4G+ Left Tube - 4G+ High Gain Right Tube
Image intensifier gain can be translated as tube brightness compared to light input, or how good a tube is at amplifying an image. This is critical in resolving objects and identifying targets in low light situations. This is why many NATO militaries around the world put in the request for higher gain systems, which resulted in the 4G+ High Gain tubes.
Image Intensifier | 4G+ | 4G+ High Gain |
Min Gain at 20 μlx | 8000 cd/m2/lx | 24000 cd/m2/lx |
Max Gain at 20 μlx | 14000 cd/m2/lx | 28000 cd/m2/lx |
Min Gain at 2x10^(-6) fc | 25120 fL/fc | 75400 fL/fc |
Max Gain at 2x10^(-6) fc | 43960 fL/fc | 87950 fL/fc |
Signal To Noise Ratio | 30 | 30 |
Center Resolution | 70 | 70 |
Figure of Merit (FoM) | 2200 | 2200 |
The 4G+ High Gain systems have double the gain output over traditional 4G+ systems. The maximum tube brightness is the same, meaning that in high light situations the brightness will not change to cause excessive eye strain, and the doubled light output comes into effect once ambient light levels decrease.
We are proud to be offering these in our lineup immediately. Stay tuned as we look to put these through their paces and write a more detailed comparison in the future.
]]>
RPO or Rochester Precision Optics is an American optical lens manufacturer that is known in the nightvision sphere for producing the high end lenses for the PVS-31A, GPNVG-18, and the next generation BNVD-Fused system for the US military. They are a well known and well established company.
The RPO 3.0 lens system was released roughly one year ago in 2022 and was met with lukewarm reception. This was not completely undeserved as it was not a clear upgrade to their 2.0 system. The previous RPO 2.0 system was known to offer higher light transmission along with lighter weight over standard milspec lenses such as Carson but the tradeoff was a higher degree of lens flare.
We understand that people are still having a hard time deciding which lenses to purchase and we receive regular inquiries regarding whether RPO 3.0 is a good choice over Carson.
Our intention with this post is to share pros and cons we have found using the best testing equipment and practices we have available to us, as well as documenting those findings to the best of our ability. Hopefully as you gather information in regards to what lens best suits your needs, this article stands as a valuable resource to allow you to make an informed decision.
The US military specification for a PVS-14 eyepiece is that it must have an eye relief no shorter than 25mm when tested with an aperture of 6mm, same as the sought after PVS-31 system used by USSOCOM which is also produced by RPO. 25mm is long enough for use with most eye protection, 6mm is the size of the average human pupil. At night a human pupil can go up to 8mm in darkness, however when viewing an image as bright as the image from a nightvision device it will typically not exceed 6mm.
To make this test as relevant as possible, our goal should be to place the aperture of the camera lens no more than 25mm from the lens of the night vision device, to mimic the same distance your eye is likely to be when operating your night vision.
Test scenarios that deviate beyond the intended design parameters will not perform as intended and will compromise test results. While it is true that the RPO 3.0 eye box is slightly smaller than a standard Carson eyepiece, testing outside of milspec parameters will skew results.
Many higher end camera lens designs force the aperture blades much deeper into the lens assembly than we would like for proper testing as this would simulate having your eye further back from the device than you normally would. What is necessary for our application is a lens with a design such that the objective lens element is compact with the aperture blades placed close behind the glass of the lens element.
An example of a lens that mimics the relationship of the human eye to the night vision device, in this case a Sony/Zeiss Sonnar 35mm. Note the small objective lens design with aperture blades right up against the objective element. This setup was given approval by a RPO representative.
An example of a lens that is less effective at mimicking the relationship of the human eye to the night vision device, in this case our Sony G-Master II 24-70. Note the distance from the front of the lens to the apertures blades. This distance is further than your eye would be from your night vision device.
Taking photos through night vision using a full frame camera is tricky to do correctly because there are many factors that lead to errors when proper consideration is not taken. Many high end camera lenses have a very large objective lens element in order to collect more light and give more depth of field. Unfortunately using lenses like this for testing will capture distorted data such as off axis distortion, significantly exaggerated vignetting, and extreme edge distortion.
For our testing we use a Sony A7R5 as it captures 8k resolution still photos. We will be using cropped sections to highlight points in this article, however we will provide a Google Drive link with all original 8k resolution photos available. For side by side comparison, we use two BCO LPMR 4Ks.
Our test devices are two Carson Industries PVS-14 monocular bodies with two matched Photonis 4G+ tubes. One set uses standard Carson lenses (Fujinon Objective with Qioptiq Eyepiece) while the other uses RPO 3.0. It is impossible to get tubes with identical specs, so it is important to note that we decided to use the slightly higher spec tube with the Carson lenses. We recognise that each tube will have slightly different brightness and tint characteristics which may affect perception of some results, however will not affect resolution. For the brightness test only one tube was used.
