Scope Brightness – Perception vs Measured

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

  1. JRS

    JRS Silver $$ Contributor

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    Look for the ISO approval. If it isn't there, don't use them.
     
  2. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    I second the above whole heartedly. The safest methods to observe the eclipse are indirect by pinhole or optical projection see:https://eclipse.aas.org/eye-safety/projection.

    Note also my addition to post #39 above
     
  3. JRS

    JRS Silver $$ Contributor

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    If you use good judgement, along with the proper protection, you'll be completely safe while viewing the eclipse. I will be using my 85MM f/1.2 with a solar filter in place.
     
  4. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    JRS,

    I'll assume that you use good judgment and proper protection. However I'll still stick to my recommendation. I will assume that there will be thousands acting on bad or no advise that will damage their cameras particularly those using smart phone cameras. Even worse will be a large number of ignorant eclipse watchers that will have some eye damage.
     
    Last edited: Aug 19, 2017
  5. brians356

    brians356 Gold $$ Contributor

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    FWIW I was contemplating driving 7+ hours north this weekend, to sleep Sunday night in the back of my pickup somewhere near the total eclipse path in central Oregon. But after hearing about the expected hordes and anticipated madness, I'm staying home for an 80% eclipse. The weather people are saying the Oregon coast will very likely be overcast, and west-central OR about a 50/50 chance of clouds. So there will be an exodus to E. Oregon. With the high fire danger, I only hope serious range fires aren't started by clueless interlopers.
    -
     
  6. brians356

    brians356 Gold $$ Contributor

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    It's starting. Glad I decided not to chase the eclipse.


    This aerial photo provided by the Oregon State Police shows a 15-mile traffic jam on Highway 26 heading in to Prineville, Ore., Thursday. (AP)
    OR_eclipse_traffic.jpg
     
  7. 284winner

    284winner Silver $$ Contributor

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    My brain again is aching over all that I just read in this entire post. Once the numbness clears, I'll go shoot at my range and TRY to forget all that I just read. This optical rhetoric is many miles over my head. Somebody please say something that I can grasp...please !!!
     
  8. brians356

    brians356 Gold $$ Contributor

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    FWIW The local evening news reported that a batch of widely-distributed "approved" eclipse glasses were being recalled, but that up to 800 had already been distributed to the local public, most to students. I stand by my earlier statement. An ISO certification will not restore your eyesight, nor will it compensate you monetarily for your disability.
    -
     
  9. JRS

    JRS Silver $$ Contributor

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    Approved by whom? And who was handing them out to students? After reading the recall article from Amazon.com, the recalled glasses were not ISO approved. I suppose that's what one gambles on when paying fifty cents for that item.
     
    Last edited: Aug 20, 2017
  10. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    I'm sorry if this thread has become too confusing and particularly if it was do to my posts. My original intent was to generate a rational discussion of the problem of perceived versus measured "brightness" as applied to scope evaluation. Since that initial post laid an egg, I used this thread to post other information not directly related to the OP. From there, the thread became somewhat free-form (not uncommon on this forum) but at least on optics topics.

    If I created your frustration by my posts, please ask for clarification and I will try to be helpful. Others following (or trying to) this thread will I'm sure also try to clear the fog.
     
    Last edited: Aug 20, 2017
  11. msinc

    msinc

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    And several posts back you were "not going to reply" to my post "at first" because you said it was "off topic"????? Really??? What part???? Best I could tell....we were discussing optics.
     
  12. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    Your initial post #11 to this thread seemed to me to emphasize the "...when it comes to a discussion of the topic of rifle scopes you can pretty much break down the participants into one of two categories...those that believe or at least will say that scopes "gather" light, and those that emphatically deny it is possible. Your attachment kind of implies that it does, but doesn't use the exact terminology. Which is something else I have always noticed about this topic...whenever scopes and optics in general are discussed there is this big play of words and their meanings. Gather, enhance, concentrate.......for some reason the use of these words sets people off in a bad way". I had I thought avoided that linguistic trap in my original post so my narrow view saw your remarks as off my topic. However, after rethinking your post I replied more positively in my #33 post. If my #50 post offended you, I'm sorry as that was not my intent.
     
  13. RDavies

    RDavies Silver $$ Contributor

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    Sorry if this is moving the subject around again, but for a while I have been saying that some people's eyes or brains see much more mirage than others and these are the people who are regularly saying they had to turn their scope down to 10-20x for example while the other half of the shooters out there were saying the mirage wasn't so bad, so they left their scope at 55x. Each group is sure they are right because they don't see what the other group sees, or their brains filter or modify the image.
     
  14. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    I cannot give you a comprehensive answer for the two group observation but I've seen the same tendencies at both formal and informal matches on our patch also. I can give you some insight from my personal experience.

