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10X42 vs 10X50

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/25/2016 at 13:50
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I understand the concept of the bigger objective lens "allowing" more light to pass through as evident by a larger exit pupil... but, is there some funny business/marketing going on here?

For example, the Swarovski EL, I'll only pick on them because I'm the most familiar with their products.  Whether you buy an 8.5X42 or a 10X50 the light transmission is shown as 90%.  The exit pupil is obviously different for both models and all the model in between.  So does this mean exit pupil doesn't really matter?  All else is the same with each model.  Is light transmission even different at all?  What's the purpose of the bigger objective lens if light is equal?

Also, how much can exit pupil truly matter?  The SLC 15X56, which has the smallest exit pupil out of their entire line has the best light transmission.  Now, I understand they don't have the field flattener lens, which is one less medium for light to pass through but these numbers don't always seem consistent to common optics theory.

What gives?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/25/2016 at 15:00
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Light transmission and exit pupil are two different things.  Exit pupil is the size of the shaft of light going through the device that reaches your eye.  Light transmission would the the amount of brightness allowed through the optical system in that shaft. 

If you have two binos both 10x42.  One is a $1500 Swaro and one is a $200 Sightron, while they both may have a 4.2mm shaft of light going through them to your eye, the bino with the better lenses/coatings/optical system is going to allow more transmission through those lenses to your eye.  So you will see a brighter image.

This IMO is one reason why comparing binos is so hard.  Everyone uses different lenses, coatings, etc, so it is hard to really compare them equally.  And everyone has preferences for what their eyes like and biases as well.  

Exit pupil matters a lot.  If that shaft of light coming through the device is larger than the pupil in your eye, then your eye is getting the largest most available image it can provide to your brain allowed by that optical system.  If the pupil in your eye is dilated to 5mm and your bino is only providing 4mm of exit pupil then your eye could handle more.  That is why if a person is view in low light a lot then a bino with a higher exit pupil is prefer.  Because the pupil in your eye is dialated to a larger size to provide more light to your eye.  Perfect example is a spotting scope.  I have a Meopta that is 20-60x80 or somehint like that.  At 20x the image looks great, but as I turn the mag up, the image gets dimmer and significantly harder to keep my eye perfectly aligned in that shaft of light.  At some point that shaft of light becomes so small it does not allow enough of the image through to give me a quality image.  For this reason I rarely turn the mag past 35ish. 

ANother exmple a variable rifle scope.  Think about when you turn a 6-24x scope up to 24x.  Everything about it suddenly becomes difficult to use.  Picky eye box, image gets dark and hard to see through.  Turn is down to 15 and the target gets much easier to see.

But in low light magnification can increase detail if you have good glass.  All the binos I own have 4 to 4.5 mm exit pupil.  In my uses, that is enough for me.  I have a 8x32 Meopta HD and a 8x32 sightron blue sky.  The Meopta smokes the Sightron in brightness and low light and detail even though they have the same exit pupil.  So you have to look at things carefully.  All else being equal. 

Hopefully all this is accurate.  I am sure the real educated folks will come along and explain things much better than I am able to. 


Edited by supertool73 - October/25/2016 at 15:11
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I appreciate your response and I hope it educated someone, but it doesn't really answer my question in any facet nor do I believe you really saw the purpose in the answer.

You are correct, the exit pupil is more prevalent and noticeable in spotting scopes or rifle scopes where large ranges of magnification are used, for instance a 3x-18x/5x-25x or a 20x-60x.

I listed the Swarovski EL as my example but let me rephrase since it seems I wasn't clear.

Swarovski Exit Pupils in mm

EL 8.5 X 42 = 4.94
EL 10X 42 = 4.2
EL 10 X 50 = 5
EL 12 x 50 = 4.16

All of these models have a 90% light transmission according to Swarovski... yet light transmission is the same... how is this possible?

