10 replies to this topic

[asaint]

Autoguiding

[CalAstro]

Over the years, many different ideas have been tried for autoguiding. Probably the most successful before the days of CCD's and such, was the "Quadrant Diode". You mention the Accutrack system with a detector that fits into the focuser tube, and I believe this utilized the same principle.

A Quadrent detector is a large photodiode that has a circular detector area usually around 10mm to 12mm in diameter. The actual detector area, if closely examined, will reveal the the light sensitive area is divided into four quadrants. Each quadrant would have a connection coming out of the back of the diode assemply and the case would be common to all. So, in reality, the device contains 4 seperate photodiodes, each one being a 1/4th piece of the pie.

When interfaced with appropriate electronics, each quadrant is connected to the mount to issue a hand paddle direction command. Therefore, to autoguide, all that is necessary is to center an object onto the detector such that its light is spread out to partially cover all four quadrants. If the light drifts such that any quadrant starts to receive less light than the others, paddle commands can be issued to recenter the object onto all four quadrants again.

This can be a very inexpensive way to autoguide if you have sufficient light. In the 70's and 80's this was a very effective way to autoguide, with the device built into an instrument for use on larger scopes. If you have ample enough light with a little to spare for autoguiding, a beamsplitter or dichroic filter can be placed into the light path, and a small percentage of the light can be directed to the autoguider. As I said, dirt cheap and simple when used on large telescopes. I still use several photometers, both photomultiplier tube and solid state, that use this means of autoguiding.

Philip E. Evans
Research Astronomer
California Center for Astronomy and Astrophysics (CalAstro)
calastro@usa.com

[werper]

In olden times?! Interesting way to lead the article. Makes me think of pre-1900, not pre-1990's - or now for that matter - as some of the finest astrophotography work today is still being shot on film.

While I found the article to be well written, it seemed like was more of a history lesson to me than a how-to, which is what the (generic) title led me to believe it was. Perhaps this article could serve as a very good intro/first part for additional parts of a comprehensive series of articles on autoguiding. (Hint hint.)

Good stuff though, please write more!

[jrcrilly]

In olden times?! Interesting way to lead the article. Makes me think of pre-1900, not pre-1990's - or now for that matter - as some of the finest astrophotography work today is still being shot on film.

Hi, Thomas.

Thanks for your comments.

I intended the "olden times" to refer to manual guiding rather to film imaging, though I'm aware of at least one very active CN member who manually guides and shoots 35mm today and gets some fine photos. The gist of the opening was meant to be that even though digital imaging might seem to be less dependent on guiding, it's pretty much as necessary there as it is for film.

I should have included a suitable intro to the article to describe its intent. The article was inspired by laziness; it is intended as a quick intro to the different types of gear used. I found myself describing the difference between using conventional NESW guide pulses and using serial guiding commands frequently enough that it seemed more efficient to post an article to which I can link in response to future questions on the subject.

I'd also like to see some more in-depth "how to" articles. If the skies here don't improve soon maybe I'll take a shot at that.

[werper]

Hi John,

I'd love to read more if you ever find yourself with the time!

You are certainly correct about guiding being just as important for digital imaging as it is for film. As I suspect many new members here are, with the new generation of "decent" inexpensive CCD cameras on the market, I'm still cutting my teeth on digital imaging and any guiding info is very helpful. (I bought a DSI last Spring.) A how-to for newbies could make you a hero to many of us!

Here's a question for you: Have yo ever come across an article here or elsewhere on the web about retro-fitting an older non-GOTO scope with digital encoders, RA & DEC motors and an RS-232 port for adding PC control and autoguiding capabilities?

Thanks for the article and keep 'em coming!

Tom

[jrcrilly]

Here's a question for you: Have yo ever come across an article here or elsewhere on the web about retro-fitting an older non-GOTO scope with digital encoders, RA & DEC motors and an RS-232 port for adding PC control and autoguiding capabilities?

Hi, Tom.

It sounds as though you are speaking of a German EQ mount. The Yahoo Roboscope group discusses retrofitting Meade Autostar motors & controllers to various mounts - might be worth a look.

http://groups.yahoo....roup/RoboScope/

[CalAstro]

The best place to start for information about motorizing and computer controlling a scope is Mel Bartels site: http://www.bbastrodesigns.com/

Mel has long since been the 'guru' of automated scope design. His site gives theory, instructions, plans, and links for just about everything you need to turn any scope into a "go-to" scope. His site even includes "open source" software (he supplies all source code) for controlling your scope.

While his main thrust is on automating "Dobs", his systems and software work equally well on equatorial scopes. If you want to know about automating a scope, Mels site is the proverbial "bible".

Philip E. Evans
Research Astronomer
California Center for Astronomy and Astrophysics (CalAstro)
calastro@usa.com

[werper]

I joined the RoboScope group on Yahoo! and found LOTS of great info. I've got more research to do, but after only one evening of studying, I "may" be able to make my mount into a RoboScope for as little as $150 - $200! Autoguiding, here I come! Very exciting!!! Thanks guys!

[Nebhunter]

Wench - bringst thou a flagon of ale. We thirst for more upon the olden days, to harken unto your words, to bring us forth into the light of the new world upon us.

[GregB]

Werper,

I just remembered I still have a complete kit to roboscope the popular GEMs as covered in the Roboscope list. I have the DS motors, Autostar controller and the Goto4all adapters for the DS motors. If interested, let me know and I can set you up at a reasonable price.

[werper]

Greg,

Thanks for the offer! However, I just received today, the Meade 493 DS motor kit and a 497 Autostar controller. Once I discovered I could Robo-tize my scope for under $200, I jumped right on it and ordered the parts. I would be interested in your Goto4all adaptors though, assuming they'd fit on a regular Celestron Polaris mount (not the GP or SP Polaris). If you're willing to sell just the adaptors, please let me know what you'd want for them.

Thanks again!

Tom

werper at cedarcreeknetworks.com
(spelled out to prevent e-mail address mining spamers)