to using the wavy washer.
Nobody who got the washer wishes they hadn't and would rather do the alt=0
trick.
The Losmandy mounts are already front-heavy, and I don't want the thing to tip
over while trying to balance the scope.
Someday, when you man up and get a BIG scope, you will enjoy not having to
crank it to zero for every little change in setup.
-- Brian?
Brian Valente portfolio
|
Only with your amazing help! Found a Bahtinov mask in the basement so I am going to check out this focus
I have a few trips to Bortle4 coming up in July/August that I really want to take advantage of
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Nice work Nick.
you've done a great job with this
Just wanted to say a huge thanks to everyone that offered help & suggestions over the last couple of weeks. I am really dialed in now.
Had a great session last night, all automated with NINA (focus, slewing, syncing w/plate solving and guiding).
Guided with zero issues for 4 hours at 0.62" RMS, dipping into the high 0.4s sometimes but hovering right in the 0.5s mostly.
I do have some occasional spikes to +/- 2" but they dont seem critical. One big spike at -6" - no idea what happened there so I will just watch out for it
The only issue I have now is I feel my focus is leading to bloated stars as my FWHMs are all in the 6-8 arc/sec range but this is not the mount. My HFR in NINA when auto-focusing is 3.5-3.6 which leads to that number.?
Going to get a Bahtinov mask for the refractor just to check the result of autofocus. There is quite a narrow window of focus surprisingly, and maybe my NINA settings are causing me to miss it
I'm really happy with the images - 10 min subs with eccentricity in the 0.5s even with the sensor tilt
-- Brian?
Brian Valente portfolio
|
Just wanted to say a huge thanks to everyone that offered help & suggestions over the last couple of weeks. I am really dialed in now.
Had a great session last night, all automated with NINA (focus, slewing, syncing w/plate solving and guiding).
Guided with zero issues for 4 hours at 0.62" RMS, dipping into the high 0.4s sometimes but hovering right in the 0.5s mostly.
I do have some occasional spikes to +/- 2" but they dont seem critical. One big spike at -6" - no idea what happened there so I will just watch out for it
The only issue I have now is I feel my focus is leading to bloated stars as my FWHMs are all in the 6-8 arc/sec range but this is not the mount. My HFR in NINA when auto-focusing is 3.5-3.6 which leads to that number.?
Going to get a Bahtinov mask for the refractor just to check the result of autofocus. There is quite a narrow window of focus surprisingly, and maybe my NINA settings are causing me to miss it
I'm really happy with the images - 10 min subs with eccentricity in the 0.5s even with the sensor tilt
|
Michael
Herman¡¯s Power Supply is the best choice..
?
Derek
|
Re: New G11 Question Concerning Stiction
Question..
Doesn¡¯t the Wavy Washer require a machined groove that not all mounts
have??
?
Not
positive, but I don¡¯t believe my mount will accept one..
?
Derek
?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of alan137
Sent: Friday, July 02, 2021 11:04
PM
To: [email protected]
Subject: Re: [Losmandy_users_io]
New G11 Question Concerning Stiction
?
There is no drawback to using the wavy washer.
Nobody who got the washer wishes they hadn't and would rather do the alt=0
trick.
The Losmandy mounts are already front-heavy, and I don't want the thing to tip
over while trying to balance the scope.
Someday, when you man up and get a BIG scope, you will enjoy not having to
crank it to zero for every little change in setup.
|
Edward Plumer
Michael Herman