Hi

Can you educate me on a few things with regards to this unit...

Does it have 10 degree FOV? This would mean its about 3.5x mag am i right? So does the day scope magnify an already magnified image? Am i right in saying the maximum FOV will be 10' regardless of scope used?

Well, no one else is replying, so I'll add some info.10 degrees is the FOV, but 1x is the magnification. This means, theoretically, that the angular resolution will be approximately the same as a PVS-14 when used with a 4x dayscope, although it's probably closer to 3x or thereabouts due to loss of image field on the tube.It also suggests that around 8x dayscope magnification is the effective limit of the PVS-27.Clipons don't have magnification - that's left up to the dayscope.

Regards
David. 

Im pretty sure it is 3x.

What the unit seems to do then is convert the 3x FOV back down to 1x on the back end which allow the day scope to see a true 3x image. This is the only way the unit can get to 20x optical. Pixelation occurs at the very top end on this unit regardless of illumination because what you are magnifying is the phosphor screen.

I can also tell you that 8x is nowhere near the limit of this unit. With Zero illumination you can get 16-18x without any serious image degradation.

I'm not going to argue issues about maximum magnifications here - it's entirely subjective. I just hold the equipment to a higher standard of performance than you're doing. If you're happy with 20x magnification, that's fine.

You are misunderstanding magnification here with angular resolution. The PVS-27 has a higher angular resolution than a PVS-14, for example. That's not magnification.

If you take a PVS-27 and look through it, without your day scope, you can see right through it like it's just got a piece of green glass in it - there's no magnification.

Magnification is the ratio of the objective lens focal distance to the ocular lens focal distance. ie, Objective/Ocular 

What ever scientific terminology is correct here there is a system magnification which seems to be around 3x. When you look down the 27 you can see the tube image like in a pvs14 it just looks really far away. All these front systems have their own FOV the higher the FOV the lower the magnification which is possible with the day scope. My bet is that if you looked at the back of the tube on a 27 it would would like near enough the same as a PVS14 with a 3x lens on the front give or take.

At 20x i can shoot a black spot off one of those shoot and see black/yellow targets on a cardboard box at 100 yards with no illumination on overcast night. A 3 inch shoot and see target is even easier.

If I look down a toilet paper tube it has a 10 degree field of view. and no magnification.
In the sense you are using it filed of view has nothing to do with magnification

Except that the PVS27 can handle much higher magnification than say the PVS22. It has nothing to do with light gathering either since i can use illumination to make up any loss of light.

If a PVS14 can get a 40 degree FOV off a small lens then why would a PVS27 need a 95mm cat lens? There must be magnification of the image on to the tube which gives a 10 degree FOV. If this wasnt the case then you would lose most of the detail even on 3x with the day optic.

I think that it puts 3x in the front on to the tube optically like a normal NV unit would and then in the back of the unit it uses some optical solution to give a 3x day optic a 1:1 conversion so there is no loss of resolution.  This is why they say 3-20x magnification on the FLIR spec sheet for the unit. There is no way you can get to 20x from a unit like the K-A UNS which doesnt look like it has any front end magnification regardless of light available.

But unlike a toilet roll tube you have to fill the PC with light focused on to the image.

If this was the case then you could just use a collimated PVS14 and put it in front of a day scope without any need for the PVS27 and get 1-20x magnification and get 40 degree field of view and with no weight penalty.

The 40deg of a PVS-14 is equally 1x as with clip ons. 40deg worth of image streched onto the cathode & phosphor equals less resolution per degree compared to a 10deg FOV.

Hi ZeroFX,

The challenge here is that you're confusing the terms, and this seems to lead you to misunderstand how that information is applied. The correct aspect of what you appear to be looking for is angular resolution.

This will tell you what kind of image you're going to get at different ranges with different equipment - especially when you mix in lens speed to the equation.

FOV is useful also, but only as a maximum value, and it's important to remember that not all clipons use the full angular resolution capabilities of the tube either. Anyway, you can't exceed the maximum FOV of the system - it will always be the lowest of any one component.

David.

Im not sure of the terms to describe what is accurate. But answer me this if you can. If i could fit a PVS14 eye piece to the back of the PVS27 instead of the rear lenses. Would i get a similar image as a pvs14 with a 3x magnifier on the front?

Not at all.

The objective focal length of the PVS-27 is 91mm. The ocular focal length of a PVS-14 eyepiece is 25mm. The raw magnification is 91/25 = 3.64x - A bit higher than the 3x magnifier. But this magnification only exists with the PVS-14 ocular.

With the 91mm eyepiece installed, the magnification is 91/91 = 1.00 Magnification.

This means that with dayscope magnification above 3.64x, resolution and image quality is lost relative to the PVS-14. After 8x, more than half the resolution is lost - and the detection and identification range doesn't change.

FOV is 10 degrees. At 3.64 reduction in FOV relative to a 40 degrees monocular, it should be 11 degrees, so we know some peripheral vision is lost to the mechanical structure inside the PVS-27 though it's still pretty good.

Let's assume that you have 10/11ths of a 64 lp/mm tube, with maximum contrast, at 91mm focal length - which is pretty much what you do have.  That's a resolution at best of around 0.00434 degrees. Or about 4cm@500m. AT BEST. 

This is the same whether you have a 4x scope or a 20x scope. It doesn't change. All you do is lose FOV as magnification increases. 

Of course, that's theoretical - In practice, you're closer to around 10 to 20 cm resolution at 500m, due to optical losses and other losses, assuming a really bright night - but that's quite acceptable.The PVS27 is quite an impressive clipon.

Regards
David

Update: Here's how to calculate FOV, basically from the objective lens focal length and usable tube diameter. If you open a spreadsheet and put in the formulas given, it should word - 
Attached File

Forgive me for dumbing this down then but im guessing i was right then when i said that you get 3.5x (3.64x) on the front of the 27 going in to the tube and they then reduce this down the back end of the unit to back down to 1x so the day scope which starts at 3x gets a true 3x image optical magnification...

That would be correct. You could say the PVS14 has objective lens magnification too, and then it "reduces" it back to get a unity magnification through the unit. Peek there with a 3x scope and you do get a real 3x magnification though the resolution will be bad because of all the lost FOV, all the lost angular resolution compared to a 27.

It's not that you can't look at a PVS-27 as having 3x the magnification of a PVS-14 - it's just that the actual magnification is 1x for both and it's important to remember this.

I get that the PVS-27 has three times the resolution, and your're thinking of this due to the front lens magnification in a traditional sense, but thinking of it as magnification instead of resolution is going to result in confusion from time to time - Otherwise how are you going to compare scopes when the magnification is specified?

Confusion seems common on front mounted units.

For me its logical to think of it as magnification since that resolution comes at the expensive of FOV. For me if i increase resolution then i expect smaller pixels or some other system to enable the increase. The PVS27 gets that resolution using optical magnification rather than higher tube lp/mm or some other system.