SGP and how it handles a lost star from PHD2

There are many times that I get a long way through an exposure only to find it fails due to a cloud. Ideally what I want is to be able to cover the scope when the cloud approaches and settle for a say a 25 min exposure that should be 30min. But what happens is PHD2 tells SGP it has lost the star and the sequence ends.

I thought that setting in Auto Guide “Restart current frame when guider distance >” would control this, but when not ticked it still stops the current exposure.

I am not referring here to any form of recovery, just the ability to salvage the current frame. Perhaps I have not got a setting right somewhere?



That isn’t an option in any program I can think of.

Before SGP I used MaximDL and there was a button in the camera control window called Stop and when clicked it stopped the current exposure and saved the image (Unless my memory fails me and I am wrong, but I could have sworn it did. Do please correct me if I am wrong). So that would be the ideal way round this. I asked if this could be done in SGP a a couple of years back was told that feature could not be done.


Argh, it’s been years since I tried MaximDL… I have tried BYEOS and I don’t think it does that. I know that when I use qDSLRDashboard it’ll do that though with some settings.

We could make it a feature request. I think when you start pushing 15-30 minute exposures you just accept you’re going to lose some of them to weather. The big thing is you’re not going to have an appropriate dark frame for that time any ways right?

A star lost message is completely different than a large error message. Large errors will restart the exposure. For star lost, you will need to have recovery turned on. This will also restart the frame, but will repair pointing and guiding prior to doing so.

We do not have access to camera features at this level. The only native driver we have written is for SBIG. Beyond this, we cannot guarantee how ASCOM cameras will respond when an exposure is aborted and download is attempted. Some drivers may support this, others will not… there is no standard (currently). This makes writing code around partial exposures difficult so we have avoided it…


OK, thanks for the reply, it was worth a try to ask, it can get rather frustrating to keep loosing frames this way, I will have to do shorter subs if clouds are likely.

Mads0100, the idea of covering over the telescope’s aperture would keep the exposure the same, so no issue with darks.


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There are two ASCOM commands to stop an exposure.
AbortExposure() stops the exposure and discards any data.
StopExposure() stops the exposure and makes the data available for download.

I’m not sure how many cameras implement both, nor am I convinced that collecting partial exposures is a good idea. Much easier to use shorter exposures so there’s less to discard.

Chris R

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@Chris Thanks for the clarification.

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Hi Chris, thanks for passing on that information.

Regarding the partial exposures, I have had a few sessions that have got as far as 29min or more into a 30min exposure. Imagine how annoying that is to find it stop at that point. When all I wanted was the exposure just to complete as I have already covered the scope over just as a cloud moved over the area I am imaging.

Obviously this feature will be of no use to anyone during automated sessions, but most of the time I am there.