Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Really confused with under/over correction, need some advice.

Optics Refractor
  • Please log in to reply
5 replies to this topic

#1 flywing1

flywing1

    Explorer 1

  • -----
  • topic starter
  • Posts: 81
  • Joined: 26 Aug 2021

Posted 03 December 2021 - 04:11 PM

My current understanding is that this lens is Undercorrected with a Positive SA, which creates an airy disk (simulated probably) as shown. Is this correct? Because I have seen multiple posts on CN and even academic pdfs either calling this overcorrected or saying that a negative SA is associated with undercorrected lens.  For example, from telescope optics site (https://www.telescop...aberrations.htm ): “spherical aberration is "overcorrected", i.e. with marginal rays crossing before paraxial rays” (sorry if I misunderstood, but this should be Undercorrected, right?).

These two images are from Edmund Optics and wiki:
https://www.edmundop...n-plates-en.pdf
https://en.wikipedia...ical_aberration

Attached Thumbnails

  • undercorrect.JPG
  • undercorrectAirydisk (Medium).JPG


#2 GOLGO13

GOLGO13

    Fly Me to the Moon

  • *****
  • Posts: 6,957
  • Joined: 05 Nov 2005
  • Loc: West Virginia

Posted 04 December 2021 - 02:07 PM

I can't help too much with the technical question you are asking. But as far as refractors go, the spacing is off for the lenses in these situations.

 

My Ronchi eyepiece says this about over correction (pretty much opposite for under):

 

Off-axis rays have another focus than on-axis rays. There can be seen many diffraction rings when focused! You have a very bad contrast when observing! Any telescope which will be used for planetary observation should not have any sperical Overcorrection, as many coma correctors introduce sperical undercorrection. both errors might be erased each other out.

 

Hopefully some of the smarter folks can chime in.


  • flywing1 likes this

#3 sevenofnine

sevenofnine

    Vanguard

  • -----
  • Posts: 2,036
  • Joined: 16 Apr 2016
  • Loc: Santa Rosa, California

Posted 05 December 2021 - 09:24 PM

Well,...since you have 230 views and only 1 reply, I will offer this: https://shopatsky.co...pes-2nd-edition. If you don't have this book, the answer to your question is most likely in it. Best of luck to you!  idea.gif


  • Polyphemos and flywing1 like this

#4 Polyphemos

Polyphemos

    Mariner 2

  • -----
  • Posts: 218
  • Joined: 05 Dec 2020
  • Loc: Northern Bay Area, California

Posted 05 December 2021 - 11:22 PM

Well,...since you have 230 views and only 1 reply, I will offer this: https://shopatsky.co...pes-2nd-edition. If you don't have this book, the answer to your question is most likely in it. Best of luck to you!  idea.gif

Awesome the book is back, and at a less than the multi-hundred $$$ price just a few months ago!  Sevenofnine, can you tell me whether the star images in the printed copy are in color?


  • sevenofnine likes this

#5 sevenofnine

sevenofnine

    Vanguard

  • -----
  • Posts: 2,036
  • Joined: 16 Apr 2016
  • Loc: Santa Rosa, California

Posted 05 December 2021 - 11:57 PM

Polyphemos,...Unfortunately, no. However, there are lots of very good illustrations that are computer generated. Ed Ting considers it the bible on this subject and highly recommends it. Some sections are written for the layman but others require a background in physics and math to understand. hmm.gif


  • Polyphemos likes this

#6 Polyphemos

Polyphemos

    Mariner 2

  • -----
  • Posts: 218
  • Joined: 05 Dec 2020
  • Loc: Northern Bay Area, California

Posted 06 December 2021 - 01:05 AM

Polyphemos,...Unfortunately, no. However, there are lots of very good illustrations that are computer generated. Ed Ting considers it the bible on this subject and highly recommends it. Some sections are written for the layman but others require a background in physics and math to understand. hmm.gif

Thank you, sevenofnine, I’ve ordered the book for less than $45 shipped to my door.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: Optics, Refractor



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics