Night Vision highly technical nod questions and some about the pvs 4 too. math gurus needed

[ghostwriter247]

So i have been reading and am new to nods and had a few questions to ensure i am understanding what I'm reading. Also I think this will help clarify for us beginners the differences between types of tubes and why not all nods are created equal though they seem to be, and help us understand the questions to ask when comparing say a tnvcc pvs 14 vs an armasight 14 (or even two 14s made by the same company and why ttey are more expensive.

Alot of this will use the pvs 4s as a discussion point. This might be a bit long winded but i figured it beats the heck out of ten posts asking how one nod compares to that nod. The first part is my understanding of just reading a bunch of threads plus my background in photography so if its wrong let me know. The questions come afterwards.

So first f stop. Light gathered is a function of fstop and objective size. so with the pvs 4 the fstop is 1.2 which is numerically low which lets in more light. the large 95 mm objective also has the ability to gather more light from the surroundings. The downside to low fstop is that it creates razor sharp depth of field meaning less of the image is in crisp focus. Now not much manufactures can do with fstop. they need it to be low to gather more light, one way around this is to use a very short focal length which in common terms most people call magnification. The longer the focal length in between the interior lenses the more magnification. the more magnification the more depth of field you have. so as magnification (or more properly focal length) depth of field goes up, This is why Nods are so finicky with focus. and the more magnification you have the more finicky the focus will be.

SNR- signal to noise ratio is a measurement of how much noise there will be in the image if there is not enough light. Noise is affected by two things, one is not enough light. the other is excessive gain, so as light goes down we see noise. as we crank gain it should intitally cure some noise and then move through to increased noise level. Its like iso on a camera. the snr is measuring how well it deals with these lack of perfect conditions. so the higher the number the less noise, and the sweet spot balancing light vs gain will be larger. Noise of course also impacts clarity of image. too noisy you lose detail. so a high snr will be more clear under a wider range of conditions.

QUESTION 1. . so given that understanding. given the same optical quality of the glass, a gen II and Gen III will perform close to one another under perfectly lit conditions(if you have a well balanced even lit ir for the gen II). one needs an ir the other perhaps not as under perfectly lit conditions noise does not come into play. This is why some gen II and gen one look great with ir or a full moon.

Here is where it gets trick for me. The following is from the omni table of classifications. The lp/mm this seems to be an expression of clarity and light gathering capabilities. This is the maximum resolution under perfect conditions.


Tube Contract lp/mm uA/lm @830 @880 SNR Gain> Gain< FOM EBI MTF25 BLR Halo Comments

mx9964 20-40 240 10@850 –– 40000 70000 n/a 2 20 @15 n/a 0 Gen2 PVS-4

mx11620 45 1550 140 70 25 20000 90000 1125 1 20 14 0.7-1.6 Gen3 PVS-4

QUESTION 2: answered

QUESTION 3: With the listed specs for lp/mm in gen two being a range, were earlier more around 20 and later tubes aroudn 40 or were they all somewhere around that range regardless of date of manufacture ANSWERED

QUESTION 4: So back to our previous discussion my understanding then is the large gain on the gen II tube is influenced by a larger tube and the larger objective lens in combination with the low f-stop right? That is why the listed gain is on par with gen iii tubes.

QUESTION 5: GAIN- im a little unsure here but im guessing that the gain listed DOES NOT mean the tube has to be in between the two numbers to pass spec. it means with the gain turned all the way down, for the gen II tube its is 40000 and with it all the way turned up its 70000 give or take correct?

QUESTION 6: Also i notice that there isnt a snr listed for the gen II tube. DO gen II tubes not have snr or is it just not listed? If not what is the snr on the gen ii tube?

QUESTION 7: with Halo i understand that gen II tubes do not suffer from halo correct? or is that just a peculiarity of the pvs 4 gen ii tube? IT IS A PECULIARITY OF THAT TUBE ANSWERED

QUESTION 8: So the similar lpmm (40 on the high end for gen two vs 45 for the gen 3) and slighty higher gain (70 vs 90) is why some people say the gen three is slightly brighter but not much better in resolution?

