Hi there. I hope I haven't used up my "stupid newbie question" allocation yet . Here's another:

I'm running Indi with a CCD and a motorised EQ mount all humming away happily, controlled from KStars/Ekos. Though I've not yet actually used this for real (having only got it working yesterday), I understand that I can use the Ekos Alignment module to get me to known places in the sky. But there's also this Guider thing, and my mount has an Autoguide socket. Why would I need to implement the Guider stuff if the Alignment module gets me to known places in the sky, and then slews?

Rob

They're two very different things:

1. Alignment: Makes your mount points to the correct place in the sky.
2. Guiding: Once you start imaging, it locks unto a specific star so that the mount tracks the exact position as it moves across the sky. This is needed because mounts are not perfect and we need to make sure it tracks our target object correctly.

Simply put, due to slight tracking errors inherent to every mount and slight misalignment to the celestial pole, the field of view drifts/rotates over time. The guide camera finds the centroid of a star and tries to keep the star within a certain region of pixels by moving the mount ever so slightly to counteract these drifts.
Think of it this way. The alignment module gets you there and the guider keeps you there!

--Jon

Thanks, got it. So in the case of my KStars/Ekos/Indi-client/Indi-server combination, can the single [ZWO ASI] CCD I have at the end of the view finder be used both for imaging and for guiding (via clever indiserver stuff) or is a separate guide camera required? If the former, how much imaging time might get taken away from me as a result?

Rob

While there are some cameras that have the capability to guide and image simultaneously, I don't believe that yours is. You would need a separate guide camera. Cameras that do both, generally speaking, don't work as well as separate cameras anyway.

--Jon

Good. Last question on this topic then: if I am to introduce a separate camera for guiding, would an off axis guider such as this work OK, or would I be better off attaching a guide scope?

Rob

Whether to use an OAG or guide scope depends on many factors. Each has their own benefits and disadvantages. It also depends on other factors such as fl and image scale of your camera. I would suggest reading up in forums like Cloudy Nights or getting a good book on astroimaging before making an investment. One good reference that was suggested to me was The Deep-Sky Imaging Primer .
I don't mean to be vague with my answer but it really is a complex subject. Hope this was helpful.....

--Jon

Understood, thanks. I see that there's an On Axis Guider as well, just to give me more things to think about. I will read and consider my options. Happy to hear more views if anyone has any.

Rob

I would definitely read more about it first and search for topics on, indeed, something like cloudynights. I use a seperate guide-scope, basically because when I started I didn't know about anything else. But it serves me well, I usually always have a proper star to guide on (needs to be bright enough etc.). Downsides though, are that it requires a really stable set-up, an extra scope on your rig will introduce more points of possible vibration etc. Besides that, it adds weight, which would be nice to save for something else.

An off axis guider, has the advantage of being light and extra flex-points in the setup are avoided. Downsides can be, difficulty in finding guide-stars (as the seperate guide-scope is usually of less focal length than the telescope, it sees more stars) and it's tricky to get set-up as it requires precise placement in the imaging train.

Eventually I might go for off-axis, but as of now, my rig was optimized to work great with a seperate scope. And if something works great, I'm not changing it soon as "working great" is not a normal thing in this hobby.

Thanks for the feedback, very useful. I've decided to have a go at this:



...since I have a Skywatcher finderscope and it looks like a cheap way to get to first base with guiding. I'm only going to appreciate the downfalls once I get there, so I might as well get stuck in. £157 to Modern Astronomy and I'll be able to get going next week.

Rob