Plate solving finderscope

[Tan usa1]

While observing at FPOA through their 30" telescope, I realized that the current system of manually looking at start  charts and then trying to find where you are pointing is very inefficient.

So I am proposing a plate solving finderscope solution. Here is the idea

1. Start remove server to Stellarium so it can talk to NINA

2. Setup NINA to connect to camera, and enter telescope parameters for finderscope (focal length), as well connect to telescope simulator

3. Take image through finderscope, plate solve using ASTAP and then do SYNC and now stellarium should show where I am pointing

 

Will this solution work? Anybody using this solution? Any tips for this automated plate solving finderscope solution?

 

[Julien Lecomte]

Not sure this is the best forum for this, but yeah, it's totally doable, as long as you properly configure things. I don't use Stellarium, but Cartes du Ciel, connected to my mount, will show exactly where I'm pointing at any given time.

- Julien

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[Akarsh Simha]

Hi Tanveer

I've been using a plate-solving finderscope for the last 2 years, and it works well. The details of how I do it are explained here:
https://asimha.net/AltAzWorkshopTalk2021.pdf

The key thing is that if the finder scope and main telescope aren't manually aligned (which is hard to do with a camera), you can do the "alignment" as follows: you'll need to center one star or object in the main telescope and find the pixel offset (x, y) corresponding to that star in the finder scope field. It doesn't even have to be within the FOV, just having a conceptual pixel offset is enough, but I think the performance may be better if this offset is small.

Then every time you solve from the finder scope, instead of simply getting that central (RA, Dec), you will instead need to pick up the (RA, Dec) corresponding to the pixel position (x, y). If your plate solver writes a WCS header (like astrometry.net does), this is fairly simple: the WCS header encodes the rotation of the north, and the arcsecond/pixel scale and you should be able to convert it. It can also encode polynomial approximations to account for field curvature etc. In fact, I think astropy has some routines (although they may be slow) to do this conversion based on the WCS header, which should be easy to incorporate.

Solving through a 1° finder scope FOV is super fast: I need only the 4100 indexes for astrometry.net which are based on Tycho2, and they can be held in memory allowing for parallel processing. Most fields solve within 3--4 seconds including source extraction, and 0.5--1 seconds for just the solve. I've noticed that it is accurate to within 5--10 arcminutes at my eyepiece. I think the primary source of error is flexure, and I imagine most Cassegrains will have even less of a problem with this.

Regards

Akarsh

[Tan usa1]

Thank you Akarsh!

We will first align finderscope using visual and a bright star. The finder scope will be a 5" F/12 scope (also have a smaller scope). 

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[Aris Pope]

I believe Nina will only sync if you are connected to the a mount. Are you using a go-to dob??

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[Les Niles]

Different, but similar, is Celestron’s StarSense.  It uses a smartphone’s camera directly, without any finder scope, and does plate solving.  There is a one-step alignment to sync the fields of view of the telescope and smartphone finder, which as Akarsh points out is needed with any finder.  It costs $230, but you get a free telescope with that which can be a benefit, or might be a disadvantage because it comes in a big box that’s hard to sneak into the house.

  -Les