Scope Brightness – Perception vs Measured

Discussion in 'Scopes, Optics, LRFs, Spotters, BoreScopes' started by Fred Bohl, Jun 29, 2017.

  1. Turbulent Turtle

    Turbulent Turtle F-TR competitor

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    Hi Chris, thanks for the quick and detailed response. You didn't mention snow, FredBohl did.

    You explained your observation with this one sentence:
    Perhaps FredBohl could post a diagram with supporting formulae that would explain why shooting from inside a hut into plentiful outside sunshine will make the target appear much brighter because your eyes are acclimated (pupils dilated) to the relative darkness of the hut. That's the main premise behind the use of powerful flashlights to blind and disorient people in the dark; flood the wide-open eye with lots of light.

    We could sure use some of your cooler weather here in south Texas.
     
  2. ChrisNZ

    ChrisNZ

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    I have a good idea what thermal torture you're going through TT- I have a good buddy ( with myriad bang sticks) in OK and have been there many times, and he out here quite a few times. Mid summer here is rarely above 85F so 100 to me is definitely torture. I don't know how people can work outside in it.
     
  3. Turbulent Turtle

    Turbulent Turtle F-TR competitor

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    We have this device called "air conditioner" that makes is very nice. That, and the pool in the backyard.

    That said, the matches June to September are brutal.
     
  4. Opticspecialist

    Opticspecialist

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    This is so interesting, I'm not very good at math, but this is the first time i've seen someone put brightness into a calculation in this way. it's something i'm going to look into. i wish i had the money and time to research, but I think there is a correlation with with a persons opinion on optics and eye color.
     
  5. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    If you mean that there may be a correlation between a persons opinion on (or choice of) optics based on how the persons perceives color, you are correct. While there is a formal definition of "normal color perception" we each have a unique color perception and that definitely influences our preferences.

    A look at the vast array of filters sold for cameras or even more so the filter effects available in image processing software would suggest that there is a need to meet a very wide set of preferences.

    Dollar wise, the largest market for optics devises is birdwatchers. Not only are they after the best quality image possible but they are obsessed with having "true color". However, they do not all buy the same binoculars and spotting scopes, they instead buy the ones that appear to give the best image and "true color" to the individual buyers perception. If you think we are particular in our assessments of telescopic sights on this forum, then visit a bird watching forum or read reviews of high end optics written by birdwatchers for birdwatchers (wear a helmet and flak jacket).
     
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  6. brians356

    brians356 Gold $$ Contributor

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    If you mean the color of their iris (blue, brown, green, etc) then methinks thy tongue lodges firmly in thy cheek. :cool:
    -
     
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  7. Opticspecialist

    Opticspecialist

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    the bird watchers are sticklers about color and image. thats a market that as a sales guy is difficult to get into as while i can appreciate the birds, i always wonder how they will taste fried or grilled. I over simplified when i said eye color, but that might be a good starting point, it's just interesting how some people will prefer one brand over the other, and certain people gravitate to certain coatings, color filters etc. perception is reality, but I know there are some correlation.
     
  8. brians356

    brians356 Gold $$ Contributor

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    I'm a birdwatcher, and used to be an avid one. The color issue is vastly overstated by birdwatchers. I can confidently say that there has rarely if ever been a bird misidentified due to some modern optic's color aberration, at least in N. America. Much more critical would be insufficient light transmission to allow an identification under low-light conditions, or insufficient resolution of distant birds at high magnification. Color perception is simply too subjective, and I am aware of no subtle variations in plumage color hue critical enough to affect an ID in the field. Dark / light plumage patterns - yes, but not purely color.
    -
     
  9. Turbulent Turtle

    Turbulent Turtle F-TR competitor

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    Would you be able to identify the Norwegian Blue?
     
  10. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    Jay may be onto something. There is a long running argument in the optics community that suggests that the color of the eye, actually the iris (blue, brown, green, etc), leads to differences in visual perception. Getting definitive data to support or refute this premise has been elusive primarily because of the differences between what the eye images and what the brain perceives.

    One theory suggests the coloration (pigmentation) of the iris acts like a filter so that a lite color iris like blue will allow more light into the eye than a brown iris. This theory seems to be supported by the glare and/or flash reaction of a blue iris eye occurring at a lower luminance level than that of a brown iris eye as shown by data in a couple of studies. My recollection of those conclusions was that samples sizes were small and the supportive statistical significances were thin.
     
