APT starts exposure before end of dithering

[Simon B]

I have graduated to APT and for the most part it is working. I can plate solve and autofocus with a skywatcher 150p and canon 550d. Pictures are also fine.

The issue I am having is with dithering and PHD2. PHD2 works find with other software but for some reason, despite playing with settings I cannot get it to dither properly with APT. Issues have been:

• the dither starts but does not stop;

• the dithering stops after the new exposure starts;

• APT says the dithering has stopped but the graph on PHD2 seems to suggest it hasn't.

I have seen other threads and have played with settings but am having no luck. Any inspiration would be greatly welcomed!

Thanks

Simon

 

 

Edited July 10, 2021 by Simon B
Misspelling

[david_taurus83]

What mount are you using? It sounds like the settle time is too short and the capture starts before the mount has recentred on the star. This can happen if there's lots of backlash, especially in the Dec axis. 

[Paul M]

I'm with David, before I tuned up my EQ6 I had loads of trouble with dithering taking ages or failing altogether.

I would also add that I've had trouble with dithering if I haven't run PHD2 calibration on the current object or at lest at the same general declination. But I've never had dithering that wasn't syncing with APT exposures. That does make me wonder about the APT/PHD2 handshaking via PHD2's server. I'm no expert on that subject so can't offer any insight.

 

[Simon B]

52 minutes ago, david_taurus83 said:

What mount are you using? It sounds like the settle time is too short and the capture starts before the mount has recentred on the star. This can happen if there's lots of backlash, especially in the Dec axis. 

It's a HEQ5. The settle time is about 20 seconds. The odd thing is, when it does stop the dithering there is almost no time at all until it starts an exposure. Probably less than a second. Then it is clear it's has not guided properly as the image has trails.

[Simon B]

29 minutes ago, Paul M said:

I'm with David, before I tuned up my EQ6 I had loads of trouble with dithering taking ages or failing altogether.

I would also add that I've had trouble with dithering if I haven't run PHD2 calibration on the current object or at lest at the same general declination. But I've never had dithering that wasn't syncing with APT exposures. That does make me wonder about the APT/PHD2 handshaking via PHD2's server. I'm no expert on that subject so can't offer any insight.

 

Thank you. The guiding works with PHD2 with other software with dithering, without any recalibration. So it is strange it doesn't work with APT.

[bottletopburly]

I’ll check what my settings are .

[david_taurus83]

What size of a dither are you using? What does the graph look like when the exposure starts?

[Simon B]

3 hours ago, david_taurus83 said:

What size of a dither are you using? What does the graph look like when the exposure starts?

The dither size is 1. The guiding looks fine when the first exposure is initiated. It then starts the dither and that is when the issues start. The dithering graphs looks like it should do for dithering (and it says on the graph that is dithering), it just does not seem to be able to stop it properly.

[bottletopburly]

what guidescope are you using 

[david_taurus83]

It's obviously not recovering quick enough before the next exposure starts. When APT sends a dither command, PHD picks a random position for the crosshair and selects a new pixel, for example. Then PHD moves the mount so the star lands on the new crosshair position. It can take a while depending on how big a shift in position it is. If there's excessive backlash in the gears it can take even longer. Try upping your settle time to 60s and see how you get on. Also, make sure the timeout time is longer than the settle time. This should cancel the dither operation and continue with the next frame. If its shorter than your settle time this could be why it's starting exposures too early as well.

[Simon B]

3 hours ago, bottletopburly said:

what guidescope are you using 

Its a 50mm Svbony guidescope.190mm focal length.

[Simon B]

2 hours ago, david_taurus83 said:

It's obviously not recovering quick enough before the next exposure starts. When APT sends a dither command, PHD picks a random position for the crosshair and selects a new pixel, for example. Then PHD moves the mount so the star lands on the new crosshair position. It can take a while depending on how big a shift in position it is. If there's excessive backlash in the gears it can take even longer. Try upping your settle time to 60s and see how you get on. Also, make sure the timeout time is longer than the settle time. This should cancel the dither operation and continue with the next frame. If its shorter than your settle time this could be why it's starting exposures too early as well.

Thank you - I will give that a try.

[Tangoringo]

I’d be interested to hear how you get on Simon as I’ve had the same issue. Keep us posted. 👍🏻

[Simon B]

Still can't get it to work, which is really frustrating. It dithered a few times correctly last night on 10 second exposures then stopped working. Makes so sense to me so have had to revert to other software.

[david_taurus83]

10s exposures is very short. You don't even need to guide. Are you sure the exposures are not overlapping the recovery time?

[Simon B]

11 hours ago, david_taurus83 said:

10s exposures is very short. You don't even need to guide. Are you sure the exposures are not overlapping the recovery time?

Ha, sorry that was just to emphasize my frustration. I was originally trying to guide of 90s. I am at a loss though. It is not at all clear why it is not working.

[david_taurus83]

Post up your guide log. There will be a PHD folder in your documents. It automatically saves a guide log each session. You can post the log up here and we can have a look.