QUESTION 9 Another seller posted this as the specs for gen three Resolution for the pvs 4 lp/mm 64 S/N 21

Photocathode sensitivity uA/lm@2856K 1800
Sensitivity at uA/lm@830nm 190

Gain fL/fc 40,000-70,000
[email protected]/mm 0.92
[email protected]/mm 0.8
MTF@15lp/mm 0.61
MTF@25lp/mm 0.38
Halo (mm) 1.25
Phosphor P-43

As you can see the gain lower resolution higher and snr lower and halo in between what is posted on this site. Are his numbers incorrect? cj and tnvc generally are on their game so i was thinking maybe he grabbed the wrong tube specs. or is the sellers lpmm of 64 just trying to be expressed in 18mm tube terms?

QUESTION 10: On the pVS 4 tubes the lowest line says acc date. Is this the date of manufacture? ANSWERED

QUESTION 11: FOV is expressed in degrees for nods. now just off the top of my head im thinking degrees times objective size or maybe focal length will tell you how many feet at 100 yards or a thousand yards. Does anyone know that formula?

QUESTION 12: does anyone know the focal length for the pvs 4s?

QUESTION 13: Last one. on the pvs 4s are the gen three tubes just drop in replacements? I thought i saw a thread saying the spacing wasn't right and you had to mill a bit to get the correct focal length? Does TNVC mill their rebuilt gen three pvs 4s, o ram i mistaken?

thanks a bunch (mostly for reading all the way through this)

 

[VJJPunisher]

for such question's one must remember alfonso's law, the heat in the meat is directly proportional to the angle in the dangle. Hope that helps

 

[marduk185]

Turn on the lights...bam! err buddy's on equal ground, screw the tech. hell ya might even win the day by flaring their vision for a sec.

 

[ghostwriter247]

wow, i think the world has stopped turning. i actually got more intelligent answers on ar15.com.

 

[alpine44]

wow, i think the world has stopped turning. i actually got more intelligent answers on ar15.com.

Nightvisonforums.com may be the better place for discussing the finer technical details.

On the practical side:

The AN/PVS-4 is NOT fussy with focus once you are past 25 yards.
The GEN III MX-11620/UV tubes will fit without modification and are a marked improvement albeit not as good as the recent milspec Gen III tubes found in the PVS14 or the clip-ons.
The AN/PVS-4 is a pig weight wise but it is relatively inexpensive and bullet proof. The lack of halo is really nice in light polluted urban and suburban environments. For pitch black forests, there are better choices.

 

[ghostwriter247]

thanks alpine! Got answers for 2, 3, and 10. Thanks guys

 

[Victor-TNVC]

Pm sent to you J.

 

[GBMaryland]

Since you sent me a PM, my 2 cents. (I think you answered question 4 yourself.)

Gen2 vs Gen3:

It's been covered, but in light polluted areas, the Gen2 PVS-4 is pretty fun. For example, you will see aircraft pretty well on clear nights with lots of start light, or around major urban areas. On the flip side, as mentioned, it's not very good in really dark (forested) environments without an illuminator.

The Gen3 version IS better, there's no doubt. However, my experience was that when you turn up the gain there is significant scintillation (due to the lower S/N ratio), especially when compared to current Gen 3 filmed and unfilmed tubes. (Probably even some really higher end Gen2 tubes... but that's speculation on my part.)

MX-11620 as a drop-in replacement:

Yes, this is the case, as the PVS-4 is a very simple device. It IS a PITA to get the split rings in just right, and I have seen units that are missing one or both of them... (The tube screws into the ocular lens housing on a PVS-4/TVS-5 [which are the same on both units], and then is held in place by two split-rings and some set screws.) It should be noted that you have to make a SERIOUS attempt to keep everything clean, as the PVS-4s are a little of a PITA when changing the tubes.

