APT multiple exposure lengths interleaved

[bobharmony]

I am planning on getting some new M42 data the next time I get a chance. Ideally I would like to set up a plan that works like this to be ready for some HDR post-processing:

1) a 180 second sub
2) a 90 second sub
3) a 30 second sub
4) a 10 second sub
5) a 3 second sub
6) a 1 second sub
7) dither
8)repeat 1-7 all night long

This would allow me to dither each set of exposure lengths without having to dither after every sub, which would chew up a LOT of time, as my dither and settle time chews up 40-50 seconds on average.

Has anyone been able to do this, or have an idea on how to do it? Scrips and External commands don't seem to allow for taking subs, or at least I can't see the option in the Help file.

Worst case, I will do all the 180 second subs in one plan with dithering between each. I will drop the 90 second subs entirely, and write a plan to so some number of each of the shorter subs without dithering. Most of the parts of those subs that will be used should have a relatively high SNR, and be less susceptible to noise.

Thanks for any ideas.

Bob

[JayTee]

Hi Bob,

The last time I had trouble with a script to automate my image acquisition, I contacted Ivo and he gave me exactly what I needed to input to get done what I needed.

Cheers,
JT

[yobbo89]

Very nice, I see you have worked out the efficiency with dithering. It's probably a more suitable way to image as with the changing sky to get an even sky background on all the frames ie if one was to mono image, r g b dither and repeat.

If I can't get anough data then I rather have a high signal mono or ha image, probs the only deturent of using that dither method for me haha

[Juno16]

Hi Bob,

JT is right, APT (Ivo) has always been a big help. So has members of his team.

If I were to give it a quick shot,this is what I would start with.

Imaging plan something like this:

Ignore the Script of Command Line entry. I forgot to cut that out.

In the manual, this is what to do to get the plan steps to loop. My camera is not connected, so I did not try this.

Then, go to the Gear and Guide tabs and set the Dither on # of images to 6.

Just a rough guess!

Thanks,
Jim

[bobharmony]

Jim, thanks! That is exactly what I'm looking for. Looping the plan was what I was missing. I will set this up and give it a try.

Bob

[Juno16]

Jim, thanks! That is exactly what I'm looking for. Looping the plan was what I was missing. I will set this up and give it a try.

Bob

Cool! Maybe it will get you started. Let me know how the “trial run” goes.

Thanks,
Jim

[Juno16]

Hey Bob,

I am sure that you thought about this, but I forgot to enter a pause step for each image to allow a bit of sensor cooling. I know that you are trying to save the 40-50 second dither time between images, but maybe a ten second pause might be a good thing?
I really don't know if that is something that is worth the time, but I just wanted to mention it.

Jim

[bobharmony]

Good thought, Jim. I usually rely on the dithering between each sub to keep the sensor temp under control. I have modified the times to 180-60-20-7-2-1 which should help a bit, but putting a pause between the 180 and the 60 may be helpful too. The whole cycle should complete in 5 minutes, adding a minute for the dither would get me 10 sets per hour. I would like to get into the 40-50 cycles range (or more if time permits), so I'll have to think about adding the pause.

I will also be trying the automated flip, it'll be interesting to see how APT handles that with this kind of plan. My first attempt at that failed miserably due to plate-solving issues, but I have worked on it since. I may be asking too much for one night

Bob

[Juno16]

No, go for it all!
You’ll be monitoring the flip anyway.
Just be careful if you mess with the flip timing. Pre-flip and post flip. The last time I was out, I got antsy and reduced the times from the default 5 minutes for each to 3 minutes and the automatic flip failed. I couldn’t re-aquire APT’s control of the mount until I restarted the PC, along with APT and PHD. Set me back a few minutes, but everything went well after that. Ivo said it was because when APT tried the flip, the target hadn’t crossed the meridian yet. Ha!

Hopefully you have some nice weather to try it out tonight. Socked in here with a 60% chance of rain today and tomorrow.

Good luck!

Jim

[bobharmony]

Interesting to know, Jim. I have played with the timers to keep the sequence going until after the target crosses the meridian. I generally can run 20-30 minutes past the meridian before flipping, so am not concerned about setting the flip for 3 minutes after the target crosses - and yes, I will be there monitoring. Sky conditions are iffy at the moment, but the real foul weather isn't supposed to move in until tomorrow late morning, so we shall see. If I have to wait until the next new moon cycle, it won't be too bad. Tonight M42 crosses 30 degrees altitude at about 2000, so I won't need be imaging in earnest earlier than that.

Bob

[bobharmony]

It clouded up quickly enough tonight to make me happy I hadn't set up for real. I tested the looping and dithering suggestions provided by Jim instead.

I started up PHD2, attached the camera to the PC then started APT. I loaded my M42 plan with a string of 180, 60, 20, 7, 2, and 1 second subs. I set "Dither on # images" to 6, and set the plan to loop 2 times in the Start options. The first 180 second sub ran, then PHD2 attempted to dither (which failed as I wasn't actually guiding). The 60, 20, 7, 2, and 1 second subs ran, each reporting that dither was skipped. The second loop started with the 180 second sub, then PHD2 attempted to dither again. The subsequent shorter subs all ran and skipped dithering, then the plan finished.

This will do what I am looking for. I wasn't expecting a dither attempt until after the 6th sub, but as long as it occurs in the same place in each loop of the sequence, I will take that.

Thanks, Jim, for the method to get this working. In 3 weeks or so when we get to the waning crescent Moon, I will give this a shot for real! I'd hit it tomorrow or Monday night, but the typical rain/snow/sleet event is moving in for a few days starting tomorrow night.

Bob