Plate solving using the 585MC pro w/ LX200 12"

[geoscoping]

Hello and thank you for taking your time to read this and maybe advise me on how I am suppose to be doing this. I'll try to make it as short as possible.

I went out on two separate occasions with my scope this past week, great clear skies and everything. I leveled my tripod and put my scope onto it. Hooked everything up and started SharpCap up. I got it to connect to my camera and mount flawlessly and began the process of bringing the star into focus. I got a bunch of stars into focus and hit the plate solve only option. After just a few seconds it found 100 stars (or so it said) but couldn't find any solutions so it failed. I tried moving the scope to find another field of stars and still it would say it found a number between 90-100 stars and would never find a solution.

The only time it did was the second night when I installed ASTAP and used that as my solver. I got it to solve twice the whole night. When it solved those two times, the stars were almost streaks across the camera and I could never get it to solve and move to a target.

Things I tried:

1) Longer exposure times, up to 5mins ( I know but I was desperate)
2) Higher gain both with longer and shorter exposure times.
3) Focusing my scope to find different stars other than the ones that were streaking across my scope, even when I was sure I was looking at stars on the screen in the picture it would say not enough stars were found and not even give me a number to how many were.
4) Moving my scope into a huge field of stars I could see with my bare eyes. Nothing.

I would appreciate any help and advise on this.
Thank you

[admin]

Hi,

the issue that you are running up against here is the small field of view of your setup - combining the ~3000mm focal length of the LX200 12" with the (relatively) small sensor of the IMX585, you get a field of view of 0.21x0.12 degrees, which is too small for the current version of the SharpSolve plate solver built into SharpCap. Astap might succeed at this size if you have installed the largest (D80) database, but if you look at the Astap web page, you can see that the effectiveness of even the D80 database fades out below 0.15 degrees FOV.

Adding more stars by longer exposures isn't helping, since the problem is the density of stars in the plate solving index/database. In fact longer exposures are opening you up to problems like trailled stars due to tracking not being perfect.

For now, the best bet is to install the Astap D80 database (if you haven't already) and see if that helps. I should also say that I have an update to the built in SharpCap plate solver in the works that would probably help in this situation - within the next few weeks I will be releasing an update that supports a new, ultra-high-res index file that should work at the field of view you are using (see this post for more info : viewtopic.php?p=49174#p49174)

cheers,

Robin

[geoscoping]

Thank you so much! I look forward to the update and I will try astap again soon to see if maybe it will work again and work completely.

You mentioned tracking and that had me thinking of a question. Should I be tracking a star or something to do plate solving?

[Menno555]

Plate solving can be done without tracking or following if your exposure time is not too long.
If you have a fast scope like an F 2 there will be no problem. Do you have a F 10 for example, then you really have to go shorter with high(er) Gain. Just experiment with exposure times and gain. The moment your stars are showing streaks, that's a too long exposure time for good plate solve.

Menno

[geoscoping]

Thank you!

[geoscoping]

Plate solving can be done without tracking or following if your exposure time is not too long.
If you have a fast scope like an F 2 there will be no problem. Do you have a F 10 for example, then you really have to go shorter with high(er) Gain. Just experiment with exposure times and gain. The moment your stars are showing streaks, that's a too long exposure time for good plate solve.

Menno

Would a focal length reducer help? I have a .63 reducer I could put on the scope in between the backend of the scope and the focuser assembly

[Menno555]

In my previous reply I missed that your equipment is mentioned in the topic title.
Like Robin pointed out, that gives a very small FOV. And indeed, if you don't track or follow, changes are your exposure times will be too long before there are enough stars showing for a plate solve and will show streaks.

A reducer could help. Below is an screenshot from https://astronomy.tools/calculators/field_of_view/ , a site where you can see an approximate FOV with combinations of equipment.
The red rectangle is your setup without reducer, the purple rectangle with 0.63x reducer. So it certainly will help to get more stars and a bit shorter exposure times.
Also, my scope and planetary camera combo (the orange rectangle) gives a same FOV as you with reducer and I can plate solve fine with that. But I use tracking.
So I think it's really a case of trail and error: try the reducer, go to a position close to your object where there are a bunch of bright(er) stars in your FOV and try a plate solve with the reducer.

Menno

Clipboard_07-23-2025_02.jpg (296.14 KiB) Viewed 1776 times

[geoscoping]

Update:

I used the 63 reducer and I got plate solves almost every time now while using Sharpcaps plate solver. I was still not able to get it to goto the target.
It would plate solve the first time, move to get the next one and fail on that one. I am wondering if this has to do with the fact that I am not polar aligned? or something like that. I was thinking however, I also didn't choose the tighter FOV when trying to do the solving, maybe that had something to do with it. But I didn't think about that until I had everything packed.

I need to work on getting PHd2 working as well. I couldn't get it to move my scope, it would lock onto a star but wouldn't move the scope to keep the star centered. But that's a question for another forum lol.

Overall, I look at last night as a success. At least I know what I'm looking for in the camera to do plate solving and I know my equipment is setup correctly so far. I just need to get this scope on the wedge.

Clear Skies
-George T.

[Gfischer]

Hi george this is george,

I think phd2 only works on equatorial mounts. Once your on a wedge you should be good.

[geoscoping]

I wasn't sure if that was the case but that does make sense. Thank you George!