Autoguiding Questions

[Striker (Tony)]

I need some questions answered regarding focal length of guide scope in respect to the focal length your imaging at.

I am imaging with the canon 20DA as you know at around 1800mm FL whilst guiding with the ST402XME through the ED80.....the actual field of view is roughly around the same if I was to take an image with both camera's but not exact..this is just a rough guess.

I am saying the canon with C11 focal reduced is roughly about the same as St402xme with ED at 600mm fl

Would there be a benifit in going to something around 900mm focal length guide scope.....I dont think a fast scope is needed for such a sensative guide camera...something like the ED100 for example.

Also a question for users of CCDSOFT...once you do guiding calibration and continue to use the same guide camera/scope combination and image on the same side of the meridian...do you calibrate every time you boot the program or does it keep the same calibration even the next day.

I have been calibrating every day I use it.

Any help is much appreciated.

Tony

[[1ponders] (Paul)]

Tony your ED 80 will be plenty long enough to guide through. If you are in doubt put a barlow in that will give you a 1200mm fl for the orion. That would be heaps.

[avandonk]

Tony I regularly autoguide a 1790mm scope with a 340mm F3.4 guidescope.
I use GuideMaster which can guide to subpixel accuracy that is 0.1 of a pixel. I use a toucam with 5.4 micron pixels so the guiding accuracy is
(0.1x5.4)/(340X1000) radians. This works out to be 0.33 seconds of arc.
Or less than one pixel on the 5DH camera on the 1790mm scope.

Hope this helps.

Bert

[Dennis]

Originally Posted by Striker

Also a question for users of CCDSOFT...once you do guiding calibration and continue to use the same guide camera/scope combination and image on the same side of the meridian...do you calibrate every time you boot the program or does it keep the same calibration even the next day.

I have been calibrating every day I use it.

Any help is much appreciated.

Tony

Hi Tony

From Page 142 of my CCDSoft Manual, Version 5 Rev 10:

"If you move a large distance across the sky, or if you cross the meridian, then you may want to do another calibration. If you are imaging at longer focal lengths (2500mm and larger), you can calibrate before every image if necessary to get the best possible modeling of your system".

and from Page 143:

"Recalibration
When should you recalibrate? The simplest way to tell is to start an autoguiding session and observe what happens. Since you can autoguide without taking an image, you can start autoguiding when the telescope moves to a new position. Observe what happens to the X error and Y error numbers. If the both stay within +/- 1.0 pixel, you will likely have good results. If both stay within +/- 0.5 pixel, then the seeing is very good, and you should get excellent results. If one or both shows values greater than +/-1.0, either the seeing is poor, or you need to recalibrate for the new position. The need to recalibrate varies greatly from mount to mount, and only experience will show you what works best for your particular mount".

With my ST7E I used to recalibrate every time I slewed more than approx 30 deg to a new object. I set up and tear down my entire system each session so maybe with a permanent set up, if the guide errors stay within +/- 1.0 pixel from evening to evening, then it appears you do not have to re-calibrate - what a blessing!

Cheers

Dennis

[Striker (Tony)]

Thanks Guys....

it really is no problem calibraring as it only take 2 minutes...just wanted to know if it is actualy needed...by the sounds of what dennis has said probably not but if you want optimal then do it.

My error's stay most of the time under .2