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# Two EPs' Transmission Curves

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### #1 Amalia

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Posted 16 May 2006 - 05:37 PM

I have found the transmission curves of two eyepieces.
not write their real names. Let's simply call them eyepiece
A and eyepiece B. I have redrawn both transmission curves
to make them fit into the same diagram. Of course I had to
simplify the curves, but I took care that they were precise
at 400nm, 450nm, 500nm etc.

Then I have calculated the transmission values for night
vision, using these numbers:

colour....nm.......% for night vision

blue......450............45%
green....500...........100%
yellow....550............40%
red........650............10%

And I have added these calculated values into the diagram,
using darker colours for the curves of night vision transmission.

Edit: I think I made an error in this diagram. I don't delete it,
my later post of the 5.18.2006. Amalia

### #2 Amalia

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Posted 16 May 2006 - 05:39 PM

-- All I know (from "reality") is this:
Eyepiece A shows a better contrast.
Eyepiece A seems to be more colour neutral -- to me.
Eyepiece B shows a golden tint.

-- What can I read in this diagram?

1 I read that eyepiece A shows a peak in the yellow, while eyepiece B
has its peak in the red.

2 I read that eyepiece A shows a flater curve than EP B.

3 I can read that the major amount of light seen by our eyes in the night
is in the green range.

4 I can see that the other colours ( = not green), while showing a rather
big difference between A and B on daylight (up to 10% and more), show
only a little transmission difference when night vision is used.

5 The only wavelength where a humanly perceptible 10% transmission
difference is noted, is in the green.

6 We use red lights to save our night vision when we observe DSOs. But
I have noted that even this red light affects my night vision, at least for a
short time (and I have read that at least one more CNer experiences the
same as I). But since red is only perceived at 10% at night vision, so why
is this felt so strongly?

7 I think even the rather big differences shown by this diagram reveal that
transmission alone "does not say everything" about an eyepiece. Even if
the differences turn out to be small considered the 10% limit of contrast
perception. I have learned on CN that there must be more factors taken
in consideration when talking about eyepieces (such as scatter, polish,
baffling, blackening of the interior etc.).

8 So all these transmission advertising we can read are not really to be taken
seriously, especially because they only write about a *transmission peak* -
and not where this transmission peak actually is, and also not about the rest
of the curve, and also not about the rest of the eyepiece's properties.

9 I remember Mardi's sentences:

Color cast of an ep; Optical glass is not all made to average transmission of
the visual waveband at ~550nm. This is the frequency of averaged transmission
where most people will see a white image of a white target, etc, 'true color' iow.
Optical glass varys from this 550nm averaged point, singly and/or in combination,
and the primary transmission frequency of a completed optic can vary from 550nm
thus giving a slight color cast to the image produced. An optic biased on the low
side of 550nm will give a "cold" or blueish tending cast upon a white target. An
optic spectrally balanced towards the highside of 550nm will give a 'warmer' image
as it is biased towards a slightly longer wavelength.

So this is why I see eyepiece A (having its peak at 550nm and a flatter curve) as
more colour neutral -- while I feel eyepiece B (having a curve which tends to the red)
as "warm" and "golden"? I think yes.

10 And finally I remember Mike's sentence:

However, if the tinting is primarily caused by the transmission
of the various glass types combined, a yellow-brown-orange tint of
white obects may be created by minor deficit of blue-violet.

I understand that a lack of blue-violet results in a warmer tint. So maybe one can
turn the definition, and instead of saying: "Eyepiece B is warm", one could say:
"Eyepiece B shows less transmission in the blue-violet".

-- Maybe you can tell me what you can read, please? ( -- or where I am wrong?)

Amalia

### #3 Moggi1964

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Posted 16 May 2006 - 05:57 PM

Amalia is a very smart lady who makes me think about my hobby.

When I finally know enough to understand what you wrote you'll be too far ahead to notice..... and I bet you're right too!

I really enjoy being made to think and appreciate how much thought you put into your 'work'.

Morris

### #4 Amalia

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Posted 16 May 2006 - 06:16 PM

Thank you, Morris!

My purpose was honestly to learn something more (I feel to be
a slow and stubborn pupil...)

If I can help you to understand, tell me, it would be a pleasure to
share my 2 cents of wisdom.

Amalia

### #5 Mike Hosea

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Posted 16 May 2006 - 06:46 PM

colour....nm.......% for night vision

blue......450............45%
green....500...........100%
yellow....550............40%
red........650............10%

Are these made-up numbers or is there a reference? Reason I ask is that I'm astonished that 550nm is so low.

