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Aberrations in astronomy

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dawson's picture
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Aberrations in astronomy

I'm planning an online meeting for my local society on "aberrations in amateur astronomy" - the exact title is to be decided and will probab;ly include how to deal with these aberrations.

I wanted to pick out the commoner issues with visual astronomy and astrophotography. 

Topics I was thinking of talking about include:

  • collimation
  • thermal currents
  • coma
  • field curvature
  • vignetting
  • cone error

What other issues and aberrations should I include? 

Thanks.

James Dawson
Nottingham Astronomical Society
https://www.youtube.com/c/NottinghamAstronomicalSociety/videos

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Some more

Achromatic, tracking, field rotation. Eyepieces bring a new set kidney bean, astigmatism,  distortion....

Regards Andrew 

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Aberrations

The first Dobsonian I had showed serious spherical aberration.

Worked just fine as a light bucket, which I what I wanted it for.

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Aberrations

pinched optics, mirrors with turned edges

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Aberrations

Insufficient Annealing of Optics

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Abberations

Could be a long meeting, James!

Atmospheric dispersion?

Regards, Graham

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How to measure and correct

Hi James - You probably need to show how to measure qualitatively using Ronchi grating as a star test. There is an excellent book on the subject - Star Testing Astronomical Telescopes by Harold Suiter although he only uses intra-focal and extra-focal image appearance. Now that is an art!.

Cheers

Alan

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Star Testing Astronomical Telescopes by Harold Suiter

Alan,

I got a copy of this book maybe a year or two ago as part of a job lot of books. I flicked through it at the time and saw some equations and complicated graphs and decided it was too advanced for me, so I stuck it on a shelf... I've now looked in it in more detail on your advice and it is a remarkably accessible book. Yes there are equations and in places, it goes off on another level, but there is a good proportion of the book which is very helpful and informative. Thank you for making me get it off the shelf.

James

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Aberrations

Thanks all for the replies. Some very useful additions to my list.

I'm planning to keep it simple (like me) and concentrate on the errors and aberrations which are common and [relatively] easy to resolve. I'll get someone to talk about star testing to make people aware of the more advanced methods of testing optics available.

Thanks.

James

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Aberrations

Another couple of thoughts. Fundamentally, even with a "perfect" telescope a star is a disc due to diffraction in the optics, and you rarely see performance at the diffraction limit as atmospheric turbulence blurs this disc.

Cheers,

Andy

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A better title for the meeting

A better title would be something like 'Optical aberrations: identifying and treating them'.

The word 'aberration' in general means something abnormal. So an 'Aberrations in amateur astronomy' would mean anything abnormal in amateur astronomy – like someone claiming to speak Venusian.

David