Objective size and Mirage reduction
- Thread starter Fred Bohl
- Start date
, and are using the technology that Canon has used for decadesTurbulent Turtle
F-TR competitor
Oh Lord, here we go again. The eternal Nikon-Canon debate. This is even worse than the S&B-NF conundrum.
Fluorite lenses are not new, they have been around for a while, for Canon and Nikon and others. The use of fluorite glass in the lens to which I linked is not surprising. As you can see, the body is magnesium and even with that it weighs 10 pounds. The two front elements, which are the biggest and heaviest glass components are fluorite glass and that alone probably saves 2 pounds on the weight. These lenses probably cost $3000 apiece. The Nikon serial number tracking site, shows about 1600 of those in existence.
The big issue with fluorite glass, beyond the cost, is that it is fragile and subject to temperature shifts. I would be terrified to even look at the lens on this puppy. You have to nurse it and be aware of temperature changes. I would have to take it outside at 0 degrees after it's been warm and toasty in the house. And then take it back inside after a 2 hour frigid photo session.
Canon has a similar lens with the same specs, but since it only costs $13,000 it must not be as good as the Nikkor lens.
Overnight, I thought some more about the question of the benefits of the eyepiece magnification and I remembered the Unertl riflescope as an example of one in which all the magnification is done by the body of the riflescope with little coming from the eyepiece. Those very long-bodied riflescopes had very moderate magnifications compared to today's riflescopes and yet as I said, they were very long and slender. They also did not have an inner tube, the adjustments were all done via the rear mount's vernier knobs. The reticle was right in front of the eyepiece. There was no zoom and the front sight even had a spring to absorb the recoil.
We have come a long way.
Now onto digital riflescopes.
Fluorite lenses are not new, they have been around for a while, for Canon and Nikon and others. The use of fluorite glass in the lens to which I linked is not surprising. As you can see, the body is magnesium and even with that it weighs 10 pounds. The two front elements, which are the biggest and heaviest glass components are fluorite glass and that alone probably saves 2 pounds on the weight. These lenses probably cost $3000 apiece. The Nikon serial number tracking site, shows about 1600 of those in existence.
The big issue with fluorite glass, beyond the cost, is that it is fragile and subject to temperature shifts. I would be terrified to even look at the lens on this puppy. You have to nurse it and be aware of temperature changes. I would have to take it outside at 0 degrees after it's been warm and toasty in the house. And then take it back inside after a 2 hour frigid photo session.
Canon has a similar lens with the same specs, but since it only costs $13,000 it must not be as good as the Nikkor lens.
Overnight, I thought some more about the question of the benefits of the eyepiece magnification and I remembered the Unertl riflescope as an example of one in which all the magnification is done by the body of the riflescope with little coming from the eyepiece. Those very long-bodied riflescopes had very moderate magnifications compared to today's riflescopes and yet as I said, they were very long and slender. They also did not have an inner tube, the adjustments were all done via the rear mount's vernier knobs. The reticle was right in front of the eyepiece. There was no zoom and the front sight even had a spring to absorb the recoil.
We have come a long way.
Now onto digital riflescopes.
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The higher the quality of glass, the higher the price. Bigger elements cost more money. Add to that the number of elements in the scope, (more elements equals more money), along with the coating of the lenses. Lenses coated on both sides are more expensive than those that are coated on one side only. Then add the cost for experienced personnel to meticulously hand assemble the higher end scopes.
Turbulent Turtle
F-TR competitor
I believe the highest magnification riflescope right now is the March-X 8-80X56. I have the March-X 5-50X56. Since the two models share the same tube, objective lens, zoom range, and so on, I think the difference might just be in the eyepiece itself. However that said, I run my March-X at between 40X and 50X during a match. I can see the difference in brightness going from 40X to 50X; to my eye it looks like about a half-stop (which is probably wrong). At 50X, the exit pupil is 1.12mm compared to 1.4mm at 40X. If you think of the 80X capability of the 8-80X56, that exit pupil size will be 0.7mm and you have better be positioned just right to be able to see. That picture will not be very bright and it's probably approaching the limits of the glass resolution. But maybe not.
