From: Milton Aupperle <milton@outcastsoft.com>
Date: June 29, 2008 12:37:08 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Re: Cables, adapters, and stuff
Hi Tim;
You can see "Flop" / "Shift" pretty easily when you changed declination / altitude by 30 degrees. Stars become unfocussed when your shooting at around 1 arc second per pixel with my C8.
My only solution is to go with the Off Axis Guider, which is the only way to get decent guiding. I've had erratic hit and miss performance when using a Guide Scope, some nights it's good, other nights you have a steady 1 arc second per 5 minute exposure time drift.
The other issue with Guide Scopes is field of view and the wider that is, the more likely you are going to pick up a Satellite Zipping through it and might have the guider try to chase that, especially when your guiding on a 8th / 9th mag star and a Mag 4 satellite rips through. There are options in Astro IIDC guiding to limit that sort of thing.
TTYL.
Milton Aupperle
On 29-Jun-08, at 11:52 AM, Tim wrote:
Milton:
I like the serial port hub idea. Last night was the first time I
really put the focuser control option of Equinox Image through it's
paces instead of just running the robofocus software on the PC, and I
was rather impressed with it.
I also think you're right about the mirror flop in SCTs. Since I'm
guiding with the 9.25", I have this problem around the zenith - which
is unfortunately where the least atmosphere is getting in my way.
Last night, I took two image sequences. The first was of M13. The
whole sequence was over before it crossed the meridian, though, and I
had no noticeable flexure or mirror movement (but I haven't processed
the images yet and they were only 5 minute exposures IIRC). But for
the Dumbell, I shot 20 minute exposures, and when I was shooting the
green frame, the scope was crossing the meridian (around 2am, I think
- I used my cell phone as an alarm to take naps while imaging). The
clear and red frames are very nice and sharp, but the first green
frame was trailed. I started a 2nd green and took another nap, and
found it had trailed again, but with a jump, and so a gap showed in
all the trails. By then, it was 3am and I had a headache from so many
catnaps, so I buttoned everything up and stared at my eyelids for the
rest of the night.
If the 9.25" was easy to take out of its forks (it might be, I've just
never done it), I'd make a cradle to support my 6" f/5 Jaegers and 5"
f/5 Jaegers together (the latter needing a new OTA), and use one for
imaging and the other for guiding. But I'd want to be able to go back
to the 9.25" for planetary imaging.
Or... ...hm. If I made a folded refractor out of that 6" f/15 lens
I have, with 2 folds, that might fit nicely in place of the 9.25".
But probably I should just rig up a mirror locking setup for the
9.25". That would require disassembling the OTA, though, to drill
holes in the backplate for lock screws.
Finally, the other way of getting around the mirror flop problem would
be to use another fixed-optic scope as the guider. But I've already
got a lot of weight on the 9.25", so I'd have to think about this a bit.
-Tim.
--- In Astro_IIDC@yahoogroups.com, Milton Aupperle <milton@...> wrote:
Hi Tim;
Your best bet is to get a multi serial port device like
USB 4-Port Serial Adapter
http://www.keyspan.com/products/usa49wg/
That gives you 4 serial ports , which should be enough for Equinox
with the temp focus controllers, assuming Equinox can use both at the
same time.
As to Flexure. I've have determined that the lions share of my
flexure is mirror movement on the C8 scope. Unless I can lock the
mirror down, a second guide scope simply will not work for me.
HTH..
Milton J. Aupperle