CG5-GT Effects of changing Custom Rate 9 and Alignment

[morayskies]

Hi All

Following a move to an area with darker skies, I am now exploring the wonders of deep sky imaging as opposed to just lunar/planetary imaging.  We all know that deep sky imaging requires good polar alignment and tracking so I have been exploring how to better align my CG5-GT.

To date the only alignment process I have carried out is a visual polar align using the built in polar 'scope followed by a two star align.  This has been good enough for lunar/planetary imaging.  I have been reviewing this process and (when the next clear sky occurs!) will try the following process;

1) Visual polar align with polar 'scope

2) Two star align

3) Add two calibration stars

4) Carry out polar align to finely adjust the mechanical altitude/azimuth adjustment of the mount

My question is this.  My CG5-GT lives up to its nickname of 'Coffee Grinder' and, to avoid disturbing neighbours, I have set the Custom Rate 9 to just 0.75 deg per second as opposed to the default 3.00 deg per second.  Obviously, this greatly increases the time it takes to slew across the sky during the alignment process especially now I'm thinking of adding 'Calib' stars to improve accuracy.  Will the accuracy of the final alignment be affected by this increased time to complete?  During a trial run in ideal conditions (ie daylight so I could see what I was doing) steps 1-4 above take between 10-15 minutes to complete.

Thanks in advance for any hints/tips/advice etc etc  

[RobertI]

I'm interested to know the answer to this too, although I would hope the software would allow for this using its clock.

For your information I successfully did guided long exposure imaging at a FL of 345mm on my old CG5 (non-goto) with only visual polar alignment but if you are planning imaging at a significantly longer focal length then it may be more critical, hopefully others can advise.

What focal length are you planning to use and will you be guiding?

Rob

[ronin]

I may well be wrong but are you mixing goto accuracy with polar alignment ?

The alignment is to enable the mount to determine the corrections that it needs to apply in order to get from point A to point B.

It is not as best I know not a better polar alignment procedure.

I would suspect that with poor polar alignment then you could get the mount/scope to track or find an object reasonably accurate as the mount will (hopefully) determine the errors in the polar alignment and then add in suitable movement to counter this.

For better polar alignment you may need to look into drift aligning, or as indicated by Rob guiding since that operates by providing continuous and up the date feedback for tracking of an object.

[morayskies]

I'm interested to know the answer to this too, although I would hope the software would allow for this using its clock.

For your information I successfully did guided long exposure imaging at a FL of 345mm on my old CG5 (non-goto) with only visual polar alignment but if you are planning imaging at a significantly longer focal length then it may be more critical, hopefully others can advise.

What focal length are you planning to use and will you be guiding?

Rob

I agree Rob, I would hope that the software allows for the time it takes to slew between stars to be aligned - especially if, like me, you use a slower slew rate than the default 3deg/sec.

For deep sky imaging I would probably be using a FL of 400m (80mm f5) although I will occasionally use my 6" f8 Newtonian so about 1200mm.  I have just got a GP-CAM and intend to use this as an autoguider so, perhaps, 'spot on' polar alignment won't be such an issue.  I have carried out planetary imaging with a webcam at an FL of about 4500mm (6" SCT with x3 Barlow) on my CG5-GT when it was roughly aligned but I did, of course, have to manually correct for image drift but this is not so critical with a planetary image as software such PIPP will correct for this and any blurred frames can be discarded.

[morayskies]

Hi Ronin

To be honest I intend to improve both 'goto' accuracy and polar alignment.  I understand that by adding 'calib' stars the 'goto' accuracy will be improved but, when looking through the CG5-GT manual, I saw there was a Polar Align routine which is there to help get the mount more accurately aligned with the NCP.  I'm guessing that a firmware update to my handset has superseded the factory installed firmware and the manual is no longer accurate - certainly in this routine anyway.  The manual describes how, after doing a two star align, you can enter the Polar Align routine and the 'scope  will slew to where it thinks Polaris should be.  You then centre Polaris in the eyepiece using the azimuth and altitude adjusters not using the direction controls on the handset.  Having tried this in daylight, I have noticed that the 'scope does NOT slew to Polaris but simply moves a short distance from the last alignment star, then back to it, and then you adjust the manual azimuth and altitude adjusters until this star is centred in the eyepiece.

I haven't had the opportunity to try this routine yet but, if the truth be known, I'm not sure how this can work.  'The proof of the pudding..........' as they say