From: "Tom Krajci" 
To: , 
Cc: , 
Reply-To: "Tom Krajci" 


>From: "James Lerch" 

- ----- Original Message -----
>From: "planetmanwest" 

> Amen, Jerry!
>...   Thank goodness for a polar axis and AC synchronous (or even DC)
> motors. Simple, cheap, dependable, accurate, and no image rotation.
> (Look Ma! No computer!)   :)
>      But you've got to admit that alt-alt-az idea makes a lot of
> sense for tracking satellites across a pre-determined arc. Ingenious!
> Though for astronomy I fail to see any advantage any of those alt-az
> spinoffs could have over an equatorial - especially in an application
> where portability is not an issue. I guess I'm just dense.
>
> - Jim S.

One of my main design goals is to try and find ways to make a tracking
mount for a larger amateur telescope.  Yes, for a smaller amateur scope, an
equatorial mount is simple to build.  What about an equatorial mount for a
larger scope...such as 30 inches or so?  Can an amateur make a well
performing mount (yes, you need computer support for motion control) that
is alt-alt or 3-axis...that is simpler than an equatorial mount?...yet
performs well enough for imaging?)

Am I barking up the wrong tree by pursuing this design investigation?


>From: "James Lerch" 

>I my case, due to my CCD equipment, I'm limited to ~30sec exposures.

Why are you limited to only 30 second exposures?  Bad tracking?  Bad
cooling?  Limited well depth?  I would recommend addressing the problems to
allow longer CCD exposures.

>To date all my work's been done on a simple motorized EQ mount.  The
>problem I
>keep running into is 'Poor' polar alignment....

With practice, good technique, and a mount that has well-behaving polar
axis adjustments...you can achieve good polar alignment before twilight
ends.

>While there is limited software that will Stack and De-rotate...

>... The stack of images is over the
>course of several hours, and even AFTER de-rotating each image
manually!...

What shortcomings does the software AIP4WIN have for stacking and rotating?
 I thought it could handle hundreds of images (as long as they all have the
same 2 stars for alignment)? See:  http://www.willbell.com/aip4win/AIP.htm

>...I have another
>problem with drift over time, I use eyepiece projection for a lot of my
>imaging.
>With eyepiece projection I get Pin-Cushion....

I would recommend finding an eyepiece with less, or no distortion.

>Now a proper, perfect polar alignment would solve all these problems.
>However I
>seem to be unable to create such a thing while in the field!

Why?  Does the mount's polar axis adjustment move in a sloppy and
uncontrolled manner?  Is there too much flexure in the mount or optics? If
we identify the problem we stand a good chance of fixing it.

>The attraction of an Alt/Az + field de-rotation, or Mel's Alt/Alt/Az is
you >just
>plop the sucker down on the ground, do a multi-star initialization, and
let >the
>computer figure out all the hard stuff.  In theory this would solve the
>problem
>of all those wasted nights of imaging.

You still rely on a non-flexing mount that points/tracks accurately.  No
such thing as a free lunch.  For good imaging performance (no matter what
mount type), you need a well-performing mount/drive system. Without
it...you're hosed, and software will not help very much, if at all.

Beware the hi-tech 'chaser of warm biscuits'....the type who never grabs
the biscuit sitting on the table...because some other technical solution is
'in the oven'...with the implied promise that "when it comes out of
the oven, it'll be the *best* biscuit you ever had!"

This high-tech biscuit chaser will never finish chasing.  His existing
technology will never mature or be honed to high performance.  He's too
busy chasing the biscuit 'in the oven'...and we all know that 'tomorrow
never arrives.'

You can't polar align?  Identify the problems and fix them.

CCD is limited to 30 seconds?  Identify the problems and fix them.

Eyepiece has pincushion distortion?  Get a better eyepiece.

Tired of manually rotating images for a stack?  Get software that can do it.

None of these are hi-tech problems, and I bet they don't require high tech solutions.

Your results will dramatically improve without resorting to new technical approaches.

Tom Krajci
Tashkent, Uzbekistan


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