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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/20/2004 at 12:39
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Question for the experts:  What is the difference between TOTAL light transmission and light transmission PER LENS SURFACE?  I have been doing a lot of research in manufacturer's websites recently and see this pop up a lot.

 

For example, Leupold claims a 99.65% light transmission per lens surface on the LPS, and up to 98% total light transmission on the VXIII.  Burris claims their HiLume multi-coating gives 99.5% light transmission per lens surface and 95% total light transmission on the Fullfield II.  Burris also 'calculates' the total light transmission of the VXI and VXII on their website to be in the mid to upper 80s.

 

I am guessing light transmission per lens surface is a factor of the lens (multi) coatings and total light transmission is a factor of the glass quality and scope design.  Am I right, or do I have this backwards?

 

thanks in advance,

Jason

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Total light is the sum of surfaces. Some companies take an average. Some take as a percentage contribution which give a lower figure. Some companies measure the amount using spectrographs. (Schmidt and Bender, Zeiss, probably Leo). This property is much more important in microscopes than binoculars or rifle scopes and makes for good sales talk. Your are correct about total light transmission being a factor of the glass and quality, however nothing is said by any one that only certain wavelengths are measured by virtually any manufacturer because they change with wavelength (what makes prisms work). If one manu. says they have x amount on their lower line of scopes and x+1 in the next line, it probably has some comparison value. To compare accross the board is almost meaningless.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/20/2004 at 17:33
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A couple of comments

 

To get total light transmission you multiply the transmission coefficient of one surface by itself as many times as there are surfaces in the scope .  For example, 99.65% for one surface means 0.9965 of incoming light is passed through one surface.  For two surfaces it is 0.9965x0.9965=0.993 (or 99.3%)  I do not know how many surfaces a LPS scope has, but for 10 surfaces total light transmission is 0.9655 or 96.55%.  Interestingly, if each surface only transmits 99.65% to get a total light transmission of 98% you can't have more than 6 optical surfaces, i.e. no more than three lenses.  I do not know exactly how many lenses a scope typically has, but it is certainly more than three.  Fixed scopes have fewer lenses than variable ones.  That's why all other things being equal a fixed magnification scope will be brighter.  Light transmission does depend heavily on the wavelength.  For a narrow wavelength range it is quite feasible to get a multicoating with transmission of 99.99% or slightly better (I've worked with these in telecom industry and there are several companies that can readily supply superefficient narrow band coatings).  Leupold's claim of 98% total light transmission has to be for a particular wavelength (color) of light. 

 

Burris website has a cutaway picture of a scope that shows 5 lenses.  For 10 optical surfaces at 99.5% each, total light transmission is 95.1% which matches their statement.  We still do not know which wavelength range they are measuring.

 

Total light transmission is just a function of the light transmission of individual surfaces.  The catch is that a scope can be very bright, but have poor resolution.  Resolution depends heavily on coatings as well as on quality and polish of the lenses.  The surface finish of the lens is typically measured in a test called "scratch and dig" which basically looks at scratches and nonuniformities of the surface.  Another useful test is an interferometric measurement called "wavefront transmission" it looks at how long it took each wavelength to go through a lens (light travels at different speed through different materials).  Nonuniformities in lens material, surface finish and coating quality can all result in poor wavefront transmission performance which correlates directly to poor resolution.

 

A good example here is with Burris Signature scopes vs. Fullfield II scopes.  They have the same coatings, hence total light transmission is going to be roughly the same for the same magnification range.  However, lenses in Signature line scopes are ground and polished to stricter tolerances resulting in better resolution than Fullfield II scopes.

 

I think I saw some tests somewhere that said that Burris Fullfield II fixed 6x scope is easily among the brightest in the world easily holding its own against expensive Euro scopes.  However, that does not mean that it's the best scope since total light transmission does not garantee top resolution.

 

I think I'll stop here. This post has been a bit too long anyway.

