Question about the new Solar Mosaic Function

[oamaruastro]

I was so excited to try the new solar mosaic function the other day, and on my first attempt to use it, it worked perfectly. But when I tried again today, it kept telling me, after I aligned with the crosshairs, that my mount was 7.5 degrees off and it might affect performance. Sure enough, when I set it to go, when it slewed to what it thought was going to be the top edge of the sun, it was quite a bit lower than that, and throughout the 8-image process it got further and further off-target. I have not been polar-aligning my mount before doing solar imaging, but try to get it fairly close to alignment with the pole--is this the reason for the errors? Are we really supposed to be polar-aligning for solar imaging to work properly?

[admin]

Hi,

I wouldn't have expected a big error from a 7.5 degree offset on the mount (someone has been deliberately offsetting by a few degrees to avoid 'pointing at the sun' warnings from their iOptron software). Maybe it depends if the error is in Declination or RA - I haven't tried following through the calculations for each sort.

SharpCap corrects for the offset by adding the known position error to the co-ordinates for each GOTO movement - that isn't exact across the whole sky globe, but since you are just moving the telescope in a box not much bigger than 0.5 degrees on a side, it should be good enough for the mosaic.

One suggestion I can make for rough polar alignment during the day is to firt tell the telescope to GOTO the sun, then bring it into view using the Alt/Az adjustments that you would normally use for polar alignment. That will get you polar alignment to within the accuracy of your normal GOTO movements (probably better than 1 degree).

cheers,

Robin

[oamaruastro]

Thank you for the reply. I did not GOTO the sun using Sharpcap--I used the AM5's own controller to do the GOTO, then adjusted with the hand controller. Would doing the GOTO in Sharpcap be a better approach (and if so, I did not realise that Sharpcap had that functionality, so I'll have to look for it). It's entirely possible that I also did something boneheaded to make it work so poorly yesterday. Next time we have a clear day and I'm not busy with other stuff I'll give it another go. But many thanks for adding this feature--I've been wanting something like this for a while now!

[admin]

Hi,

yes, there are buttons in the Mosaic tool to get SharpCap to move the mount to the Sun/Moon - they are at the bottom left of the window - see the screenshot here : https://docs.sharpcap.co.uk/4.1/#Mosaic%20Alignment

I don't think that will make much difference though, as SharpCap should work out the offset as part of the alignment procedure.

One thing that I forgot to mention is that once you are past the alignment stage and adjusting the panel overlaps, etc, there are four buttons that you can use to make SharpCap GOTO each of the 4 edges of the Sun/Moon. Using these should place the edge of the solar/lunar disc in the middle of the field of view (SharpCap uses the alignment results to calculate the correct co-ordinates to GOTO taking account of any mount error). Those buttons are basically there to test the alignment - if they don't get the edge of the disc in the middle of the camera then it's worth going back and retrying the alignment. See https://docs.sharpcap.co.uk/4.1/#Adjust ... 20Settings

Hope this helps,

Robin

[oamaruastro]

Thank you again for the replies to my question. This morning I had another try with the mosaic tool, and again it told me that I was something like 7 degrees off (or something like that), and that I might want to realign. But when it started to shoot the mosaic panels, it seemed to be going pretty well at first, though toward the last few panels it went a bit off.

Is it possible to do the three-step alignment process and then have it go to the first panel and ask if it is correct, giving an opportunity to adjust it by slewing to align the intended FOV with how you slew the scope? It is a bit of a salve for a bonehead like me, but it might help to make the system work a bit better?

[admin]

Hi,

it might be possible to have a test run where it went to each panel and then didn't take any images... That might help check. That was kind of what I was expecting the four buttons that goto the top/left/botton/right of the disc to do - if you try each of those and it puts the edge of the disc in the center of frame then the alignment is good.

cheers,

Robin

[oamaruastro]

Thanks, Robin,

So if I do a test run, and it's not quite right, is there a way to adjust it within the testing process, or do you have to start the alignment over?

Thanks,

James

[admin]

Hi James,

really you have to do the alignment over again, paying good attention to centering and approaching the align points from a consistent direction to avoid backlash causing errors.

The problem is that while you can tell if the GOTO position is off from the target shown in the UI, it's not easy to decide how *far* off in a way that is accurate enough to help refine the alignment. The choice of one of the four edges of the disc as the align point is essential because that point is easy to pick out in the image and isn't subject to interpretation or guessing about where it is.

cheers,

Robin

[oamaruastro]

Thanks again for the replies and the help, and sorry for what are probably very basic questions. It seems that I have a 50:50 record of getting the mosaic function to work properly or not, and wonder if my approach for slewing to the sun could be the issue. I have generally been using an ASIAIR to find the sun, and then once it's centred in my FOV I disconnect from ASIAIR and connect to my laptop and then use Sharpcap to do my shooting. Is there a better way for me to slew to the sun and give the Sharpcap function a "leg up"?

[admin]

Hi,

that approach should be fine - the mount should remember the co-ordinates when you switch between one device and the other, and SharpCap should cope with the offset between the true co-ordinates and the mount co-ordinates anyway. You could try using the 'Goto Target/Co-ordinates' from the tools menu in SharpCap, or the 'Goto Sun' button in the mosaic planner window, but I don't think that will make much difference.

I am writing some code at the moment that might allow 'automatic' alignment in the mosaic tool - just get it so that SharpCap can see the edge of the solar disc and one button press should run through a fully automatic process. I don't know if it will work for sure yet, but it seems promising and may improve accuracy. Just need to finish the new code then get some clear sky... Maybe March or April then

cheers,

Robin