Celestial hemisphere:  Northern  ·  Constellation: Lyra (Lyr)  ·  Contains:  IC 1296  ·  M 57  ·  NGC 6720  ·  Ring Nebula
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M57 - a star test?, Tom Gray
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M57 - a star test?

Getting plate-solving status, please wait...
M57 - a star test?, Tom Gray
Powered byPixInsight

M57 - a star test?

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Description

Nothing to write home about, but a useful star test...

Imaging the central star in M57, along with the three fingers, is sometimes used as a test of optics. I took this 14 minute image (30s subs) to test my WO Zenithstar II 80ED semi-APO (semi in that it is an air-spaced doublet using FPL-51 glass).

I think it passed this test, and I'm pleased with the uniform starfield, and lack of vignetting. The focus was a little soft and conditions did not allow time to collect RGB data to check for other abberations. Perfectly sufficient for my less than critical eye, and a welcome addition to my (homemade) astroimaging platform.

This was one of William Optics early scopes (2007) which I bought in 2014 to use as a guide scope for my LX5. Unfortunately its weight at ~3kg was excessive and I ended up using this primarily as a visual scope on a Stellarvue M2 mount - it gives great views, especially with the binoviewer or a 2" 'spacewalk' eyepiece. At native f6.8 it is reasonably fast, although the 3" aperture takes time to gather sufficient photons to boost the SNR. With my 2/3 camera, it gives a slightly wider field than my 8" SCT pushed to f3.3

I'm rambling on...but another step in my astroimaging journey.

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  • Final
    M57 - a star test?, Tom Gray
    Original
  • M57 - a star test?, Tom Gray
    B
  • M57 - a star test?, Tom Gray
    C

B

Description: I did tweak the stars in my image to 'average location' to overcome the slight loss of focus (by hand using Envisage 'magic eye'). This is the original stacked and aligned in Penumbra, with gentle brightening and sharpening, to show the detail. Quite decent, if not exactly a scientific test!

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C

Description: Ouch...
At f3.4 ish, a 4m exposure is quite sufficient to show that an 0.5x reducer is too much! I must seek out a 0.8x reducer/flattener to use with my Zenithstar II 80ED. Any suggestions to suit my modest astrophotography budget?

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M57 - a star test?, Tom Gray