 

Ilya



Edited by koshkin
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/20/2004 at 22:23
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Koshkin, that particular wavelength ( color ) would be the green spectrum which is the peak of what the human eye can capture. This relates to what is referred to as the cones or rods in the human eye that are the most sensitive to. This falls between 477-570 or so nM. It would only make sense for a scope/binocular manufacturer to use this measurement of color as it would be to their own benefit for advertising stats.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/21/2004 at 02:18
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You are probably correct, Roy.  Green is right in the center of the visible range, and I would expect them to maximize the transmission there.  It does not have to be that way though.  A broadband coating can maximize transmission anyywhere in its spectrum. That just depends on the recipe.  For example, if memory  serves me right, Zeiss claims that their German built scopes have a maximum transmission at the blue end of the visible spectrum.  Steiner Predator binoculars (which you own, I think) maximize the transmission of their broadband coatings on the red/brown end.

Ilya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/17/2004 at 12:34
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Don't know why Steve Optics PM'ed this to me instead of posting it...but here it is.

 

 

Hey Chris,

 

Could you please forward this message to:SCJason, Dale Clifford,Koshkin and Roy Finn

 

Hey scjason,

 

The answer to your question is actually quite complex, I do not have the time as I am a very slow typer to answer it correctly, so here is a simple version.

 

Dale, Kos and Roy, all make great points and bring up many important issues when trying to answer actual light transmission in bino's and scopes.

 

Actually though, when Burris, Leupold, Nikon ect. advertise "Light Transmission"  they are only referring to "white Light !"

 

Fact, as light passes through an optical lens, coated or non coated, all shades of all colors in the spectrum bend. That is all except the "white light"

These companies are advertising how much white light transmission the have or actually they are trying to tell you how little reflection and refraction they have.

 

As Koshkin points out, this has very little if anything to do with Resolution and Contrast.

 

Resolution and contrast have everything to do with how you see the object you are looking at through the instrument !!

 

To stop by the store and compare the Simmons $20.00 scope to the $1000.00 scopes you will quickly assume the Simmons to be brighter by looking across the store at a well lighted display. However, to compare them at dusk outside looking at a dark object with no artifical light shining on it you would quickly realize why some oprics sell for thousands.

 

Not only do all shades of colors bend, the real confusing is in the fact that the only way to get the colors directed into the same path is by using a series of lenses each with a specific coating formula to direct a particular color a certain way.

 

This is one reason their are 11 or more lenses in a quality variable scope.

 

Hope this helps a little

 

Steve Optics  

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/17/2004 at 13:20
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I am not sure what Steve means by "white light".  Typically white light means a combination of different wavelengths, from red to blue.

 

>>

Fact, as light passes through an optical lens, coated or non coated, all shades of all colors in the spectrum bend. That is all except the "white light"

>>

 

I am not sure how this makes sense.  Any light bends when going through one media into another, i.e. from air to glass and vice versa.  Fluorescent lighting actually produces a spectrum fairly close to sunlight, I think.  Producing a coating optimized for white light means a broad band coating optimized for the whole product range.  A lot of spectrometers and interferometers still use incandescent bulbs which output more radiation at the long wave end of the visible spectrum: red, yellow, orange and near IR.  At sunset and sunrise, i.e. low light conditions, blue light transmission may be a little more improtant than in the middle of the day.  That means that something optimized with a incandescent lighting would not be optimal for hunting.

 

Anyhow, I may be misunderstanding what Steve meant.

 

Ilya

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/08/2004 at 13:23
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Steve,

Your answer is good, but there are several points of confusion:

Most important: the coatings on the lenses have nothing to do with "color correction". They reduce reflections, but they do not cure Chromatic Aberration, or change the angle at which any color of light is bent.

Second: there is no such thing as "white light." White is the sum of all colors. It does not exist on its own, and it is pretty much determined by the overall blend of the different colors and our brain's interpretation of them. That is, we "make" white light in our brains. Our brain has the original "auto white balance"...and can adjust our perception of white over a wide range of subtle shades of "off white." Which is the reason we have to have either auto or manual white balance on cameras...since they are much less forgiving of color bias than our eye/brain.

Most manufacturers measure transmission over the "visible spectrum" generating a curve that matches the transmission of each individual frequency (color) of light. They then might average those figures from the curve, or they might take the "high point" for their published figures, or they might select a particular color of light that they think is most important (in the green wavelengths generally, since that is the range the human eye is most sensitive to). There is no standardization for the measurement of transmission in the US. I think the European Union has such a measurement standard, or one in draft from at least.

