From: Milton Aupperle <milton@outcastsoft.com>
Date: July 4, 2005 5:58:50 PM MDT
To: Astro_IIDC@yahoogroups.com
Cc: Willie Strickland <willie@igc.org>
Subject: Re: [Astro_IIDC] infrared filters
Hi Willie;
On 4-Jul-05, at 3:13 PM, Willie Strickland wrote:
Focusing - IR filter
--------------------
The biggest problem I am having is focusing. On several of these
nights, the seeing & transparency were near excellent and the views I
was getting in the eyepiece and in my 10" Dob, setup nearby, were
very nice. I expected to get good movies. I got better movies, but
still not that good, yet.
Having read past messages here and other places, I believe that the
lack of IR filter is a magor factor here. Is that correct?
For planetary it will not make nearly as much difference as one would think and your losing some light too.
Here is an articles on the pros and cons of using or not using an IR filter:
http://www.leadbeaterhome.fsnet.co.uk/IR_FAQ.htm
and
http://www.leadbeaterhome.fsnet.co.uk/IRB_with_Saturn.htm
For lunar / solar / long exposure ( much greater than 1 second) it can make a difference.
Focusing - Seeing
-----------------
One night I had excellent seeing until around midnight and then it
deteriorated significantly for a couple of hours and then improved
steadily as the night progressed. I noticed that the scope was
'tracking' much better during the periods of better seeing. At one
point I held Jupiter within 1 or 2 ticks of center using 2x pixel
zoom for over an hour. I dont remember the exact time frame. I left
to respond to someone's request and came back some time later to find
it right where I left it. Very impressed.
All of that to say, I realize that excellent seeing is a major factor
in keeping the image centered on the chip. Correct? On other nights
it would bounce around erratically.
It is a major factor. If it's jumps around that much there isn't much point in taking images as they all wind up being "mush". As a rule of thumb, I put a 4mm or 6mm eyepiece on and if the target isn't sharp and steady for more than 10 seconds at a time with my eyes, it probably is not worth trying to take high resolution images. However you can still wind up with lulls in the turbulence and suddenly it goes dead steady and the limiting factor is your scope's resolution, not the atmosphere.
I have had maybe 3 nights in Calgary over the past 2 years where the seeing was perfectly stable and I have photos from those nights on my home page:
http://www.outcastsoft.com/AstroImages/Luna_040430_2300.jpg
http://www.outcastsoft.com/AstroImages/Luna_040426_2225.jpg
and
http://www.outcastsoft.com/AstroImages/Jupiter_040501_000112.jpg
2005 has been an absolute bust for good seeing so far.
Focusing - finding the object
-----------------------------
Occasionally this has been a problem. I got a flip mirror from
scopestuff.com and now I dont have to keep swapping the Fire-i and
the eyepiece. But I get the object absolutely centered in the
eyepiece and then try for a long time to find the object on the chip.
I spent almost an hour trying to get jupiter on the chip one of the
first nights I was out.
Couldnt focus at all on anything other than a very bright star.
I am using a reticled eyepiece which gives me a FOV of about 15' -
20' I estimate. Using the formula from the Help file, I estimate
that the FOV of the Fire-i/NexStar combo is about 6' x 4.5'.
Are you using using the camera at prime focus or with a Barlow, right? My experiments using afocal with an eyepiece have never panned out well at all.
No real question, just dont have a handle on how best to do this.
Simply been trial and error for me and very sporadic success. I
thought I had it nailed and then one night I couldnt even get Jupter
in without considerable time expended.
My usual approach with finding an object with the Unibrain and other web cameras is:
1) Put a bright star or terrestrial object in the center of your FOV with an eyepiece and also align the finder scope on it.
2) Put the Camera on the scope at prime focus (no Barlow or Eyepiece projection). For stellar objects, increase the Brightness to around 190 and increase the exposure time too (i.e. set Base CCD to 133 ms and set exposure time to 133 ms). I also like to do check mark the "Display Image Sharpness" item too, and watch the numbers change as I move the scope left/right/up or down. It can pick up very subtle changes in image brightness, which can help you figure out if your getting close to faint or very out of focus objects.
3) Move the scope until the object or defocussed blob appears and then center it in in the Preview window.
4) Now adjust your focus until its' a minimal disk and then reduce exposure time and brightness and focus again.
5 )Now that it's centered in your FOV, adjust the Finder scope so that it's also centered on the object too. They may not be aligned to the same position that you would use with an eyepiece.
6) Now add in the Barlow (if your going to use one), refocus and and recenter the Finder Scope too.
I've used the above technique with the MAK 127 mm aperture scope and a focal length of 4980 mm (field of view about 2.5 ' x 1.8') with Jupiter and Saturn, but you have to make sure your finder scope is aligned well too.
Also if your adapter is not perfectly centered on the center of the CCD imaging area (which isn't actually the center of the CCD chip) , then the Camera FOV wanders as the camera is rotated. So try and keep the camera left in one rotational position.
Brightness/Gain
---------------
Saturday night was our regular monthly star party and several other
club members stopped by to see what I was doing. A couple of those
are experienced Toucam users and curious why I didnt get a Toucam.
They always volunteered that they "get much clearer images than I was
getting." One of them said I had my gain way too high. As I turned
the gain down I began to loose the edges of the disc, they turned
scolloped sort of. I had seen this before and used it to help me
decide how much gain to use.
One thing I would do is switch to color imaging. Focussing in monchrome with a color cameras on stars or Jupiter doens't work as well as in color - at least for me it doesn't.
And white balance is not a big deal either nor is image processing more complex and to get an idea of what is "normal" is simply point the camera at a white piece of paper in daylight outdoors (with no lens) , adjust brightness exposure until it's about 50% brightness (say middle grayish tones) and then adjust Red or Blue sliders until it becomes truly gray. If the lighting is not changing too much or you and the camera aren't moving around (i.e brightness changes will affect color balancing) , you can also just hit the "Color Balance" button and Astro IIDC will color balance it for you.
Anyway, I cant say that I have any good procedure on determining the
gain setting. I usually increase the 'Base CCD Exposure Time' in
order to keep the brightness down to 80 or less. And I use the
lowest value for 'Base CCD Exposure Time' I can get away with and the
fastest Camera FPS it allows. I adjust the focus and the gain to get
the sharpest, most symmetrical disc of the planet. Any suggestions?
What you describe is what i more or less do. I keep gains as low as possible (80 to 150) and then adjust CCD exposure time to make it bright enough.
However Jupiter is a hard object to focus sharply on, it's a featureless white fuzzy blob, with indistinct gradational edges. Usually I try and get one if it's moons in the field of view and fine focus on them instead.
HTH..
Milton J. Aupperle
President
ASC - Aupperle Services and Contracting
Mac Software (Drivers, Components and Application) Specialist
#1005 - 815 14th Avenue. S.W.
Calgary Alberta Canada T2R0N5
1-(403)-229-9456
milton@outcastsoft.com
www.outcastsoft.com