  11. brians356

    brians356 Gold $$ Contributor

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    Very interesting nevertheless, and it passes the sniff test anyway, if you accept the premise that the iris is not absolutely opaque.
    -
     
  12. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    Back when I was paid to resolve such problems for machine vision systems, that expression fell into the same list that included: military intelligence, government work, always right and never lies.
     
  13. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    I have been thinking about this a lot since your July 23rd posting. At first I was not going to reply as it appeared to be off topic. However, I've come to believe that you may have hit on the primary reason that not only the optics topic but many on this site become arguments rather than discussions. In the past, I even went so far as to suggest to the site boss (Paul) that we needed a glossary so that we all would be using the same terminology to preclude some unnecessary arguments. You have astutely pointed out that the selection of the terminology in such a glossary would itself lead to arguments as our preconceived beliefs shape our preferred selection of terminology. "Don't confuse me with the facts, my mind is already made up."
     
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  14. brians356

    brians356 Gold $$ Contributor

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    A man convinced against his will
    Is of the same opinion still

    -
     
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  15. JRS

    JRS Silver $$ Contributor

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    Here is the response I received from my Ophthalmologist:

    The only conclusive difference between blue eyes and brown eyes is that blue eyes are more sensitive to light since there isn't much pigment to absorb the light rays.
     
  16. brians356

    brians356 Gold $$ Contributor

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    Then it's true that "the iris is not absolutely opaque". It's translucent. Therefore it's not unlikely (if unproven) that iris color leads to differences in visual perception.
    -
     
  17. JRS

    JRS Silver $$ Contributor

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    Perhaps, in theory. Much testing was performed with tennis, rugby and baseball players. Actual proof, at least at this point, does not exist.
     
  18. msinc

    msinc

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    Yes sir, it's not just optics for sure and it's really not this forum either...I see this same issue in many things I have to deal with on a regular day to day basis....how many times I have said to myself, "if we could all just get on the same page!!!!!"
     
  19. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    Returning to my original post above, I have some additional input thanks to email from old friends.

    First some basic information about the eye: magnification (cornea + relaxed eye lens) about 15x also the high resolution and best color perception is the 0.3 mm diameter fovea area of the retina. Therefore to fully illuminate the fovea only, the maximum entrance pupil at he cornea is a 4.5 mm diameter spot. The iris acts a diaphram or stop to limit the light entering the eye and the optimum opening is 2.5 mm diameter for minimum diffraction and aberrations of a normal eye. In typical daylight luminance, the normal eye iris opening is 2 to 3 mm diameter.

    On to the additional input. An ophthalmologist friend that has participated in our scope tests in the past has been following this thread and after his discussions with colleagues offered these tidbits:

    1. When the fovea is exposed to all or nearly all of the scene luminance, the brain perceives the scene as that on the fovea and effectively ignores the rest of retinal image.

    2. If the image on the fovea, even when at high luminance, is less than the full size of fovea, the brain will perceive the accommodated image brightness to be proportional to the area of fovea illuminated.

    Note that this suggests that for small exit pupil sizes even at very high luminance, the brain will perceive that smaller as dimmer even it is not.

    Added 8/16:

    In the conditions of item 2 above, the autonomic nervous system is operating to protect the eye and cone cells from the high luminance while the optic processing system of the brain is attempting to interpret the less than full illumination of the fovea. Since the autonomic reaction is relatively slow with most of the change occurring in the first minute but full accommodation taking about ten minutes while the brains image processing is much faster at under 0.04 seconds.

    Therefore the brain must be changing our perception of the brightness throughout the accommodation period. As a consequence, when we compare scopes we should be careful to make our observation time at least 1 minute but preferably 10 minutes for each in addition to insuring that the target and it's illumination remains constant.
     
    Last edited: Aug 16, 2017
  20. brians356

    brians356 Gold $$ Contributor

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    Good info Fred.

    I would like to chime in here with a related-topic caution: Apparently some of the "eclipse glasses" being sold to the public are inadequate and therefore "fake". Unless you are 100% sure about what you have, I recommend not looking directly at the sun through anything.
    -
     
    Last edited: Aug 15, 2017
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