From: Mark Gaffney <markgaffney@me.com>

Date: August 29, 2010 12:14:55 AM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: guiding last night...

Milton, 

Is this better...?The previous attempt was confused by placing it at the end of the message after the other attachments..

In one of your messages on this subject you say that you use a guide rate of 0.5x or 0.75x for 1100 mm focal length..You also say you have the starting rate at 7.0 seconds & the min pixel distances at 25 for RA & 20 for Dec (this is in a message on the 19th August early in the morning here- 6.06 am).

Can you hazard a guess what I should be using for 2350 mm?

The Kwiq scope is pretty much the same item as my 9 x 50 finder from my C10. It`s been sold now as a complete deal to my uncle so I couldn`t cannibalise it`s finder- which can be done by removing the EP attachment screw in..(I tried this whilst waiting for the Kwiq scope to arrive)

Entering 50 mm aperture & focal ratio of F9 into "CCD calc" gives a FL of 450 mm. With the Scorpion this gives a chip size of 5.3 x 7 mm, an image scale of 2.01 arc/sec/pixel & a FOV of 40.3 x 53.7 arc minutes. Does this sound right?

On the CG-5 it is suggested that most of the backlash inherant in the gears is removed by doing the final approach to the alignment stars with the Up & right directions.

My initial Go To`s when doing 3 star alignments (the first two) slew the scope below the star in question. By the 3rd star this has improved considerably (it`s on the opposite side of the meridian). I understand this is not unusual with Celestron mounts & that with any added callibration stars positioning gets better & better for Go To slews.

In many directions however I`m often somewhat limited for choices..

I`ll have another look at Analyse RA/Dec tracking option when I get a chance but one of my problems is a missing pin in the end my AC 240-12 volt adapter. This has been a pain with intermittant connections for a while so I`m looking into a replacement. It`s been tripped over pulling the socket apart more than once..

Callibration of the Mount controls took considerably longer with the new settings than the previous ones..

Mark.

On 29/08/2010, at 1:00 PM, milton_aupperle wrote:

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