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Re: [ATM] RE;1/8,1/16-1/20th debate.

OK, I'll jump in here with all my ignorance, but what the heck...

The differences between a just ok optic, and a near perfect optic ?may? be 
revealed by observing the off-axis images.

For instance, take the 6" F/8 Newtonian reflector example.  Also for sake of 
argument, we've selected an eyepiece that will give us a 1/2 degree field of 
view, which is roughly a 15mm eyepiece w/ a 40 AFOV which results in 80x 
magnification.   If the Earth's Moon is centered, the periphery of the moon will 
be 1/4 degree off-axis.

Crunching this scenario thru Zemax, I find the following: (BTW, I'm only 
modeling what is happening at the focal plane as a result of the primary mirror, 
not what else may happen to the wave front as it passes thru the atmosphere, the 
elliptical secondary, an eyepiece, and an observers biological optical system)

Table best viewed with fixed width font

550nm reference on a 6" F/8 Newtonian primary, induced errors are pure primary 
spherical aberration. Each case used best focus for on-axis image.


Excellent Mirror (conic constant = -1)

    P-V WF ON-axis =  0.00 waves (1/9x)
    RMS WF ON-Axis = 0.00 waves (1/9x)
    Strehl on-axis = 1

    P-VWF 1/4 degree off axis = 1.15 Waves
    RMS WF 1/4 degree Off Axis = 0.073 wave (1/13)
    Strehl 1/4 degree off axis = 0.813


OK Mirror UNDER corrected (Conic Constant = -0.61)

    P-V WF on axis =  0.10 waves (1/10)
    RMS WF ON-Axis = 0.03 waves (1/33)
    Strehl on axis = 0.963

    P-VWF 1/4 degree off axis = 1.14 Waves
    RMS WF 1/4 degree Off Axis = 0.079 wave (1/13)
    Strehl 1/4 degree off axis = 0.783


OK Mirror OVER corrected (Conic Constant = -1.39)

    P-V WF on axis =  0.10 waves (1/10)
    RMS WF ON-Axis = 0.03 waves (1/33)
    Strehl on axis = 0.964

    P-VWF 1/4 degree off axis = 1.15 Waves
    RMS WF 1/4 degree Off Axis = 0.079 wave (1/13)
    Strehl 1/4 degree off axis = 0.783


Just OK Mirror UNDER corrected (Conic Constant = -0.05)

    P-V WF on axis =  0.25 waves (1/4)
    RMS WF ON-Axis = 0.075 waves (1/13)
    Strehl on-axis = 0.802

    P-V WF 1/4 degree off axis = 1.15 Waves
    RMS WF 1/4 degree Off Axis = 0.10 wave (1/10)
    Strehl 1/4 degree off axis = 0.651


Just OK Mirror OVER corrected (Conic Constant = -1.95)

    P-V WF ON-axis =  0.25 waves (1/4)
    RMS WF ON-Axis = 0.075 waves (1/13)
    Strehl on-axis = 0.802

    P-V WF 1/4 degree off axis = 1.18 Waves
    RMS WF 1/4 degree Off Axis = 0.10 wave (1/10)
    Strehl 1/4 degree off axis = 0.652


Or another way to look at this is:

A perfect 6" F/8 has a diffraction limited field of view of ~0.5 degree FOV

A 1/10 P-V WF 6" F/8 has a diffraction limited field of view of  ~0.48 degree 
FOV

A 1/4 P-V WF 6" F/8 has diffraction limited field of view of ~0.05 degree FOV

(diffraction limited in this case being defined as Strehl ratio of 0.8 or 
greater)

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)
http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"

" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "
                                                           Calvin Coolidge
----- Original Message ----- 
From: "John Moore" <jamoore42@yahoo.com>
To: "ATM" <atm@atmlist.net>
Cc: "John Moore" <jamoore42@yahoo.com>
Sent: Friday, July 08, 2005 07:11
Subject: [ATM] RE;1/8,1/16-1/20th debate.


> Hi all,
>
> I will not attempt to give any type of in-concrete answere for this debate,
> because there is none, I only wish to add my 2cents;
>
> for the Edification of further optical research,,,here goes;
>
> I agree with Mr.Tudor, he expressed-it very well, thanks matt.
>
> now,,,not ignoring what matt said, I think that[imho],
> given an atmosphere that "Fluctuates", and just for
> this scenario,, lets say we are observing on a night
> that has decent-seeing on our mythical seeing-scale,,
> by our estimate its a .5~ night,ok,, now it would seem
> during our hours of observing that night, there would-be
> times of .2~seeing or better, for just a couple of
> seconds, would there-not??,,
> which would give the owner of an optic in the[1/20~,,98strehl range]
> a "couple-of second's" view of what his scope is
> capable of !!
>
> let the lashing begin!!
>
> John putting-on his armor.,,,,
>
> John moore.
>
>
>
>
>
>
>
>
>
>
> ---------------------------------
> Sell on Yahoo! Auctions  - No fees. Bid on great items.
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