The issue remains incoming light, which is dictated by the size of the objective. Also, if we are approaching the resolution limits of the glass, then we will need more of it and that will require a bigger objective lens. If we are into the resolution limits, we do what they do with camera lenses and grow the front of the lens longer. If refraction lenses are too long, we can use catadioptric lenses, (folding the light path with mirror), but that presents new problems and you will really have a Hubble-type riflescope on top of your rifle.
I think the way forward is with digital scopes, using a great camera-type lens in front and getting the image on a good sensor with a high pixel count. You can then expand that picture digitally and let software do its thing. (Imagine a 40MP 4/3 sensor.) Of course, it will require a battery to operate.
ETA: The lenses for a 4/3 sensor are nowhere as big and bulky as the corresponding lenses for a 35mm-size sensor. Your 200mm lens for the 35mm camera would be like a 400mm lens to the 4/3 sensor (8x instead of 4x).
The issue remains incoming light, which is dictated by the size of the objective. Also, if we are approaching the resolution limits of the glass, then we will need more of it and that will require a bigger objective lens. If we are into the resolution limits, we do what they do with camera lenses and grow the front of the lens longer. If refraction lenses are too long, we can use catadioptric lenses, (folding the light path with mirror), but that presents new problems and you will really have a Hubble-type riflescope on top of your rifle.
I think the way forward is with digital scopes, using a great camera-type lens in front and getting the image on a good sensor with a high pixel count. You can then expand that picture digitally and let software do its thing. (Imagine a 40MP 4/3 sensor.) Of course, it will require a battery to operate.
ETA: The lenses for a 4/3 sensor are nowhere as big and bulky as the corresponding lenses for a 35mm-size sensor. Your 200mm lens for the 35mm camera would be like a 400mm lens to the 4/3 sensor (8x instead of 4x).
Most of this comes down to the quality of the lenses. A poor 56mm objective lens will not give the detail, brightness and color that a high quality 45mm objective lens will. Magnification does affect image brightness. As we zoom in on an image (increase magnification), brightness drops. Try it with a zoom lens on a scope. It determines how well you can distinguish detail and color.
Turbulent Turtle
F-TR competitor
Thank you for those words of wisdom, Captain Obvious.
Actually, the neat thing about a digital scope with say a 4/3-size sensor is that for the primary image capture you do not need a humongous lens. Beyond that, while the ISO range of the 4/3 sensor is nowhere near the APS-C or 35mm sensors, it's still quite usable and provided you keep up the HDR, you could boost it to 3200 or 6400 and let the software clean it up for you. I can see where the D-Riflescope would have the standard 4/3 lens mount and you can just select the lens you put on there and tell the software what you just put on. By removing all but the objective lens group to focus the image on the 4/3 sensor is the first focal plane, you remove a lot of the cost of the optical lenses. You could even have the D-Riflescope autofocus the lens. Opens up a lot of possibilities.
Actually, the neat thing about a digital scope with say a 4/3-size sensor is that for the primary image capture you do not need a humongous lens. Beyond that, while the ISO range of the 4/3 sensor is nowhere near the APS-C or 35mm sensors, it's still quite usable and provided you keep up the HDR, you could boost it to 3200 or 6400 and let the software clean it up for you. I can see where the D-Riflescope would have the standard 4/3 lens mount and you can just select the lens you put on there and tell the software what you just put on. By removing all but the objective lens group to focus the image on the 4/3 sensor is the first focal plane, you remove a lot of the cost of the optical lenses. You could even have the D-Riflescope autofocus the lens. Opens up a lot of possibilities.
Turbulent Turtle
F-TR competitor
Some already exist:
https://www.atncorp.com/smart-hd-weapon-sight
I'm looking for something with much more magnification.
https://www.atncorp.com/smart-hd-weapon-sight
I'm looking for something with much more magnification.
Fred Bohl
Gold $$ Contributor
For those of you that mention resolution testing - from an old post see the attached.
Also while digging thru some old test data, I found some light transmission test results for those same scopes. We did not publish the results but in summary, the light transmission ES at the exit pupil was 90 to 94% of that at the objective of the tested scopes.