Tube Specs
PVS-14 | Carson | RPO 3.0 |
Tube | Photonis 4G+ | Photonis 4G+ |
SNR | 34.75 | 34.15 |
Resolution | 70 lp/mm | 70 lp/mm |
Gain | 11772 | 11869 |
EBI | 0.14 | 0.15 |
Each photograph was taken on the same camera in a controlled setting. Light input is controlled by our Hoffman Engineering ANV-126A Nightvision Test Set inside our dark adapted clean room. Each PVS-14 was manually focused and verified by eye as well as the Hoffman Engineering HVS-126 Digital Test set to ensure proper focus. The camera was manually focused to the PVS-14 each time. Resolution tests were attempted multiple times each to ensure consistent results, only the best results for each system were used in order to avoid sampling bias.
For a quick gain comparison, we used an autogated NNVT tube at around 1600 FoM. Specific specs don't matter as it was the same tube, the only part changed was the objective lens using the same tube and eyepiece. Only the objective lens was tested here as only input affects tube noise, clarity, etc.
Gain was measured at 0.100 mfL (milli foot Lamberts) using a Hoffman Engineering ANV-126A's Gain Probe. Only the objective lens was changed between tests, and was manually focused prior to each test as focus affects accuracy of the gain reading. As gain constantly fluctuates slightly due to randomization of scintillation, 5 consecutive readings were taken to find an average.
Objective Lens | Carson (Fujinon) | RPO 3.0 |
Reading 1 | 3383 | 3514 |
Reading 2 | 3380 | 3510 |
Reading 3 | 3384 | 3509 |
Reading 4 | 3380 | 3508 |
Reading 5 | 3376 | 3514 |
Average Gain | 3380.6 | 3511 |
What this means is that at this light level (default gain test level on a Hoffman ANV-126A) the image from a RPO 3.0 objective lens is 3.9% brighter than the image from a Carson lens. This is due to the improved light transmission RPO lenses offer due to their advanced aspherical element designs that reduce the number of elements inside the lens assembly.
The RPO 3.0 system, being more comparable to Carson, has improved lens flare over 2.0. The cost is reduced light transmission, so while RPO 2.0 offered 9% improved light transmission over Carson on the objective lens alone, 3.0 is reduced to around a 4% improvement over Carson.
During our testing we found that there are instances where RPO 3.0 displayed more dramatic flaring than the Carson, and there were instances where Carson displayed more dramatic flaring than RPO 3.0. Lens flares occur when light is scattered by a lens system. In an effort to ensure both the Carson and RPO 3.0 setups experienced the same lighting conditions a pair of BCO LPMR 4K recorders on PVS-14s on a MOD Armory Bridge were used. This way a side by side real time comparison the difference between Carson and RPO 3.0 can be seen in real time.
It is easy to observe in the screen grabs below, there are moments where Carson sometimes had the advantage, and there were also moments where RPO 3.0 had the advantage.
The reality is they both have similar degrees of lens flare but have specific characteristics in specific situations at specific angles. If there has to be a winner, I would say Carson has slightly better lens flare characteristics overall.
This part is quite simple
Carson | RPO | Weight Reduction | |
Objective and Eyepiece (O-Rings, no Diopter) | 96 g | 60 g | 36 g |
Objective and Eyepiece (O-Rings, with Diopter) | 116 g | 68 g | 48 g |
What this means is that in a monocular setup weight is reduced by 36 grams just by using RPO lenses. A further reduction of 48 grams can be had by also using our 3D Optimized Lightweight Diopter. On a binocular setup 72 grams can be saved on the lenses alone, and a total of 96 grams using diopters on a binocular setup. This is significant, as on a binocular setup you are reducing system weight by 15-20% depending on the setup. For example a BNVD-1431 Mk.II using NNVT tubes is reduced down to 482 grams.
RPO lenses are also significantly more compact than Carson. Left is a RPO PVS-14, right is a Carson PVS-14. Same tubes, both focused to infinity with diopters set to 0 using a Hoffman Engineering Diopter Scope.
Distortion is a normal occurence in any lens design. All have it to some degree, we just get used to it. RPO has slightly more zone 3 distortion than Carson. Here are comparison images taken with a Sony A7R5, Sony/Zeiss 35mm showing distortion using the distortion reticle in our Hoffman Engineering ANV-126A.
Carson:
RPO:
Vignetting is also a normal characteristic of all lenses, some more than others. Note that the vignetting effect on Carson is more gradual than RPO. Carson darkens out more in zones 2 and 3, whereas RPO maintains even brightness for most of zones 1 and 2 and then falls off in the outer half of zone 3. For this reason, RPO vignetting is more apparent at first glance due to the fall off at zone 3, despite having less vignetting in zones 1 and 2.
Carson Zone Reticle:
RPO Zone Reticle:
Carson Blank Background:
RPO Blank Background:
Note that both tubes exhibit uneven screen brightnesses with irregularly shaped brighter regions in the center. This will in some cases cause some comparisons to appear that Carson is brighter or RPO is brighter depending on the region that is cropped, however overall RPO maintains a slightly brighter image. Do note that brightness is not being measured here as different tubes will have slightly different tints that cameras will pick up differently. That is why our brightness test was conducted using the same tube.
