How do autoguiders work?

[gurney]

Hi there,

dumb question alert! :withstupid:

...*looks embarrassed, takes a deep breath*...

How do autoguiders work? that's the nub of the question. But with it is the question "do autoguiders and CCD cameras have to be matched in any way?"

So I've never seen one in action, or even really seen pictures of one. Just seen them referred to a lot of times. I can understand the principles behind one (point at star, then some sort of controller or pc keeps that star stationary in view by finely adjusting the telescope's movement I guess).

But my understanding totally breaks down with it comes to how the thing actually plugs into a telescope, or in conjunction with another camera. What cables might go where and so on and so forth. And whether you need another smaller scope piggybacked on the main scope doing the imaging and so on, or whether you can have both autoguider and main imaging camera looking through the same scope somehow.

Anyway - enough of the dumbness!

I look forward to enlightenment. Ta!

[Whippy]

AFAIK, the basic principle of autoguiding is where basically a computer controls the tracking of the mount. A continous feed of images are fed from a camera into the computer, a guiding program then follows a star on the images and corrects the mount accordingly.

There's a few different ways of doing this but my own set up is has one camera and one scope for imaging, and another camera and scope for guiding. The guiding camera has two ports. One goes to the computer and one goes straight into the mount. A program called PHD does the guiding for me.

Tony..

[Paxo]

Gurney,

If you are still contemplating the LX200, then it has an autoguider port built into the mount. The mount has several ports on the LX200R, theres the handset port, computer port, focuser port and a reticule port. Tony has already explained the basic principle, but what you need is something to convert the signals from a camera into movement vectors that the mount can use. In Tony's case, this is inbuilt into his camera which has an autoguider port, so he simply runs a cable between the camera autoguider port and the mount autoguider port, and software such as PhD (free) takes care of all the calibration etc (PhD stands for press here dummy). In my case, my guiding camera , A Meade DSI II,has no autoguider port so I have to use a small piece of hardware (called GPUSB) which plugs into a USB port, and converts the signal and passes the ovements via a cable to the autoguider port on the mount. All you have to do, in either case, is tell PhD what camera you have (only certain ones covered) and what mount you have (how the signal is to be transferred).

I hope this helps, download PhD and take a look at the cameras covered etc, some people use modded webcams, some of the more expensive imaging cameras (such as the SBIG) range contain a secondary guiding camera inbuilt, just as with the universe, the complexities and combinations are endless, but this is a good start.

Regards

Steve..

[gurney]

Many thanks guys, it's that practical info I was after.

The scope I'm getting (hopefully) is an LX200 classic, so I'm not sure what it's got on the mount. We'll have to wait and see!

[Paxo]

Gurney,

If you want to have a look at the features and operations before you make a decision take a look at http://www.meade.com/manuals/index.html where you can download the manual of your choice.

Steve..

[brenchen]

Sorry to dig this back up, but I think it's relevant to this thread:

Does the orientation of the guide scope/camera in its longitudinal axis matter?  If it does not, if the guide camera is seeing the stars moving left and issues the guide command for the mount to move left, and the guide camera is actually upside down, wouldn't the commands issued be in fact moving the wrong direct?  Or does PHD work out the correct signal to send to the mount so it moves correctly?

 

Answering myself:  I read somewhere else that PHD works it out which signal it should send for the tracking to be correct.

[Merlin66]

Yes,

The calibration routine looks after the camera orientation........