Also while digging thru some old test data, I found some light transmission test results for those same scopes. We did not publish the results but in summary, the light transmission ES at the exit pupil was 90 to 94% of that at the objective of the tested scopes.
Attachments
Turbulent Turtle
F-TR competitor
Yep, the bigger the objective the better the resolution. In optics, bigger is better. Where have I heard that before?
Fred Bohl
Gold $$ Contributor
I want to revisit the issue of high magnification effect on perceived image "clarity".
Assuming you have 20/20 or corrected to 20/20 vision (1MOA resolution) and are considering modern very good or better scopes, the resolution of the scope is diffraction limited by the clear diameter of the objective lens. A key issue occurs when the diffraction limited resolution times the magnification equals the users visual resolution (1MOA for 20/20 vision). Let us call that value the "Match Magnification".
At less than match magnification the effective scope resolution is limited by the user's visual acuity. Above match magnification the effective scope resolution is diffraction limited by the objective diameter. Also, at even higher magnification, the diffraction interference effects become more noticeable and are often misinterpreted as "fuzzy" or "blurry" edges of fine details.
The match magnification values for some popular scopes are: Weaver T-36x-40mm = 20.7x; Leupold 40x-45mm & 45x-45mm Competition = 23.3x; March 40x-52mm, 50x-52mm & 60x-52mm = 26.9x; and Nightforce 12-42x-56mm = 29x. Note that with a variable such as the Nightforce, your perception of the correctly adjusted view would be limited by your visual acuity up to 29x but over that it would be diffraction limited and as the magnification was increased above 29x you would perceive more diffraction effects and if not accustom to these effects you might interpret the view as becoming more "blurry" with increasing magnification.
Your perception of what you are seeing is always a product of a very marvelous visual system. While your eyes are the very good basic input devices, your brain's image processor is doing the heavy lifting. It is most impressive in its ability to adapt (learn) with experience to better process the images from you eyes. The adaptation of most interest to our discussion is how the brain's image processor takes the blurry image from our diffraction limited eye lenses and gives us a perceived clear image. The brain has learned what has or is expected to have sharp edges and adapts to remove (filter) edge blur in perceived version.
When we first look thru a telescope that is by definition diffraction limited and has a magnification above the Match Magnification (say 36x) we will initially perceive the burry edges until our brain accumulates enough experience to adjust the edge filter. If we then move to an even higher magnification (say 50x), we have to again accumulate enough experience for our brain to again adjust it's edge filter to provide a blur free perceived image.
Another adaptation our brains have to adjust to with experience (practice) is that above the Match Magnification we are in what astronomers call "empty magnification" territory. Empty magnification means that there is no more detectable information in the image as magnification increases.
The benefit of increasing magnification over the Match Magnification is to make a particular area of an image a larger portion of the image area while removing irrelevant information. Then the brain's image processor can concentrate on providing us with the most useful perceived image information.
Assuming you have 20/20 or corrected to 20/20 vision (1MOA resolution) and are considering modern very good or better scopes, the resolution of the scope is diffraction limited by the clear diameter of the objective lens. A key issue occurs when the diffraction limited resolution times the magnification equals the users visual resolution (1MOA for 20/20 vision). Let us call that value the "Match Magnification".
At less than match magnification the effective scope resolution is limited by the user's visual acuity. Above match magnification the effective scope resolution is diffraction limited by the objective diameter. Also, at even higher magnification, the diffraction interference effects become more noticeable and are often misinterpreted as "fuzzy" or "blurry" edges of fine details.
The match magnification values for some popular scopes are: Weaver T-36x-40mm = 20.7x; Leupold 40x-45mm & 45x-45mm Competition = 23.3x; March 40x-52mm, 50x-52mm & 60x-52mm = 26.9x; and Nightforce 12-42x-56mm = 29x. Note that with a variable such as the Nightforce, your perception of the correctly adjusted view would be limited by your visual acuity up to 29x but over that it would be diffraction limited and as the magnification was increased above 29x you would perceive more diffraction effects and if not accustom to these effects you might interpret the view as becoming more "blurry" with increasing magnification.