Our resolution test uses our Sony A7R5 which is capable of taking 8k resolution still photos. This greatly exceeds what any night vision device is capable of, including the human eye for that matter at this focal length. Cropped images will be used here, Google Drive link with all RAW files will be at the end of this article.
There is also some necessary clarification regarding chromatic aberration as there seems to be a gross misunderstanding of what this is. This phenomenon is colour separation when light travels through optical elements caused by different wavelengths refracting at slightly different angles through the element. Blues are known to be more difficult to focus uniformly. The bottom image shows a close up of chromatic aberration through a Carson eyepiece, the colour separation on the right and left sides of the box can be clearly seen.
Center aberration comparison:
Carson:
RPO:
Zoomed in:
The number 5 designates the entire column of line pairs as Group 5. The Element number is the row. We can see that both lenses perform well and can read Group 5 Element 4. However with RPO you can somewhat make out Group 5 Element 5, whereas with Carson Group 5 Element 5 is not able to be deciphered.
Note that horizontal elements are clearer than vertical line pairs. The reason for this is Group 5 line pairs are slightly to the left and right of center. All lenses exhibit some degree of chromatic aberration. This can bee seen as the slight colour separation at the left and right of the reticle edges. Aberration and image separation occurs outward from center.
The Milspec (Carson) eyepiece design has remained relatively unchanged for 20 years, and was optimized for green phosphor. RPO was designed with white phosphor in mind, which is why there is less colour separation on the eyepiece side when viewing white phosphor images.
Edge Resolution Test
The same test was conducted but with the resolution reticle shifted to the edge of the screen. To landmark and make the test consistent, the collimation box was set to the edge of viewable area.
Carson:
RPO:
Zoomed in:
Both systems are excellent in that they maintain a good resolution throughout the image. Group 5 Element 2 is decipherable on both sides. However with the horizontal elements Carson is legible up to Element 3 whereas RPO is somewhat decipherable to Element 4. Though, it should be recognized that this part is slightly subjective.
At the edge, chromatic aberration in Carson is more apparent as well which contributes to resolution loss.
It is reasonable to conclude that RPO has marginally better edge resolution in this area, the border between zones 2 and 3.
While not part of this test, it should be noted that both systems lose a lot of resolution in the outer half of zone 3. It is perceived that RPO loses a bit more in the extreme edge. Note that in this area of zone 2 RPO displays less vignetting than Carson.
No lens system is perfect, each system has unique offerings. What lens you decide to choose comes down to a number of different factors and trade offs and hopefully this article helps you decide which best suits your needs from a technical perspective.
Anecdotally, I enjoy RPO lens systems enough that in my current personal collection of 10+ devices, none use standard Carson lenses. They are all either RPO or some sort of rare connoisseur/collector lenses.
Google Drive Link to Carson Images: Click Here
Google Drive Link to RPO Images: Click Here
]]>
Here we conducted a side by side test. For this test, we used our Hoffman ANV-126A digital NVG test set with USAF resolution chart. We used a RNVG (Ruggedized Night Vision Goggle) and used a 4G+ tube on the right side, and either a ECHO or ECHO+ tube on the left side depending on the test. This is why in the videos the center rectangle is different on the sides, the Hoffman uses it for collimation however the light levels between the sides are calibrated to be equal.
The test uses RPO 3.0 objective lenses as these lenses provide increased transmission and have the best center resolution and contrast. We used Ether eyepieces as they provide the most generous focal distance for larger pupils, as we needed a high magnification lens in order to see the finest line pair sets. In general testing using a large objective camera should be avoided as most eyepieces are only meant for a 6mm pupil at 25mm focal distance. Exceeding these specifications results in significant edge distortion and vignetting and will significantly skew results. However, since we are using Ether eyepieces and we are only testing the very center of the image the results are considered acceptable using even testing grounds.
Since our tests use a resolution chart, only tubes of similar resolution were used for the test in order to mitigate resolution as a major determining factor of results. We were hoping to convey the differences a user would generally experience from differences in gain, SNR, and tube technology. We also performed an additional test using a pair of brand new, soon to be officially released, BCO LPMR 4K recording devices to show how tubes react to a gradual reduction of light levels.
As can be observed, the 4G+ retains better resolution, less noise, and overall higher performance than ECHO in all light levels.
One can observe that the ECHO PLUS tube in this test performs admirably. It is our belief that this specific ECHO PLUS tube may have been a 4G fallout tube (tube intended as 4G but failed due to a larger than acceptable blemish), as the contrast, resolution, and other characteristics seem better than the average ECHO PLUS tube we have seen.
In general, 4G+ retains noticeably better image quality than ECHO and ECHO PLUS tubes. These are tested in what one could call a laboratory setting, whereas in real life performance these minor differences in contrast and system resolution (different from tube resolution) are immediately noticeable in low to medium light situations and tangibly affect user experience.
