Plate Solving fails after changing focal lengths

HI all,

I am a new SGP user, but have had great success (100% success) using the following:

C8 with Hyperstar, approx 390 F/L., ASI 294.

I am in the process of changing to

C8 with 6.3 reducer, approx 1450 fl

I have had no success with plate solving using this configuration. I have had no issue plate solving with APT using the same.

I have the focal length correct in the new profile, and have tried several different exposure times for the plate solving.

I am confident I have some setting wrong and would appreciate any advice!

Thanks, Bill

Bill, did you also change your camera scale setting to the new value? Should be .75 with the C8 and reducer you mentioned. Focal length looks like it would be 1280mm.


Thanks for your quick response! I will change that now. I was given the 1450 by a friend using the same setup as me, but I will change that as well.
One quick question, When i load the profile for this particular setup, does it populate the control panel, or do i need to go into the control panel and change that as well ?

Thanks, Bill

The control panel will populate with the changed setting. You need to apply the updated profile to whichever sequences you use it with so the new setting carries over by using the File pulldown menu.



I made the changes you suggested and SGP did move to M81, but would never finalize by centering the target. I could see M81 on my screen, but would never move it to center. It would eventually go into recovery mode.
I tried this several times and it never worked properly.

I did check it with APT and it solved at once.

Any further suggestion would be greatly appreciated.

Thanks, Bill

Under the telescope tab check your Sync Behavior setting. You may have to change it from Sync to Target Offset depending on your mount.


Thank you for the suggestion. I tried all the sync settings and the result did not change. It basically kept M81 in the corner of the screen.

Thanks, Bill

I had a similar problem where the centering process would send corrections to the mount to move it in the direction it needed to go after plate solving the image, but there was no apparent movement or at least very little. The next image it would take to plate solve was virtually the same as the first. It seemed to have to do with backlash in the mount and the software was not sending a large enough correction to overcome the backlash. I increased the number of attempts it should try to make before failing and this seemed to help, although it was taking several attempts before finally moving the direction is was supposed to go.

Hi - some mounts do not like sync commands. In the case of Paramounts, for example, I have a pointing model and it would be corrupted by further syncs. I disable the syncs in its ASCOM driver properties and use target offset as the sync method in SGP.
I believe that EQMOD users have the same issue if they have a pointing model in EQMOD. With the centering process in SGP, one really does not need a pointing model.

Thanks Buzz,

Last night I had the same issue. It centered perfectly on M42 but would not finish. I ended up shooting with APT

Is there a way to force SGP to continue and begin shooting in this case?

Thanks, Bill

Yes, just do slew and not slew and center… or widen the centering tolerance. If the mount has a lot of backlash, it is going to need some attention.


Also thanks for the advice on the pointing. I found other articles that say the same. I changed it to dialog,

Thanks, Bill


Thanks for your advice! It corrected the problem and I shared with my friends who plate solve.

Thanks again, Bill


You had such good advice on the plate solving, I wondered if I could run a question by you regarding the settings on automatic focus? Seems to be my last hurdle.

Thanks, Bill

Bill, you need to decide on an approach; some use offsets between filters, others autofocus when they change filter. I used to do the former but I have so many possible combinations of scopes, flatteners and reducers, I decided to just AF each time, especially since CMOS is so much quicker at downloading.
In regard to AF triggers, I have AF on filter change, 1 C temp change and after 15 exposures. The latter is to catch any bad AF ruining an entire stable-temperature night.
I have an odd number of steps, either 7 or 9, with a step size of about 25 x 4 micron steps. This works well with f/5 to f/7 scopes. The step size changes with aperture ratio, faster lenses need smaller values. I bin exposures 2x2 (even with CFA cameras) and limit the field by about 20% with about 5 second exposures (sometimes more on NB filters).

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Thanks for this great answer. I think your answer far outweighs my understanding at this point. My setup is not that complicated.

I use the C8 with Hyperstar (f/2) and OSC’s (ASI), so I am not changing filters at this time. I use the Celestron focus motor, and have no problem getting into focus.

I do not have any environment tool. ( I have the TEmp plug in, but not supported).

What i find is that when it attempts to autofocus that it finds the best focus, but does not lock into or solve to it. It fails after a few attempts and resets to last best focus.

I use 1x1 binning on the focus shots.

That is sorta where I am at the moment.

Thanks again for your help.