The scenario:
Long FL OTA with an ONAG/Lodestar.
I’ve commenced a sequence on a new target. Set PHD2 to a 5 sec integration time and manually selected a guide star with a good profile and SNR.
All is well. I go to bed.
Come flip time, SGP goes through its routine and finally it’s time to restart PHD2. Of course, it uses the very same 5 sec integration time. But the guide stars are all faint with resulting very low SNRs.
Were it possible to up the integration time to 10 secs or even longer (well aligned, “premium” mount), there would be less risk of a “guide star lost” event and an aborted sequence.
Assuming this is a possibility, would it be an SGP matter or a PHD2 matter where the change had to be made?
I’ve yet to actually have an aborted sequence and lost imaging time, but I have awakened to find PHD2 guiding on a star with hair-raisingly low SNR!
Terry, you can set the exposure time in PHD2 to any value you want. The predefined exposure durations go up to 15 seconds, but you can also use any duration you want by entering a custom exposure duration value.
Thanks, Andy.
But somehow, my “scenario” has been misunderstood.
The first time out on any given target, I have no idea about what guide stars will be available after the flip.
So, whatever value I have set PHD2 to before the flip, when I have manually selected an appropriate guide star, may be quite inappropriate after the mount flips. And I may not be awake to manually change it to a reasonable value.
To better describe what I am getting it, it would be useful if SGP and PHD2 were able to, not just automatically select a guide star, but also automatically up the integration time to a user-specified minimum SNR value if the pre-selected time is too short.
Hope that makes it more clear?
In my case, my mount guides well at 30 secs. It makes no sense for it to be hanging on to a faint guide star with a perilously low SNR after the flip just because of the integration time I manually set on a bright star before the flip.
In that case you can use the Auto Exposure setting. In the brain you would enter the minimum and maximum exposure duration values, and a target SNR value and PHD2 will adjust the exposure duration to reach the desired SNR (but never outside the specified min/max exposure range.)
One thing to be aware of is that when Auto-exposure is enabled and SGP tells PHD2 to start guiding it will start out with the max exposure duration, then adjust the exposure downward until the target SNR value is reached. For that reason you probably don’t want to go excessively high with the max exposure time.
Andy:
Thanks very much for this. It’s a nicety I was too unsophisticated to make use of when I first started using PHD and had forgotten about the capability since setting things up . . . if I understood the settings at all that is. Likely, I did not!
I will start using auto immediately!