It is also notable that 4G+ employs improved autogating which provides a better dynamic light experience than ECHO technology. The image from a 4G tube is noticeably better than ECHO because the 4G production line employs more stringent quality standards and uses higher quality parts. Low light performance, resolution, contrast, and dynamic light performance are all improved. We have noticed that ECHO tubes have variations in quality between tubes in the image screens, fibre optic inverters, and front end protective coatings. These minor variations are not noticeable to most users, and can only be spotted by users with extensive experience under different systems as well as a keen eye to spot very specific differences in texture and depth.
Many people ask how 4G+ compares to Gen 3. There is a wide variation in tube quality with Gen 3. When compared to Elbit and L3 tubes, 4G+ is actually in the same league but not top of the league in terms of image quality due to lower brightness. 4G technology offers improved bright light suppression over Elbit and L3, however Elbit and L3 offer better low light performance due to increased tube brightness and sensitivity. However, it is important to note that while the 4G+ produces a darker image, the image does not appear to be of significantly lower quality. If gain is lowered on an Elbit or L3 tube to the same brightness as 4G+, the image quality is very similar. Noise, resolution, and the ability to resolve an image are very similar.
In short, 4G+ tubes are noticeably better than ECHO and ECHO PLUS. They fall short but are in the same league as Elbit and L3. They are roughly equivalent to OMNI era ITT/Harris green tubes in terms of image quality and ability to resolve objects, though I would consider 4G+ superior because of improved gating.
Whether or not the cost of 4G+ is worth it over a standard ECHO or ECHO PLUS for the end user is up to them and their individual needs. For the average end user, it is likely not worth double the price of an ECHO system. But for the nightvision collector and connoisseur, it is a fantastic addition to a collection and very satisfying to use. I have certainly added a set of 4G+ with RPO 3.0 to my own collection.
]]>We have always had a goal of providing transparent information to the consumer, as the nightvision industry tends to be shrouded in secrecy and disinformation.
Weight:
Immediately, we can see that the 3.0 objective weight is roughly the same, whereas the eyepiece is significantly lighter. For some reason RPO decided the lightening cuts on the body of the objective were not worth the effort. Both remain significantly lighter than standard Mil-spec offerings due to their more advanced optical designs.
Without getting into too much detail as some of this information is controlled, a standard PVS-14 objective lens makes use of 8 individual optical elements. RPO was able to cut that down to 6 elements in the 2.0 lens system by introducing the use of polymer aspherical lens elements. The 3.0 system further reduced that down to 5 elements.
The eyepiece on the other hand is significantly lighter. A standard Mil-spec eyepiece makes use of 3 elements: 2 spherical elements and an asphere. RPO was able to reduce that to 2 elements. Don't worry, the outer element is glass for increased wear resistance.
Another reason why the eyepiece is lighter is the viewing area diameter was decreased from 29mm to 26mm. As stated in one of our previous postings, increasing lens size increases weight by roughly the cube of the increase in diameter or eye relief. The diameter change of roughly 11% would project to a weight decrease of 28%, but paired with the improved use of aspherical elements resulted in a weight reduction of just over 30%. The prediction checked out. It is also notable that the 3.0 eyepiece is shorter, more on that later.
Gain:
RPO 2.0 lens systems always had higher transmission than Mil-spec systems, and therefore produced a slightly better image in low light situations. With the 3.0 system, we wanted to test that. We only tested the objective lens for this as it is the only part that contributes to the tube input, which affects the amount of noise and the usability of image produced.
Test parameters were set such that the same tube was used for all tests, and we tested 5 different 2.0 objective lenses, and 5 different 3.0 objective lenses. Each lens had a gain reading taken 3 times for an average. The reason the gain reading is taken 3 times is because the gain reading can fluctuate based on random scintillations. That is why gain fluctuates more in the low light test where scintillations are more visible.
For low light, we tested at 0.006 mfL which correlates to 2x10-6 fc on a spec sheet
For high light we tested at 0.628 mfL which correlates to 2x10-4 fc on a spec sheet.
Note that a spec sheet only measures tube gain, system gain is always much lower than tube gain as it accounts for many more factors. We are not testing with a low spec tube. We also alternated 2.0 and 3.0 objective lenses in our test sequence in order to ensure our results were not skewed by calibration drift. All tests were conducted with a recently calibrated Hoffman ANV-126A test set.
2.0 at 0.006 mfL 11003, 11062, 11092 Average: 11114.2 |
3.0 at 0.006 mfL 9745, 9906, 9865 Average: 9867.8 |
2.0 at 0.628 mfL Average: 5145.9 |
3.0 at 0.628 mfL 4905, 4909, 4911 Average: 4877.7 |
From this, we can see that 3.0 actually has on average 11% less gain in low light and 5% less gain in high light. That sounds bad, but really it's not; it is a trade off. As stated in our previous lens article, RPO sacrificed flare suppression in favour of higher transmission. With 3.0, RPO sacrificed some transmission in exchange for excellent flare suppression.