There is a 25mm tube that was a cascaded tube for the stinger, and it's typed about on various forums and so on... no idea if that truly works with a PVS-4. However, if you did get a hold of one, I tend to think the USG might want it back.

Additional parts issues:

It is extremely difficult to find variable resistors with the same number of ohms / and size for the PVS/TVS unit. Basically, it does not appear that they are made any more. So if one of those variable resistors / potentiometers / varistors (take you pick of naming convention) croaks, you've got a somewhat useless PVS-4/TVS-5.

Another thing that tends to break on them are the wires for the illuminated cross-hair in the objective lens. I'm told by STANO that there used to be a repair facility for that, but at this point you're really talking about getting a new objective unit if you want crosshairs. Don't get me wrong, the PVS-4's are super durable... but I have had this happen to me. [Of course, if you purchase one form TNVC, or any other REPUTABLE dealer, you'll get a warranty and people who will take care of you. EBAY is NOT your friend for NV optics... maybe NOS parts.]

 

[ghostwriter247]

Thanks for the input gb. really apppreciate your reply. I didn't know about the potentiometers. I had heard about the cascaded tube in gen 3.

There was some discussion of a gen 2 +1 Thats an mx9644/uv part number correct? It can be identified by the UV on the on of it? its a cascaded 2+1 which is different than the cascaded three tube that won't drop in due to focal length issues? I saw some discussion on an old thread here about a gen 2+1 but Im not sure it was ever figured out if that was the UV designation or not, or if it was drop in or not. Some information suggests it was made from march 99 on, was there a true difference or was it simply an updated part number form within the military system with no actual differences in specs?

This questions seems the simplest, Im surprised no one addressed it.

QUESTION 5: GAIN- im a little unsure here but im guessing that the gain listed DOES NOT mean the tube has to be in between the two numbers to pass spec. it means with the gain turned all the way down, for the gen II tube its is 40000 and with it all the way turned up its 70000 give or take correct?

 

[marduk185]

yes

 

[decider]

Somb

 

[decider]

QUESTION 1 - Yes
QUESTION 2 - Not so fast young padawan, the answer is not the question, the question is the answer
QUESTION 3 - Probably
QUESTION 4 - No
QUESTION 5 - Not correct
QUESTION 6 - Yes
QUESTION 7 - More than likely
QUESTION 8 - No
QUESTION 9 - Yes
QUESTION 10 - Probably not
QUESTION 11 - see link: http://www.hyper-ad.com/tutoring/math/calculus/images/const_riemann_int_666.gif
QUESTION 12 - No
QUESTION 13 - Yes, ram them.

My work here is done!

 

[GBMaryland]

BTW, I believe the attached picture is the infamous cascade tube (it could also just be some wacky atypical Litton tube), and other is the MX-11620/UV I put in my last PVS-4.

 

[ghostwriter247]

That does look atypical. Did you have any focus issues when you installed it? Did it give better than expected performance?

 

[ghostwriter247]

BTW, I believe the attached picture is the infamous cascade tube (it could also just be some wacky atypical Litton tube), and other is the MX-11620/UV I put in my last PVS-4.

Any idea where i can get a gen 3 tube? night vision depot is out.

 

[Delta4-3]

Any idea where i can get a gen 3 tube? night vision depot is out.

Try Kobe at Optics HQ.

 

[compasscall]

BTW, I believe the attached picture is the infamous cascade tube (it could also just be some wacky atypical Litton tube), and other is the MX-11620/UV I put in my last PVS-4.

No, not a 3+1 cascade/hybrid but it is a very nice glass input FO inverting wafer tube (double proximity focused). That tube is the Gen III upgrade (MX-11620 P/N 510-7330-306) for the passive sight in the LAV-25A2. The tube is also a direct drop in for the AN/TVS-5 night sight, not modifications, direct drop in. Though it's not quite a direct drop in with the AN/PVS-4, only a single and minor modification is needed for it to be a drop in.