### #6 Joe Cipriano

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Posted 16 May 2006 - 06:58 PM

Yea - I thought (although I'm probably wrong) that maximum sensitivity was at 555nm - although I can't remember if that's under full light or night vision...

### #7 Amalia

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Posted 16 May 2006 - 07:11 PM

I don't really understand the word "made-up" (and my internet
dictionary does not know it either), but I think to understand
I have taken these numbers from the deleted homepage of
C. Losch (I have saved it on my HD).

He writes that his source is DIN (= Deutsche Industrie Norm = German
Industry Norm), DIN 5031. Right now I have googled "DIN 5031
spektrale Empfindlichkeit" (spectral sensitivity) and found two
controversy results: ("night vision" means here: mesopic)

#1
http://www.led-info....en/i_eiudef.htm
(red line = daylight vision, dotted red line = night vision {blue is an night insect}
-> 550nm at 65% at night vision
(and yellow at 580nm !)

#2
http://www.ahlborn.c...ile.php?590.pdf
page 2, at the bottom, left is day vision, right is night vision
-> 550nm less than 40% (but I doubt this is a precise diagram)

#3
Ah! This is better:
http://de.wikipedia....d:Vlambdaps.png
blue = night
-> 550nm at 48%

I can't continue right now, it is too late.

Good night!

Amalia

### #8 Joe Cipriano

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Posted 16 May 2006 - 07:46 PM

Ah, so the 555nm max is photopic (full light)...

My apologies...

### #9 Mike Hosea

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Posted 16 May 2006 - 10:20 PM

OK, I also found a graph here:

http://www.atmsite.o...ns/vissens.html

Looks like the numbers Amalia gave are similar. For a given wavelength one can just plug in to the formula

0.992*exp(-321.9*(lambda - 0.503)^2)

So for 550nm, this evaluates to 0.487. This is probably a regression fit, and we aren't told the statistics behind it, so there's probably no point in carrying a lot of decimal places.

This is a very interesting train of thought.

### #10 Guest_**DONOTDELETE**_*

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Posted 16 May 2006 - 11:03 PM

### #11 photonovore

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Posted 17 May 2006 - 12:23 PM

One thing to keep in mind when talking vision and planets is that it is not scotopic vision one utilizes when viewing Jupiter, Saturn, apparitions of Mars, etc, but photopic vision. In fact, any target brighter than ~6magnitude will be a wholly photopic target. Also, the eye's contrast senstivity doesn't begin to degrade until target brightness is at about the level of Uranus. Even when one's eye's are night adapted, the cones don't shut down but are available as target illumination allows. This is why, even when fully dark adapted, one can see brilliant color in even the dimmer of relatively bright stars telescopicly.

So, the frequency to optimize when viewing planetary targets would be ~550nm, not ~500nm.

### #12 Mike Hosea

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Posted 17 May 2006 - 01:33 PM

Yes, but I think Amalia meant for the context of this thread to be entirely (or almost entirely) about the scotopic context. I had speculated that the warmness or coolness of the eyepiece wouldn't matter that much for faint fuzzies, and she had other ideas. Now that I see the shift between the photopic and scotopic relative sensitivity curves, I have other ideas as well.

### #13 Amalia

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Posted 17 May 2006 - 01:58 PM

Yes, but I think Amalia meant (snip)

Right in this moment I was thinking about: "What did I intend

I think (now...) that the point of departure was to understand
how these two eyepieces differ in the three adaptation modes.
And which EP is better suited for which situation. And also
to understand why these eyepieces are made this way.

I have other ideas as well.

I am still trying to understand all the informations you all gave me,
and I am trying to find the continuation, and also the questions
which have to follow. Right now I will try to draw a new diagram to
get a better understanding of the cyclone in my head. (I had a long
day, and my thoughts are very slow, but I feel extremely curious
and... even more curious, and like standing at the threshold of a
deeper understanding).

Amalia

### #14 Amalia

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Posted 17 May 2006 - 02:11 PM

But first of all, let me thank you:

@ Joe: No apologies needed!

@ Mike: Thank you for the link -- this diagram seems to be slightly
more accurate than the one I found.

@ Armand: Thank you for these links -- I have got some similar
links, even two times. But, or I was not ready to understand their
content, or they were too difficult for me. These two seem way
more understandable.

