I have a Celestron C14 non edge, microtouch and feathertouch primary mirror focusing. I have followed the autofocus setup instructions in the help file ( many times, I know them by heart )
No matter what I do, I can’t get a v curve, spent hours on it… The best I get is a random set of points and I end up focusing by eye. I have tried many options and I use 9 points with a step size around 65 (as calculated using helpfile instructions, but I’ve tried varying the step size between 40 and 90).
So I’m writing to ask if there are any plans to provide alternative focusing algorithms which favour SCTs? I think it would be a great enhancement for sgpro
@Paulkirk,
Can you describe your setup in more detail? It sounds like you have TWO focusers, a microtouch and a feathertouch, and the feathertouch moves the primary mirror?. I assume it replaced the stock focusing knob on the C14?
Does the microtouch sit in the light path, for example, between the C14 and the camera?
Which focuser is connected to SGP?
What many (most ?) SCT users do who have a focuser in the light path is to put it at the half-way mark, then use the other focuser that moves the mirror to manually focus fairly well. Then that focuser is locked and the mirror is locked, and only the focuser in the light path is used with SGP.
Trying to have SGP control a focuser that moves the mirror is probably extremely difficult due to large amounts of backlash needed.
I mentioned the focuser but it’s irrelevant other than to know that it is a motor driven ascom standards focuser which acts on the primary mirror via the celestron focus knob. It’s pretty standard stuff. I also made my own focuser and wrote a driver for it, but the results are same re sgp autofocus.
The problem is that the way SGP currently addresses focusing on my SCTs (C11 and C14 ) just does not work. I have the backlash taken into account, and as stated, I know the procedure inside out. It doesn’t work on my scts.
As you know, there are other algorithms available to facilitate autofocus, it was just to ask if Ken has any plans to implement a different solution for SCT.
I’m always open to the idea that I MAY have missed something, but I’ve been with SGP from the start.
all the best,
Paul
I have a 12" Meade OTA with an Optec focuser. The camera is attached to the Optec focuser. If you have a focuser on the Celestron focuser knob – remove it. On an SCT, the focal plane moves 4x as much as the mirror moves.
SGPro needs to have a reasonably focused camera to start with. On my OTA, I move my Optec focuser to its mid travel point. Then using only the Meade built-in focus knob, I bring my camera to a pretty good focus. Then I lock the built-in focuser. From here on, I only use the Optec focuser with the SGPro auto focus routine. The amount of backlash is set in the Optec focuser ASCOM control.
In SGPro, set the number of steps to 9 and set the steps between frames to a value of about 2% of the total step size of the focuser. You must avoid pushing the focus frames to the point where the star images become donuts.
The FWHM range is 3x from best focused star to worst focused star. Adjust the steps between frames to stay within that limit.
@Paulkirk, @chasmiller46 and I do the same thing to focus our SCTs. He basically said the same thing I did, so neither of us consider it “irrelevant”.
If you’re having problems focusing your SCT and other people aren’t, it’s very likely it’s something in your system or your process, and not SGP’s fault.
Having said that, if the image is WAY out of focus and you see donuts, SGP’s focus routine won’t handle that well, but as far as I know, other software don’t handle donuts well either. Normally you won’t see donuts unless it’s the first focus of a day and the last focus was taken in the early morning when the temperature was quite different. SGP has an option to compensate for that.
thanks for the replies. I have two scts and I’m quite capable of following the help guide
I very rarely get a v curve. We shouldn’t be defensive about this. There is obviously a problem, and it’s just a straightforward question about whether Ken is considering providing other focusing solutions which favour SCTs.
basically, what you’re saying is that it’s not possible to achieve focus with a focuser attached to the celestron native 10 x reduction gearing. My focuser has as much gearing as needed to sweep through the CFZ. So different types of focuser will be able to achieve focus, provided they can address movement through the CFZ. What makes your focuser better than mine i wonder all the best
Paul
I will say most of my time at the start of an imaging session is devoted to getting my Celestron 11" Edge HD to focus. I also feel it takes way too long to get a good curve but this may be inherent to the SCT. What I have found is the SCT is very limited in its focal range before you get donuts. Also, the temperature (inside the scope) is critical. How I proceed to waste the least amount of time is:
cool down the scope by opening the roof to the roll off a few hours before imaging.
I have made a small fan to apply to the vents of the scope while I’m preparing the equipment.
I move the primary mirror about 20,000 clicks in each direction to help “move” the air inside the scope. This may be voodoo.
I then take single images in Frame and Focus to get the smallest HFR.
once achieved, I run the auto focus program. I typically use 5 stops to avoid reaching the donut (HFR 0.00) point. I may start with 7 steps, but once focused I reduce the steps to 5. Sometimes I have to change the step size by 10-20 clicks so as not to reach the dreaded donut. I also don’t waste time letting the whole program run. If I see the curve skewed to one side, I reset the focus point and start over with a new run.
I typically refocus every 1 degree C change or every 60 minutes.
I fortunately don’t have alot of mirror flop but of course I compensate for backlash.
I also find that the longer the focal length used, the harder it is to get good focus at the onset. Hyperstar is way easier than with a 0.7 focal reducer or @ 2800mm FL.
I still have times when upon refocusing, SGP can’t do it and it goes back to the prior mirror position, takes another image and tries again. This can cost considerable imaging time in the middle of the night. Focusing is a PAIN in the … Always thinking about moving to refractors hahaha
P.S. I have the same focusing set up as Paulkirk. Feathertouch to replace the original Celestron focuser and Starizona Microtouch applied to the Feathertouch for autofocus.
@ra_dpdal,
I’m not familiar with the Feathertouch or Microtouch, so could you please explain in more detail what goes where?
I understand that the Feathertouch replaces the rubber knob on the back of the Celestron, but am not sure what you mean by the “Microtouch applied to the Feathertouch for autofocus”. Is the microtouch physically connected to the Feathertouch or is the Microtouch in the lightpath?
Either way:
Which focuser does SGP control?
How well does this work for you?
Do you have any suggestions for @Paulkirk? His setup is different than mine and what @chasmiller46 has, so we can’t give him any specific guidance.
I assume the “20,000 clicks” is the number of steps you move the Feathertouch focuser? Does moving the mirror allow more space behind the mirror for air to flow? Or something else?
The Feathertouch is the motor drive part that physically does the primary miror movement via the celestron focuser knob. It fits onto the C14 once the standard focuser knob has been removed.
Microtouch is the Focus motor controller and this uses an ASCOM driver to faciliate the necessary interactions with SGP. Both are commercially available and widely used products, supplied by Starizona in Tucson. My experience of both products is extremely positive.
thanks for the explanation @Paulkirk. I understand now, just 1 focuser.
I’m very curious if @ra_dpdal has the same issue as you give they have the same setup.
What do you use for backlash on the focuser? And do you do it in SGP or the focuser driver?