The FO input MX-11620 looks like it was one of the latter units out of Garland, really nice tubes!

ghostwriter247, try

Ident Marking Services Night Vision

Outer Edge Optics Home Page

I^2 Night Vision Home

Summit Night Vision Image Intensifier Tubes - MX-11769, MX-10160, MX-10130, M814, M851, M890AV, M890, 18mm, 25mm, Gen 3, Gen 2, Gen II and Gen III Night Vision,

Night Optics USA | Night Vision | Thermal Imaging
(Night Optics sold back most of their stock of the refurbed PVS-4s but may have some tube still lying around or may know where to send you)

 

[ghostwriter247]

No, not a 3+1 cascade/hybrid but it is a very nice glass input FO inverting wafer tube (double proximity focused). That tube is the Gen III upgrade (MX-11620 P/N 510-7330-306) for the passive sight in the LAV-25A2. The tube is also a direct drop in for the AN/TVS-5 night sight, not modifications, direct drop in. Though it's not quite a direct drop in with the AN/PVS-4, only a single and minor modification is needed for it to be a drop in.

The FO input MX-11620 looks like it was one of the latter units out of Garland, really nice tubes!

ghostwriter247, try

Ident Marking Services Night Vision

Outer Edge Optics Home Page

I^2 Night Vision Home

Summit Night Vision Image Intensifier Tubes - MX-11769, MX-10160, MX-10130, M814, M851, M890AV, M890, 18mm, 25mm, Gen 3, Gen 2, Gen II and Gen III Night Vision,

Night Optics USA | Night Vision | Thermal Imaging
(Night Optics sold back most of their stock of the refurbed PVS-4s but may have some tube still lying around or may know where to send you)

Compass,

How did the night optics gen 3 units perform? There are still some new in box inventory available.

 

[compasscall]

The NightOptics units were rather stellar, really clean well performing systems.

Not sure on all the resellers that bought these refurbished systems but the they should all perform similarly.

If you can pick one up in the mid $2000 range, assuming your after a Gen III system, your paying a reasonable sum, not a deal but reasonable.

 

[ghostwriter247]

I have to clarify but this looks like a NO dealer and they are at $2599. she is supposed to get back to me tomorrow on whether its slightly used or new in box. The other Night optics I saw were more than tnvc's, thats what concerned me, was the low price for a gen 3 unit. But its returnable as well

 

[GBMaryland]

No, not a 3+1 cascade/hybrid but it is a very nice glass input FO inverting wafer tube (double proximity focused). That tube is the Gen III upgrade (MX-11620 P/N 510-7330-306) for the passive sight in the LAV-25A2. The tube is also a direct drop in for the AN/TVS-5 night sight, not modifications, direct drop in. Though it's not quite a direct drop in with the AN/PVS-4, only a single and minor modification is needed for it to be a drop in.

The FO input MX-11620 looks like it was one of the latter units out of Garland, really nice tubes!

So, my question for you is: how is the LAV-25A2 tube a drop in replacement for the TVS-5, but not the PVS-4? The base of the units (everything behind the objective lens) is the same... unless you have a 3 inch eye piece, which doesn't change anything really.

You've got me wondering.

Ghostwriter:

In so far as a source... just buy a Gen 3 from TNVC! (By this, I just mean get a Gen 3 PVS-4 from them...)

 

[ghostwriter247]

So about 1 year or two ago there was a thread on arf.com about fitting the 3+1 into a pvs 4. it was a kit with a new switch casing and focus ring and itt f4845. I managed to piece two and two together and managed to track down the original seller without input from the buyer. Dont even ask how lucky or hard that was(depending on your point of view) but the main thing that came out of it is the retaining ring on the pvs four has to be machines flush with the case on the objective lens. It was a direct bolt on fit for a tvs five. I dont know whether this is true or not as i havent seen either in person. CJ was the one who explained the mod to the original poster. The thread ended with him needing to know if it was going to stand up to recoil. He did get the itt 4845 to focus after machining. adn the pictures of the increased gain were stellar. he never answered back about the recoil issue and i havent got an answer back from him on the recoil issue. I sent him an PM. Unfortunately the original seller was out of the kits.

