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Low-Light Performance Calculator |
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opticsmike
Optics Apprentice Joined: September/09/2008 Location: Amherst, NY Status: Offline Points: 185 |
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Posted: October/06/2008 at 17:35 |
For anyone interested, I've created a Low-Light Performance Calculator with interactive graphical comparisons at http://scopecalc.com I hope for this to grow into a community-based project that can help to make scope selection easier for everyone, but much work will need to be done gathering data to make accurate comparisons among different scope brands and lines. See the site for details. ...example usage with pre-filled values comparing five Zeiss Diavari Victory rifle scopes: |
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lucytuma
Optics Jedi Knight Joined: November/25/2007 Location: Wisconsin Status: Offline Points: 5389 |
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Looks like a nice winter project, thanks and good luck with it.
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"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not." - Thomas Jefferson
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Roy Finn
MODERATOR Steiner Junkie Joined: April/05/2004 Location: United States Status: Offline Points: 4856 |
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How will this help a layman like myself determine which scope will outperform another based on punching in fixed number values for different scopes.
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opticsmike
Optics Apprentice Joined: September/09/2008 Location: Amherst, NY Status: Offline Points: 185 |
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Until resolution and light transmission are known with a single standard across all scope brands and lines, this will only be useful when comparing scopes of comparable quality optics. This is perfect for when you are considering several scopes from among the same scope line or among different lines that are known to be about equivalent in optical quality and want to know how much more effective one will be over another for low light. Then you can consider that effectiveness with other considerations such as size, weight, durability, features, reticle selection, and cost etc.
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Roy Finn
MODERATOR Steiner Junkie Joined: April/05/2004 Location: United States Status: Offline Points: 4856 |
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Thank you. I have no formal education in this area, however, I am wondering how this will differ from using what is known as Twilight Factor to make comparisons between scopes, bino's and spotters of like quality. I think TF and Relative Brightness calculations are useful to those who are in the market for new optics for rough comparisons only.
Edited by Roy Finn - October/06/2008 at 20:18 |
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opticsmike
Optics Apprentice Joined: September/09/2008 Location: Amherst, NY Status: Offline Points: 185 |
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The explanation from the site outlines the improvement over Twilight factor...
Apparent Brightness Factor:
The Apparent Brightness Factor is the perception of the amount of target light through the scope relative to the perception of the amount of target light with the single unscoped eye. Apparent brightness is calculated as the cube root of the total light factor, which is the basis for modern computer color space brightness scaling and is also the apparent brightness of a 5-degree target in the dark with a uniformly dark background and surround. If the unscoped eye pupil luminous flux is 1 lumen and the scoped eye pupil luminous flux is 50 lumen, then the Eye Pupil Luminous Flux Factor is 50x, and 50 times the amount of light from the objects within the field of view of the scope is reaching the eye pupil through the scope than without the scope, although the light from the objects through the scope will appear 3.6 times as bright than with one eye without the scope. If you consider that one eye is closed when looking through the scope, then only 25 times the light is reaching the one eye through the scope than with both eyes open without the scope, and the objects through the scope will appear 2.9 times as bright as with both eyes open without the scope. Both the unscoped eye pupil luminous flux and the scoped eye pupil luminous flux are the amounts of light reaching the eye pupil from only the objects that are within the field of view of the scope. Apparent Brightness Factor = (Practical Eye Pupil Luminous Flux Factor)^(1/3) Low Light Performance: Low Light Performance = (Apparent Brightness Factor x Magnification)^(1/2) |
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opticsmike
Optics Apprentice Joined: September/09/2008 Location: Amherst, NY Status: Offline Points: 185 |
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Ok, I've replaced all of the technical jargon with words that are easier to relate to. I hope this helps. An update of the definitions from my previous post here is on the site now.
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Roy Finn
MODERATOR Steiner Junkie Joined: April/05/2004 Location: United States Status: Offline Points: 4856 |
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opticsmike, at first I didn't realize that you could plug in your own eye pupil diameter, although I'm sure the calculator is using a standard number for comparisons between scopes. Now that I plugged in the eye pupil diameter and exit pupil diameter, I can see where you are able to make more accurate comparisons between scopes than you could by just using TF data. I will say that most of the folks who visit here are looking for the kind of information that the calculator will not be able to capture such as glass and coating differences, stray light efficiency and overall design differences that will set one scope apart from the next. In other words, usually someone will come here and state that they are shopping for a new 3-9x40, and they want to know what differences exist from same. Now if there was a way to capture say, contrast and image resolution, that would be interesting. Frankly, I have no ides how a consumer would be able to determine those factors.
Roy Roy |
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cheaptrick
MODERATOR Joined: September/27/2004 Location: South Carolina Status: Offline Points: 20844 |
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Tagged.