Light transmission should be different if the exit pupil is different since all other variables are equal according to "common knowledge".  Unless of course the small differences in exit pupils are so minor that light transmission is not altered enough to leave that 90% figure.  If this is the case, what is the purpose of the 10X50 to begin with?  If light transmission is the same then it seems like what, a marketing strategy?

Furthermore, Swarovski SLC 15 X 56 has a 3.73 mm exit pupil.  .43 mm smaller or roughly 10 percent smaller than the smallest exit pupil listed in the EL column.  Yet the SLC 15X56 has the best light transmission of the entire Swarovski line, I believe 93%.  This is in part due to the lack of field flattener lens, this is understood. 

Yet in binoculars at least comparing the same model with different magnification ranges, why would a person pay more for a 10X50 when a 10X42 has the same light transmission, the same magnification, in a smaller/lighter package?


If the human eye needs a light transmission change of 3-5% before it becomes perceptible, than advertising a 10X50 as being a better binocular for light transmission is just a marketing hoax...is this correct or am I being presumptuous?


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/25/2016 at 15:47
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Ok, hopefully I am grasping your question better.  I think you are trying to make it so exit pupil and light transmission depend one upon the other.  They don't.  Exit pupil is not the light transmission that is going through the optical system.  It is simply the size of the band of light going through the system.  How bright the light is in that band of light is the light transmission.  Shine a 3o lumen light through a paper towel tube and hold it right  next to a wall.  The circle of light on the wall will be roughly same size as the paper towel tube. Shine a 300 lumen light through it and while the circle stays the same size the light on the wall will be much brighter.  Move that paper towel tube back a few inches and the size of circle increases making more of hte wall light up.  It will do the same to your eye, it provides a larger spot of light (or image) for your to look through.  Same with optics, a better optical system allows a higher lever of light transmission through the device.  And larger exit pupil gives you are larger image to see.     

Quote All of these models have a 90% light transmission according to Swarovski... yet light transmission is the same... how is this possible?


Here you are showing sizes of exit pupil, but that does not correlate with light transmission per say.  The lenses/coatings/optical system is what allows that 90% number, it has nothing to do with the exit pupil. 

Why the 15x is 93% I am not sure.  Maybe a more efficient optical design in that model vs the others. 






Edited by supertool73 - October/25/2016 at 15:54
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Originally posted by Brocksw Brocksw wrote:

What's the purpose of the bigger objective lens if light is equal?


The brightness of light is 90% but not the size of the band of light.  With a larger band of light it provides more light to your eye.  It is still passing 90% of that light through, but now you went from 4.5 mm to 5.6 mm of light reaching your eye.  That is 20% more of that 90% brighness reaching your eye.  So it make the image appear brighter if your eye can benefit from it.  If your eye can only dialate to 5mm and you have a bino with 7mm exit pupil it won't give you a brighter/better image. 


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/25/2016 at 16:03
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SOOO....if you change the size of the paper towel tube from 4.16 mm to 5 mm with everything else being identical... you're not introducing more light into the optical system?

If your answer is no, you have me all screwed up.

If your answer is yes... then does this mean that 90 percent for the 10x50 is not the same as 90% for the 12X50?  If so, how would one quantify this in simple terms?  There is roughly a 30% difference in  area (mm^2) of the exit pupil when comparing a 12X50 (13.59 mm^2) and a 10X50 (19.63 mm^2).  I don't believe there is a 30% difference in light transmission or a 27% difference in light transmission (since 27% is 90% of 30%)....


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/25/2016 at 16:11
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We have probably reached the peak of my understanding of this and maybe I passed that a while back and am just shooting BS at this point.  I apologize if that ends up being the case.   Hopefully Bill, ILya, or one of the others can help explain better.

But I am going to say no and yes.  You are introducing more light because the exit pupil increased by 17%.  But the amount of light (the quality of light) that passes through any point of that optical system is still 90%.  So no matter the size of the exit pupil the transmission is still at 90%.  But you have increased the size of the band of light by 17% so your eye has a larger image(because of the lager band of light) to look at.  But that may or may not benefit you.  Way to many others factors to say one way or the other. 


