Re: Unguided imaging


cford81@...
 

Hi Roland,

I recently got APCC working with SGPro with my AP1600GTO and after building a pointing model, I have been doing unguided imaging at 2400mm. Not quite as aggressive as your 3500mm but the stars are perfectly round for 10-15 minutes. I only start losing it after that which may be due to any number of factors. 

As I control with SGPro there is an unguided mount dithering option in that software that is super useful and makes it very simple. So yes, unguided imaging is a must have feature for me.

Chris



From: "chris1011@... [ap-gto]" To: ap-gto@...
Sent: Wednesday, June 28, 2017 3:05:20 PM
Subject: [ap-gto] Unguided imaging

 

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


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