Please note that we are testing flare suppression in worst case scenarios, and is actually better than shown in this video. The BCO LPMR 4K has an excellent sensor with excellent contrast software. The downside of that is that it picks up the contrast in lens flare more than is perceived by the user. The rings on the 3.0 are significantly easier to see past than the 2.0. The edge streaking by light sources, and concentrated flare points are significantly improved.
Resolution and Contrast:
In conversation with a high level optical engineer with significant experience working in night vision optics, we discussed some other reasons why RPO may have reduced gain output. While on its own, higher gain is better, often times you reach a point where higher gain begins to work against MTF (modulation transfer function) which determines resolution. If bright areas are brighter, but dark areas are also brighter, this can reduce contrast. Whereas if bright areas are brighter but dark areas are made darker through selective filtering, overall gain readouts will be reduced but contrast and resolution are improved.
Testing in this area was inconclusive, but leaned toward the 3.0 system providing marginally better resolution. Using the same tube, resolution was tested using a Hoffman ANV-126A and HVS-126A digital calibration system which removes human subjectivity from resolution measurements. Subjectively, line pairs appeared marginally clearer with the 3.0 system. In our testing, we repeatedly tested a high spec tube for resolution using both the 2.0 and 3.0 complete lens systems. With 2.0, the system was halfway between Group 5 Element 4 and Group 5 Element 5, which correlated to 45 lp/mm and 51 lp/mm respectively. However, the 3.0 system was consistently able to read Group 5 Element 5, correlating to 51 lp/mm. Because both systems were able to read Group 5 Element 5, the test is inconclusive. However because the 2.0 system was not able to consistently read it, it can be loosely inferred that the 3.0 system produces a marginally higher resolution.
This is also why we tell people that tube resolution on a spec sheet is one of the least important specs to pay attention to. There are other vendors that will mislead consumers into believing that high resolution tubes are a must, and will publish "tests" that try to push it as fact when they are obviously using unmatched tubes that differ in other areas, or simply didn't have one of the systems focused properly. It can be quite blatant. That is not to say resolution does not matter, it absolutely does. But prioritize other specs, and prioritize lenses. There is no point in using a 72lp/mm or higher tube when poor quality glass is going to drop your resolution anyway. The lens system is one of the most important factors in determining the performance of a night vision device. Don't use low cost substitutes in this area.
User Experience:
The RPO 3.0 vs 2.0 comparison is full of trade offs, and the user experience highlights this. The 3.0 system produces an absolutely beautiful image.
When building the goggle, it was immediately noticeable that the 3.0 lens system was much shorter than the 2.0 which was roughly similar to a standard Mil-spec system.
This leads to the goggle being shorter than a standard goggle, and to be honest it looks quite novel. It also means that using it in a standard diopter produces sub optimal results, whereas it fits perfectly in a low profile diopter such as the ones we produce.
In the above picture, a goggle is being tested on our Hoffman ANV-126A system. The eyepiece on the left is RPO 3.0, the one on the right is RPO 2.0. Both diopters have been set to zero using a Hoffman diopter scope. This shows how much shorter the goggle can become when using the 3.0 system.
Another thing that is of note, is the zone 3 distortion. There is more zone 3 distortion with the 3.0 system than 2.0 and standard Mil-spec. However the distortion is so far on the periphery that it does not seem to have much affect on the user experience due to how far out it is, and the fact that zones 1 and 2 are clear of that issue. It is also not recommended to mix 3.0 objectives with other eyepiece systems, as the objective and eyepiece are designed to work together. Doing so will result in a more distorted image (we tried).
Because the viewable area is slightly smaller as stated prior, the eye relief is also slightly shorter. It is noticeable to someone that has extensive time behind night vision devices, but may not be noticeable to most users. It is not a significant hindrance and is still very comfortable to use, and produces enough eye relief to be used comfortably with an Avon FM53 gas mask.
Conclusions:
In conclusion, we do not think it is fair to say that one system is definitively better than the other. There are too many tradeoffs.
2.0 has higher gain, less distortion, and better eye relief.
3.0 has better contrast, better resolution, and better weight reduction.
Both are excellent systems, and people with legacy 2.0 systems should not feel the immediate need to upgrade. For customers looking to get into which lens system to go with, we are looking at potentially carrying old stock of the now discontinued 2.0 system to compliment the 3.0 offering to provide more options. In extreme dark conditions such as a forest with full tree canopy, the increased gain of the 2.0 system may be more beneficial. In dynamic lighting situations where flare suppression and contrast are more beneficial, then the 3.0 system may be the system of choice. Each user is different and their needs will be different. We try to provide as much detailed information as possible to help users make informed decisions.
]]>Some of you may have noticed certain discrepancies on spec sheets from different companies. The main specifications that are measured differently are EBI and gain. Many European tubes measure specs in SI units whereas US measurements are often imperial. Russian tubes use a mix.
fc: foot-candle = 1 lumen per square foot
fL: foot-Lambert = 1/π or ~0.3183 candela per square foot
μlx: microlux = 1/1,000,000 lumens per square meter
phot: phot = 1 lumen per square centimeter
1 foot-candle = 10.7639 lux
20 microlux = 1.8581 x 10-6 foot-candles
1 phot = 10,000 lux
(fL/fc)/(cd/m^2/lux) = π
Explaining these conversions would be rather time consuming, but if you have a decent grasp of basic mathematics you should be able to perform all the conversions necessary using the above units and conversions.
