First timer, focusing (?) problem

Discussions of Electronically Assisted Astronomy using the Live Stacking feature.
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Re: First timer, focusing (?) problem

Post by psy1280 » Thu Oct 10, 2019 10:05 pm

Much thanks chongo,

I did, in fact, play with the histogram (for hours)...I'm going to try your suggestion of a longer exposure, etc.. So, you don't think my "halo" is a photographic artifact?


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Re: First timer, focusing (?) problem

Post by turfpit » Fri Oct 11, 2019 10:21 am


M31 is a huge object. The following shows what can be expected to be 'seen' by various telescope/camera combinations. The diagram from the centre outwards:
  • an SCT 8" with focal length 2032 and CCTV camera with a 720x576 capture area
  • refractor 81mm with focal length 625mm with CCTV camera
  • refractor 66mm with focal length 400mm with the CCTV camera
  • refractor 66mm with focal length 400mm and ~$1000 CMOS camera with a ~4500x3500 capture area

M31-FOV.JPG (43.96 KiB) Viewed 139 times

key.JPG (44.93 KiB) Viewed 139 times

The image was generated via the Astronomy Tools Field Of View Calculator

astronomy-tools-FOV-calculator.JPG (90.73 KiB) Viewed 139 times

The SCT with the CCTV camera will only be able to capture the core of Andromeda. Adding a 0.5x reducer will not really improve things.

M31-0.5x-reducer.JPG (39.44 KiB) Viewed 139 times

I would consider M27 & M15 more realistic targets for the SCT + CCTV + 0.5x reducer combination.

M15-0.5x-reducer.JPG (41.37 KiB) Viewed 139 times

M27-0.5x-reducer.JPG (35.48 KiB) Viewed 139 times

Using the Astronomy Tools FOV Calculator during observation session planning to identify suitable objects for various equipment combinations can save lots of wasted time and disappointment.

From my previous post in this thread
to achieve results will require hard work, discipline, attention to detail and patience

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