    Over a period from 2005 to 2013 I developed cataracts in both eyes and in 2013 had the natural inner lenses removed and replaced with interocular implants (distance vision only). In 2005 my visual acuity was correctable to 20/20 (6/6 rest of world) and by 2013 had deteriorated to correctable to 20/40 (6/12). Post repair my visual acuity is now 20/15 (6/4.5) without corrective lenses (hooray!).

    To your point - as my vision deteriorated the amount of detail that I could see in the mirage lessened even with the same scopes and magnification. Now I'm seeing more detail in the mirage than I ever had even with corrected to 20/20 (6/6) visual acuity.

    Incidentally, I fall into a third group that never did turn down the magnification to "reduce the mirage" as I see that as "smoothing the truth out of the data". With enough practice my brain can process that rich mirage data field into reading the wind far better than I ever could with flags.
     
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  15. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    RDavies,

    Another consideration that may help explain your two groups of shooters is visual acuity. Persons of different visual acuity perceive their observed world differently due to the difference in the level of detail seen and perceived.

    Using our high power scopes may actually add some degree of perceptual confusion. Our scopes are by definition diffraction limited optics in that the entrance pupil or clear objective diameter is of finite rather than infinite size thereby limiting the resolution of the instrument. The perception problem occurs when the user's magnified acuity equals the diffraction limit of the instrument - call this the Match Magnification. Below the Match Magnification, resolution is limited by the users visual acuity which is what the eye/brain visual system is accustom to. Above the Match Magnification, resolution is limited by the scope objective diameter and further increases in magnification add no more distinguishable detail which is not a normal experience for the eye/brain visual system.

    To put this into some numerical terms, the following table is based on the data from my post above. I've used the Dawes Resolution Limit with the clear objective diameter for my March scopes to calculate the Diffraction Limit and Match Magnification.

    visacuitychart.png

    Even though I'm very experienced in using high power scopes and it was a very gradual (8 year) transition for me to go from 1 MOA to 2 MOA acuity due to my cataracts, the 1 month change from 2 MOA to 0.8 MOA was initially very confusing and it took me about 3 months to retrain my eye/brain system to adapt to the change.
     
    Last edited: Sep 1, 2017
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  16. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    The email responses I have received to my last post (#55 above) request clarification of two issues. My replies use a March 10-60x 52mm specs and last post data.

    First question - What is so different below and above "Match Magnification" to the shooter?

    Below Match Magnification the image presented to the brain by the scope is within normal experience. With increasing magnification, the target and surroundings appear closer and the detail visible keeps increasing as expected. The brain's image processing will do it's normal filtering/corrections to adjust the perceived image to show what we are accustom to seeing.

    Above Match Magnification the image presented to the brain by the scope changes to an abnormal situation. With increasing magnification, the target and surroundings appear closer but there is no corresponding increase in detail. The brain may be confused by this abnormal situation as it has little experience with how to filter/correct the perceived image. NOTE: with practice, our brain will adapt to this new situation and develop the necessary filters/corrections to present a useable perceived image.

    Second question - Why use more than "Match Magnification"?

    For the example scope and a shooter with normal 1 MOA visual acuity - at 10x the field of view is 120 MOA and base level of detail; at Match Magnification 27x the field of view is 44 MOA and 2.7x the level of detail; at 60x the field of view is 20 MOA but there is no more detail than at Match Magnification. The important figure of merit is the field of view since the important aim point occupies more of the visible field ("aim small miss small") and extraneous surroundings are excluded.
     
    Last edited: Sep 7, 2017
  17. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    visacuitychart.png Another email has noted that I've made a grievous error. In the table in my #55 post above, 20/40 ft. (6/6 m) should have been 20/40 ft. (6/12 m). My sincere apologies to our international members and or readers.
     
    Last edited: Oct 24, 2017
  18. brians356

    brians356 Gold $$ Contributor

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    An error, sure, but not a grievous one I hope. More of a typo, really. Your copy editor should have caught it. ;)
    -
     
  19. Fred Bohl

    Fred Bohl Gold $$ Contributor

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    Unfortunately, I'm both the author and copy editor pre-publiclication and you folks are the final copy editors. Throughout my 40 year engineering career I kept re-learning and preaching that you cannot check your own work. Now that I work alone when posting here, I trust you good folks to find and advise me of my typos.

    The little group of us - now 3, down from 5 - surviving optics experimenters have been working on creating and testing protocols for useful comparative scope testing. Would those of you that are interested in our endeavors rather I keep posting in this thread or start a new one hopefully more focused on the scope testing topic?
     
  20. brians356

    brians356 Gold $$ Contributor

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    If a new scope topic arises (not perception vs brightness) I suppose a new thread is warranted.

    My engineering training was in software engineering. Probably the Prime Directive therein is "Thou shalt not test your own code." And it takes ten times the effort and resources to properly test non-trivial code as to create it. Reality intrudes.
    -
     

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