Upgrade to a Thermal Scope or Wait for Better Resolution

[Clive Ward]

If you've not had experience of a decent thermal rifle scope, then you will never see the attraction. Especially if your point of reference is a consumer type 'spotter'.

For the long range shooting we do here in the UK, IFOV as explained by Bruce is very important. When I got into thermal shooting many years ago, I completely bypassed the units available at the time and went straight for 75mm / 17 Micron combo. With that combination you can easily 100% identify a fox at 300 yards. Not as a foxy shaped 'blob', but as an actual fox.

Sensitivity is also very important. Instead of seeing a silhouette of an animal you can see the heat detail of eye sockets, ears, etc.

Things are getting better and we have 12 micron units coming into production scopes now. This brings new challenges because the resolution of the thermal core is now better than the resoution of the lenses used in rifle scopes (moving element). We've done a lot of testing and unfortunately 75mm might have a calculated IFOV of 16mm, but in practice it can never resolve this detail due to resolution loss in the lens system and shows no more detail than a smaller lens. The only solution to this is to have a completely fixed lens, that you then cannot adjust focus.

Touching on lens quality. You can also have two thermal scopes with the same identical FPA and the scope with the smaller lens will resolve more detail due to higher precision in the lens system.

After lots of testing and lens designs, the very best, next step we have managed to achieve is a 'true' IFOV of 21.8mm

Not a massive leap, but we're using the latest military spec 12 micron shutterless core with <40mK sensitivity. Also a very precise F1 lens system and a large 1024x768 OLED display. It should be the very best image available for quite some time to come yet.

The upside is we can now produce a better scope with better image than a 75mm in a smaller package at a lower price. Exciting times.


Cheers





Clive


Cheers





Clive

 

[mealiejimmy]

OK, we've discussed resolution and magnification in thermal devices, but maybe we should discuss thermal imagings "dirty little secret" - aka Non Uniformity.
I say it's thermal imagings "dirty little secret" because it's almost never mentioned in any promotional material for thermal imagers and in few manuals supplied with thermal imagers
Users of Pulsar thermal (and most other brands) will be well accustomed to that annoying click and the image freezing for a couple of seconds when you have the calibration set to auto
During "calibration" the device is trying to minimise Non Uniformity.
So, what's Non Uniformity?
In a perfect thermal sensor, if all the pixels receive exactly the same amount of heat, they would all produce exactly the same electrical signal.
In reality, that doesn't happen - when all the pixels receive exactly the same amount of heat, they all produce slightly different electrical signals, and worse, even if that level of heat input remains the same for a period of time, the signals at the output of each pixel will not only be different, but they will also change with time.
This variation in output for the same input is Non Uniformity, and before any thermal imager can produce a decent image, the problem of non uniformity has to be tackled.
Non Uniformity in the type of thermal sensors used in spotters and scopes cannot be eliminated, but it can be temporarily reduced to a level which results in a usable image.
Maybe a good analogy to explain the effects of non uniformity is to imaging yourself looking at the outside world through a window.
If the window is clean you get a good view of the world, but if the window is dirty, your view of the world becomes less clear.
You can think of non uniformity as being the dirt on the window - the more non uniformity , the less clear the image.
Keeping the window clean enough to get a reasonable view of the world is what we call Non Uniformity Correction or NUC and there are plenty of thermal videos on You Tube where phrases like "how is it NUC'd", or "I NUC'd it before I took the shot" can be heard
The two methods of NUC used in thermal spotters and scopes are known as "calibration" and "shutterless", with calibration being much more common.
AFAIK, other than PARD and the thermal scopes sold by the Night Vision Store, all the other brands of thermals available on the UK market use calibration as their method for reducing Non Uniformity.
So, when a thermal imager "calibrates" what actually happens?
Firstly a shutter moves in front of the thermal sensor to prevent thermal radiation from the outside world reaching the sensor - that's the clicking sound.
The shutter is normally a thin, matt black coloured slice of aluminium, and as well as blocking thermal radiation from the outside world, the shutter itself acts as a uniform source of thermal radiation.
With the shutter in place and all the sensor pixels now receiving the same amount of thermal radiation, the electronics in the thermal resets the output signal of every pixel to the same value, so that we now have a situation where each pixel is receiving the same amount of heat and producing the same signal.
That process of resetting the output of every pixel is not instantaneous, and this is the source of the time delay that happens when the thermal calibrates.
It's fair to say that the image produced by a thermal which uses calibration to carry out NUC is at it's best immediately after calibration but will inevitably degrade with time.
When calibration is set to automatic, the thermal will decide when calibration is required, but when set to semi- auto or manual, the user decides when to calibrate.
When set to automatic calibration, the thermal may calibrate several times in short succession after it's switched on and whenever scanning the thermal introduces or removes large hot or cold items from the field of view (e.g nearby cattle)
Clearly, when set to auto, there is a possibility that the thermal will decide to calibrate just as the trigger is about to be pulled, so some thermals now include a count down timer display to warn the user that calibration is going to happen.
As the name suggests, thermals which use the "shutterless" method of NUC don't have a shutter and don't "calibrate" in the way described above.
Rather, NUC in a shutterless thermal is a continuous process programmed into the firmware - and that's about as much as I know of the detail of how it works
In practice, shutterless clearly has the advantage that you never hear that annoying click and the image never freezes, so there is no possibility of a shot being lost or missed because the thermal decided to calibrate.
The downside to shutterless is that the image quality is not as good as a thermal which has just calibrated.
However, the image quality on a thermal that calibrates, degrades with time, while the shutterless image quality does not change
I own and use thermals which NUC using both methods, and I really don't have a preference for either method and I certainly would not make it a deal breaker when choosing a thermal.

