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  1. Omid

    blackouts at AFOV of greater than 60 degrees- why

    No problem, and you are welcome :)
  2. Omid

    blackouts at AFOV of greater than 60 degrees- why

    Hi Kimmik, Thank you for the clarification. OK, so you experienced blackouts on the smaller size NL models. Your experience could be due to the small exit pupil size and, in addition, spherical aberration of the exit pupil and, further due to vignetting of the field rays. I am afraid your...
  3. Omid

    blackouts at AFOV of greater than 60 degrees- why

    As I said, I have no opinion on whether NL binoculars have black-out problems or not. I don't own these models and I don't follow their reviews or user opinions. So, have you experienced blackouts while looking through Swarovski NL binoculars? And then you have tested their eyepieces for...
  4. Omid

    blackouts at AFOV of greater than 60 degrees- why

    I didn't say anything about Swarovski NL binoculars; what I mentioned are general facts of visual optics :)
  5. Omid

    blackouts at AFOV of greater than 60 degrees- why

    Spherical aberration of the exit pupil is the main cause. Yet, another cause is vignetting of the field beams coming from the edges of field of view. Up to 50% vignetting is considered OK in designing visual instruments: your binoculus might create a nice 5mm circular exit pupil for the central...
  6. Omid

    blackouts at AFOV of greater than 60 degrees- why

    Ed (Elkcub) gave the accurate technical answer in post # 11. I will add one more point: The eye does not see a wide angle field of view all at once as in a wide-angle camera. It rotates and scans the field (the sharp field of view of human eye is about 1 degree). The entrance pupil of the eye...
  7. Omid

    Focussing: Just Do It!

    Hi Lee! Excessive field of view is when the eye doesn't positively see the field stop as a "frame" surrounding the "magnified view". @Binastro: Very nice story! It proves my point ;)
  8. Omid

    Focussing: Just Do It!

    An excessively large field of view will interfere with your perception of horizon. In the natural world, your peripheral vision constantly monitors the position of ground relative to your body. If you look at the world under magnification, your peripheral vision will see (more correctly, sense)...
  9. Omid

    Is "3-D" More Natural in Porros or Roofs?

    Thank you Binastro, Binocularbirdfreak and wdc for your contributions. I am studying effect of magnification on perspective and on stereoscopic vision. Very complex yet interesting topic...
  10. Omid

    Focussing: Just Do It!

    Thank you and sorry for late reply. Yes, that's what it means. The sharp field of view of human vision is only 0.5 to 1 degree wide depending how strictly you define sharpness. This means, in your typical binoculars with 60-degree apparent field of view, only 1/3600 of the visible area is seen...
  11. Omid

    Focussing: Just Do It!

    Less than two months ago, I was invited to a prominent optical manufacturing company in Europe. During my visit, I gave a 3-hour talk on Visual Perception for the company's executives and R&D engineers. I organized my talk in two parts. During part one, I considered the human eye as a camera and...
  12. Omid

    Focussing: Just Do It!

    Thanks! I had not seen this one ;) Here is my current understanding based on all that I have read and learned: As a biological creature who needs to see to function and survive, much of our "world" is outside the radius of 3m for which no accommodation is required. Accommodation is required to...
  13. Omid

    Focussing: Just Do It!

    No. Lag of accommodation refers to the fact that human eye doesn't accommodate enough on objects which are too close and accommodates too much on objects which are far. At some intermediate distance (called the resting point of accommodation, about 80cm to 1.5m), the eye accommodates accurately...
  14. Omid

    Is "3-D" More Natural in Porros or Roofs?

    Hi Henry, First, let me thank you for your extremely valuable post (#1). This is the only kind of content that interests me these days: how looking through magnifying optics affects our perception of space. The exact technical answer to your question is that both models provide diminished...
  15. Omid

    Focussing: Just Do It!

    You are underestimating yourself! The human eye is not a camera. You eye likely has about 1D residual accommodation! French vision scientist Yves Le Grand associates this capability to the retina/brain adaptation to the really high chromatic aberration of the eye's natural lens (which is more...
  16. Omid

    Focussing: Just Do It!

    Answer 1: Tests on monkeys with full range of accommodation has shown that their eyes accommodate between 2.5D to 3D during light sleep. Ref.: Gerald Westheimer, Sidney M. Blair, Accommodation of the eye during sleep and anesthesia, Vision Research, Volume 13, Issue 6, 1973 Answer 2: Yes! If...
  17. Omid

    Focussing: Just Do It!

    Hi again John, The reason for suggesting a split-image view finder was to enhance focusing precision. The reason for suggesting a close-focus lens was to be able to measure images as close as possible in case you asked a young adult person to volunteer for this experiment. Thanks again for...
  18. Omid

    Focussing: Just Do It!

    Hi John, I edited out my suggested experiment since I figured it would cause you undue trouble and likely lead to erratic results. Now, since you already took the trouble to do an experiment, I'll write some additional notes: Regarding your experiment: What is your near point of vision when...
  19. Omid

    Focussing: Just Do It!

    Hello again, The formula you used in Post #1 is called the Gaussian lens formula. Here in the alternative Newtonian version: This version of lens formula will simplify your calculations especially when you need to consider a shift or gap between the focal planes of the objective and the...
  20. Omid

    Focussing: Just Do It!

    Ahhh! You hadn't told me that you and Hennessey were colleagues! OK, then YOU are the original source on instrument myopia ;):). I remember you introduced me to the books by Mouroulis and Ebenholtz. But did you also introduce me to Gibson? I have since found and read the main three books by him...
  21. Omid

    Focussing: Just Do It!

    John, Your analysis of focusing a Keplerian telescope in Post #1 is well done and nearly entirely correct. I invite you to repeat your analysis but this time using Newtonian lens formulas. This will make image position calculations much simpler. I tried to help a forum member do a similar...
  22. Omid

    New Horizons II

    Keplerian telescope operating at finite conjugate - Part III Jessie, Thank you again for taking considerable time and thinking around the problem I posed. :unsure::D The problem I asked you to solve is extremely simple if one thinks clearly but it can get extremely confusing if one doesn't...
  23. Omid

    New Horizons II

    Jessie, You did not follow my instructions! Instead of calculating what a Keplerian telescope does, you made two "popular assumptions"! (Of the two assumptions you made, only the first one is correct. You'll learn why the second assumption is wrong once you do the homework.) OK, I'll give you...
  24. Omid

    New Horizons II

    I agree that it is a matter of opinion to say which of the two control loops is primary. Both functions are very important to our vision. Yes, it is. I happen to know a little bit about feedback control systems because my doctoral advisor, Prof. Bruce A. Francis, was one of the world's most...
  25. Omid

    New Horizons II

    Topic: Afocal Keplerian telescope operating at finite conjugate You are most welcome. Before you "research" further, please read post #201 in this thread and try to answer the question. Draw a diagram like the one I had attached on a piece of paper, then turn off your computer, pick up a...
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