From: "Tim" <tjp314@pacbell.net>

Date: October 21, 2005 3:51:10 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: Grid Pattern

Duane, Alan:

A quick couple comments here...

--- In Astro_IIDC@yahoogroups.com, Alan Friedman <alan@g...> wrote:

Any focusing tricks that I don't know about? There seems to be a lot 

of play between focus

and not focus.

A good focuser with zero image shift is ideal. Focus gets harder as the 

image size imcreases because you lose contrast and sharpness. For this 

reason a smaller image size might be the right way to go (f30, say) 

unless the seeing is very good.

Since my 9.25" is mounted in the roof of my house, I'd have to run up and down the ladder 

to fine focus, so I sought a motorized focuser.  After looking at the various options, and 

realizing that most (all?) of the motorized crayfords probably have cords  that are too 

short, I bought a Robofocus.  It requires a PC port, though.  I could probably use a usb 

adapter and Virtual PC on my Mac, and have been meaning to try that, but for now I use 

my PC laptop for focus control.

I'm very happy with the choice of the Robofocus.  Especially if  one has more than one 

scope, it's cheaper in the long haul than buying a motorized focuser for each scope (you 

can buy just the stepper motor and drive belt/gear combo for another $100 and move the 

cabling from one scope to another, since the software is on the computer).

A manual alternative that I "discovered" that works well for use at the scope (and only 

costs a few bucks), is  what I affectionately refer to as my "Armstrong digital 

microfocuser".  

Armstrong - because it's manual

Digital - because you use your fingertip

Microfocuser - because it adds very fine adjustment capability to a standard focuser.

"Equipment" you'll need to "construct" an ADM:  6" "Quickclamp".  I first roughly focus on 

my target using the focus knobs, then I clamp the quickclamp onto the focus knob and 

push it back and forth a few degrees at a time with my fingertip.  Only thing you have to 

be careful of is clamping it on the knob in such a way as the end of the clamp isn't in a 

direction where it might poke you in the eye in the dark.

I needed something like this because I used to mount my 6" f/10 Jaegers on a Super 

Polaris mount - a  configuration a good friend of mine termed "Gross Chinese Underkill."  

Focusing at high power was always very frustrating, because the image took so long to 

settle down.  With the ADM in place, though, it didn't move much while I was focusing.

Just some thoughts.

-Tim Parker