Hi All,

I've been using the 17" F8 astrograph for various mount development and testing. One of the items on my test schedule was to do unguided imaging. I wanted to see if it was practical to do this at 3500mm focal length with a truss tube telescope, and what is a practical exposure time for each sub.
Seeing conditions are not the best around here this time of year, so further tests will be done as conditions improve over the summer. Preliminary tests show that accurate imaging with this setup can be done with 20 minute subs and possibly even 30 minutes if the modeling data is carefully done.

This is a portion of an unguided imaging test using MaximDL to show the position of the guide star. The pixel scale is 0.88 arc sec per pixel. Tracking is on the order of 1/4 arc sec RMS for periods up to 30 minutes:

https://www.astromart.com/common/image_popup.asp?image=/images/forums/834000-834999/834121.jpg&caption=


This unguided LRGBHa image was taken using this method over a period of about 3 hours. Subs are 10 minutes for LRGB and 15 minutes for the H-alpha:
https://www.astromart.com/common/image_popup.asp?image=/images/forums/834000-834999/834117.jpg&caption=

This is a 20 minute unguided H-alpha image:
 https://www.astromart.com/common/image_popup.asp?image=/images/forums/834000-834999/834118.jpg&caption=

I know these aren't great images but they prove that it can be done.
One thing that occurred to me is the fact that guiding allows an easy and automatic method for dithering the image. If you take a number of unguided images that lie on the same pixel or very close to each other, you don't get the automatic noise reduction of a set of dithered images. So my question is this: is unguided imaging a must have feature?

There is more to come along these lines ... later :^))

Rolando