Edited by supertool73 - October/25/2016 at 16:20
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Although you didn’t pull my chain, I would like to speak to this. If I am out of line please just disregard. I’m used to it; I have kids. The figure you offered indicates a maximum difference of only .8mm. That’s pretty small, especially when used during the day. While some observers need to quantify EVERYTHING, there is really no need when working with real world optics, as so many of the differences people quibble about are well below their threshold of recognition (sensory threshold), anyway.

I will offer only one of dozens of answers by asking a question of my own:

Which provides the brightest image, a binocular with a 5mm pupil but used the BEST coatings and a Schmidt-Pechan prism or a bino offering a 4.2mm pupil but uses an Abbe-Koenig prism with REALLY GOOD coatings? And who on the forum could say they could ignore a half dozen other parameters to state with 100% certainty that the largest exit pupil wins, hands down?

ALL the binos you mention are world-class. But, they all have mechanical and optical difference that observers will never notice, but which may make a difference.

A few years ago, a Steiner ad showed a hunter kneeling with his rifle, butt on the ground and pointing at the clouds while he looked through his binocular. The caption read: “WHEN EVERY SECOND COUNTS.”

For my money, when EVERY SECOND COUNTS, only an idiot continues to look through a binocular while his rifle is pointed at the clouds.

Just a thought

PS They probably say the binos off the same exit pupil because at their level and with their agenda it's like splitting hairs with an ax,




Edited by WJC - October/25/2016 at 16:21
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/25/2016 at 16:25
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Originally posted by supertool73 supertool73 wrote:

We have probably reached the peak of my understanding of this and maybe I passed that a while back and am just shooting BS at this point.  I apologize if that ends up being the case.   Hopefully Bill, ILya, or one of the others can help explain better.

But I am going to say no and yes.  You are introducing more light because the exit pupil increased by 17%.  But the amount of light (the quality of light) that passes through any point of that optical system is still 90%.  So no matter the size of the exit pupil the transmission is still at 90%.  But you have increased the size of the band of light by 17% so your eye has a larger image(because of the lager band of light) to look at.  


I think it should be clarified that the differences in exit pupils should be measured in area not diameter?  At least, I believe they should...

This would mean the diameter of the exit pupil increased by 17% but the area increased by 30%

Regardless, I think we are on the same page now and the 90% percent is relative to the exit pupil's size.  90% percent of it to be exact.

Now in my mind this brings the question of how much real difference is there between those magnification ranges?  Like I've stated the 10X50 exit pupil has 30% more area/17% more diameter than the 12 X 50....  but what is the real difference in light transmission?  It can't be 30% or 17% or any figure close to that...

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/25/2016 at 16:35
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No because exit pupil does not increase transmission through the glass.  Transmission is the quality of the glass.  It lets through 90% regardless of how big it is.  Exit pupil is the size of the glass.  (size of the band of light)

You are only going to benefit from it in certain situations, as our eyes can only use so much are certain times of day. 

This is off the Zeiss site. 

Quote Imagine you're planning to build a house. To make sure the rooms are bright, the windows should be as large as possible - right? That brings us to the first factor, the so-called "exit pupil diameter". This is calculated by the formula "lens diameter divided by magnification" and basically specifies the diameter of the light beam exiting the eyepiece. By way of example, at 10 x 32 it's 3.2 mm, and at 8 x 56 it's 7.0 mm. You can compare this geometric value to the size of a window in a house.The window might be huge - but how clear and clean it is is described in binoculars by the transmission value, meaning the percentage of light that actually passes through it. Premium binoculars have values around 90%. The VICTORY HT binoculars (HT stands for High Transmission) set new standards with their new SCHOTT glass, T* coating and the bright Abbe-König prism system. They let up to 95% of the light pass, corresponding to clear, clean windows. 
How do these factors interplay? A large exit pupil diameter only makes sense if the eye pupil is also wide open, so all the light can reach the retina. Which is mostly at twilight. In contrast, the advantage of high transmission is always plain to see. Of course the gain can be felt the most at twilight, when it's all about achieving maximum light efficiency. Yet also during daytime, when the pupils are only opened about 2 to 3 mm wide, there is more light available, ensuring that even in the shade all details can be seen clearly and in full brilliance.
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/25/2016 at 16:36
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Originally posted by WJC WJC wrote:

