We're gonna need a bigger dither


I have been imaging recently with a 200 mm lens and STT 8300. It is being done unguided with “dither by mount” and it has run very smoothly.

The problem is that even with “extreme dither” selected, the dither is very small. It would be even worse for the commonly used 135 mm lenses.

Can I suggest one of two things to provide a bigger dither?


  1. A scale factor that would multiply the dither by a user selected amount (say a range of 1-5 - probably both + and minus).


  1. Just one more larger dither, at least 2-3 times more than the present maximum. Since “extreme dither” is already used, maybe you could call it “ludicrous dither”. :wink:


Increase the dither scale. Worked for me.


That will not work in the case. That is a PhD setting and, as I mentioned, this is “dither by mount” for unguided imaging.

PhD is not even running nor needed and, in fact, would make things much more complicated than they need to be since at 200 mm with pro-track I can take up to 30 minute unguided with perfect stars.


I would also like more control of direct mount dithering when using camera lenses for wide field work. With an ASI1600 + 16mm lens, my image scale is 43.9"/pixel, so I would need dither pulses of around 15 seconds at x1 sidereal rate. I don’t know if my EQ6 mount or EQMOD accepts pulses that long, so perhaps they could be broken down into a sequence of shorter pulses.


Another alternative for very large dithers would be for SGP to simulate a manual nudge to a random direction by the user (as if the user pressed the telescope control direction buttons momentarily).

That would be preferable to waiting for a 15 second guide pulse to complete at x1 sidereal.


Some capture software by other companies provide an unguided dither option that performs a small slew.


I am pretty sure that is what SGP does. It is the inability to increase the scale further that is my issue.


Jared has stated here that the “Direct Mount Guider” sends guide pulses, with Extreme being a 1 second pulse: Dither without guiding

A 1-second guide pulse can barely clear DEC backlash on some mounts, so I hardly consider 1 second to be “extreme”.

For the Direct Mount Guider, there needs to be a way to specify the desired pulse duration instead of only 5 hard-coded values (which are not even documented in the manual or the UI). There also needs to be an alternate method that slews or nudges.


Agreed, hard coding set values is easier but pretty inflexible and not that much easier than something like a scale factor.


The reason why it is not currently user editable for pulse length is that we’re confined to the UI that exists. So what’s a “on the edge of sane” value for the largest pulse length you’d want? 30 seconds?



You know what is going to happen - CCDMan will be happy with his 200 mm lens and then someone comes along with their 10-mm Samyang… :slight_smile:


Not sure what you mean by “UI” in this context. I assume you mean your programming framework?

As far as my specific (200 mm F.L and 5.4 micron pixel size), the 1 sec pulse (assuming that is what “extreme dither” is) is maybe 20-30% of what would be ideal, so by that standard minimal for my situation would be 3-5 sec.

Buzz is correct that sooner or later someone will want a bigger dither (135 mm lenses are pretty common for astronomy, for example) so having more dither available would be better for those folks. That is why it would be more ideal if the UI would allow a slider or numerical input scale factor.

Bottom line is I suspect that if a few more possibilities were available at maybe 3 sec, 6 sec, 12 sec, and 24 sec, that should pretty much cover it for any conceivable use, regardless of how that is implemented, UI-wise.

I would also agree with the post that stated that the dither should be better documented (and the dither by mount renamed to “direct dither”, or “unguided dither”) so as to let the user know exactly what is happening.


More just that it’s a drop down and swapping it out for another control element is annoyingly difficult with the UI framework (in a non horrible manner at least). With a slider you still have the same issue of having a min and max. The real issue is just that the current max isn’t enough.

Next 3.0 release:



That looks super! Am I correct that the current “extreme dither” is a one second pulse?


That is correct.



If we change the dither scale in PHD2 settings ?


This is for people that are doing unguided imaging and still want the mount to “fake” a dither. PHD2 is not involved here.