Finally, there is only approximate correlation between the measured transmission of optics and their perceived brightness. Perceived brightness is a factor of the amount of energy coming through, but it also depends on the overall contrast of the image, the intensity or purity of the colors, and the particular color balance of the image. In fact, in my experience, color contrast is as important to perceived brightness as is transmission. In the end it is all about how much color and detail you can see in low light situations. A well baffled optic (that is one in which most of the reflected light is captured before it degrades the contrast of the image) with excellent color correction might well deliver better color and detail in dim light than an optic with great transmission (very little reflected light) but with poor baffling (so what light is reflected does, in fact, degrade image contrast), and poor color correction (so the colors are muddy to begin with). Only actual side by side tests can determine which optic performs best for your eye in the twilight.

Anyway, I am not sure this is of much help.

Keep up the good work in trying to educate folks to the realities of consumer optics.



Best regards,

Stephen Ingraham
__________

Birding and Wildlife Product Specialist
Carl Zeiss Optical, Inc.
Carl Zeiss Sports Optics Division
13005  N. Kingston Avenue
Chester, VA 23836 USA

 

- emailed to me with the request that it be posted on this thread.  CF

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: June/07/2011 at 13:44
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So why does not the industry set a standard of comparison based on an agreed standard set or sets of conditions. That way the consumer could evaluate based on objective data rather than subjective opinion?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: June/07/2011 at 14:19
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I feel both baffled and illuminated by the transmission of all this info but I do see the light, white or otherwise. Dudes, my microwave's beeping at me. Time for 500 ccs of lunch. Pass the sauerkraut!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: June/07/2011 at 14:35
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FROM 2004 fellas. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: June/07/2011 at 17:25
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But still "worthy"...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: June/07/2011 at 20:17
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Yes, another long dead thread risen from the dead. And, a good question. Why no standard.
Part of it is, beyond wave lengths, reflection, refraction, etc, etc, much is subjective.

Edited by tahqua - June/07/2011 at 20:18
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: June/07/2011 at 22:56
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Although I obviously wasn't a member here in 2004 I had the same question then and for that matter many years prior. Why doesn't some optics geek ( complementary) set up a lab test protocol
and become the consumers guide of optics? Unless of course it costs  millions to do so.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: June/08/2011 at 09:37
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Originally posted by M-100 M-100 wrote:

Although I obviously wasn't a member here in 2004 I had the same question then and for that matter many years prior. Why doesn't some optics geek ( complementary) set up a lab test protocol
and become the consumers guide of optics? Unless of course it costs  millions to do so.


because even if someone sets a standard, and all the manufacturers conform to that standard, which is a stretch in itself, individual buyers will still have differences of opinion  because much of why we like certain optics has more to do with brand recognition and how it looks to us, than how it conforms to some measured number.

pretty sure it would amount to a whole lot of work for nothing.  marketing ploys, brand recognition and personal preference would still win out.
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OK.  Since this thread came from the dead...

Which standard do you mean? 
What are you looking to standardize?

ILya
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I'm no engineer ( optical or otherwise) so don't attack my numbers. This is just an example to answer ILyas question.
I was thinking of a numerical performance scale. 
Say an optic could resolve the difference between a 1mm hexagon and a 1mm circle under a specified
light condition at a standardized distance, it would be rated a 99 for resolution for that condition. Any practical optical component that is objectively measureable could be rated in this manner for the use of the consumer. I hope that makes sense.
Possible or not?
Practical or not?
 
 
 
 
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Except everyone's optical perspective is different...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: June/08/2011 at 13:19
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Originally posted by M-100 M-100 wrote:

I'm no engineer ( optical or otherwise) so don't attack my numbers. This is just an example to answer ILyas question.
I was thinking of a numerical performance scale. 
Say an optic could resolve the difference between a 1mm hexagon and a 1mm circle under a specified
light condition at a standardized distance, it would be rated a 99 for resolution for that condition. Any practical optical component that is objectively measureable could be rated in this manner for the use of the consumer. I hope that makes sense.
Possible or not?
Practical or not?
 
