What is 'autoguiding' ?

[EA2007]

Hey kids,

I should know this but I guess its one of those things that everyone but you knows about and when you search for it you can never find an answer.

So, what is autoguiding and how does it work ?

Hope everyone is having a good day, I am, its sunny-wahey!

[Sam]

This is when you have a camera that sends commands to a mount (sometimes via a computer) to keep a certain star in the same place to allow very long exposure imaging. There are a heaps of different ways of doing it. The plan for my setup is to use a modded SPC900 webcam on a ST80, which is mounted on my 8" Newt. The webcam will be run by an application called Guidedog. A star is selected and if it starts to move in the webcam picture then guidedog will send commands to my HEQ5 (I have to get it upgraded first) to counteract the movement.

The reason this needs to be done is because the tracking capability of the mount isn't accurate enough for long exposure imaging, it's really only good enough for about 120secs (assuming perfect polar alignment) and typically I can only push mine to 90secs. There's a lot more to it than this but my understanding is still quite limited on this topic.

Some cameras are designed for guiding and will send the commands direct to the mount (depending on the mount) without having to go through a computer. Some cameras can do the guiding and the imaging in one, therefore, negating the need for a guidescope.

From what is posted on this forum it seems most people have a guidescope with a separate camera to the primary imaging camera.

hope that helps

Sam

[EA2007]

Thats a great help.

So basically you have your main scope with your imaging camera and then a seperate smaller scope (usually ontop) with a webcam or similar which is just used to track a star? Would any old scope be suitable for a guide scope?

Which mounts work with the software/autoguider?

[Sam]

I am using a Skywatcher ST80 as my guidescope because it's quite light and at 80mm aperture it should be able to get enough light for plenty of star choices. You could probably use almost anything. It all depends which scope you want to use as your imaging one. I'm a bit fuzzy on the mounts but I know that the Skywatcher HEQ5 and EQ5 pros versions are able to be guided because they have the stepper motors (quite fine control). I'm not sure what other mounts are compatible. My mount is a bog standard HEQ5 so it needs the upgrade before I can use it for autoguiding. There are some mounts that are built so well they can track accurately enough to allow for exposures of 8 mins or so, they come at a price though.

That's about the limit of my knowledge on this stuff. When I get my autoguiding setup going I'll be on a steep learning curve!

cheers

Sam

[EA2007]

That's fine enough, thanks for your help.

Just I am thinking of using my Celestron Starhopper 8" mounted on a HEQ5-pro. Then placing a very old and pretty basic Bresser beginner scope as my guide scope. But its all a long way off, just getting ideas for what is possible and what is needed.

[Sam]

sounds like a similar setup to mine http://stargazerslounge.com/index.php/topic,24959.msg254621.html#msg254621.

[EA2007]

Very very similar, have you had any trouble focusing the 8" scope? I cannot get enough down focus on the focusing knob. I know that the Skywatchers come with a dSLR adapter but my Celestron doesn't seem to have anything.

Do you know of anything to solve the problem?

[blinky]

I think Kaptain Klevstov uses an old camera lens to autoguide with!

[Sam]

Very very similar, have you had any trouble focusing the 8" scope? I cannot get enough down focus on the focusing knob. I know that the Skywatchers come with a dSLR adapter but my Celestron doesn't seem to have anything.

Do you know of anything to solve the problem?

I know what you mean! I had to move my primary forward about three centimetres. I did this by screwing some wood on the bottom of the primary mirror cell where the collimation screws go and then putting some longer screws through that wood as the new collimation screws - basically extending the length of the collimation screws, that way I could still use the same locking screws and collimation screw springs. I think the Celestron and the Orion are made in the same factory in China so I imagine yours is pretty similar. I had to be careful to make it very secure. Because I moved it such a short distance I don't think it stuffs with the optics too much. Now it works a treat! Though I had to by an extension for visual observing!

The focuser on my scope didn't have any attachment either - I bought the 2" attachments to reduce some of the distance.

Sam