The figure you offered indicates a maximum difference of only .8mm. That’s pretty small, especially when used during the day. While some observers need to quantify EVERYTHING, there is really no need when working with real world optics, as so many of the differences people quibble about are well below their threshold of recognition (sensory threshold), anyway.



A .8 mm difference is significant when calculating a percentage of difference by area.

10 X 42 = 4.2 mm exit pupil is an area of 13.85 mm^2
10 X 50 = 5 mm exit pupil is an area of 19.63 mm^2

That's roughly 29.5% increase in size.

12 X 50 = 4.16 mm exit pupil with an area of 13.59 mm^2
8.5 X 42 = 4.94 mm exit pupil with an area of 19.17 mm^2

The SLC line is all rated at 91% transmission except for the 15X56 which is 93%
8 X 42 = 5.25 mm exit pupil with an area of 21.65 mm^2
10 X 42 = 4.2 mm exit pupil is an area of 13.85 mm^2
15 X 56 = 3.73 mm exit pupil with an area of 10.93 mm^2

So the percentage of light transmission is 90%, 91% or 93% (depending on the model) of all of the light traveling through that sized exit pupil.  Example, 90% of the light reaches your eye when looking through a 10X50 5 mm exit pupil and 90% of the light reaches your eye when looking through a 12X50's 4.16 mm exit pupil.

Once again, what is the real quantifiable difference?



Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/25/2016 at 16:40
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Originally posted by supertool73 supertool73 wrote:

No because exit pupil does not increase transmission through the glass.  Transmission is the quality of the glass.  It lets through 90% regardless of how big it is.  Exit pupil is the size of the glass.  (size of the band of light)

You are only going to benefit from it in certain situations, as our eyes can only use so much are certain times of day. 

 


Correct, light transmission is the same regardless of exit pupil.  However, the amount of light allowed to travel through the exit pupil changes with the size of the exit pupil.  For instance, all things being equal, window clarity, cleanliness, pupil dilated size, a bigger window allows more light into the house.  That same 90% represents a larger portion of light than the 90% of the smaller window.

Again, what is the quantifiable difference?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/25/2016 at 16:47
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Originally posted by Brocksw Brocksw wrote:

Originally posted by supertool73 supertool73 wrote:

No because exit pupil does not increase transmission through the glass.  Transmission is the quality of the glass.  It lets through 90% regardless of how big it is.  Exit pupil is the size of the glass.  (size of the band of light)

You are only going to benefit from it in certain situations, as our eyes can only use so much are certain times of day. 

 


Correct, light transmission is the same regardless of exit pupil.  However, the amount of light allowed to travel through the exit pupil changes with the size of the exit pupil.  For instance, all things being equal, window clarity, cleanliness, pupil dilated size, a bigger window allows more light into the house.  That same 90% represents a larger portion of light than the 90% of the smaller window.

Again, what is the quantifiable difference?


I bet that completely depends upon the persons eye who is doing the looking and the circumstances of the looking

In daylight its probably not even noticeable.  In low light to my eyes a 8x42 is noticeably brighter than a 10x42 all else being equal. My Ziess 10x45 is much brighter than my Meopta 10x42 or 12x50.  I can see deer several minutes before than with the Meoptas.  Quality. 

Ultimately like Bill said there likely is not enough difference that we can even see it in most cases.   
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Supertool you've educated me on my original post or at least helped me clarify things in my own head that 90% in the EL example is not the same for all models/Exit pupils.  90% is 90% but 90% of a different size pie...

