Have your best photos printed at Deep Sky Printing .

We use Kodak Color Metallic paper for an exquisite finish.
Online ordering. Rapid turnaround.

Custom Search

 My Equipment

(Page 6)

HOME
Equipment
Page 2
Page 3
Page 4
Page 5
Page 6
Page 7
Page 8
Page 9  

 

Feb 18 2015:

Mother nature has bee anything but cooperative in allowing my to test and use the new TPO10RC scope. However, I was able to squeeze in a few nights to do some testing. In doing so, I have discovered that I have some drifting probably due to differential flex between the main scope and the 50mm guide scope I'm using. I had always had this drift but it was hardly noticeable when using the SN8 scope at f4. The TPO10RC , however, at f8 having a focal length of 2000mm was considerably more sensitive to any small movement in the equipment.

I had tried various things including purchasing sturdier mountings  from ADM for the guide scope as well as  playing with the guiding adjustments in PHD2 but nothing seemed to do the trick.

Since the TPO10RC has rather slow optics at f8 I need to use 10 second exposures to get the image quality I needed. But at 10 seconds I usually got elongated stars due to the drift. I finally decided to bite the bullet and get a focal reducer. After doing some research on the web I decided to go with  the Astro-Physics .67 telecompressor CCDT67 ( see image at right)

This device did the trick. No it didn't fix the drift I was experiencing but it made it more tolerable. The device reduced my focal ratio to f5.3 and reduced my focal length to 1341mm from 2000mm. This did two thing for me, having faster optics allowed me to use shorter exposure times and still get the illumination I needed and it also reduced the high sensitivity to small amounts of motion in the mount. What I as shooting at 10 seconds I can now do at 5 seconds with  much  better result. I can even run at 15 seconds, however, at that  speed I start getting elongated stars. I have a pug in for Photoshop that  helps round elongated stars. So technically I can get usable images at the slower speed.

Most people that  suffer from drift due to differential flex between the guide scope and main scope move to an OAG ( Off axis guider). This device samples a small part of the main image via a prism and sends it to the guide camera. Since the guide image and main imager are all on the same focal axis there is no flex possible between the two.  At some time I may need to go to that  configuration should I want to take exposures longer that  15 minutes but for now I'll stick with  the 50mm guide scope. Its very fast optics and wide field of view makes it easy to find a suitable guide star as well as easy to locate an object that  isn't in the FOV of the main scope.

Now if the weather would cooperate so I can get out and take some decent pictures I'd he a happy camper. This is February 2015. I haven't been able to do much since I bought the scope in October of 2014.

Nov 1 2015:

       I think I finally beat the drift problem. It seems that  there were multiple causes.

  1. I had read that there is a glitch in the RA motor controller of certain  Atlas EQ-G mounts. The tracking rate is too slow. This causes the stars to drift to the west. Fortunately this problem was discovered a while back and Chris Schillito ( Mr. EQMOD) provided a means to correct for that  in the driver program for them mount.  After trial and error I realized that  this was also affecting my mount. By applying the proper correction (+3) to the guide rate the west drift was minimized.
     
  2. When I first started to use the TPO10RC I opted to use an Orion Mini guide scope to keep the overall weight down on the mount since the mount is rated for 40 lbs and I was very close to that. The problem with that  setup was that  the arc second per pixel of the 50MM guide scope and  DSI was large at about 16 arc sec per pixel and the imaging scope/camera combination is in the neighborhood of  1 arc second  per pixels. This difference causes the main image to move more for a small movement of the guide image correction. This  16:1 ratio caused elongated stars and also contributed to the drifting.
    My solution to this was to use my Orion ED80 as a guide scope. The resolution of this setup is closer to the resolution of the main imaging setup and virtually eliminated any drift as well as minimized the elongation to the stars on very long exposures ( > 15 minutes).

    Yes, I am probably over the posted weight limit for the mount, however, it performs as good as it always has and doesn't seem to mind the extra load.
     
  3. The last thing I did was check and correct my polar alignment. Not sure if this contributed to drift or elongated stars but improving the polar alignment certainly  didn't hurt anything

(stay  tuned for updates )

00