From: "Tim" <tjp314@pacbell.net>
Date: November 30, 2007 11:04:49 AM MST
To: Astro_IIDC@yahoogroups.com
Subject: larger chip cameras. Was: Re: First light ... Mars
Hi Alan:
What larger chip camera did you/are you referring to?
One thing I've considered is the monochrome 5mpixel Grasshopper
camera. The pixels are small, so I'm thinking that a barlow might not
even be necessary for planetary imaging (just "ROI" around the
planet). And there are enough of them and the chip is big enough
(2/3" format) that they could be binned 2x2 or even 4x4, and still
have enough pixels to take decent size deep sky images.
Problem is, the 5MP Grasshopper is a $3500 camera, which is about what
I paid for my ST2000. And the grasshopper isn't cooled.
Reason I am intrigued by this concept is that, once I have my scope
aligned and the cameras running, I close the doors beneath the scope
and sit in comfort at a desk while I robofocus and image away. I'm
almost, but not quite, completely robotic now. I still have to
manually open the roof hatch and swing the Nexstar up from its stowed
position. But these days it only takes me about 5 minutes to do that,
wake the scope up from hibernation, and close the doors beneath to
keep thermals from the house out of the optical path, and I'm good to go.
And really, though I do still have to climb up onto the platform and
open the doors to swap out cameras or barlows, that doesn't take
really take all that long either. I'm just getting lazy in my old age.
When I'm done observing, it really only takes me about 2 minutes to
shut everything down, hibernate the scope, stow it and close the hatch
cover.
I just wish the space was big enough to accomodate my 12.5". But an
11" would fit as well as the 9.25"... ...hm....
-Tim.
--- In Astro_IIDC@yahoogroups.com, Alan Friedman <alan@...> wrote:
I think I've determined tthe following rule of thumb: moments of good
seeing occur when you sleep - so just don't do that and you're all set.
Seriously - the weather tools (Clear Sky Clock included) seem to be
much better at predicting poor seeing than good. Steady seeing is a
very transient event in mid - northern latitudes, often measured in
seconds rather than minutes. One of my reasons for moving to a larger
chip camera was the frustration encountered in making mosaics with
the 21BF04 - finding one half of a crater sharp and the other mush
due to the change in stability during the time it took to move the
camera. When imaging an object below 40 degrees in altitude, as it
passes above the rooftops in the adjacent houses, I can almost
pinpoint the energy loss for the homeowners as I watch the onscreen
image respond to the various heat leak distortions.
I wish I could say that the joy is in the hunt for those magic
moments... but it is a cold and tiring job setting up the scope night
after night only to put it away with nary a frame collected.
cheers,
Alan
On Nov 30, 2007, at 11:54 AM, Milton Aupperle wrote:
Hi Jim;
Nice image.
I was out after Mars last night for about 1.5 hours when it was -17°C
(light cross winds so it was about -20 to -25°C on exposed flesh) but
the sky was clear and will be the only clear skies I get this week.
The scope sits outside on the balcony under a barbecue grill cover
and is always in equilibrium with the outside air.
According to the 300 mb plot and clear sky clock, i should have had
seeing that was 4/5 or better - however it wasn't even close. I had
turbulence that moved the disk +/- 5 arc seconds and sporadic bursts
of motion that turned mars into a 30 arc second boomerang or even a
50 arc second donut. This was imaging at 9 ms exposures at prime
focus of 2000 mm. Even visually stars were soft little balls due to
turbulence and instead of pinpoints, they were tiny. As I moved my
cameras and laptop back inside, I decide to have a quick peak and M42
for this year, as it rises majestically over the newly xmase
decorated 20 story crane that now blocks the only remaining view to
the south.
What I'm doing from now on is to try and quantify what factors
produce "good seeing" here. So I grab snaps of the predicted
turbulence and where the jet stream is, then take some movies of a
bright star and record my visual observations. I hope I can then get
a better handle on what factors "point" to good seeing here.
TTYL..
Milton J. Aupperle
.