Autoguiding

[andys]

Can someone provide some advice as to how to go about autoguiding. I have a skywatcher 150mm Newtonian on an EQ3 with dual axis motor drives and an EOS350D.

[h0ughy (David)]

no wonder you have had no anwers yet mate. Sorry to say you haven't a hope in hell of achieving your goal with that hardware! Autoguiding for that flavour of mount won't happen until you get a heq5 or eq6 mount with syncscan or the pro versions. there are other mounts like the celestron flavour or meade, or losmandy mounts, but an eq3, sorry!

[[1ponders] (Paul)]

I agree with h0ughy there andys. I have an EQ3 mount and I don't think you will find anything off the shelf to do the job you want.

[Dennis]

Hi Andy

I don’t have an EQ3 so bear with me.

You say your EQ3 has dual axis motors – these are great for tracking the stars, planets and galaxies. Your EQ3 has two axes, the Right Ascension (RA) axis and the Declination (DEC) axis, each with a motor. To make your mount track accurately, you need to align the RA axis with the South Celestial Pole and this will then allow your RA motor to drive the RA axis to compensate for the Earth’s rotation.

Your RA motor should turn your RA axis (very slowly) once every 24 hours (approx) so that when you look at a star in the eyepiece, it will remain in the field of view (FOV).

Now auto guiding is something completely different. When you mount is tracking, it is just chugging along at a fixed rate to keep a star in the FOV of your eyepiece. But, your mount and gears are not perfect – they will have errors so that the star will move in the FOV; hopefully it will remain in the FOV but it will certainly drift.

Now, if you were to put a high powered eyepiece with illuminated cross hairs into the focuser and centre this star on the cross hairs, you could compensate for this random and unpredictable movement, by manually pressing the motor movement key to constantly bring the star back to the middle of the cross hairs whenever it drifts off, which it will do every few seconds.

This is essentially what an auto guider does, but automatically. A CCD chip in the auto guider watches the star and if it moves, it sends a signal to the motors to bring it back to a known position.

I strongly suspect that your EQ3 mount does not have auto guiding capability, which is only found in the more expensive mounts in the form of a special connector and electronics. So it would seem your mount can track, but not auto guide.

However, if you fit a digital camera on top of the telescope and make manual adjustments as described above, you will be able to take long exposure photos (if your camera allows this) usually up to 30 seconds. By taking several you can then stack them together and obtain some quite nice wide field photos.

Cheers

Dennis

[h0ughy (David)]

thanks Dennis for that short explanation!

Andy as Dennis said you should be able to achieve something, why even Ballaratdragon's imaged on an eq1, but know the limitations and i am sure you can achieve a good result to start with!

[Dennis]

These naming conventions of EQ1, EQ2, EQ3, CG5, LDX75, Heq5, EQ6, etc really confuse me.....I haven't a clue about their functions and capabilities....why can't they stick to simple names like GPDX and EM200.

Cheers

Dennis

[sejanus (Gavin)]

How much does an off the shelf autoguider generally cost anyway?

[xelasnave]

mmm how much have you got?
alex

[xelasnave]

Sorry.
Go for an eq6 seems they can be had around $2000 (down on what I paid only a month ago so shop around) .. I have a 150 ar and they recon the eq6 can manage one... add a camera, a web cam $200 approx or LPI (I have but I doubt it will cut it) or a Meade DSI ( $300 / $400?) and a lap top or desk top on wheels.
The 150 ar is a lot of scope for any mount simply because it is long and therefore touchy.. I am on the same trip, having got the mount, a lpi, lap top, etc I am ready for my first nights of dissapointment in preparation for the day it all will work.
Good luck, oh and good luck for you to.
alex

[xelasnave]

I didnot cover a guide scope or illuminated reticle, electric focuser etc but I thought what you can do is use the 150ar as your guide scope piggy backing the 350d canon.. even with standard lens you will be happy with the results from even your mount.. I have done some wide fields with exposures up to 45 minutes with 300d unguided with my old mount (the one that came with the 150ar) very satisfying if you have not tried that.
alex

[Dennis]

Originally Posted by sejanus

How much does an off the shelf autoguider generally cost anyway?

Most of today’s auto guiders require a computer to operate them from, so you’ll have to factor that into the cost.

I was lucky to pick up an Orion Deep Space Star Shooter from Ron at Sirius Optics some time ago (at a nice club discount too - thanks Ron!). The current prices are around the $595 mark I think, although the camera has now been discontinues due to supply problems to Orion in the US.

I purchased it specifically for auto guiding as it had a Peltier module for thermo electric cooling (TEC) which gives me a nice, clean field in which to find a star. Without the TEC, once you start exposing for say 5 or 10 secs to find a guide star, you also get thermal noise in the form of hot pixels and the camera may try to guide on a hot pixel, or become confused by hot pixels.

There are modified webcams that can be used and I have heard of people using LPI’s and DSI’s.

So, for less that $550, I managed to meet my requirements of:

• Lightweight at the focuser to minimise loading and flexure.
• TEC to minimise thermal noise.
• Reasonable chip size of 742 x 582 pixels.
• USB connection to PC for fast downloads.
• Dedicated auto guider.
• Nice software interface with Craig Stark’s free PHD Guiding as I don’t like the bundled Maxim Essentials.

Cheers

Dennis

[sejanus (Gavin)]

That sounds pretty decent. I've got a few laptops (ISP nerd engineer) so no worries in that department.

thanks

Gav

[andys]

yep, I'm an IT nerd too. Has anyone tried out this:

http://www.store.shoestringastronomy.com/eq_mod.pdf

it allows you put an autoguide port on an EQ3 dual axis controller (which is what i have)

I've read somewhere that it's possible to give an EQ3 a bit of a tune to make it tighter and reduce "play" in the mechanism.

[[1ponders] (Paul)]

You can improve the EQ3 mount by modifying the directions in this website

http://www.astronomyboy.com/cg5/index.html

[andys]

that looks extremely useful! thanks

[Dennis]

Here is a link to a web page showing how someone converted their EQ3-2 into a GoTo mount.

Of interest are the following comments:

May 2003: This setup is a very nice economical portable GOTO system for visual observing. BUT it is only right to point out that the EQ3-2 mount, although sturdy, is not a High Precision instrument. Periodic Error is quite high at around 70 arc-secs peak to peak, and a little jumpy as well. Not really suitable for long focal length long exposure astrophotography. As a wide field camera mount, particularly piggybacked using the Stellarvue (or whatever telescope is on the mount) as a guide scope, it should serve well.

Added later (2005!) Periodic Error Control is now available for the Autostar, although the training is lost unless the mount is PARKed. But this can reduce the periodic error to +/- 10 arc-seconds or better, so considerably improves the long exposure capabilities of the mount.

Auto guiding with a PE of ±10 arc secs seems feasible, if the gear errors are smooth.

Cheers

Dennis