Now I'm trying to find an answer to quantifiable differences between the pies.
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10-4.  I will shut up now and let those in the know talk.  Big Smile
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/25/2016 at 16:51
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Originally posted by supertool73 supertool73 wrote:

10-4.  I will shut up now and let those in the know talk.  Big Smile


Hopefully we haven't screwed this up so much that someone who actually knows gets turned off...
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My friend, I don't have a horse in this race. In addition, I have learned the hard way that it is really not a good idea to buck the popular wisdom. But, after 45 years of repairing military and civilian optical instruments—including more than 12,000 binoculars—and speaking with thousands of optical customers, I have also learned that there's a big difference between MATHEMATICAL optics and PHYSIOLOGICAL optics. One looks good on a whiteboard; the other in reality.

For example: Let's say your binocular has a 5mm exit pupil, but on a relatively bright day your pupil is constricted to 2.5mm. On that day, just what is that exit pupil buying you?

cheers
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Originally posted by WJC WJC wrote:

My friend, I don't have a horse in this race. In addition, I have learned the hard way that it is really not a good idea to buck the popular wisdom. But, after 45 years of repairing military and civilian optical instruments—including more than 12,000 binoculars—and speaking with thousands of optical customers, I have also learned that there's a big difference between MATHEMATICAL optics and PHYSIOLOGICAL optics. One looks good on a whiteboard; the other in reality.

For example: Let's say your binocular has a 5mm exit pupil, but on a relatively bright day your pupil is constricted to 2.5mm. On that day, just what is that exit pupil buying you?

cheers



Well light transmission usually isn't an issue on a bright day.   

I thought it would be fairly obvious by the detailed nature of the conversation that I'm really trying to discern the difference in light transmission in quanitifiable units or at least in concise terms. Light transmission is usually most talked about and most important in twilight hours when my pupils are going to be trying to gather all the light they can... This is obviously why I'd be curious as to how much you can squeeze out of binos by playing with exit pupil... How much difference does it make?
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I understand the answers you are looking for; optical research is a good field to grow in. All I have been saying is that, from my perspective (if I’m allowed one), it’s just peeing up a rope, because about 90% of conversations that make some people weak in the knees deal with things that are well below their sensory threshold, anyway ... they can’t really see it. ‘Talk about it a lot? Yes. Come up with dubious reasons for it? Yes. Actually see it? In most cases, no. I will stand by what I have said, already, and bow out.

On another thread, you asked about testing a bino, especially inside. I think vignette #18 (PDF attached) will illustrate what I have just said.

18 “IT’S ‘TACK SHARP’ FROM THE CENTER TO THE EDGE.”

More than one seasoned observer has praised his binocular for allowing him to see being “tack sharp” images all the way to the edge of the field. But even though the binocular may have that capacity, we humans don’t.

The observer may see a crystal clear image in the center of the field, then, on seeing an equally crisp image at the edge of that field, supposes all points in between must provide images of equal sharpness—all the time. From a mathematical standpoint, that may very well be so. But to the brain, it just isn’t. Sure, field curvature is under control; the binocular is working fine. But, what’s really going on?

A Reality Check

Concentrate on the tiny space between “y” and “s” in the word “crystal” on the first line of the paragraph above. If you’re unwavering in your concentration, you’ll notice the most you can make out is that one word. A few people can’t even do that. Now, with your eyes frozen on that tiny space, try to see the “T” in “The” at the beginning of the sentence or the “r” in “center.” Although the separation in this example is certainly less than one would find in a binoculars field of view, it’s plain to see our sharply focused field is very, very restricted—not by the physical optics of the binocular … but by physiological optics controlled by the brain. Observers with a quality instrument can easily come away with the wrong conclusion because they aren’t paying attention to the millisecond eye movements that place the edge of the binocular’s field of view in the center of their own.

