Why doesn’t nightvision have optical zoom?
- Thread starter Sniper308
- Start date
Ratsbadboy
Well-Known Member
As I understand it it's purely down to the weight and cost of the lens itself. There already is optical zoom night vision units in the form of rear add ons, the Pard NV007 comes to mind where the unit simply looks at the reticle and the zoom is done via the lens (I know the 007 has digital zoom but nobody in their right mind uses it).
Makes sense, you're zooming in on a tv screen rather than the actual object I suppose
Yes. If you put the device at the rear, behind the day scope, the day scope can do the magnifying as usual.
But if the device is at the front, or is a standalone weapon sight, all the "zoom" can do is magnify part of the display.
The more pixels there are in the display, the longer it takes for the image to degrade, but you will never see more information than you get at the native magnification if the device.
But if the device is at the front, or is a standalone weapon sight, all the "zoom" can do is magnify part of the display.
The more pixels there are in the display, the longer it takes for the image to degrade, but you will never see more information than you get at the native magnification if the device.
Bavarianbrit
Well-Known Member
The old Photons scopes were upgraded by folk on the nightvision forum with M42 threaded camera lens to improve what the digi sensor was seeing. An 80-135 camera zoom lens might work there.
BenBhoy
Well-Known Member
It could be done but I'd bet you wouldn't pay the money they would need to charge for a digital scope to have optical zoom
You can have optical zoom on an NV spotter (e.g PARD NV019)
But if you put an SLR type zoom lens in front of a digital sensor it will not hold zero throughout the full range of magnifications the lens can produce
As has been said, when the Yukon Photon appeared, some clever guys figured out that the existing 50mm objective lens (x5 magnification) could be replaced with an SLR zoom lens with the same thread (Probably M42)
There was a bit of a rush to buy zoom lenses with focal lengths up to around 135mm
At 135mm the magnification of the Photon was around x14 - and no pixellation - great!!!
The problem was that the scope could only be zeroed with the lens at one selected focal length. As soon as the focal length was changed, the zero shifted
And therin lies the root of the problem - making a zoom lens that holds zero throughout its full range of focal lengths
Holding zero is not a feature required of camera lenses so they continue to be produced at reasonable prices
Nerdy bit coming up - so avoid if you wish
Most digital scopes (day/night and thermal) have objective lenses that can be adjusted to get a focussed image at different distances
If you look closely, as the focus ring is turned, the lens moves backwards and forwards - but does not rotate.
Also, these are fairly simple lens assemblies with only 2 or 3 elements, so as long as there is no rotation of the lens elements relative to each other or to the sensor they can be made relatively economically with no noticeable change of zero as the focus is adjusted
Zoom lenses are much more complicated - they have anything up to 11 or 13 glass elements, some of which rotate relative to each other as the focal length of the lens is varied
If we imagine a single light ray from the centre of a target entering the exact centre of the front of the first element of the lens assembly then, if the lens is perfect, that light ray will exit from the exact centre at the rear of the lens and then enter the exact centre of the next lens in the lens assembly. If the second lens is perfect, the light ray will exit the exact centre of the rear of that lens. That process would be repeated through each element of the lens assembly with the light ray eventually exiting the exact centre of the final element of the lens assembly and then hitting a single point on the sensor
Unfortunately perfect lenses don't exist (although you can pay a lot of money to get them arbitrarily close to perfect) so that the light ray exiting each lens element will not be in the exact centre of the lens and not at exactly 90 degrees to the axis of the lens. That means that the light ray enters the next lens slightly off axis and that error will increase as the light ray passes through more and more elements
If the individual lens elements do not rotate relative to each other, it is possible to get the errors in each lens to somewhat cancel out leaving only a very small fixed error when the light leaves the final element of the lens
When individual lens elements rotate relative to each other, all bets are off because there is no way to know exactly where a light ray coming out of a lens that rotates will actually enter the next element in the lens, making impossible to know where a light ray entering the front of the lens will actually hit the sensor when it exits the lens
For digital scope manufacturer, the choice is either an extremely expensive optical zoom lens or digital zoom which costs nothing to implement
You don't have to be Brain of Britain to know which option they all choose
Cheers
Bruce
Rear add-ons like the PARD 007 use the scopes optical zoom to magnify the target
As you correctly said the 007 does have digital zoom, but, IMHO it serves no purpose
Cheers
Bruce
Digital scopes all have a built in limit in terms of how much detail they can display
That limit is simply the size of a sensor pixel divided by the focal length of the lens. The answer to that simple calculation is an angle, but an easier way to think about it is to ask what area can a single sensor pixel "see" at a given distance
For example, a thermal scope has a sensor with 12 micron pixels (the number of sensor pixels is not relevant) and a 50mm lens
At a distance of 100m, a single sensor pixel "sees" as square with sides 24mm long ((12/50)*100))
In comparison a HIK Alpex 4k has a sensor with 2 micron pixels and a 50mm lens so, for the Alpex at 100m a single pixel "sees" a square with sides 4mm long ((2/50)*100))
In other words, because the Alpex 4k sensor pixels are 6 times smaller than the thermal pixels, the Alpex 4k image is 36 times more detailed than a thermal scope with the same size objective lends
Glass scopes don't have that type of limit on how much detail they can display and any decent variable magnification glass scope viewing a target at 100m will see detail much smaller than a 4mm square
Cheers
Bruce
That limit is simply the size of a sensor pixel divided by the focal length of the lens. The answer to that simple calculation is an angle, but an easier way to think about it is to ask what area can a single sensor pixel "see" at a given distance
For example, a thermal scope has a sensor with 12 micron pixels (the number of sensor pixels is not relevant) and a 50mm lens
At a distance of 100m, a single sensor pixel "sees" as square with sides 24mm long ((12/50)*100))
In comparison a HIK Alpex 4k has a sensor with 2 micron pixels and a 50mm lens so, for the Alpex at 100m a single pixel "sees" a square with sides 4mm long ((2/50)*100))
In other words, because the Alpex 4k sensor pixels are 6 times smaller than the thermal pixels, the Alpex 4k image is 36 times more detailed than a thermal scope with the same size objective lends
Glass scopes don't have that type of limit on how much detail they can display and any decent variable magnification glass scope viewing a target at 100m will see detail much smaller than a 4mm square
Cheers
Bruce
I have read with inerest Bruce’s reply’s and can sum up in layman’s terms.
Because it doesn't. Suck it up.
Because it doesn't. Suck it up.
If you want optical zoom on night vision get a Ludicrous Lumens or a PVS14, attach to an appropriate day scope and you can optically zoom to at least 20x with NO pixilation.
Same as you can do with a PARD 007, Sytong HT66 or any number of home made rear add-ons
You don't need to spend a huge amount of money to get optical zoom from an optical scope with a rear add-on, because the optical scope is doing all the optical zooming - just like it does in daylight
The difficult and expensive part is replacing the fixed focal length lens of a digital scope with a variable focal length lens that keeps zero throughout its zoom range
Cheers
Bruce
Indeed, but the image produced by a Pard is no where near as good as a PVS14 or the Vulpine MK3. I say that having owned and used all 3
Cheers
Nick
I didn't mention image quality (which is somewhat subjective anyway) - I was merely saying that any rear add-on can use the scopes optical zoom to enlarge the target seen in the add-on without pixellation
Cheers
Bruce
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