Unguided Dithering in 4.09357 64 bit

[CraigG]

Hello All-

I have a question regarding the randomness of pulse signals sent from SC to my mount via ASCOM.

I recently migrated to 4.0 and was excited to see an option to dither frames without guiding via ASCOM. I've tried to keep this rig as simple as possible so it's sans guidescope or other extras. It's a ASI 2600mc riding on an iOptron CEM40ec and I've had good success manually dithering up to now by pressing buttons at the right time in iOptron's Commander software.

SharpCap connects with the mount via ASCOM to iOptron's Commander software just fine and I'm able to make mount movements with the directional arrows in the camera control box. I've set the dither interval to 4 frames (120 second subs) and up to 10 pixels movement. I have also set the CEM40ec to accept guiding commands.

What I'm finding is even though a dither movement occurs as scheduled, say 3 pixels, the movement is basically along the same track that the mount was moving before the dither. The randomness of the dither doesn't seem to be there as you would expect when guiding with PHD. The result of the continued straight line movement is of course walking noise. Checking and unchecking the 'RA Only' box in Settings makes no difference in dithering response.

So looking for any suggestions on how to promote more randomness in the dither process. Should'nt I expect to see pulses that take the mount in different directions?

Thanks everybody!
Craig

[admin]

Hi Craig,

the first thing to do is to check the SharpCap log - every dither movement when you are using that mode should give a log entry along the lines of

Code: Select all

Random dither of (1.5,-3.7) arcsec; rates are {some numbers}, pulse guide times are (1.221,3.453)s

Where there are two numbers together in brackets, the first is the RA movement, the second the Dec movement. If one of the numbers is always zero then we have a problem that the dithering is only moving in one direction because that is what is being requested by SharpCap. However I expect that's not the case, and that for some reason the mount movement isn't quite doing what we hoped. It would be interesting to see your log just in case anything is amiss. Also, try increasing the movement amount for dithering significantly, in case for some reason movement in one direction is slightly 'sticky' and doesn't start straight away.

cheers,

Robin

[CraigG]

Thanks Robin...always good advice to check the log! Depending on what it tells me I'll try bumping up the movement to see if that helps. If not, it'll be on to the iOptron forum.

Really enjoying 4.0 by the way!

Best wishes,
Craig

[CraigG]

Hi Robin-

Took a look a the log and there are XY pulses showing in the dithering function. Since you expressed an interest in seeing the log I'm sending it along. I guess I'd like to know if you see anything that might be the cause before I pursue a possible issue with the mount.

Thanks so much!
Craig

[admin]

Hi Craig,

that looks kind of OK as far as I can see in the log - the guide rate of 0.00208 degrees per second works out to be 0.5x sidereal rate, which is about typical, so the pulses of ~1 second or so should move about 7-10 arc seconds. There are only 2 dither movements in the log, but the Dec direction looks different in both of them. I have just checked the code and as far as I can see it should correctly send the commands to the mount after logging the information about the dither movement.

Next step would be to capture a new log but with the option to log additional mount communication info turned on (logging page of the settings) before opening the camera. This will log the exact commands sent to the mount - we should see two 'PulseGuide' commands for each dither (one for each direction).

cheers,

Robin

[CraigG]

Very good Robin. Thanks for taking a look and I'll try your suggestion next time out.

Cheers!!!
Craig