Jump to content


Photo

What does "RTA" Tell me about a Primary

  • Please log in to reply
3 replies to this topic

#1 gaz-in

gaz-in

    Viking 1

  • *****
  • Posts: 821
  • Joined: 17 Dec 2007

Posted 20 February 2013 - 08:19 PM

Hi All,

I was looking at a primary that had an RTA of 0.23 . What does this tell me about the quality of the mirror?

Thanks In advance for the inputs

#2 Jason D

Jason D

    Fly Me to the Moon

  • *****
  • Posts: 6665
  • Joined: 21 Oct 2006
  • Loc: California

Posted 20 February 2013 - 08:24 PM

Hi All,

I was looking at a primary that had an RTA of 0.23 . What does this tell me about the quality of the mirror?

Thanks In advance for the inputs


RTA stands for Relative Transverse Aberration. Basically, it means that all focused light rays off your mirror will be confined to a diameter of 23% the length of the airy disc diameter. RTA of 0.23 represents an exceptional mirror.

Jason

#3 gaz-in

gaz-in

    Viking 1

  • *****
  • Posts: 821
  • Joined: 17 Dec 2007

Posted 20 February 2013 - 08:31 PM

Thanks, It is an Ed Stevens Mirror with a Strehl of .991, RTA of 0.23 and a peek to valey wave of <1/20. Another mirror I am looking at is Strehl 0.993, RTA of 0.73, and a peak to valley wave of <1/20. Is there realistically a difference between the two (assuming you can believe the ratings).

#4 Jason D

Jason D

    Fly Me to the Moon

  • *****
  • Posts: 6665
  • Joined: 21 Oct 2006
  • Loc: California

Posted 20 February 2013 - 08:38 PM

Thanks, It is an Ed Stevens Mirror with a Strehl of .991, RTA of 0.23 and wavefront of <1/20. Another mirror I am looking at is Strehl 0.993, RTA of 0.73, and wavefront of <1/20. Is there realistically a difference between the two (assuming you can believe the ratings).


Mine is also Ed Stevens with 0.992 Strehl and 0.26 RTA. Do not read too much into these numbers. These numbers are based on measurement samples. I sould say all these mirrors are more or less the same in terms of Strehl/RTA (good quality mirrors). Base your decision on other factors.
Jason






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics