Re : ATM Prime focus

[Bratislav Curcic <epabcc@epa.ericsson.se>]

Tom Mchugh wrote :

> All of the great reflectors have corrective optics of one 
> sort or another even when they are used as prime focus
> imagers. Just because the Hale telescope, to mention one,
> has Prime focus capability (as well as coude and cassegrain)
> does not mean they do not use additional optical elements
> juse before the plate or imaging device to correct for off
> axis avberrations--the main one being coma. Yet they refer
> to those images as prime focus images.

So having multiple element corrector (in some cases up to 5 or 
6 elements!) _doesn't_ count, but having flat mirror (which
doesn't add one iota of aberration) DOES ? In first case it is
still PRIME focus, but in second _isn't_ ? Sorry, but I can't 
buy that logic.
BTW, some of the correctors will have enough optical power to
form REAL image on their own. What gives ?

> If any on the list ever get into lens design, and come
> across some formulae which are not clearly based on the
> Conrady sign convention, and not otherwise defined, then you'll 
> know what I am referring to when I speak of standards of terminology.

Yeah. Try to tell that to professional designers of ray trace programs.
Standars galore. Guys from Beam (Stellar Software) for example use term 
"SHAPE" to define departure of the surface from sphere. Any idea where
that may fall into Conrady convention ?
 
Bratislav