From: "milton_aupperle" <milton@outcastsoft.com>

Date: August 28, 2010 9:00:01 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: guiding last night...


Mark;


--- In Astro_IIDC@yahoogroups.com, Mark Gaffney <markgaffney@...> wrote:


Hi Milton,

I don`t know if you`d be interested in my guiding log from last night  

whilst attempting to image NGC 6744 again?


The text files you posted are not guide logs that Astro IIDC created. They are html files of stuff or have been mucked up somehow.


Even with Precise Go To being used on my CG-5 mount I`m still missing  

the target somewhat.


Then it isn't polar aligned or you have mechanical issues.


Rod Mollise, replying to my post to the Celestron AS-GT group agrees  

that I should add more callibration stars in the east to the 2 usually  

begun with in the west until my Go To`s improve. (I usually use just 3  

stars).


I use one  star within 60 degrees of my target and get it within 10 arc minutes of center. If my polar alignment is off, then that doesn't happen and it could be way off. If I have gear binding because the mounts worm gears are to tight, then that causes a similar issue. If it's too loose something similar may happen again.


Also centring these stars on the IP camera control crosshair with the  

DSLR as I`ve done with All star PA may help..

Polar Alignment was given a clean bill of health..i.e. Azm : -00* 00'  

00" & Alt : -00* 00' 00" in Display Align..


Actually you don't know this unless you try tracking a reasonably bright star and see what changes you get over time. I use the "Analyze RA/DEC TracTracking…"in Astro IIDC to determine this at 2 meter focal lengths. If the star drifts vertically up / down more than 3 pixels / arc seconds over 5 minutes, it's not quite polar aligned.


With the guiding I`ve turned up the autoguiding rate on the mount to  

0.75 % of sidereal (from 0.50 %) as you suggested, set the start time  

at 7 seconds & Min RA Dist at 25 pixels (instead of 20) & Min Dec Dist  

at 15 pixels (instead of 10)..


I never suggested you increase the auto guide rate. I asked you to look at it and see what it's set to, in case you've never looked at it. Just blindly changing things without thinking why your doing it is just a way to frustrate yourself going forward.


The scope is imaging at the full 2350 mm FL & the Kwiq guidscope (with  

the Scorpion 20SOM) is 50 mm in diameter I think..


The aperture of the guide scope means basically nothing. The important thing is the Focal length of it. Unless you know what that is, you have no idea what your image scale is on the Scorpion's 4.4 micron pixels.


If you determine that each pixel was 3 arc seconds (I have no idea if that's even close), then to get 20 pixels of RA motion when calibrating, it has to move 60 arc seconds. So if your setting the guide rate to 75% of sidereal, then it will need 80 seconds to move 20 pixels on the CCD. That's way too much.


If that's the case, then you want to increase the auto guide rate and / or  decrease the pixel movement amount or you'll be spending a lot of time waiting for it to complete the calibration.


I know that the ASTRO IIDC calibration routine will automatically abort if it ever takes > 60 seconds to move in one direction.


HTH..


Milton Aupperle