Celestron RASA 8

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Harmonious
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Celestron RASA 8

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Post by Harmonious »


I now have both a RASA 8 and a ZWO ASI 183 Pro (20 mega-pixels, 5496×3672). The 183 is known to have amp glow that becomes worse with longer exposures. At some point calling for darks or cropping.

Sometimes when i change targets I raise the gain and shorten the exposure to aid in framing the object. As a result I sometimes forget to change both settings before live stacking commences. That sets up this thread.

One good way to use an f/2 scope and a high resolution /small pixel camera is to reduce gain and go long, up to the limit allowed by sky brightness. This works although a three minute exposure might be in the DSO drying category for EAA. What about the other extreme very short exposures and higher gain along with live stacking?

Using the latest version of SharpCap Pro I did not have any luck with 1s exposures, just a lot of dropped frames. Two seconds proved to be the threshold. I started with gain at the max the lowered it until I had a useable image, 300 to 350 seemed good. Results varied a bit depending on where the target was in relation to the first quarter moon and local light sources. The image noise level was very high, but after a few frames much improved.
Snappy EAA presentations and it should work with alt az mounts.

These images were all taken at 2 seconds and gain 300. Unguided. The frame count and time are in the file names. The objects are M13, M106 and comet C 2017 T2 Panstarrs.
Stack_206frames_412s.jpg
Stack_153frames_306s.jpg
Stack_456frames_912s.jpg
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