@ Mardi: Thank you for reading in my mind the exact question I was

Amalia

### #15 Amalia

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Posted 17 May 2006 - 03:47 PM

ROUND 1:

There are some things I don't understand:

#1
http://www.photo.net...tt/vis00010.htm
seems to be wrong, as it shows the sensitivity peak of the rods
at 550nm. All other sites (and Mardi) say it is at 500nm.

#2
The same site
http://www.photo.net...tt/vis00010.htm
shows in the 4th and 5th picture the relation between the photopic
sensitivity of the rho, gamma and beta sensors in our eyes, and,
in the next picture, the resulting total sensitivity. Seems logical to me.
But, why do all other sites, like
http://www.atmsite.o...ns/vissens.html
show the total sensitivity with a totally different curve?

#3
It seems that the colour green is perceived better because it
stimulates two types of sensors at the same time (gamma and rho).
But the diagram of this site (sixth picture)
http://www.atmsite.o...ns/vissens.html
does not show this. Actually it shows green being less easily
perceived than blue. This seems very strange to me. Blue
strongest? Looking around... hard to believe.

#4
But also these two sites are not really congruent (always speaking of
the "resulting total sensitivity diagrams"):
http://www.atmsite.o...ns/vissens.html
http://en.wikipedia....wiki/Cone_cells

#5
I use this diagram: (it is permitted to copy and use it)

### #16 Amalia

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Posted 17 May 2006 - 03:50 PM

... according to the idea (or theory, or fact) that we have three kind
of colour receptors, and that green is perceived stronger because
it stimulates two receptors at the same time, so the total sensitivity
should to my understanding be something like this:
(I have made an approximate addition of the sensitivity of all three
sensors based on the diagram of my last post).

### #17 Amalia

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Posted 17 May 2006 - 04:16 PM

There must be some error somewhere, or I have not understood
this completely. Maybe you understand this better?

And now:

ROUND 2:

One thing to keep in mind when talking vision and planets is
that it is not scotopic vision one utilizes when viewing Jupiter, Saturn,
apparitions of Mars, etc, but photopic vision. In fact, any target
brighter than ~6magnitude will be a wholly photopic target. Also, the
eye's contrast senstivity doesn't begin to degrade until target
brightness is at about the level of Uranus. Even when one's eye's are
night adapted, the cones don't shut down but are available as target
illumination allows. This is why, even when fully dark adapted, one can
see brilliant color in even the dimmer of relatively bright stars
telescopicly.

So our eyes seem to behave in a "fuzzy logic" and not in a "yes - no - logic".
Like these examples:

A - Daylight Situation: photopic vision, which means we see the main
visual impressions with the cones, while the rods remain active,
but are perceptible mainly at the border of our eyes' field of view,
among other detecting movements.

B - Observing e.g. Moon, Saturn etc.: photopic vision

C - Observing a Bright Open Cluster (with bright stars, like M45):
photopic vision (But are the nebulae in M45 also seen with the
cones? No. So here we have an interaction, because the "rods never
sleep").

D - Observing a Bright Galaxy (like M31): While the total brightness of
M31 is more than 6mag -- when I observe it with a telescope the
resulting brightness gets distributed (spread) over a larger area.
So here the scotopic vision is dominant. And e.g. M42's colour
shows that the cones are still active.

E - Observing a Faint Nebulous Object: Only scotopic vision -- but the
cones are still ready to show us a nearby orange star.

Isn't it?

Amalia

### #18 photonovore

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Posted 17 May 2006 - 06:00 PM

Amalia, for some more info/intrepretation re; target illumination and the interrelationship between photopic mesopic and scotopic vision and how this applies to acuity (visual contrast & resolution), take a look at the first post i made in this thread. You can have even more fun & learning playing around with trolands and millilamberts and log functions... It's a fascinating topic, our eyes and the way they work, isn't it? .

### #19 square_peg

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Posted 17 May 2006 - 10:50 PM

Great thread!! Many thanks to all involved.

### #20 Amalia

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Posted 18 May 2006 - 03:18 PM

But at least I found out myself, but still... :o and one more time :o .

First error: I have (linguistically) misunderstood Mike's post:

Yes, but I think Amalia meant for the context of this thread to be
that the warmness or coolness of the eyepiece wouldn't matter that much
for faint fuzzies, and she had other ideas. Now that I see the shift between
the photopic and scotopic relative sensitivity curves, I have other ideas as well.

My apologies, Mike!
Now that I understood what you meant, well, I wanted to know *what you
found out about my ideas/experiences*. I know this is a quite funny question.
I found out: In my very first diagram I have only converted the eyepieces'
transmission curves into night vision -- but I have not understood that I had
to convert the curves also into daylight vision -- to be able to compare them!