Gain is a number that expresses the ratio at which the light input measured is amplified in its output. The input is measured in foot-candles (fc) in the US, and lux (lx) in SI units. Output is then also measured differently, using foot-Lamberts (fL) in the US and candela per square meter (cd/m2) in SI units. This will be expressed as fL/fc in the US or cd/m2/lx
We will refer back to the the conversion of (fL/fc)/(cd/m^2/lux) = π, which means that to convert from SI to US gain units, you simply multiply the SI gain number by π, or divide by π to convert to SI.
However one thing to note here is that the conversion is not exact, as the inputs for gain testing are different. US tubes have gain measured at two different light levels:
2 x 10-6 foot-candles (this is the main one people look at)
2 x 10-4 foot-candles
Whereas European tubes are generally measured at 20 microlux
20 microlux = 1.8581 x 10-6 foot-candles
What this means is that while the conversion will be approximately accurate, there will be a margin of error as gain ratios tend to be higher as input light decreases. SI measured tubes will have their gain levels slightly inflated over US measured devices.
As an example of the slightly inflated gain, the datasheet for a specific model of Photonis ECHO tube lists two gain values:
Gain at 2 x 10-5 lx: 8,000 - 12,000 cd/m²/lx
Gain at 2 x 10-6 fc: 25,120 - 37,680 fL/fc
For clarification, 2 x 10-5 lx is 20 microlux. When both numbers are converted to fL/fc, the gain levels are:
Gain at 20 μlx: 25,132 - 37,699 fL/fc
Gain at 2 x 10-6 fc: 25,120 - 37,680 fL/fc
Note that there are some night vision companies that will change the way tube specs are measured in order to make their tubes look better than they actually are, so when comparing different tube models it is important to pay attention to the units used alongside the numerical figures provided.
Equivalent Background Illumination is one of the most misunderstood specs that we pay attention to. It is often explained as a number that determines the darkest environment a tube can see in to, which is not wrong but is completely misunderstood. EBI is like when you turn your computer on, your display turns on but is still black. Even though it is still blacked out, you can tell that it turned on because it is a slightly "brighter" black. That brightness would be EBI for a tube.
EBI on US spec sheets is measured in phot, an empirical unit that expresses one lumen per square centimeter. I like to think whoever decided on this unit was intoxicated when the decision was made.
On US spec sheets, EBI is expressed in phot x 10-11. Bruh. That's like measuring halo in kilometers instead of millimeters. Microlux is a better unit for this. All you do is move the decimal over one place.
1.0 x 10-11 phot = 0.1 μlx
What this means is a 0.25 EBI on a European spec sheet is the same as 2.5 EBI on a US spec sheet. For you astronomers out there, make sure the 0.1 EBI tube you're thinking about buying isn't actually a 0.1 μlx tube that would show up as 1.0 EBI on a US measurement.
]]>NNVT tubes are non gated whereas ECHO tubes are gated. ECHO tubes are rated 1600 FoM to 2000 FoM, whereas NNVT tubes are rated 1200 to 1600 FoM but generally average around 1400 FoM.
For our comparison, we are using Carson lenses. Fujinon OEM Carson objective, with Qioptiq OEM Carson eyepieces.
NNVT:
23.01 SNR
60 lp/mm
0.18 EBI
10800 gain
Photonis ECHO:
27.32 SNR
67 lp/mm
0.08 EBI
9873 gain
The NNVT tube is right in the middle of the line of our batch from a spec perspective. The ECHO is an above average ECHO. One thing that was notable to us was the NNVT shipment we received had very few blems, whereas clean ECHO tubes are relatively very rare. We had to hand pick a clean one for this comparison as it is a performance comparison, not a tube cosmetics comparison.
Relatively bright moon, some stars overlooking subarban homes. You will notice that the NNVT tube is slightly grainier because of the lower SNR but overall, it is a very comparable image.
Overlooking a pond, near full moon to the left outside of the field of view. Image clarity is very comparable.
Here we have a dynamic light and flare test. In this case I think the NNVT tube does better than the Photonis ECHO, as ECHO tubes are notorious for their "Rising Sun" style flare out of point light sources. Though, the ECHO does do a slightly better job of seeing past the initial orb flare. Again, these are both with the Fujinon objectives and Qioptiq eyepieces.
Another dynamic light test, but this time less direct. Streetlights down a street, you can still see the "Rising Sun" style flare from the ECHO tube. Same as before, it is much easier to see past the orb flare with ECHO than NNVT.
It is very difficult to tell from these photos, but while the ECHO has marginally better clarity in well lit areas, the NNVT tube actually has noticeably better clarity on point light sources. The reason for this is the NNVT tube is based on XD4/XR5 technology and not wide spectrum technology that ECHOs use for their photocathodes. What this means is that the NNVT is photosensitive to a much narrower band than the ECHO, which means that light focuses more evenly. While it can be advantageous to have wide band photosensitivity, it can in some cases decrease resolution due to different wavelengths focusing differently through the same lens.
