Re[2]: [ATM] over&under correction.

[Richard <cnc@cncservo.co.uk>]

Hi Scott,

Monday, July 11, 2005, 5:41:38 PM, you wrote:



SM> Not only is there no difference in summary quality measures, the in focus
SM> diffraction patterns are exactly the same. Also, the extrafocal diffraction
SM> pattern in one case exactly matches the infrafocal diffraction pattern in
SM> the other for the same amount of focus travel. So, based solely on optical
SM> theory there's no difference at all between the two cases.

SM> Of course I defer to others on which condition is easier to fix.

SM> Mike Peck


SM> Extending this discussion to ask the question "which is worse, a tenth wave
SM> edge rolled down or up" I would conclude that either of these defects,
SM> occupying otherwise equal areas, position and magnitude on the mirror, will
SM> have the same impact on contrast transfer.  I make this observation only
SM> because over the years I have heard much commentary regarding the need to
SM> avoid even the slightest amount of turned edge, but relatively little energy
SM> spent warning against residual turned up edge.  In my (perhaps overly
SM> simplistic understanding), a zonal error of slope Y and amplitude X has the
SM> same impact on MTF regardless of sign, even if for other reasons, one is
SM> more easily detected via the star test than the other.  Comments?

SM> Scott Milligan


SM> _________________

SM> Michael Peck
SM> email mpeck1@ix.netcom.com
SM> Wildlife photoblog! http://wildlife-pix.com
SM> Amateur telescope making
SM> http://home.earthlink.net/~mlpeck54/astro/astro.html 

SM> _______________________________________________
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Scott, can you please use the normal > quote symbol when
quoting. What with lack of quote marking and digest replies
containing unmarked excerpts from several messages, many
messages on this list are getting impossible to follow or place
in thread. Sorry for quoting the whole message here but I
thought it was needed.

-- 

Best regards,
  Richard in the UK



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