Dithering 10micron mount

Sequence Generator
1

Hello

I do not guide at F840 with my 10micron mount. Stars are pinpoint sharp with 5min subs without dither.

If I activate dither in SGP:

  1. Guiding interface>Direct mount guider
  2. Dithering options>Dither=0,1s or any other higher value
  3. Settle at < 0,10s
  4. For Xs

I always get trails on the brightest stars, as if the sub will start before dither will end, or as if sub still active when dither begins. Longer dither time => longer trails. Increasing settle times or reducing settle pixels does NOT change anything.

I have installed the latest version of oficial softwares, drives and firmwares:
SGP 3.0.3.151, ASCOM 10micron 1.4.2.0, ASCOM Platform 6.4 SP1, Mount Firmware 2.15.14

Thanks for your help
Martin

2

Martin, you probably have done it but in case it may help, this is my setup.

I do not see the same parameters that you mention on my SGP versión. I do not have any space to write 0,1s as you can see on the included drawing.

In my setup, “For 4 sec” are enough for autoguiding to settle. You have to have a check mark on the square.

With 4 sec I do not get any trails.

If still does not work increase your “Settle” value to 0.2 pixels or more and see if this improves your results.

I think to settle at <0.1 is hard to achieve at least with my mount.

Good luck

Renan

3

Hi Martin

I have a GM1000HPS in my home observatory and I use direct mount and dithering and have not seen the star trailing that you mention, although I have not yet upgraded to the latest SGP release .151 but am using the version before.

I use a delay time of 2 seconds set in the Sequencer so there is a pause of 2 seconds before the next image is taken. This is different to the ‘Settle’ setting in the Auto Guide tab in the control panel. This should solve the problem you are seeing.

HTH

Barry

4

Hello Renan and Barry! Thanks for your answers!

My parameters at Dither are different because I have choosen “Direct Mount Guider”. I have no guider. The parameters at Settle seem to have no effect on the (bright) star trails. Below are some examples of my trails at the same star with short (0,1s) and longer dither durations.

image
image image

Barry, yours is a good point, will try it next chance and report.

Martin

PS.: Ken, could you please confirm if the Settle parameters have no effect when using “Direct Mount Guider” ? In that case they could be shown greyed out.

5

The settle parameters should still be in active for the Direct Mount Guider. If you can post a log I can verify.

Thanks,
Jared

6

Here is the link to my log file
https://1drv.ms/t/s!AuflUIwNAnYhoXDR-eRnc9KA5IBX

Thanks
Martin

7

Martin - just a thought, I used to get very similar appearance stars with a GM1000 during model making on the plate solve images. That was on an old level of firmware, where the mount was still adjusting itself several seconds after a slew.

8

Hi Martin,

I am curious to know whether the same would happen when you use Per Frejvall’s ASCOM driver instead of the 10Micron 1.4.2.0. This reminds me of an issue I had in Maxim DL, not in SGP, when images were taken during nudging for calibration.

Juergen

9

Martin

Just picking up on Juergen’s point, I use Per’s ascom driver and not the 10 Micron one.

As well as my home observatory’s 10 Micron mount, I share two 10 Micron mounts with my imaging partner in Spain. We have used one unguided for a year with SGP and Per’s driver, also dithering, without observing the trailing you have.

HTH.

10

I run 2 GM2000’s with the official 10 Micron driver, one from a friends home and the other at the same site you are Barry. I have no problems with trailing on any of the setups.
0.1s is a very little time to settle, i set it to 2-3s and never had problems so i suggest you increase your settle time.
I will also advice you to both update your firmware and to the newest official 10 Micron driver. I found this combination fixed some problems regarding refraction updates.

11

Martin
I agree with @Xplode the latest firmware has new functionality and refraction data can be fed directy into the mount (eg using MGBox) and I too have found this helps with unguided performance.

Barry

12

Thanks for all your comments.
Drivers and software are already the newest versions.

@Xplode; settle is 0,1pix and 5s, not 0,1s. I think this combination should be enough to settle before the next image. In theory, if I did understood the meaning of the pix value, increasing it should be counterproductive to my problem.

How many seconds should I dither at FL840 ?

Jared could you take a look at my log file?

This weekend I want to make more tests and report.

Thanks for your help!
Martin

13

I must have misread your first post.
5s settle should be more than enough if your OTA is a stable design, but i do suggest you test both shorter and longer settle times to see if there is a difference

I’m 99% sure the pixel value has nothing to say for dithering with an unguided mount, why?
Because SGP is normally using PHD to measure that value with the image from the guidecamera, when doing unguided there’s no way to measure that value.
When setting a dither value remember to also take into account the autoguide speed of the mount (i assume the dither happenes at autoguide speed)

14

It’s certainly settling after the dither. The distance is erroneous and can be ignored when using direct mount dithering. Your “distance” is always 0 as we can’t measure it.

[12.05.18 02:26:09.574][DEBUG] [Sequence Thread] Distance is below 0,1, starting timer…
[12.05.18 02:26:14.740][DEBUG] [Sequence Thread] Distance stayed below 0,1 for 5 seconds, done settling…

You’ll also notice that there is about 5 seconds between those timestamps.

Thanks,
Jared

15

Hello Jared,

I got rid of trails now, but noticed that the image moves a lot in the frame and brings the object very near of the image border.

I use 0,10s dither, I think the pixel displacement should be very small with that small value or not?.

What does this 0,10s actually mean? That the mount will move for 0,1s?
At what speed does the mount move while dithering?

I can send you my log file because it does not fit here (3MB)

Thanks, Martin

16

We send a guide pulse for 0.10 second. The rate is likely set in your ASCOM driver or the guide rate of your mount. But it should be less than 1x sidereal.

Thanks,
Jared

17

Thanks for your quick answer Jared.

Question to the “unguided” 10micron users:

What is your autoguide speed and autoguide pulse length you use for dithering?

Martin

18

Worth noting is that there appears to be an issue with the settling. Essentially if you want to settle for 5 seconds and you have a 1 second dither pulse you need to settle for 6 seconds as the pulse dither is not waiting to start the settle. Also if you have no settle then the image is immediately starting…so you’ll certainly want to have some amount of settling. Working to address this now.

Thanks,
Jared

19

Hi,
I share your issue.
Attached a 30s exposure with dithering set at 5s and no settling after the dither.
In another thread I am struggling with this. It all did not make any sense.
Now I came across this thread and Jared’s explanation, I think I am starting to unserstand my issue.
My 10m1000hps mount takes 15 s to settle in DEC. The RA settles in 1 s. (By looking at the HC display).

rosette%20nebula_30sec_1x1_L_frame5-9small

20

Yes, I believe there are a couple of bugs in how the direct mount dither is working. I’m working on addressing them now.

Thanks,
Jared