10 replies to this topic

[dmilner]

I've been doing astrophotography for several years now. I initially started with the AVX mount then bought a Paramount MX+ for a more permanent setup. I've used the MX+ for probably about 7 or 8 years while the AVX has sat in my garage. Unfortunately, the observatory I had the MX+ set up in got to where it wouldn't open anymore and I've taken the mount down and put it into my garage as well until I get another one built. Fortunately, I still have my AVX on the original tripod which is mounted on a Wheeley Bar and can easily be rolled out onto my driveway.

However, since it has been so long since I've used the AVX, I've had to relearn how to use it. I've got the Polemaster attached to the mount so I can polar align just fine. I've also got the StarSense Autoalign mounted onto the SCT. My problem is that even though the polar alignment seems to be pretty accurate (as indicated by the Polemaster program), I can not get the StarSense calibrated to the optical axis because I can never figure out what star in my field of view in the eyepiece StarSense thinks I'm looking at even if I move the OTA in a spiral pattern to find a bright star. The axis of the StarSense must be relatively far off the optical axis because after I think I've calibrated on the correct star and redone the autoalign, I still can't get the OTA to line up with even the moon (doesn't even appear close to the field of view).

While I'm sure I'm doing something wrong, I've thought about attaching one of my ZWO cameras to the OTA instead of an eyepiece and plate solve to determine where the OTA is actually pointing (what coordinates is the center of the image). Then from there move the OTA via the hand control until the plate solve indicated I was positioned on the correct star and then continue the calibration and autoalign process. Does this sound reasonable or am I thinking about this incorrectly?

[DirtyRod]

The AA sounds like a reasonable path although using a really big and bright target like the moon should be enough to get your OTA, finder, and the SS aligned and calibrated to then refine it on Vega, Arcturus, etc.

[Notdarkenough]

No, you can't reverse engineer an SSAA calibration! I have tried doing the same thing with my Evo 8HD. It came with StarSense, I used it for years and loved it.

 

As I got into imaging, I upgraded the Evo to a CEM70. For the first time in several years, a few months ago, I got the 8HD back in the Evo for some beginners planetary imaging. By this point I had blahbity blah, and moved the SSAA mounting point, etc. The upshot is my original SSAA calibration was no longer accurate. I also don't have a good finderscope as I always used the SSAA. I made several attempts to do a new SSAA alignment and calibration, using an ASI camera instead of the eyepiece as my eyes have gotten worse. No joy. Rigged up guide gear and used that to platesolve, successfully. But there is no way to feed that plate solved solution back into the StarSense camera.

 

I missed my window in March for the excellent planetary opportunity. My next effort will be to start over; get a good finderscope, set up with eyepieces and someone who can see well, erase the stored SSAA calibration, and try again. I have been using the 8HD for DSO stuff for those years, and planetary needs a different approach. 

 

Sorry.

[mlord]

I can not get the StarSense calibrated to the optical axis because I can never figure out what star in my field of view in the eyepiece StarSense thinks I'm looking at ..

StarSense AutoAlign (SSAA) doesn't "think you are looking at" any specific star.  It internally plate-solves for the view it has of the sky, which may or may not have a star at the centre.  

 

StarSense Calibration is the firmware/software means of accounting for a slight offset between the centre of view of the StarSense Camera, and the centre of view through the actual telescope.

 

It has been reverse-engineered long ago, and consists simply of the pixel coordinates within the camera view, where the offset for the telescope centre would be.  The default is 640,480, as the camera resolution is 1280x960.

 

The semi-automated Calibration procedure used with SSAA is designed to figure out that offset without being too technical.  But easy as it can be, it is still demanding of attention to detail.  UP and RIGHT for the final movements of the skyward end of the optical tube -- that's the biggest mistake that most people probably make.

 

Cheers

[deansjc]

I hesitate to contribute here but.... there is a calibration step in the SS routine for SS to "know" what object your scope is pointing to (= axis).

Isn't this sufficient for purpose?? Perhaps I've missed your objective?

[mlord]

.. there is no way to feed that plate solved solution back into the StarSense camera.

The "way" would be thus:

 

Align with StarSense.

Do a "go-to" to a decently bright star.

Note where in the eyepiece camera view that star is located.

Now centre the star in the eyepiece camera view.

Measure the difference between the initial "go-to" position, and the centred position.

Scale that difference to be an offset within the SSAA camera resolution of 1280x960.

Issue an AUX command to save that "Calibration offset" to the SSAA (this is a known command).

 

All doable, just nobody has yet automated it.

Edited by mlord, 15 June 2025 - 03:58 PM.

[dmilner]

Align with StarSense.
Do a "go-to" to a decently bright star.
Note where in the eyepiece camera view that star is located.
Now centre the star in the eyepiece camera view.

I understand the procedure for calibrating the StarSense with the optical axis. My problem is being able to find the bright star after the "go-to" so I can "Note where in the eyepiece camera view that star is located." If I can't even find the star in my field of view or anywhere close, how can I center the star in the eyepiece camera. That's why I was hoping I could plate solve to determine which way I needed to move the mount so that the star would show in the field of view and then be able to center it. I've even tried, as DirtyRod suggested, of going to the full moon thinking I'd at least be able to see the glare and therefore know which direction to move the mount...but no such luck.

[mlord]

I understand the procedure for calibrating the StarSense with the optical axis. My problem is being able to find the bright star after the "go-to"

Use a wider-view eyepiece.  35mm perhaps.

[maniack]

I understand the procedure for calibrating the StarSense with the optical axis. My problem is being able to find the bright star after the "go-to" so I can "Note where in the eyepiece camera view that star is located." If I can't even find the star in my field of view or anywhere close, how can I center the star in the eyepiece camera. That's why I was hoping I could plate solve to determine which way I needed to move the mount so that the star would show in the field of view and then be able to center it. I've even tried, as DirtyRod suggested, of going to the full moon thinking I'd at least be able to see the glare and therefore know which direction to move the mount...but no such luck.

You should attach a finder scope of some sort to your OTA, and align it with the optical axis in the daytime on a far away object. A basic red dot finder is fine for this. Then you're able to find the bright star at night time by centering it in your finder, then centering in your eyepiece.
 
The manual alludes to this:

 

USING WITH A FINDER

Although StarSense replaces the need for a
finderscope, you may still wish to use a finder for
quick reference, or to assist with the one-time center
calibration of the StarSense camera and telescope.

[speedster]

You might replace the eyepiece with a camera and proceed through the SS calibration until it asks you to pick a star.  Pick one and then use NINA, or other software, and slew and center the coordinates of the star.  When NINA is done, finish the remaining SS calibration steps.

[Notdarkenough]

I tried that with SharpCap, but it didn't work for me.