From: Mark Gaffney <markgaffney@me.com>

Date: September 18, 2010 4:22:29 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] hot pixels..

Milton, 

I`m attaching an inset snapshot of the Scorpion`s camera window that shows these white spots which I`m pretty sure are the same ones that had me fooled..

I did a 2 star & 4 callibration star alignment recently early in the morning when I had Canopus, Sirius, Rigel & Betelguese as the eastern callibration stars..

I think the first star in the west was Achernar, I can`t remember what I used for the 2nd, perhaps Altair..

Achernar  (in the south west) was a strange spider bite double star in the 25 mm EP I think because the Moon was directly behind the scope causing some sort of reflection. 

It`s likely I had some troubles with Altair also because of the Moon..

I don`t remember what state my PA was in this particular night..

I re-tested the Go-To`s back & forth on this occasion & Rigel, Betelgeuse & Sirius were all inside the EP each time I slewed to them..Canopus was a strange one as it was a little outside the EP FOV..

Achernar was inside the FOV because I remember seeing the spider bite again..it`s likely I avoided slewing back around to Altair in the north west because of the moon..I`m at 153* 07' 59" E & 29* 23' 22" S..

I`ve altered both PA & initial alignments since..

I had a problem with my AC-12 volt adapter having an intermittant connection which often had me re-aligning. 

It just took a slight nudge & I lost power at this time..

I`ve since bought a new adapter-the old one had been tripped over more than once dislodging the tip which was replaced when tripped over. 

I`ve used last alignment on the scope in such a situation but I believe it`s not as reliable as say hibernate in memorising the old position (I think a sync is recommended with LA..) which I never got around to doing when using it..

Mark.

On 19/09/2010, at 4:38 AM, Milton Aupperle wrote:

Mark;

On 18-Sep-10, at 11:48 AM, Mark Gaffney wrote:

Milton,

I worked out a possible cause of my guiding problems..

I doubt that this is the primary cause. Your mount has 2+ arc minutes of slop / binding on the RA axis and I have no ides how much on the Dec. That's why you get such weird calibrations and your GOTO doesn't work.

I`ve just opened the camera window inside the house here for the  

Scorpion, with the camera attached to the Kwiq guidescope but with the  

lens cap on..

The same faint artefacts that I thought were stars are there now, so  

I`m guessing these are in fact hot pixels?

Why "guess".  See page 73 of the Astro IIDC 4.05 manual. That is a real example of hot pixels.

Put the lens cap on (doesn't even need to be the scope attached), look at the image on screen. Are there "star"s there or not?

This is one of those cases where an image as a jpeg of what your seeing would be useful.

If I was guiding on hot pixels wouldn`t this cause these strange  

callibration problems..?

Possible, but your mount still has horrific slop. That's very evident because your GOTO doesn't work reliably and has nothing to do with "hot pixels".

Only if the hot pixels were really excessive and your guide star is very faint. Search for the phrase "Hot Pixel" in the Astro IIDC manual which describes how to use dark frames to eliminate this.

Milton J. Aupperle