 
 
 

As a matter of background, at the moment I am a Technology and Business Development Manager for a company that makes the equipment for all manner of optical measurements including lens testing, camera testing, etc.  I deal with this stuff every day of my life.

There are perfectly quantifiable ways of measuring light transmission, contrast, resolution, etc.

How are you planning to transfer that knowledge into what your eye actually perceives?  
Under what lighting conditions?  With what targets in mind?

More importantly, how are you planning to pay for all that?

Scope manufacturers, for obvious reasons, have zero interest in releasing such data (and they have most of the necessary equipment).

Let's say, I decide to go ahead and set up a lab for such measurements.  That will require an investment of somewhere between $75k and $200k for a truly comprehensive set up, depending on the extent of the testing and on the variety of the measurements I would need to make.

How do you propose I recoup the costs of the equipment and the time invested?

ILya
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Hi Guys,
Thought I would throw some more wood on the fire.
To go back to the OP and the question and some of the answers......with what intrument are you testing light transmission with?
Usually you use something called a spectrometer. Am I correct on this Ilya and other optics guys?
 
Now this intrument can be made by many companies but the idea is to compare the light traveling through either a lens, group of lenses or the whole scope to a known light source within the tester. You can test at certain wavelengths or test the overall performance at say....the visible spectrum of light which is what we would be talking about here lets just say a little below 400nm to a little above 700nm (bear with me guys as I am just giving aproximations).
 
I have had 2 scopes manufactured by the same company tested on 2 spectrometers made by the same company, however one tester was "modified" in some way and the other was bone stock. The readings were 3-4% different. When I contacted the tester company and started to delve into this I found that numerous things can be done to alter the readings of these units.
 
So I guess is what I am saying is using just a spectrometer to measure light transmission will only be accurate if the same unit is used and the scopes are set up the same way ie: the reticle moved out of the light path as this can make a huge difference in readings.
OR if the unit is calibrated and in stock condition and has not been fooled with by a non factory person.
 
I do tests here on a calibrated Perkins Elmer spectrometer that is factory stock and I use the findings for internal use only unless someone asks me to perform a comparision and then I will run one. The calculation of light transmission and the reality of what you get through a completed scope can be vastly different.
Sorry for ranting, but in this instance the equipment used can play a large factor in the end result.
Thanks,
Paul
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Thanks for chiming in, Paul.

Spectrophotometer would indeed be an instrument useful for measuring light transmission.  However, with any grating-based instrument, you have to be pretty careful about selecting spectral resolution carefully.  That can have a considerable effect on your results.

If I were to put this kind of a setup together for an instrument the size of a riflescope, I would be inclined to assemble it myself out of various COTS pieces since the needs of an imaging instrument go a fair bit beyond what a typical spectrophotometer does.

Either way, light transmission is only one of the tests that you might want to do.  We make test equipment that can measure almost anything you can imagine.

The pertinent question is as follows: if I give you thirty pages of numbers and plots that describe the optical performance of a riflescope in excrutiating detail, how will you get out of that any useful or actionable information on the actual field performance of that same riflescope when coupled with your Mk1 eyeball?

ILya
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Thanks to all both past & present for all the great input.Thanks CF for a terrific site that us mere mortals can have a chance to learn so much for free Excellent
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You can find transmission curves for many binoculars at www.allbinos.com

I thought transmission at about 550nm was a sort of  "standard" . The swedish magazine Vapentidningen measured transmission at 500- 550nm in their big test some years ago. Burris got 9/10 points for the Fullfield II 3.5-10x50 , that means a transmission between 90-95% (same points as the Zeiss Victory). As others here have explained lighttransmission is not the same as twilight performance, but one (important) of many factors.

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How are you planning to transfer that knowledge into what your eye actually perceives?
If there is trustworthy objective data that says an optic performs at a lab rating of 90% and another at 50% for the factors I am purchasing for I will purchase the 90% performer. Or are you saying that for some eyes the lesser performer will "appear" better?
 
