From: Willie Strickland <willie@igc.org>

Date: July 4, 2005 3:13:16 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: infrared filters


I have imaged on 8 different nights since 6-22.  I am having a lot of fun.  I will post some images when I get the chance.  Since I am brand new at all this, I have viewed these nights more as developing and learning a procedure than actually imaging.


I have worked on Jupiter almost exclusively since it is so bright, but after it sets I have imaged bright stars for practice and even tried some images, without success, of bright areas of the milky way.


Here is my setup.


   1. Borrowed NexStar8GPS which tracks quite well it seems to me

   2. Fire-i webcam with lens removed

   3. No infrared filter yet

   4. Homemade adapter for eyepiece

   5. iBook and Astro IIDC

   6. External Firewire drive for working directory

   7. Dark site  http://cleardarksky.com/c/PaulMeyObTXkey.html

   8. Almost exclusively using Monochrome mode to simplify my choices

   9. I have read the whole Astro IIDC Help, but dont understand it all



Problems/Questions:


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?


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.


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'.


One of my friends suggested always focusing on a bright star that is nearby the object first.  After finding that on the chip and getting it in focus, then move to another object.


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.


The biggest culprit here seems to be the fact that the camera and the eyepiece are not parfocal.  There is quite a bit of difference.  I have learned that approx. 3/4 turn of the rough focus knob on the NexStar gets me close.  But that  hasnt helped consistently enough. One night I tried not using the flip mirror and would focus the eyepiece and then remove it and add the camera.  I need more experimenting or advice here.


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.


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?



Thanks for taking the time to read such a long post.


Having lots of fun,

-- 

Willie Strickland

willie@igc.org