A thought experiment

[powerlord]

I'm wondering if anyone has every done this, and if not, if anyone wants to, and even if they don't it's interesting to think it through...(to be clear I AM NOT GOING TO DO THIS).

Seems to me testing, tuning guiding is tricky in that you can only do it outside with clear sky, etc - and that's when you want to be imaging.

And if, say you want to have a business of tuning mounts, you want a reliable way of doing it all day every day ?

How about this:

- shoot some wideish field 4k60 footage of east or west (doesn't need to be, just an idea) on a good clear night. fov should be chosen to ensure stars resolve to a decent FWHM (2?). Note day, time. It should be at an AZ that is equivalent to where you could put a tv/monitor on your wall 3 feet or so from the mount..

In house, mark dot on ceiling precising north of a position on floor the correct distance back to reasonably accurately represent polaris (this all works best if your room is orientated N/S)

Position tripod so that polaris centred. and set mount to date and time of video footage.

Mount tv to wall in east or west in AZ location matching the footage.

calculate 'FL' of guidescope by plate solving, pointing it at tv (i.e. won't be actual FL, but will be whatever it works out to.

Now, setup mount, goto or adjust direction to point main scope at tv, and plate solve.

Now should be tracking. Set up/calibrate PHD2.

Start guiding. It should now be guiding based on the tv.

It's not that important to be super accurate here I'd imagine as the point that we are trying to test is how good  the guiding can be, not how good the PA is, etc.

The benefit it at least seems to me, is once you do all the above once, and record positions on floor, ceiling, FL for guidescope, tv/monitor wall position.. you can now set it up again any time very quickly.

Thoughts?

Or is there a simpler way ? home planitarium ?

 

 

[scotty38]

What about focus?

[Astrobits]

1 hour ago, scotty38 said:

What about focus?

That was my first thought too.

Nigel

[Astrobits]

Simple optics. 1/object distance +1/ image distance = 1/focal length.

If you are dealing with a telescope of focal length 2 meters then putting the object ( TV screen ) 2 meters away results in an image at infinity. OOPS!

If you can put the TV screen 4 meters away then the focus will be 4 meters from the scope. You will need more than 8 meters of space and how to rigidly connect the sensor to the telescope over 4 meters of length will be a problem.

It might work for very short focus telescopes.

Nigel

[AstroKeith]

Another 'problem' is the angular size of the pixels on the tv. They are going to be 25 arc sec at 8m range. Not much of a test for guiders!

[powerlord]

yeh focusing the scope and guidescope would be tricky for sure. with an OTA. But we are trying to test guiding here, not telescopes. Just use a camera ? a DSLR and regular lens will have no issues focusing on tv ?

[powerlord]

2 minutes ago, AstroKeith said:

Another 'problem' is the angular size of the pixels on the tv. They are going to be 25 arc sec at 8m range. Not much of a test for guiders!

offt. ok that's an issue. what resolution tv, and size of tv is that based on ? For example at 2m, a 4k ipad pixel size is going to be massively smaller than say, a 1080p 42" tv at 2 meters.

is there a combination that would work I wonder ?

 

[AstroKeith]

12 minutes ago, powerlord said:

offt. ok that's an issue. what resolution tv, and size of tv is that based on ? For example at 2m, a 4k ipad pixel size is going to be massively smaller than say, a 1080p 42" tv at 2 meters.

is there a combination that would work I wonder ?

 

That would be better - at 4m I make it 5 arcsec per pixel (iPad Pro at 264 pixels/inch).

So put the iPad 20m away!

[powerlord]

hmm, ok still a problem then. Oh well. 

[wimvb]

I guess that’s why mount tuning companies rely on feedback from clients rather then verifying in the field before shipping the mount back.