Not enough stars to plate solve

[Cybermystic]

I have 2 observatories, one with a C11/Hyperstar on a wedge, the other with an array of refractors on a Paramount. I need to polar align both setups. I thought the Hyperstar rig was going to be impossible and tackled it first. I got "Excellent" polar alignment in under half an hour. Two things were in my favour (I now realise) - an 11" mirror caught plenty of photons so that Sharpcap could easily see enough stars to plate solve, and being on a wedge, rotating the scope by 90 degrees leaves the scope pointing through the dome aperture - so no issues there.

Now we come to the refractor array. The first issue is that Sharpcap does not appear to be picking up enough stars for a plate solve (it has done so sporadically, but not well enough to continue). The refractor is a Sky90 with a Starlight Xpress M26C OSC CCD. MaximDL shows plenty of stars in the frame with a 10s exposure and bin 1. Sharpcap doesn't show enough stars even with bin 2 and up to 20 s exposures. I am guessing this can't be right. There is an additional problem. How do I swing the GEM mount through 90 degees AND keep the scope lined up through the aperture at the same time?

[Cybermystic]

I just saw on another post to increase the sensitivity (it is at the default 75 and I didn't try this). So I will give that a go next outing, but if there's anything else I can try, please let me know. I am assuming that there really should be no problem with a Sky90 refractor and a Starlight Xpress M26C OSC CCD??

[Menno555]

Hello and welcome

In the SharpCap settings under Plate Solving, do you have the Focal Length specified? If SharpCap is used for multiple scopes, this setting should be set to Do not use.

Menno

[Cybermystic]

Thank you Menno - I think Do Not Use looks like the default (?) and I didn't change anything in there - but I'll go down to the observatory and check.
Greg

[Menno555]

Greg, I forgot to mention the sensitivity. By that, did you mean the Star Detection Noise Threshold in the Plate Solving options?
If so, you could indeed try to set that lower to, for example, 50 (which is the default in my SharpCap).

Menno

[admin]

Hi,

the focal length setting will have no effect for polar alignment plate solving, but turning up the sensitivity or using a display stretch may help - see

https://docs.sharpcap.co.uk/4.0/#Stuck% ... enabled%3F and
https://docs.sharpcap.co.uk/4.0/#!2!Min ... %20Stretch

There is no need to move exactly 90 degrees - anything from about 30 degrees or more of rotation should work, and you can start in any RA position (the home position is just a nice convenient starting point). This may help you arrange the whole procedure to work without moving the dome slit.

cheers,

Robin

[Cybermystic]

Thank you Robin,
I will give both of those a try next time I see some clear sky (could be a while).
Greg