If you have ever driven under NVGs, this is why green lights always look slightly out of focus compared to red lights and other street lights. Green focuses differently through most PVS-14 lenses.
In low light, the NNVT tube is brighter because it has a higher gain and higher EBI. The ECHO produces a clearer image.
Overall the NNVT tubes are quite impressive given the price point, and definitely provide an incredible value for the cost. We are very excited to begin offering NNVT tubes in our units now that we have done testing to ensure the tubes are of good quality. These units will be available at a significantly friendlier price point without the significant performance sacrifices involved in using lower quality housings and lens systems.
Stay tuned for further qualitative and quantitative comparisons for both image intensifier tubes and lens systems that we will be conducting using our Hoffman Engineering ANV-126A.
]]>Not all PVS-14 lenses are made equal. Some are very similar, some are the same, and some are in completely different ballparks. There are so many different PVS-14 systems, it can be incredibly confusing.
To start, there are tons of different brands of PVS-14 lenses, many of them can be identified by their CAGE codes. For example, Carson Industries lenses are marked 1XEP3, Elbit Systems lense are marked 13567, etc. If you are not sure what lens you have, look for the markings located just under the knurling of the lens. However, some of them will look suspiciously similar, and that's because they are the same. Most companies that have lenses, don't actually make lenses themselves. They are typically outsourced. The biggest manufacturers are Qioptiq (Singapore) and Fujinon (Japan?). Qioptiq makes objective lenses for Elbit, and have also made them for Carson as well as many other manufacturers. Fujinon makes objectives for Carson and L-3, as well as many other companies. It gets very confusing because different companies will swap lens suppliers depending on contract requirements, pricing, etc. For example, Carson Industries currently uses Fujinon objectives, however in the past they have used Qioptiq. L-3 currently uses Fujinon as well, however in the past they have used Edmund Optics.
In this article we are mostly going to talk about the PVS-14 objective lenses that are commonly seen in Canada, or lenses we plan to offer: OE, ADI, Fujinon, Qioptiq, Edmund, RPO.
OE: Optronics Engineering is an Israeli defense company that produces PVS-14 lenses, assemblies, and tools. Their lenses are sold under brands such as AGM, Apache, Alpha Optics, and various other lower end wallet friendly brands. We explored their use in our early days and determined that the quality is too low for us to feel good about selling. These are uncoated for glare suppression, don't seal, aren't water-tight, and lack optical clarity.
ADI: ADI Trident lenses originate in Taiwan and are relatively new. They came out a year or two ago and and cater to the international market where US Milspec lense are hard to come by. They are an upgrade compared to Optronics but have their issues. We sold a few of them in our early days, but quickly dropped the product once we tested and found that the lenses do not seal and are not water-tight.
Fujinon: Fujinon is a large Japanese company that makes a lot of different lens systems. They make excellent PVS-14 objective lenses that are used by the US military. Carson Industries currently uses Fujinon, as does L-3. They can be identified by their deep blue coating and single row of knurling. It is likely that these lenses are made in Japan.
Qioptiq: Qioptiq is historically one of the largest suppliers of PVS-14 lens systems in the world. Their lenses are made in Singapore, and have been standard for the US military and law enforcement for over a decade as ITT/Excelis/Harris/Elbit have been continuously using them and supplying them. They can be identified by their dull, light blue lens coating and double row of knurling.
Edmund: Edmund Optics discontinued their PVS-14 objective lenses many years ago. They were made in the US, and are now highly sought after by collectors for their high quality. L-3 used Edmund lenses in the past for their systems. Edmund lenses can be identified by their beautiful Tiffany coating and deeply clear reflection.
RPO: Rochester Precision Optics have been making night vision lens systems for a long time. They are known for making the lens systems for the NVD BNVD series, as well as the very highly regarded L-3 PVS-31 lenses. RPO lenses are newcomers to the PVS-14 market, and are of excellent quality, though their main selling point would be the extreme light weight. They can be identified by their low profile, polymer construction, and deep clean coating with a colour halfway between Fujinon and Qioptiq blue.
One of the most important aspects of a lens is the coating. Not only does the coating boost transmission, but the coating should suppress lens flare. The following image compares the lenses in an urban environment underneath a building light to illustrate the lens flare pattern.
It is evident that OE is the worst, as there is no coating. ADI has less flare pattern, however the light causes a foggy appearance throughout the image. Fujinon is the first one to offer good flare suppression, however a crescent flare pattern is still visible. Qioptiq has similar flare suppression, but has a slightly different circle pattern. Edmund seems to have the best flare suppression with a long mushroom pattern. RPO has a bit more flare in a crescent ring pattern. RPO lenses apparently have increased light transmission over other lenses, but at the cost of slightly more lens flare.