Your perception of what you are seeing is always a product of a very marvelous visual system. While your eyes are the very good basic input devices, your brain's image processor is doing the heavy lifting. It is most impressive in its ability to adapt (learn) with experience to better process the images from you eyes. The adaptation of most interest to our discussion is how the brain's image processor takes the blurry image from our diffraction limited eye lenses and gives us a perceived clear image. The brain has learned what has or is expected to have sharp edges and adapts to remove (filter) edge blur in perceived version.
When we first look thru a telescope that is by definition diffraction limited and has a magnification above the Match Magnification (say 36x) we will initially perceive the burry edges until our brain accumulates enough experience to adjust the edge filter. If we then move to an even higher magnification (say 50x), we have to again accumulate enough experience for our brain to again adjust it's edge filter to provide a blur free perceived image.
Another adaptation our brains have to adjust to with experience (practice) is that above the Match Magnification we are in what astronomers call "empty magnification" territory. Empty magnification means that there is no more detectable information in the image as magnification increases.
The benefit of increasing magnification over the Match Magnification is to make a particular area of an image a larger portion of the image area while removing irrelevant information. Then the brain's image processor can concentrate on providing us with the most useful perceived image information.
Turbulent Turtle
F-TR competitor
I was under the probably-mistaken impression that 20/20 vision was more like 2 MOA, hence the size of the Highpower targets. However, irrespective of that, your wonderful treatise is the best piece I have read explaining why you cannot trust anyone's impression, or even worse, comparison of riflescopes. And for that, I applaud you.
Fred Bohl
Gold $$ Contributor
Normal vision is defined as 20/20 (1 MOA acuity) your 20/15 (0.8 MOA) is better than normal so you need less magnification to resolve the same detail. For your 56mm objective diameter the Dawes resolution limit is 0.035 MOA and the Match Magnification is 0.8/0.035 = 22.86
Tim Singleton
Gold $$ Contributor
Help me to understand something
In other threads it's said that a modifier disc is a bad thing they just fool you the mirage is still there and the target isn't where you think it is
If the modifier decreases incoming light does it not reduce the amount of mirage effect?
In other threads it's said that a modifier disc is a bad thing they just fool you the mirage is still there and the target isn't where you think it is
If the modifier decreases incoming light does it not reduce the amount of mirage effect?
Fred Bohl
Gold $$ Contributor
Tim,
Mirage effects such as apparent target displacement from actual and distortion of the target image occur due to air turbulence between the scope objective and the target. Nothing repeat nothing including power reduction in variables or using a Modifier Disk changes the actual effects they only reduce your ability to see those affects.
Having said the above, I will admit that there are conditions in which the mirage effects are so bad that the only way to shoot is to reduce the information overload. I use fixed power scopes and when necessary, a Modifier Disk. That way I retain the magnification (aim small miss small) and reduce the brain overload caused by bad mirage. The negative of this technique is the higher probability of not detecting the true target position and therefore getting some embarrassing large "fliers" on the target.
Update 11/24 - found some old data on a test of mirage effects I did locally. Over a 600 yard distance and with moderate mirage and 12 mph wind, the maximum target displacement of apparent location to actual location was 6 inches. Even at 600 yards a 6 inch miss is quite a "flier" for anyone.
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Fred Bohl
Gold $$ Contributor
Denys,
At the time of your post, I was a little embarrassed about replying to your complement. Given the opportunity afforded by Tim's post to review the thread I've reconsidered. Over the years I've been posting on this forum I have had few if any such complements. So thank you very much and I'm sorry that my thank you was so long in coming.
ohiodan
Gold $$ Contributor
Hard to believe this thread got started by a few comments on a March aperture reducer.... From a shooter's point of view, the aperture reducer is good thing because it increases the depth of field. That allows a shooter to see mirage over hundreds of yards instead of only a few yards, see pickups/let offs and velocity changes quicker and more accurately. Most shooters spend zero time worrying about a darker image or any of the rest, it's all about seeing what's going on so we can make better decisions. When mirage is thick and you're using an aperture reducer, the image in your scope is much closer to the targets actual position! We've all seen the black center of a target look like a bouncing ball during thick mirage. An aperture reducer will minimize the amount of movement, also make it easier to see the lines on the scoring rings.
Dan P.
Dan P.
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