Glad to help Martin. Over the years I have mentioned how effective SGP has been with the current feature set in running a dual camera/scope setup. And many folks are doing it. Here are some links to past discussions that cover most of the issues you may want to consider.
The setup you have outlined is right on: one fully configured scope/camera that controls PHD2, mount, and dome. The other just takes images controlling just its camera, filter and focuser. Very simple.
One potential problem when running this on one pc is, if you have two of the same focuser or camera. The driver must be able to support 2 on the same pc. I have two ZWO cameras and the ZWO driver does support 2 cameras, even of the same model.
In the Batch PreProcessing script in PI on the Light tab the top box is labeled “Cosmetic Correction”. Check the box and choose the “Cosmetic Correction” format that you have created. Creating the “Cosmetic Correction” requires you to point to your “Master Dark”, then choose a “Hot Pixels Threshold” and a “Cold Pixels Threshold”. I select values that produce a fixed pixel count of about 9000. In practice, most stacked images have no noticeable hot or cold pixels, a rather perfect result. Sometimes there are a few, and I just use the Clone tool to fix them, an easy and quick process. There is one feature of the “Cosmetic Correction” format dialog that I don’t think many people know about. I have found that with a particular camera or Master Dark, there would be a few very noticeable hot pixels that the routine did not fix. These would always be where 2 or 3 hot pixels were neighbors and the routine was not sophisticated enough to detect them. For those, there is a manual feature that lets you provide a list of specific coordinates for these bad pixels. And of course you only do this once. But I have not needed to do this for a couple of years.
Dithering has the following negative aspects:
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It wastes imaging time because it can only be done while both cameras are idle. Time that could be productively taking more images.
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To avoid wasting a large amount of time on 1 of the 2 cameras, any implementation of dual dither support will require that the exposure times on the 2 cameras be coordinated such that one is an exact multiple of the other. For example 3 minutes on the main camera and 2 minutes on the secondary camera will waste 1/3 of the time on the slave camera. There is no such restriction if you don’t dither. I choose any exposure length I want on each camera.
If you still feel the need to dither, there are several approaches that allow you to do this. They are covered in the topics linked to above. To summarize:
- Main camera/scope is a small FOV doing the dither every 5 frames. Slave is wide field, so either the small FOV dither does not affect it much, or you only need to throw out 1 in 5 frames. If your wide field exposure is half that of the narrow FOV, you only lose 1 in 10 images.
- Imaging a target over several nights will produce a natural dither if your centering process differs by more than 2 or 3 pixels from night to night. And you can simulate this on one night by creating multiple targets that are the same target.