I was a little disappointed. A kit for a 3+1 even if i have to pay a machinist would be awesome.

 

[GBMaryland]

So about 1 year or two ago there was a thread on arf.com about fitting the 3+1 into a pvs 4. it was a kit with a new switch casing and focus ring and itt f4845. I managed to piece two and two together and managed to track down the original seller without input from the buyer. Dont even ask how lucky or hard that was(depending on your point of view) but the main thing that came out of it is the retaining ring on the pvs four has to be machines flush with the case on the objective lens. It was a direct bolt on fit for a tvs five. I dont know whether this is true or not as i havent seen either in person. CJ was the one who explained the mod to the original poster. The thread ended with him needing to know if it was going to stand up to recoil. He did get the itt 4845 to focus after machining. adn the pictures of the increased gain were stellar. he never answered back about the recoil issue and i havent got an answer back from him on the recoil issue. I sent him an PM. Unfortunately the original seller was out of the kits.

I was a little disappointed. A kit for a 3+1 even if i have to pay a machinist would be awesome.

Interesting.

So the body of the PVS-4 and the TVS-5 is the same as far as I know. I've owned both at the same time. The primary difference is that the objective lens assembly is 155mm vs 95mm.

If you can see the PVS-4 in the picture, there is no room between the object side of the PVS-4 body housing and the objective lens.

 

[ghostwriter247]

Yes the bodies are the same. Cj talked a guy through modifying an pvs4 lens by machining the inboard lens retaining ring. The seller of the kit ( a different person) mentioned the pvs 4 had to b machined flush with the objective casing so I'm assuming, since I haven't seen either in person, that the lens retaining ring sits a bit above on the pvs 4 objective and the tvs five's lens retaining ring does not extend outside the back of the objective casing. It was a tiny bit to shave off a mil or two.

I wish I could source a kit. A 3 plus one tube in a pvs 4 that worked would be really cool.

 

[GBMaryland]

Yes the bodies are the same. Cj talked a guy through modifying an pvs4 lens by machining the inboard lens retaining ring. The seller of the kit ( a different person) mentioned the pvs 4 had to b machined flush with the objective casing so I'm assuming, since I haven't seen either in person, that the lens retaining ring sits a bit above on the pvs 4 objective and the tvs five's lens retaining ring does not extend outside the back of the objective casing. It was a tiny bit to shave off a mil or two.

I wish I could source a kit. A 3 plus one tube in a pvs 4 that worked would be really cool.

So you are saying that they machined the lip around the lens retaining ring to allow the extended size of the 3+1 tube to fit in the housing... and that the lip is likely not as pronounced on a 155mm objective for the TVS-5?

 

[ghostwriter247]

thats my guess, but i havent handled them. Here is the original thread where cj talks a guy through the kit and how it worked out. PVS-4 and ITT 4845 - AR15.Com Archive I managed to track down the seller from the photograph of the kit in the thread. This is his response

"The modification on those wired bodies (THE BATTERY PART) were done by the manufacturer. The modifications were few, relatively simple and would allow the use of glass input tubes, at least with the TVS-5 objective. The PVS-4 objective needs a slight modification, the lock ring for the most rearward lens cell need to sit flush to the back of objective housing."

He goes on to say he is out of the kits, but they were made as a bolt on replacement for the tvs 5s.

i havent actually handled them so i don't know for sure. Your understanding likely will be better than mine since you have one to look at.