Next we have a cluster of urban street lights roughly 100m away. This should depict how well the lenses focus light and prevent excess light from blurring other parts of the image. OE is very bad, in that other lights that aren't even in the field of view are casting rings throughout the image. ADI has less flare, but the street lights wash out nearby parts of the image. Fujinon, Qioptiq, Edmund, and RPO all look very similar as they are all US Milspec systems held to a very high optical standard.
These are zoomed in pictures of Zone 1 of the image on all six lens systems. Because of the high light, most of the images look very similar. OE and ADI are slightly blurrier, while Fujinon, Qioptiq, Edmund, and RPO look very similar as they are legitimate US Milspec systems.
It is important to note that while pictures and videos are the best things we can offer to digitally convey the experience a lens has to offer, it is very difficult to convey things such as lens distortion through images, they have to be experienced. OE has a noticeable amount of distortion. ADI also has distortion, however it is less in the center and more extreme in zone 3 compared to OE. Fujinon, Qioptiq, and Edmund are equal in this regard and have the least distortion, and are perceived as having no distortion. RPO has a slight degree of distortion compared to other US Milspec systems, one of the costs of being so low profile. However this distortion is very marginal and will not be noticed by most users. It certainly has not bothered any users.
Unfortunately full moon just passed a few days prior to these photos being taken, so the illumination level is extremely high even in the middle of the night. A segment will be added in lower light levels to compare light transmission more appropriately. This comparison is intended to be an ongoing project, so more comparisons will be added as appropriate.
Currently, Opfor Night Solutions offers Carson Industries objective lenses (Fujinon) on most of our products. In some cases Edmund lenses will be available. We are currently developing lightweight diopter assemblies so that RPO lightweight low profile lenses will also be available in the future.
]]>Many people like custom colours or custom patterns on their gear. We have never been a fan of rattlecanning any piece of gear, let alone expensive nightvision. Some other companies have offered Duracoat or wraps. Duracoat is much easier to apply as it does not need to be heat cured, and camo wraps are cheap and easy for end users to apply themselves. Let's be honest though, wraps are glorified stickers. Nightvision doesn't deserve to look like it came out of a Kinder Egg. Duracoat is a paint job, Cerakote is a finish.
That being said, the Cerakote process generally requires baking to cure. Air cure Cerakote does exist, but it is not condusive to patterning. The heat required can deform thermoplastics on 3D printed housings such as the Katana (which is why they only offer air cured solid colours), and can damage or dislodge internal electronic components on other housings.
The BNVD-1431 and BNVD-1431 Mk.II are perfect for this, as the pods do not contain any electronic components and are able to withstand the curing process without deforming. That is why we are now able to offer Cerakoted pods with our complete builds at an introductory rate of $250 CAD. Please contact us to discuss the pattern you'd like prior to placing an order.
If you already have a built set of nightvision and you'd like to inquire about coating, please feel free to contact us as well, however the rate will be higher as it will involve a full disassembly of the unit, removal of electronic components, followed by a full re-build and purge.
]]>Nightvision can be very endearing to the owner, and picking your own tube makes it more personal. We don't believe in making our customers pay more for a choice, we believe that customers should pay for what they actually receive. Some other vendors price tubes individually, while others charge a selection fee regardless of tube quality on hand.. We considered both options, but ultimately decided on another process that we think is the most transparent and beneficial to you, the customer.
Our Process
Photonis Echo tubes are some of the best tubes for the price. In order to lower the cost, Photonis does not test for blem specifications or halo size to put on to the spec sheet. We consider that to be an issue, so we have taken it upon ourselves to take each tube we receive, put it into a nightvision device, and document both the screen quality and halo size as both are extremely important factors in determining tube quality, and tube matching for binoculars. We take pictures through every tube so the customer can see what the screen quality is like, and we compare halo sizes with those from known devices in order to estimate halo size from a specific tube.
This is an extremely time consuming process, however we feel that it is the only way to ensure product quality and match tubes to the best of our ability. To find out more about our matching process and how we enhance our selection, check out our other blog post on why we only use Variable Gain MX10160 tubes.
Straight from Photonis, Echo tubes are 1600-2000 FoM and range from relatively clean tubes, to sometimes having large dark spots. Most tubes will come with a small spot here or there. Halo values typically range from 0.7 to sometimes larger than 1.0.
Select Tubes
In order for us to classify a tube as Select, it must meet all of the following requirements:
Here is an example of a tube that met our select standards (the small red spot is a laser burn on the camera sensor and does not appear in the tube image):
Here is an example of an otherwise fantastic tube at 1950+ FoM and 0.8 Halo, but did not meet our select cosmetic standards because it had too many dark spots:
Our hand select program allows customers to choose between "Standard" and "Select" tubes at purchase. Regardless of which route the customer chooses, the customer may, after consultation, hand pick their own unit from any tube or tube pairing we have in inventory that falls within that grade.
Our units are meticulously built, and we hope that this provided some insight on the work that goes into tube selection for each unit. We want our customers to be certain that their unit is right for them. If you have any questions, do not hesitate to reach out.
]]>