Is it possible with 3.3 to dither without guiding and no live stack?

[Menno555]

Like the title says
For now I still do a manual dither (random tiny manual slew every x exposures) but few months back it was suggested that with SC 3.3 that might be possible to do automatically with the help of PHD2. Mount is the Ioptron CEM25EC connected through Ascom.
I don't use/have guiding and do not use the Live Stack. I did see in the Sequencer that there are dithering commands but since using the Sequencer with the main UI active is not possible, that is not working then.

Menno

[nexusjeep]

Hi Menno,
PHD2 will not do blind dithering as it moves the guide star co-ordinates to dither and then re-centers this moved star it would have to be a feature of the imaging software to dither in the way you are describing I believe NINA and APT may have a feature if Robin is looking for what others do. Can I ask why you do not guide out of curiosity.

Cheers
Nick

[Menno555]

Hi Nick

Few months back Robin mentioned that maybe with the 3.3 version it would become possible to do a random dither using PHD2. Not on star but purely on motion. It is possible within PHD2 to use it without guide star. At least, that is what I gathered on the story.

And I don't guide for 2 reasons.
I have a Meade 8" ACF STC f/10 (2032 mm) scope, so my FOV is small. This is by choice. I do have a 0.63x reducer but don't use that much. This small FOV makes it difficult to get a good star.
And second (main) reason, my mount. I have an Ioptron CEM25EC and the tracking of that mount is just insane. I did some testing with it with f/10 on 5 minutes exposures and with manual tweaking of the sidereal tracking, the stars do not move. I even did test with a 2.5 x Barlow (so FL 5080 mm) and the stars do not move with 1 minute exposures. But for my Bortle 8 those 5 minutes are too long: max for me is 180 seconds and that is easily tracked rock steady with that mount. This together with an Ioptron Ipolar polarscope which gives excellent polar alignment.
In SharpCap I use the crosshairs and zoom in something like 400x on a star and then watching for any movement. It takes around 10 minutes to get the right rough setting for the manual sidereal tracking and start capturing. And then like another 10 minutes to finetune that setting with 0.001 increments.
Expensive mount but 0% regrets

Menno

[admin]

Hi,

I had to go off and check this, but PHD2 can only dither what you are guiding. I tried turning off the guide output so that it thought it was guiding but wasn't sending anything to the camera or mount and that definitely kills off dithering too. The reason is that when you dither in PHD, what it does is basically move the target point for the star by a random amount and then lets the normal guiding corrections bring the star back over the new target point.

The only way for this to work without PHD would be to have a separate random dithering option built into SharpCap that would use the mount's PuseGuide functionality. Something for the future maybe.

Cheers, Robin

[Menno555]

Okay, thanks Robin.
I did check the sequencer for something with the mount steering (together with a delay and repeat) that maybe can help with this. For me it's not important that the whole field stays in the same place, I crop always anyway.
So I did find "Offset the mount position by RA=x, DEC=y". Those values which go from -24 to +24, are those degrees? Because that would be way too much of course then
And if those values are degrees, would it be very hard to add minutes and seconds in the Sequencer?

Menno

[admin]

Hi,

I suspect that the values will be hours in RA and degrees in declination as those of the standard units. You should be able to enter fractional values – for instance -0.0001. Quite how accurate the mount will be making such small movements, I have no idea.

Cheers, Robin

[Menno555]

Thanks Robin

I did try fractional values but that didn't work ... but forgot that SC takes my PC decimal settings, so it will not work 0.0001 but with 0,0001 and that works.
Okay, I will try that. The prediction is that it around 4 weeks or so there will be at least half a night of clear skies, so I'll report back then :p

Menno

[nexusjeep]

Menno if you are anything like me that 1/2 a night will also coincide with a full moon directly in front of the target and most of Elon Musk's starlink satellite's.

Cheers
Nick

[Menno555]

Ah yes, of course ... something like that will happen for sure :p