Aberrations in astronomy

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    James Dawson

    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? 


    James Dawson
    Nottingham Astronomical Society

    Andrew Smith

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

    Regards Andrew 

    Paul Leyland

    The first Dobsonian I had showed serious spherical aberration.

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

    Robin Leadbeater

    pinched optics, mirrors with turned edges

    Ron Arbour

    Insufficient Annealing of Optics

    Graham Winstanley

    Could be a long meeting, James!

    Atmospheric dispersion?

    Regards, Graham

    Alan P Buckman

    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!.



    James Dawson

    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.



    Andy Wilson

    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.



    James Dawson


    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.


    David Arditti

    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.


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