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opticsmike
Optics Apprentice Joined: September/09/2008 Location: Amherst, NY Status: Offline Points: 185 |
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Roy, my hope is that a measuring standard could be developed for light transmission, resolution , and contrastp; and people that do have the means to take measurements could contribute the data. Maybe I'd consider buying the tools needed to take the measurements and send them out to people that I could trust. Just a thought at this point.
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Roy Finn
MODERATOR Steiner Junkie Joined: April/05/2004 Location: United States Status: Offline Points: 4856 |
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I have had long conversations with folks here and also some industry folks that I've gotten to know over the years and a standard of light transmission sounds like it would be a challenge to say the least. I don't know of any two companies that test their products the same as others do. In a very competitive market, manufactures want to be able to claim high light transmission figures and I believe that we as the consumers are only getting partial data at best. Take Bushnell for example, claiming, "world's brightest riflescopes". They claim 95% light transmission at 550nm. You know as well as I do that figures for the middle of the color spectrum are not necessarily going to provide the kind of data that would indicate what would work best for light (color) transmission toward the lower end of the color spectrum, say 400nm or so. Zeiss claims their transmission numbers are averaged across the visible color spectrum which, IMO, is much more accurate and realistic. Leupold makes claims of nearly "98%" light transmission, but God himself can't figure out how they are arriving at their claimed figures. When you consider then number of lenses in a variable riflescope, that figure would be practically impossible to obtain. I know Steiner also measures across the entire visible spectrum as well. As I stated before, I have no formal education in this field, but it is something that interests me. I started to gain interest in this by accident so to speak as a family member suffers from macular degeneration. Having a special interest in sporting optics was just a natural progression into vision concepts.
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opticsmike
Optics Apprentice Joined: September/09/2008 Location: Amherst, NY Status: Offline Points: 185 |
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We can devise an impartial standard for light transmission in low-light conditions to measure by.
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Roy Finn
MODERATOR Steiner Junkie Joined: April/05/2004 Location: United States Status: Offline Points: 4856 |
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The standard would be the easy part. I'm just not sure how an instrument could be used to capture what the human eye actually sees in real life conditions. An instrument will collect data at a standard rate. What you see through a riflescope and what I see could be very different depending on age, health, weather conditions etc. etc. And yes, I realize that even though our vision differs, the relationship between scope A and scope B should be the same regardless.
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opticsmike
Optics Apprentice Joined: September/09/2008 Location: Amherst, NY Status: Offline Points: 185 |
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To be usable as a factor, light transmission only needs to be measured as a percentage of the amount of visible light through the scope, not the perception of it.
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opticsmike
Optics Apprentice Joined: September/09/2008 Location: Amherst, NY Status: Offline Points: 185 |
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For those who are interested, the following is how the calculation is performed. To help make this easier to understand here, I'll substitute "Luminous Intensity" with "Light Intensity" and "Luminous Flux" with "Light", and "Factor" with "Gain"... EyePupilDiameter = 7 mm Given two of the following properties: Magnification, ObjectiveLensDiameter, ExitPupilDiameter Objective = 56 mm The third can be deduced by... ObjectiveLensArea = 3.14159265358979323846 x (ObjectiveLensDiameter/2)^2 ...To calculate final caluclation as a factor of initial LightIntensity: ObjectiveLensLight = ObjectiveLensArea x LightIntensity EyePupilArea = 3.14159265358979323846 x (EyePupilDiameter/2)^2 UscopedEyePupilLight = EyePupilArea x LightIntensity ExitPupilArea = 3.14159265358979323846 x (ExitPupilDiameter/2)^2 ExitPupilLightIntensity = (ObjectiveLensLight / ExitPupilArea) x (LightTransmission/100) x LightDiffractionFactor if (ExitPupilArea <= EyePupilArea){ ScopedEyePupilLight = EyePupilIlluminanceArea x ExitPupilLightIntensity EyePupilLightGain = ScopedEyePupilLight / UscopedEyePupilLight PerceivedBrightnessGain = EyePupilLightGain^(1/3) LowLightPerformance = (PerceivedBrightnessGain x Magnification)^(1/2) This is reflected in the following calculation with pre-entered values... |
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cheaptrick
MODERATOR Joined: September/27/2004 Location: South Carolina Status: Offline Points: 20844 |
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"Mr. Koshkin....Mr. Koshkin...please pick up the red courtesy phone."
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Offline Points: 13182 |
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Did someone call?
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Offline Points: 13182 |
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What can I do for you CT?
ILya |
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cheaptrick
MODERATOR Joined: September/27/2004 Location: South Carolina Status: Offline Points: 20844 |
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I'm getting dizzy just reading about this guys low light calculator.
(You know how I get sometimes.)
I'd like to see what your take on this instrument is.
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Ed Connelly
Optics Retard God of no Chihuahua Joined: December/16/2007 Location: USA Status: Offline Points: 24225 |
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( " But, Ollie, I didn't understand a word of what that man said...I'm in the dark and he's feeding me mushrooms....." )
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