[ATM] optimal thickness of Schmidt correctors

[Paul A. Valleli]

I believe the Kepler Telescope utilizes a 60-inch
Schmidt with an array of CCD detectors at the
spherical focal surface. It would be interesting to
know the thickness and aspect ratio D/T since it had
to withstand the rigors of launch. I believe it was
made in Germany.

Paul

---- Original message ----

  Date: Sat, 14 Jan 2012 12:46:15 +0100 (MET)
  From: Dominic-Luc Webb <dlwebb at canit.se>
  Subject: Re: [ATM] optimal thickness of Schmidt
  correctors
  To: ATM Superheros <atm at atmlist.net>
  >On Fri, 13 Jan 2012, Richard F.L.R. Snashall
  wrote:>>> On 1/13/2012 11:25 AM, Dominic-Luc Webb
  wrote:>> >>> > I have access to pretty good
  cocktail of numbers to brew>> > some equations,
  but no experience with applying them>> >
  intelligently to the present question.>> >>>>> I'm
  sorry, I don't remember exactly where it was, but
  I recall reading>> D/50 to D/40.>>>>First, thanks
  for all this input! You guys are great!>>I recall
  something like this too and this is what the
  thickness>actually is in the rare cases I could
  get info for a modern>commercial scope. One
  solution some people have used is to>scale down
  the original 48" Polamar Schmidt camera, but
  that>breaks all the rules. The original corrector
  (replaced only>recently for transmission reasons)
  is 53" diameter and 3/8">thick (D/141)! A scaled
  down 8" would only be 0.06" thick!>There are other
  broken rules: it is plate glass! Minor>deviation
  from common ATM practice: it was optimized
  for>435.8 nm. This has been known to me since many
  years and is>how I first started my designs with 6
  mm plate glass>optimized in the higher UV. The 48"
  Palomar camera>represents my starting point when I
  first started "dabbling">with this design.>>Source
  of 48" Schmidt info is R.G. Harrington
  PASP(64/381):271-281.>1952.>>I have PDF of this
  ref if anyone wants it.>>Main point is that
  something has changed over time and I am>curious
  why. People seem to be using thicker glass than
  needed>and at same time even the pros have used
  thin plate glass on the>correctors for the
  largest, most impressive Schmidt cameras
  ever>built.>>It seems there is no good reason,
  mechanical or optical, to not>use 6 mm thickness
  even for a Schmidt corrector around 400
  mm>diameter, above which gets into the largest
  Schmidt cameras>in the world.>>Dominic-Luc
  Webb>>_______________________________________________>ATM
  mailing list http://www.atmlist.net/