4865Re: Questions On APO Strehl Ratio
- Sep 2, 2002
--- In tmboptical@y..., "garyjmo" <garyjm@v...> wrote:
Interesting topic, and my US$0.02 on it:
> Hello all,
>> Hey Gary...
> I understand that strehl ratio takes into account all aberations in
> a refractive system.
From Suiter's book, "a lens is a filter". The way I look at it, since
the lens is a filter and a star is an impulse function then the strehl
is a measure of the impulse response. This characterizes the lens
fully. I've seen some strehl's calculated at wavelengths from red
thru blue, which should give an indication of the lens color error.
If the strehl is high using white light, it would seem it is well
color corrected, but I'll leave that comment to the expert.
> I have also heard that .95 is the cut off for a
> really great optic.
Seems like .95 is up in the stratosphere, which let's face it, if your
on the TMB or AP group that's what your looking for. Suiter says 0.8
is "diffration limited" (or 1 / 14 RMS wavelength deviation).
> Okay, so when comparing a .95 with say a .99
> strehl APO, what are the visual differences? Is there any
> difference in focus or just out of focus? How would the difference
> manifest itself?
What Wayne said...
> On what objects would this difference be most apparent?
In my opinion; planets, the moon and especially close double stars
with significant difference in magnitude. Energy from the first ring
of the airy disk would be thrown into the adjoining airy disk making
I've take it you've read Roland's and Thomas' papers on star testing?
Also checked out the tech data on Markus's website about TMB lenses?
There is also the abberator program that let's one test 'what-if'
hypossis. The only problem with this program is I don't see how one
can input a strehl value.
Also Markus posted a .95 and a .99 airy disks in this news group once
and asked all to find the higher one. There was visually no
difference and the polling results proved that.
> Thanks for helping me to gain a better understanding of optics...
Learning is part of the fun
San Juan Capistrano, CA
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