A Talk with an Optometrist

Wanting to be certain I’m not sharing more than I know about this subject, I called on optometrist, Dr. Edward R. Ford, of Ford Family Eye Care in Twin Falls, Idaho who offered the following:

“The corneal thickness centrally is thinner than it is peripherally, thus causing a change in refractive error from the eye’s central line of sight to its peripheral line of sight.  Now, aside from the optics of the cornea, aqueous, pupil, lens and vitreous not being perfect, perhaps the largest issue with the eye’s peripheral vision lies at the level of the retina.  As you know, the retina consists of photoreceptors called rods and cones. The rods provide light sensitivity and motion detection, while the cones provide the detail and color vision. The center of the retina, known as the macula, consists of the highest concentration of cones while the peripheral retina has the higher concentration of rods. With that in mind, it makes sense that the central retina or macula gives us the sharpest acuity, while the peripheral vision does not.”

This, of course, explains the value of that millisecond eye movement that most observers never notice. 

A Test for Edge Resolution

Because edge sharpness is important to some observers—who speculate a great deal about just where an off-axis image starts getting soft—I hope to offer a quasi-scientific test to add a little firm data to the speculations.

I once believed the Nikon Prostar 7x50 binocular provided a slightly crisper off-axis image than the Fujinon FMT-SX of the same magnification and aperture. Discussing this with a friend, he wondered if I had a way to really know for certain; he, too, had an interest in the outcome. Thus I came up with the following test.

The Needed Particulars:

1. Some sort of rotary table graduated in degrees and fractions that is either heavy enough to be stable lying on a flat surface or that can be affixed to a rigid table top, and that can be precisely adjusted with a micrometer head or a smooth moving lead screw. I used a machinist’s 8-inch rotary table. It was heavy enough to be rigid just sitting on a table and had a micrometer adjustment.

2. A homemade “L” bracket or binocular tripod mount that uses a short ¼”-20 bolt to fasten to the binocular’s axle.

3. A round piece of metal turned to fit the hole in the middle of the rotary table and drilled to accommodate a short ¼”-20 bolt to fasten the “L” bracket or tripod mount to it.

4. A black and white resolution chart gauged at one line per millimeter placed on a well-lighted wall 30 feet from the rotary table.

********************

Photos                                       Rotary table, tripod bracket, and resolution chart

********************

The procedure:

1. Note: Unless the binoculars to be compared—should a comparison be the goal—are of the same aperture and magnification, the test will be invalid.

2. Secure the binocular on the “L” bracket or tripod mount to the center of the rotary table (or similar fixture).

3. Turn the rotary table to place the resolution chart directly in the center of the field of the telescope you will be using for the test and set the angle at “zero.”

Note: To get the most from this test you should:

—Use the same telescope for all measurements.

—Use the same eye for all measurement.

—Always turn the micrometer or lead screw in such a way as to move the binocular in the same direction.

—Perform all the tests or comparisons within a reasonably short timeframe as fatigue, headaches, caffeine, alcohol, medications, or even too much, or too little, water in your system can affect visual acuity.

4. Start slowly turning the micrometer or lead screw to move the image of the resolution chart toward the edge of the field.

5. The instant at which the lined resolution chart turns to a solid gray box, stop the test and write down the results—the angle off-axis at which the resolution lines turned gray.

6. “Zero” the set-up and start the second iteration.

7. Perform the test 5 times in all, being fastidious about stopping each iteration as soon as the resolution lines turn to a gray square.

8. Throw out your lowest and highest readings and take the average of the 3 remaining iterations. This will give you a good idea about how far off-axis (or how close to the edge of the field) the binocular will resolve that particular resolution chart.

By the way, although I was sure the Nikon provided a slightly crisper image, the test didn’t bear it out. Both binoculars resolved all the way to the edge. Even when half the chart was out of the field for both binoculars, the remaining half continued to show individual resolution lines. A more aggressive and conclusive test might have been to move the resolution chart 10 feet farther away and perform the same test again.

