Dither only (no guiding) using ASCOM mount pulse guiding

Discussion of using SharpCap for Deep Sky Imaging
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neilbarber
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Joined: Wed Oct 27, 2021 8:59 am

Dither only (no guiding) using ASCOM mount pulse guiding

#1

Post by neilbarber »

I'm having a job to understand part of it. It's in the Sharpcap settings under Guiding. I am using 'Dither only using Ascom mount pulse guiding' I'm having a job to understand the settings in there. I have the HEQ5 with the WO Z61ii & asi533mc. It's the first 2 boxes that I'm have a problem with. At the moment, without guiding with PHD2 or any other program I can get 120sec to 180sec exposures without the stars elongating. I have 'Max dither step' set to 10 and 'Settle Threshold set to 2 (Oh I have the Minimum Settle time at 6 sec.) but I'm getting some star trailing in some of my image ( dither every other image @ 120sec exposures). Have I got these settings about right and should I expect a few shots to have the star trails.
Thanks for any help.
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Re: Dither only (no guiding) using ASCOM mount pulse guiding

#2

Post by admin »

Hi,

ok, so when you use this option, SharpCap stops imaging, sends a small random pulse guide command to your mount to make the dither movement and then starts imaging again.

The only settings that apply if using dither only guiding are

* Dither in RA only
* Maximum dither step
* Minimum Settle time

The maximum dither step is measured in *arc seconds*, not pixels, when using this option. SharpCap is simply asking the mount to move for a certain period of time and has no idea how many pixels that will be. Most mounts can report their pulse guiding movement rate, which will likely be sidereal rate (or maybe half of it). SharpCap will calculate the length of time needed based on the distance to be moved and this movement rate and then send the pulse guide command for that duration.

If you are seeing trailing then it's possible that you need to increase the minimum settle time value. If there is a bit of backlash in your mount movement then a dither in -ve RA may be followed by a short period while the mount takes up the backlash - if you start the next imaging frame during that period then you may see a bit of trailing. Also, make sure you are using the latest SharpCap 4.0, as I have made improvements to the code that keeps frames captured during the dither out of the stack in the last month or so.

Hope this helps,

Robin
neilbarber
Posts: 13
Joined: Wed Oct 27, 2021 8:59 am

Re: Dither only (no guiding) using ASCOM mount pulse guiding

#3

Post by neilbarber »

Thank you Robin .... have the latest version so that's ok. I'll try to extend the settle time and see how we go. A lot to take in for a 70 year old just starting...lol. Must work out how to use PHD2 as that must help a lot but that's more to get my head around
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