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Guide scope secrets!

jonifive

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jonifive

jonifive

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Right you lot, I've been here a little while now and love it, but, I have noticed that an awful lot of you talk about guide scopes.

Sadly because I am a bit stupid, it only dawned on me in the last hour as to what the hell you were talking about, and why everyone wants an ed80!!!

I did a search but not too many answers came up, so here are my questions...

1. What software does the webcam/guidescope system use?

2. how on god's earth does it work?

3. and what is offset/axis guiding?

4. Once I know these secrets will I have turned to the dark side?

Q you lot to bombard me with science.....

Cheers from a slightly confused Jonathen

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Kaptain Klevtsov

Kaptain Klevtsov

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1) I use K3CCD Tools for guiding, as it will guide and image simultaneously using only one camera - great for planet stuff. A normal webcam can be used but that restricts the guide star as it has to be bright enough to show up on the webcam. Long exposure modified webcams can also be used, but this restricts the guiding frequency (how often the correction pulses can be generated) as you can't guide faster than the guide camera takes images. It does, however, mean that you get a lot more stars to choose from.

Other software, such as Guidedog or Maxim are popular and free, and some cameras come with dedicated accessory guide cameras with proprietary software.

2) It works by having a cable from the computer to the mount through which it sends directional pulses to realign the 'scope to keep it on target. It works out the direction that the mount needs to be moved by analysing an image taken by the guide camera, such that if the guide star moves on the camera chip the software tells the mount to move to put the guide star back in position.

3) There are (at least) three ways of autoguiding.

Manual guiding should be banned as you need to watch the guide star and hit the left or right (or up or down) button at the rightime and in the right direction for hours to keep the guide star centred on a cross-hair guiding eyepiece. A more boring thing I can't imagine.

The more common method is to fasten two 'scopes together, and use one camera on each 'scope. One is used for imaging while the other is used for guiding.

The less common method uses a small prism or mirror which pokes through the side of the focuser tube to "borrow" a bit of light from the edge of the frame, ideally not going to land on the imaging chip. This diverted light has to be carefully arranged so that it contains a star which can be used for guiding.

The last method uses an imaging camera which has two chips. One for imaging and a second one for guiding. These last cameras need a big focuser tube to cover both chips and they need a suitable star on the guiding chip.

4) Yes.

The best bit about autoguiding is that you can spend on a guide 'scope and webcam and save thousands on the worlds best mount. Autoguiding is cheap and easy, a Paramount isn't.

Some more snippets of information:-

The guide scope can be a piece of junk, you needn't worry about false colour, you just need a lit up dot on the screen. I use a very cheap and cheerful T mount 500mm camera lens that I have had for twenty years.

The guide camera can be the webcam that you have for planets, you don't even have to use a filter (best not to in fact).

Small clouds send autoguiding crazy. If the guide star disappears, the software guesses and sends the mount off wherever it feels like and loses your goto alignment.

The guide 'scope doesn't need to have the same focal length as the imaging 'scope. One third is a commonly quoted ratio, so a 500mm FL guide 'scope would be fine for a 1500mm FL imaging setup.

Some guideing software (Guidedog at least) has an automatic calibration routine for setting up.

There's probably more to it than this, but most of the points are covered.

Captain Chaos

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jonifive

jonifive

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Thanks CC

Once again an excellent and comprehensive answer to my newbie questions.

I assume you would need a goto mount for this and it wouldn't work on my HEQ5, and i suppose it is a good way of tracking for those of us who are not so good at alignment.

Thanks again my friend....educational.

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barkis

barkis

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Thanks from me too CC, that little condensed primer has added a bit to my sparse knowledge on autoguiding. I thank Jon. as well for asking the question, we are both wiser now, but still in need of more answers. I am sure the help will be forthcoming when we ask for it.

Ron. :police:

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