PS Could someone please tell me how to post a PDF, like possible on so many other forums?

 




Edited by WJC - October/25/2016 at 22:14
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2016 at 06:19
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A 42 mm objective allows a certain amount of light to "enter"... 90% of that, according to Swarovski, passes through.  A 50mm objective allows approximately (under ideal conditions) 16% more light to "enter"...

Therefore, the answer is obviously "NO", the same amount of light is not available with a 42mm objective as with a 50mm objective, but 90%, according to Swarovski, of the available light gets through...


To get a subjective "feel' for this, take the total light passed through (90%) and multiply by relative brightness (exit pupil squared)... to make it easy, take a 10x scope with a 42mm objective...  exit pupil squared (relative brightness) is 17.64.  Multiply relative brightness by total pass through... 0.9x17.64 = 15.876...you get a number that is perhaps meaningful in comparison of several riflescopes (or binoculars) if you believe the manufacturer's transmission numbers.  With a 50mm objective, 10x scope... 5 squared is 25, 25x0.9=22.5... Perhaps an indicator of "actual relative brightness" at the ocular at a certain power utilizing manufacturer's transmission numbers.  If I played with it a bit it might provide a data point useful in optic selection. 

Interesting exercise on the spur of a moment...



Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2016 at 09:56
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I don't know about you guys, but I never pay attention to any manufacturer's light transmission numbers. There is really no standardized way of measuring, so each manufacturer can come up with whatever LT# they want depending on the way they test.  

I can tell the OP that, having owned both the 10x42SV and 10x50SV at the same time, comparing them on tripod mounts, that the 10x50 is noticeably brighter in suspect light than the 42mm version.   The 42mm SV is still very much a standout though, and almost as good as it gets IMO (I reserve the "as good as it gets" for the 10x50SV, which is absolutely amazing).  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2016 at 10:28
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Originally posted by Kickboxer Kickboxer wrote:

A 42 mm objective allows a certain amount of light to "enter"... 90% of that, according to Swarovski, passes through.  A 50mm objective allows approximately (under ideal conditions) 16% more light to "enter"...

Therefore, the answer is obviously "NO", the same amount of light is not available with a 42mm objective as with a 50mm objective, but 90%, according to Swarovski, of the available light gets through...


To get a subjective "feel' for this, take the total light passed through (90%) and multiply by relative brightness (exit pupil squared)... to make it easy, take a 10x scope with a 42mm objective...  exit pupil squared (relative brightness) is 17.64.  Multiply relative brightness by total pass through... 0.9x17.64 = 15.876...you get a number that is perhaps meaningful in comparison of several riflescopes (or binoculars) if you believe the manufacturer's transmission numbers.  With a 50mm objective, 10x scope... 5 squared is 25, 25x0.9=22.5... Perhaps an indicator of "actual relative brightness" at the ocular at a certain power utilizing manufacturer's transmission numbers.  If I played with it a bit it might provide a data point useful in optic selection. 

Interesting exercise on the spur of a moment...






So where do you come up with 16%? 

Relative brightness between the 2 equations you show is more like a 30 percent difference (simply taking 15.876/22.5).  Does relative brightness have any other correlation to objective lens diameter or area aside from the exit pupil itself?  For some reason I have the idea that the area of the objective lens or exit pupil is not being taken into account enough... for instance the area of the exit pupil in the 42 mm optic you reference is equal to 13.85 mm^2.  There has to be some correlation to relative brightness using that figure instead of or in addition to the exit pupil squared (17.64)?  Or is the area of the exit pupil completely irrelevant?

Interesting stuff indeed...
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"I don't know about you guys, but I never pay attention to any manufacturer's light transmission numbers."