Based on the curves of this site
http://www.atmsite.o...ns/vissens.html
it looks like this:

### #21 Amalia

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Posted 18 May 2006 - 04:01 PM

Amalia, for some more info/intrepretation re; target illumination and the interrelationship between photopic mesopic and scotopic vision and how this applies to acuity (visual contrast & resolution), take a look at the first post i made in this thread. You can have even more fun & learning playing around with trolands and millilamberts and log functions... It's a fascinating topic, our eyes and the way they work, isn't it? .

Mardi, it really seems that my way of having fun is a strange one...
I had a look at your post, and I did not understand very much of
it, so today I re-read only the first part, and now I start to understand

Just wait some days, and we will be able to debate about Troll-Land
and Millilambert! Now I will try the last diagram for today, so
maybe I will finally discover "if and why" these *in reality* different
tinted eyepieces also show a different view *in theory*.

Amalia

### #22 Mike Hosea

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Posted 18 May 2006 - 04:18 PM

Well, I don't know if these two eyepieces show it, but I was thinking of a hypothetical situation where average and peak transmission were similar, yet under scotopic vision there might be a significant difference. Something like:

400nm: eyepiece 1 = 85%, eyepiece 2 = 60%
450nm: eyepiece 1 = 95%, eyepiece 2 = 80%
500nm: eyepiece 1 = 99%, eyepiece 2 = 80%
550nm: eyepiece 1 = 99%, eyepiece 2 = 99%
600nm: eyepiece 1 = 90%, eyepiece 2 = 99%
650nm: eyepiece 1 = 80%, eyepiece 2 = 99%
700nm: eyepiece 1 = 68%, eyepiece 2 = 99%

Average transmission
eyepiece 1: 88%
eyepiece 2: 88%

Peak transmission
eyepiece 1: 99% (@550nm and others)
eyepiece 2: 99% (@550nm and others)

Average transmission after filtering by scotopic vision:
eyepiece 1: 27.35
eyepiece 2: 23.76

Relative difference in perceived brightness with scotopic vision, eyepiece 1 versus eyepiece 2 = 27.35 / 23.76 = 115%

Obviously I contrived this example to illustrate the principle, but as soon as you pointed out the spectral sensitivity curve for scotopic and photopic vision, and I subsequently noticed that the one for scotopic vision was shifted to the left from the one for photopic vision, I realized that something like this could happen, at least on paper. Consequently, I no longer believe what I told you in the other thread, at least as a general rule.

I don't find the photopic subject to be very interesting in this context. Possibly for a few not-so-faint fuzzies or in really large scopes it might have some application. With planetary observation there is a lot of excess light. In fact, I'd bet good money that you could design a planetary eyepiece with an element that absorbed 20% or so like an ND filter, and if you didn't let people use it on any DSOs or try to locate faint moons of Saturn, just let them test it on Jupiter, they'd probably say that it was one of the most contrasty planetary eyepieces they'd ever seen.

### #23 Amalia

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Posted 18 May 2006 - 04:54 PM

I have understood (only today) that you changed your way of

Great! You bring some light into this my darkness... I have tried
to copy your calculations with the only difference that I used the
Wikipedia data about scotopic vision, and my resulting transmission
difference becomes even slightly bigger:

### #24 Amalia

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Posted 18 May 2006 - 05:48 PM

Mike, I have to say you are a genious!
You invented an example, and I right now put in the
real numbers of the initial (true) eyepieces A and B --
and I get the exactly same result as you in your example:

### #25 Amalia

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Posted 18 May 2006 - 06:53 PM

Now that the mystery about the scotopic behaviour of
the two eyepieces is resolved, I try to recapitulate, using
words. These were the three sentences of the beginning:

-- All I know (from "reality") is this:
Eyepiece A shows a better contrast.
Eyepiece A seems to be more colour neutral -- to me.
Eyepiece B shows a golden tint.

So, as a result, it seems that it was not the importance
of the golden tint which resulted in a weaker contrast.
It seems that the low transmission of eyepiece B in the
blue-violet range caused the contrast difference. This because
the night vision causes a "vision-shift to the left", which
means a bigger importance of a high transmission of the
cyan-blue-violet light.

I think the relative absence of the blue in the eyepiece B
helps to give the impression of a warm eyepiece.

I would even go that far to pretend that a "cold eyepiece"
will be a better eyepiece for faint deep sky objects.

Thank you all so much for helping me in this research!

Amalia

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