sensasi: [sct-user] Re: RoboFocus settings

Jumat, 08 Februari 2008

[sct-user] Re: RoboFocus settings

--- In "carter646831" wrote:

>
> I have a RoboFocus that I use to focus my Meade 8" Classic LX-200.
I'm using CCDSoft 5 version 5.00.186, and a SBIG ST-7XME.
>

Here goes, but you may not like my answer. <G>

I have a RoboFocus driving the knob of an 8" LX3 OTA on an LX200
Classic mount with CCDSoft. I'm close to your setup though my 2080 OTA
may have less backlash. My Robo is set for Max travel of 10493 and
backlash of 20 when moving out. I have CCDsoft set for small step=1,
large step=10, and no backlash so it won't fight the Robo setup. I set
@Focus to 10 cycles starting in
. Your needs will vary.

I occasionally use @Focus, but I too find it erratic. A lot depends on
the seeing and in Southern Connecticut seeing is almost always poor. I
use a procedure I found on line, which is reversed from the Robo manual:

Find approximate focus
Step out 6 large steps
start @Focus

I watch the curve and note the graph peak. Sometimes @Focus will back
up to the computed peak, other times it will miss slightly but I know
from the graph where to tweak it. Someday I may try more cycles to see
if @Focus works better.

This procedure does the 10 cycle inward search with no backlash
compensation to confuse the measurement. It ends with a LONG delay as
the focuser goes out to the computed point. Each time CCDSoft issues
an outward movement the Robo backlash adds 40 counts worth of time
(backlash=20). Unfortunately if CCDSoft wants to make a final movement
of 47 counts out it issues 4 large and 7 small steps. The compensation
adds 11*40 counts of additional time, an overhead of 9:1! If your
Classic OTA has a backlash of 100+ you may find @Focus rather painful.

Most of the time I move to an initial point from my list of Robo
points for each setup (focal reducer, camera, etc). I then tweak
manually using the Focus screen of CCDSoft. The backlash compensation
is not a big problem when I manually focus with CCDSoft. I tend to
move out in a few large steps then in using small steps.

Don't get me wrong, I love my RoboFocus! I've used it for years since
Chris Peterson talked me out of a linear focuser. I've not been
impressed with Linear focusers on SCTs I've seen at Star Parties. I'm
sure @Focus works much better on a tight focus OTA in a good steady
dark sky.

Leo Taylor