Small focal length, small exit pupil, large AFOV

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Don Pensack United States of America
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Re: Small focal length, small exit pupil, large AFOV

#21

Post by Don Pensack »


Test stand transmission is what is measured in eyepieces when transmission is measured. There are at least a dozen long lists of transmission measurements on line, and in every single case, they are measuring a difference between input and output in lumens.
If you want to use the word transmission to denote something other that what everyone else means when they refer to transmission, like in philosophy, you must first define what you mean by it.
You said, "transmission that describes the energy flow through the system and determines image quality. It includes both absorption and scattering processes."
That's fine, but it is not what is meant by the word transmission as it is used in either the transmission tests or even in the common parlance, where it means how bright the image is after passage through the system.
In mirrors, it refers to reflectance %. The curves you see there are reflection %, ignoring scatter, wavefront error, absorption by surface layers, etc.
Damage to the wavefront entails a lot of factors, but the measurement of that is not referred to as "transmission".

You're right that we were speaking different languages here. We don't disagree on anything other than the definition of the term.
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Re: Small focal length, small exit pupil, large AFOV

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Post by notFritzArgelander »


Bigzmey wrote: Mon Sep 06, 2021 8:02 pm Great discussion! While I am a great fun of well made minimal glass EPs I end up having a few short FL widefield EPs. Notably, XW5 and XW3.5. After so many rounds of comparison on variety of targets I came to the conclusion that in 95% cases a well made widefield is as good as a good minimal glass EP, but provides better ergonomics. On occasion there is an extra faint galaxy or a tight double where Ortho or Plossl would push it slightly to a visible realm. So, most of my sessions are carried with modern complex EP designs (mainly for the comfort of observing) but I always keep a set of Plossls and Orthos in my EP case, and they save the day (or night) on occasion.
Yes, indeed. The modern complex designs certainly have their pleasurable uses. I especially enjoy them when indulging in field sweeping. Folks with astigmatism often need to use them. But, like you I'm never without a set of Abbé or Ploessl orthoscopic eyepieces for critical observing.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: Small focal length, small exit pupil, large AFOV

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Post by notFritzArgelander »


Don Pensack wrote: Mon Sep 06, 2021 8:38 pm Test stand transmission is what is measured in eyepieces when transmission is measured. There are at least a dozen long lists of transmission measurements on line, and in every single case, they are measuring a difference between input and output in lumens.
If you want to use the word transmission to denote something other that what everyone else means when they refer to transmission, like in philosophy, you must first define what you mean by it.
You said, "transmission that describes the energy flow through the system and determines image quality. It includes both absorption and scattering processes."
That's fine, but it is not what is meant by the word transmission as it is used in either the transmission tests or even in the common parlance, where it means how bright the image is after passage through the system.
In mirrors, it refers to reflectance %. The curves you see there are reflection %, ignoring scatter, wavefront error, absorption by surface layers, etc.
Damage to the wavefront entails a lot of factors, but the measurement of that is not referred to as "transmission".

You're right that we were speaking different languages here. We don't disagree on anything other than the definition of the term.
Well, now that we agree on the facts I guess I have to defend my use of transmission? :) My usage and JG's is indeed the common usage in physics and physical optics. It is how transmission is defined in texts on radiative transfer which I learned at university in the late 1960s and practiced after graduate school into the 1980s. I don't think at this late date that I'm going to change my usage of transmission. After all Chandrasekhar's lectures made a fairly deep impression on me. ;)
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: Small focal length, small exit pupil, large AFOV

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Post by j.gardavsky »


notFritzArgelander wrote: Mon Sep 06, 2021 8:57 pm
Don Pensack wrote: Mon Sep 06, 2021 8:38 pm ...

You're right that we were speaking different languages here. We don't disagree on anything other than the definition of the term.
Well, now that we agree on the facts I guess I have to defend my use of transmission? :) My usage and JG's is indeed the common usage in physics and physical optics. It is how transmission is defined in texts on radiative transfer which I learned at university in the late 1960s and practiced after graduate school into the 1980s. I don't think at this late date that I'm going to change my usage of transmission. After all Chandrasekhar's lectures made a fairly deep impression on me. ;)
The problem of communication in our hobby astronomy with the regard to the equipment is in a widespread use of the marketing soft terminology, which replaces the basics of optics.

The most frequent failures are:

A.Violation of the conservation (or at least not increasing) étendue in optical systems without an external energy input.
This is in a way similar to the entropy violations.

B. Neglecting the wave optics, and the finite speed of light.
- The wave optics is complementary to the light rays, and it is not replaceable with the light rays only. Ignoring it, leads among other cases to the wrong statements about the aberrations, and specifically about the chromatic aberration. The higher order aberrations are still safe, as mostly not known among the brain storming participants.
- Not knowing the finite speed of light, and that there is also the propagation vector, leads often to a fatal violation of causality. And yes, this applies to the eyepieces, binoculars, etc., whatever they might be just simple, or even highly sophisticated.
- Another case of ignoring the wave optics results in the plain language notion of the focus plane or focus surface.
Instead of a focus plane/surface in an optical system with lenses, there is a shell, the topology of which is defined by the diffraction patterns of the lightwaves with their different wavelengths. Numerically it is about the finite extent (length and diameter) of the point spread "packages" for a set (continuum) of wavelengths.
Technically, this is a set of the irradiance profiles for the wavelength, like in this exapmle for a single wavelength,
irradiance profile through a lens.jpg
irradiance profile through a lens.jpg (9.9 KiB) Viewed 1640 times
generated by a continuum of the propagation k vectors.

The interpretatory failures ad A. and ad B. may coexist,
like the dead/alive Schrödinger's Cat, but somehow even more complicated, as the collapse in the strict sense of the regular Quantum Mechanics does not happen completely, because of the finite velocity of light.
A very nice example for the interpretatory failure of this kind, and a fatal violation of the causality, has been on Cloudy Nights about 1/2 a year ago, when discussing the binoculars.

Best,
JG
6" F/5 Sky-Watcher achro, 2" BBHS Star Diagonal, 2" zenith prism, 1.25" Takahashi prism
Leica 82mm APO Televid
Eyepieces: Docter UWA; Leica B WW and WW Asph. Zoom; Leica HC Plan S and L, monocentric; Pentax SMC XW, O-, XO; Tak MC O, Carl Zeiss B WW, and Pl, E-Pl, S-Pl, W-Pl;
Swarovski SW; Baader Symmetric Diascope Edition; Nikon NAV SW, ; TMB supermonocentric; Rodenstock; Vixen HR; TV Delos
Filters: Astrodon, Astronomik, Baader, Balzers, Zeiss West and East, Lumicon
Binoculars (7x42 up to 15x85): Docter Nobilem, Leica Ultravid, Nikon Astroluxe, Swarovski EL Swarovision; BA8 (Kunming Optical)
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Re: Small focal length, small exit pupil, large AFOV

#25

Post by notFritzArgelander »


@j.gardavsky it's a difficult problem to be sure. Communicating complex technical ideas in a marketing context is fraught with oversimplification. Now I'm tempted to look up that discussion on CN and see what is happening. I'll occasionally read there but have never, well almost never, hardly ever posted there.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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