Image Solver Problem w/ Wide View Dataset

Reggie Jones

Hi Adam.  Working on the Telescope Live M78 to Bogeyman dataset.  Have a combined RGB image and I've only executed DBE with yet.  Next step is to use Image Solver to get an astrometric solution so I can  use SPCC.  I've used the original coordinates in the FITS Header, coordinates for Barnards Loop, coordinates for NGC 2071 (not quite the center of the image) and coordinates for the star HD 38856 (little closer to the center) and all have not worked.  The script runs very slow through many iterations trying to get an acceptable putative star pair.  After about 30 mins, I stopped the process each time.  need your thoughts on what I need to do differently...

I've attached some reference info for your info.  Here is also a link to the image data.  

https://www.dropbox.com/scl/fo/9u150c02vyhjgh2ha4k0e/h?rlkey=qn488dj1i450dkf8j1r4umgj7&dl=0

While this script has been fairly straightforward to use, I have problems using it similar to this one - I did not see a specific tutorial on this script in your library but I'd be really happy if you could direct me to one if it exists.

Thanks

Reggie

BlockHead

Reggie,

This image solved without an issue. 

The coordinates provided in the file are fine.

There is only one other number to contend with and that is the focal length or platescale.

But ask yourself... which value has great fine control? I hope you agree it is the focal length since it has a magnitude of HUNDREDS. A 10%-20% error of focal length is enough to cause issues with widefield images. 

The actual focal length of the optics is 530mm. I would bet money they are using a focal reducer and you did not take that into account. A typical 0.66 - 0.75X  focal reducer would do this. Do you see? You used 360mm as the focal length.  

So here are the lessons...

1. I solved the issue in 20 seconds because I saw coordinates that at a glance passed the sniff test.

2. I knew if there an error it had to be in the focal length/plate scale.

3. Between these two values..I should change the focal length.

4. I ASSUMED NOTHING. I do not believe published values. I didn't even look. I simply adjusted to what I thought the image looked like (looked similar to the 500mm Tak Epsilon). So I inputted that.

5. Solved with no issues..because that is close enough.

I would bet money your values are not accurate and if you do look at the published values... they will agree with the 530mm effective focal length (or platescale of 1.46"/pixel)

-the Blockhead

Reggie Jones

Thanks Adam.  I did not even consider the focal length I used would be incorrect for this equipment setup because of the use of a focal reducer.  I took the equipment setup at face value from the Telescope Live website and used a focal length of 387mm.  Just to confirm you'd have won big on the bet, I checked and got the specs for this optical tube from Takahashi and you're spot on (attached).

Now I need to rethink the correct equipment settings I've been using for the other TL setups I use.  I should have thought of all this in the first place but it's a great lesson to relearn.

Just another fine example of why I am a member of your site.

Thanks as always - Reggie