Everybody put your hands on the monitor and say ... Amen.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2016 at 12:39
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Originally posted by Brocksw Brocksw wrote:

Originally posted by Kickboxer Kickboxer wrote:

A 42 mm objective allows a certain amount of light to "enter"... 90% of that, according to Swarovski, passes through.  A 50mm objective allows approximately (under ideal conditions) 16% more light to "enter"...

Therefore, the answer is obviously "NO", the same amount of light is not available with a 42mm objective as with a 50mm objective, but 90%, according to Swarovski, of the available light gets through...


To get a subjective "feel' for this, take the total light passed through (90%) and multiply by relative brightness (exit pupil squared)... to make it easy, take a 10x scope with a 42mm objective...  exit pupil squared (relative brightness) is 17.64.  Multiply relative brightness by total pass through... 0.9x17.64 = 15.876...you get a number that is perhaps meaningful in comparison of several riflescopes (or binoculars) if you believe the manufacturer's transmission numbers.  With a 50mm objective, 10x scope... 5 squared is 25, 25x0.9=22.5... Perhaps an indicator of "actual relative brightness" at the ocular at a certain power utilizing manufacturer's transmission numbers.  If I played with it a bit it might provide a data point useful in optic selection. 

Interesting exercise on the spur of a moment...






So where do you come up with 16%? 

Relative brightness between the 2 equations you show is more like a 30 percent difference (simply taking 15.876/22.5).  Does relative brightness have any other correlation to objective lens diameter or area aside from the exit pupil itself?  For some reason I have the idea that the area of the objective lens or exit pupil is not being taken into account enough... for instance the area of the exit pupil in the 42 mm optic you reference is equal to 13.85 mm^2.  There has to be some correlation to relative brightness using that figure instead of or in addition to the exit pupil squared (17.64)?  Or is the area of the exit pupil completely irrelevant?

Interesting stuff indeed...

42mm is 84% of 50mm... 16% differential for amount of light that can possibly enter the objective.   The numbers for "exit pupil" and "relative brightness" are just calculated figures of merit... they have little meaning, other than being interesting (for some of us), for anything related to what the human eye actually experiences/sees.  They tell you that given all the proper conditions, there should be a visual improvement in brightness with 50mm vs 42mm given same magnification.  We already know that there is more light available from the entrance... if there are no significant restrictions due to design or glass/coating quality, the end result should be obvious. 

I DO, mostly, believe some manufacturers transmission numbers... Swarovski, Zeiss, S&B, Meopta, Nikon, etc... have a reputation to uphold and would get a lot of bad press for misreporting.  Now, there are things that can make the numbers slightly better, or worse, (depends on whether using best case or worst case calculations) but generally, they try to be accurate.  When someone advertises 99.6 or 100 percent light transmission, I tend to question their veracity. 


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2016 at 13:13
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A great topic and conversation.

If I'm way off base just say so.  In a very simplistic way, isn't it similar to lumens vs. Lux with flashlights.

One is total amount of light and one is intensity.

So you have 90% light transmission through the glass.  With a certain exit pupil size you could calculate the total amount of light being transmitted through the objective.

Increase that exit pupil size with the same transmission efficiency and the total amount of light passing through to the objective is greater.

Now, if your eye's pupil is only dilated to 3mm and your binocular has a 5mm exit pupil, you most likely won't see much difference compared to a binocular with the same 90% light transmission but only has a 3mm exit pupil.

BUT, your eyebox could be more forgiving since you have some margin of error for eye placement.

Here is an example I've personally experienced.

I have Nikon Monarch ATB 10x32's and a buddy has Leica 10x50 Ultravids.  In bright daylight the images are fairly comparable between the two.  The image is nicer through the Leicas but both are bright and clear and it's easy to view wildlife through either.

Now let's move to dusk.  The Leica's keep looking great while the Nikon get's dimmer and dimmer much faster.  It was truly night/day difference at sunset looking through both.

In that case I suspect both light transmission AND exit pupil both played roles in showing the drastic difference in quality between the two binoculars.  

Sound reasonable?
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