Under what lighting conditions?  With what targets in mind?      
In my fantasy lab those test parameters would be specific to the type of optic being evaluated. A target scope might have only one general spec for light condition where a hunting or tactical would need several. As long as all optics of the same type were evaluated by the same standard the scale would be valid IMO.
 
More importantly, how are you planning to pay for all that?
How do you propose I recoup the costs of the equipment and the time invested?
Having  "Business Development Manager" in you job title I am sure you have a better grasp on that
than I do but I if you established an unimpeachable creditability level either the producers would come to you for your rating or you could become the Consumers Guide of the optics industry.
 
Scope manufacturers, for obvious reasons, have zero interest in releasing such data (and they have most of the necessary equipment).
I rarely trust their info anyway "figures don't lie but misdirectors do apply the figures"
That is the whole point to my original question.
You asked another poster about the application of many pages of data. I was not asking for an analysis of all factors present in the function of an optical device. Only the practical factors that the consumer would be concerned with in making an educated purchase. 
 
So I guess the answer to my questions are
Yes it is possible
Not very practical
"Caveat Emptor"
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Originally posted by M-100 M-100 wrote:

How are you planning to transfer that knowledge into what your eye actually perceives?
If there is trustworthy objective data that says an optic performs at a lab rating of 90% and another at 50% for the factors I am purchasing for I will purchase the 90% performer. Or are you saying that for some eyes the lesser performer will "appear" better?

Yes.  Depending on the type of shooting you do and on the specifics of your eye, different scaling would have to be used.  For example, something that ranks very highly on a scale developed with young eyes and target shooting in mind, will likely not work very well for an older set of eyeballs looking for a low light hunting scope.  Then there are the obvious complications involving different exit pupils.  For different eyes a lower performing scope with a large exit pupil can work better than a high performing scope with a large exit pupil.  Then, there is a question of eyerelief: depending on how good your peripheral vision is, you might have a clear preference for scopes with eye relief on the short side or on the long side (eyepiece size also plays into this).  Then there is a question of lighting: in low light your eye pupil dilates and the depth of of field of your eye changes considerably requiring somewhat different scope properties.  Unfortunately, the eye pupil dilation is markedly different for different people.
 
Under what lighting conditions?  With what targets in mind?      
In my fantasy lab those test parameters would be specific to the type of optic being evaluated. A target scope might have only one general spec for light condition where a hunting or tactical would need several. As long as all optics of the same type were evaluated by the same standard the scale would be valid IMO.

Not that simple.  See above.
 
More importantly, how are you planning to pay for all that?
How do you propose I recoup the costs of the equipment and the time invested?
Having  "Business Development Manager" in you job title I am sure you have a better grasp on that
than I do but I if you established an unimpeachable creditability level either the producers would come to you for your rating or you could become the Consumers Guide of the optics industry.

"Consumer's Guide" implies  that consumers pay for this service.  Practice shows that consumers are very unlikely to pay for this service, since they can get effectively the same information for free from a few collective impressions of reasonably skilled observers on the internet.
How much would YOU be willing to pay for such a service?

 
Scope manufacturers, for obvious reasons, have zero interest in releasing such data (and they have most of the necessary equipment).
I rarely trust their info anyway "figures don't lie but misdirectors do apply the figures"
That is the whole point to my original question.
You asked another poster about the application of many pages of data. I was not asking for an analysis of all factors present in the function of an optical device. Only the practical factors that the consumer would be concerned with in making an educated purchase. 

So what are those practical factors in your opinion? 
I can think of a few personally, that I talk about in my reviews.  However, I have no idea how to make those numbers relevant to a typical consumer.  In the end, I would have to look at those numbers and interpret them for a specific consumer and his requirements.  If I have to do that anyway, how is that different from what I do now, when I spend some time with several scopes side by side and make recommendation based on what I saw?  When I first started doing this, I would take scopes into my lab at work and do all sorts of measurements.  That took a lot of time and satisfied my curiosity, but did not yield any actionable information that I could not get from spending some time with the scopes in my hands.
 
So I guess the answer to my questions are
Yes it is possible
Not very practical
"Caveat Emptor"

See my comments above.
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