Before the rush

Before the rush
by evan-pak

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With my current astrophotography setup it is not possible for me to capture the full andromeda galaxy in one picture.


  • Telescope: Celestron C8 SGT XLT (f: 10, focal length: 2003mm)
  • Mount: Celestron Advanced VX
  • Camera: Canon 7D Mark II (EOS)
  • Optics: f/6.3 Barlow lense (reduces f to 6.3, focal length to 1200mm)

So now I am wondering, what if I mount two f/6.3 Barlow lenses behind each other, will the focal length then get multiplied by the factor 0.63*0.63=0.3969?

This way it would be possible for me to capture some of the wider entities.
The base magnification with my setup (with no barlow lenses) is at around 80x.

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up vote 6 down vote accepted
  1. Focal reducers (decreasing focal length) are not Barlow lenses (increasing focal length)

  2. By inserting a focal reducer the focal point is moved inward the tube, chances are you will not be able to mount your camera in the correct position without modifying the telescope when the focal point is moved even further.

  3. The telescope has its maximum usable field of view and while it is possible to decrease the apparent focal length by adding extra lenses, below certain point it will be only decreasing the image size without adding any new area (or in other words, only adding black border/vignetting)

These are general rules. I don't know if it will be possible to catch the full galaxy using your specific setup.

share|improve this answer
I see. My field of view would look something like this with the 6.3 f reducer: Image. So stacking field flatteners is not possible then? I guess I could try to do mosaic pictures – RononDex Jan 22 at 12:47

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