As you can see from the thread. the modification to the rear retaining ring allowed it to work but the OP never got back to the thread on whether the clearance between the glass tube and the original lens stood up to recoil. So based on your picture. i would say there is simply more clearance in the pvs 5. if the sellers info is correct. I dont know if it needs to be flush, but the OP on arf did machine it and achieved focus with the new nonstandard bodies seen in the kit photos.

ANyway a neat bit of lore to add into the pvs 4 body of knowledge about the fable 3 + 1 tube.

I sent a pm to the OP about the recoil issue but i don't know if he doesn't frequent arf anymore, but he hasn't gotten back to me

 

[compasscall]

QUESTION 7: with Halo i understand that gen II tubes do not suffer from halo correct? or is that just a peculiarity of the pvs 4 gen ii tube? IT IS A PECULIARITY OF THAT TUBE ANSWERED

ghostwriter247,

Halation is present in ESI single proximity focused tubes, the ones used in both AN/PVS-4 and AN/TVS-5 systems as well as many others. Though halation is not as apparent in ESI single proximity focused tubes as it is in double proximity focused tubes, it is present. It's important to make the distinction here that halation in the 9644 tube results from the spacing between the MCP output and phosphor screen, this would be considered the secondary halo effect in a double proximity focused tube. The most likely source for info, at least that which is repeated and extrapolated on the inter web, regarding halation in ESI single proximity focused tubes (MX-9644 etc...) can be found in a collection of papers titled 'Selected Papers on Image Tubes. I've attached an excerpt from one of those papers below, the information should look familiar.

Halation in an MX-9644/UV image intensifier:



Excerpt on ESI tubes 'Selected Papers on Image Tubes':



Excerpt on 3+1 hybrid 'Selected Papers on Image Tubes':

 

[Travis S]

Holy cheese balls that's a lot of good info!

 

[compasscall]

So, my question for you is: how is the LAV-25A2 tube a drop in replacement for the TVS-5, but not the PVS-4? The base of the units (everything behind the objective lens) is the same... unless you have a 3 inch eye piece, which doesn't change anything really.

You've got me wondering.

For clarity sake, the LAV-25A2 gen III tube (P/N 510-7330-306) is not a hybrid, super inverter or 3+1, it is just a standard double proximity focused module with a fiber optic inverter. A hybrid 3+1 tube is not bigger than a typical MX-9644/UV tube and is nearly as light, the weight is way less than the 25mm fiber inverting tubes.

The following annotated images should help to put the puzzle pieces together for you, though it's not complete, it should provide you with an a-ha moment. ghostwriter247 was clearing a lot up for you as it was and hope this adds to his input.

Here you go:













*This will be a continually evolving post with more photos added as they are annotated.

 

[ghostwriter247]

Couldn't resist Vic's sale. Have a gen 3 unit on the way.

 

[huntler]

delete

 

[GBMaryland]

So, let me ask a follow-up for I2, IMS, MOD Armory, and Night Optics... When you say hand selected using the test set, I know what that means.

However, I'm curious as to if these current surplus PVS-4s are using the newer production MX-11620 tubes? Also, are later production tubes better than the earlier production MX-11620 tubes? (This seems to be how things have worked out with the 18mm variants now use in everything. Even when you talk about the product procedures for the normal filmed ones, for example.)

 

[compasscall]

So, my question for you is: how is the LAV-25A2 tube a drop in replacement for the TVS-5, but not the PVS-4? The base of the units (everything behind the objective lens) is the same... unless you have a 3 inch eye piece, which doesn't change anything really.

You've got me wondering.

GBMaryland

Did my followups answer questions or are you still wondering about the TVS-5 and PVS-4?

 

[GBMaryland]

You bet... it was very interesting to note!

 

[compasscall]

Good deal, both are very neat units!

 

[GBMaryland]

Update: TVS-5 Usage Expert

Just for the record, I get all my information on the TVS-5 from my expert!

 

[compasscall]

Just for the record, I get all my information on the TVS-5 from my expert!

Lol, inescapably obvious!