Image Dimensions Too Low - Plate Solving Errors

[Evan]

Hi everyone,

I am new to the hobby and looking for some help. I'm using ASTAP + NINA to plate solve. When it works it takes about 30-45 minutes to finish polar alignment due to constant errors. Maybe 1 out of every 10 tries will result in a successful measurement. After stringing together 3 successful measurements I'm told my alignment error. Then begins a long process of correcting. I'm using an ASI120MM Mini + ZWO Guide Scope + EQmod.

I've updated my lat/long/elevation in EQmod, updated my guide scope settings in NINA. Achieved what I think is good focus on my guidescope camera. I gather what I think is a sufficient number of stars in the sample images. Turn on sidereal tracking . I'm not sure what I might be missing? I often get an "image dimensions too low" error but after several automatic retires it will suddenly achieve a measurement before reverting back to the aforementioned error. Should I instead plate solve off of my main scope (80mm/380mm FL)? Is an ASI120MM insufficient to plate solve with?

Any help would be appreciated!

[han.k]

Evan,

" Dimension too low" message indicates the binning/downsample is set too high. Since the ASI120 has only 1280x960 pixels you should set the binning at 1x or 0x (=auto).

Furthermore the mount should have some stabilizing time before it takes an image.

If you don't get other warning messages then you should be good to go.

If you still have problems send me an image and a screenshot of the setting as focal length, sensor size.

Cheers, Han

[Evan]

Hi Hans,

Thanks for the response. I tried again, this time using a camera with an APS-C sensor on a 80mm refractor with a .8x reducer/flattener. Plate solving still failed, however when I bumped up the 'Solver Search Radius' from 10 to 50 I was able to plate solve successfully and polar align to within 3 arcminutes.

The following night I tried again and again I saw plate solving errors again. One was a warning that there were not enough stars in the image, though to me the image showed several dozen sharp stars. (I bumped up exposure time to 20s and the error continued). Later it simply gave me a plate solving error without additional details.

My equipment, with a field flattener in place, has a focal length of 384mm and ratio f/4.8 with a settle time of 5s.

[han.k]

One was a warning that there were not enough stars in the image, though to me the image >>showed several dozen sharp stars.

That is strange. Send me a link to one or more images which fails so i can have a look. Maybe the latest nightly build of Nina could help to retrieve a solve failed image. It will save a failed image to a new directory:
https://bitbucket.org/Isbeorn/nina/issues/1133/mechanism-to-support-users-with-image

Looking to your screenshot, the stars don't look so sharp but it it should still solve.

Han

[Evan]

Thank you Han. I will try again tonight and send more information. Perhaps my stars are too out of focus. I am using an autofocuser and thought the algorithm had sufficiently sharpened them.

I appreciate the time you're taking to help me!

[han.k]

The numbers of stars look more then enough. For your setup a few seconds exposure should be sufficient. There must be a simple explanation for your problem. As usual an image tells more than thousand of words. :)

[Michael Heald]

Hello! Just following up with this.
I used ASTAP in SGPro without difficulty with my SBIG ST402 at 765x512 and 8"LX200 at a focal length of 1150mm with a FOV of 12x20 arcminutes. I used the D50 database.
I've tried NINA a few times. I get the message ASTAP warning - small image dimensions. I am binning 1x1. I tried the D80 database with the same results. I use Astrometry.net as blind solver.
Is this a warning I can ignore and is autogenerated with the small field, or is it something with NINA? Do I need to do something about it? Thank you.
Mike

[han.k]

Hi Michael,

The warning was introduced in ASTAP a few years ago as soon you go below something like 1250x900 pixels. You can ignore it. The message can't be switched off. It is just that solving become less reliable but it can work. A FOV of 12x20 arcminutes is very small. Best is to install the D80 and remove/uninstall the D50.

Is ASTAP solving reasonable reliable with your FOV?

cs, Han

[Michael Heald]

Thank you for your note. ASTAP worked well in SGPro with Astrometry.Net as Blind solver backup. Curiously, it could not plate solve M67 even when dead on with the field, even though the field had lots of stars.
In any case, I've gone from D50 to D80 and I'll see how that does with NINA.
Thank you for your help.
Mike