Cheers

Bruce

 

[Blackwood Outdoors]

OK, we've discussed resolution and magnification in thermal devices, but maybe we should discuss thermal imagings "dirty little secret" - aka Non Uniformity.
I say it's thermal imagings "dirty little secret" because it's almost never mentioned in any promotional material for thermal imagers and in few manuals supplied with thermal imagers
Users of Pulsar thermal (and most other brands) will be well accustomed to that annoying click and the image freezing for a couple of seconds when you have the calibration set to auto
During "calibration" the device is trying to minimise Non Uniformity.
So, what's Non Uniformity?
In a perfect thermal sensor, if all the pixels receive exactly the same amount of heat, they would all produce exactly the same electrical signal.
In reality, that doesn't happen - when all the pixels receive exactly the same amount of heat, they all produce slightly different electrical signals, and worse, even if that level of heat input remains the same for a period of time, the signals at the output of each pixel will not only be different, but they will also change with time.
This variation in output for the same input is Non Uniformity, and before any thermal imager can produce a decent image, the problem of non uniformity has to be tackled.
Non Uniformity in the type of thermal sensors used in spotters and scopes cannot be eliminated, but it can be temporarily reduced to a level which results in a usable image.
Maybe a good analogy to explain the effects of non uniformity is to imaging yourself looking at the outside world through a window.
If the window is clean you get a good view of the world, but if the window is dirty, your view of the world becomes less clear.
You can think of non uniformity as being the dirt on the window - the more non uniformity , the less clear the image.
Keeping the window clean enough to get a reasonable view of the world is what we call Non Uniformity Correction or NUC and there are plenty of thermal videos on You Tube where phrases like "how is it NUC'd", or "I NUC'd it before I took the shot" can be heard
The two methods of NUC used in thermal spotters and scopes are known as "calibration" and "shutterless", with calibration being much more common.
AFAIK, other than PARD and the thermal scopes sold by the Night Vision Store, all the other brands of thermals available on the UK market use calibration as their method for reducing Non Uniformity.
So, when a thermal imager "calibrates" what actually happens?
Firstly a shutter moves in front of the thermal sensor to prevent thermal radiation from the outside world reaching the sensor - that's the clicking sound.
The shutter is normally a thin, matt black coloured slice of aluminium, and as well as blocking thermal radiation from the outside world, the shutter itself acts as a uniform source of thermal radiation.
With the shutter in place and all the sensor pixels now receiving the same amount of thermal radiation, the electronics in the thermal resets the output signal of every pixel to the same value, so that we now have a situation where each pixel is receiving the same amount of heat and producing the same signal.
That process of resetting the output of every pixel is not instantaneous, and this is the source of the time delay that happens when the thermal calibrates.
It's fair to say that the image produced by a thermal which uses calibration to carry out NUC is at it's best immediately after calibration but will inevitably degrade with time.
When calibration is set to automatic, the thermal will decide when calibration is required, but when set to semi- auto or manual, the user decides when to calibrate.
When set to automatic calibration, the thermal may calibrate several times in short succession after it's switched on and whenever scanning the thermal introduces or removes large hot or cold items from the field of view (e.g nearby cattle)
Clearly, when set to auto, there is a possibility that the thermal will decide to calibrate just as the trigger is about to be pulled, so some thermals now include a count down timer display to warn the user that calibration is going to happen.
As the name suggests, thermals which use the "shutterless" method of NUC don't have a shutter and don't "calibrate" in the way described above.
Rather, NUC in a shutterless thermal is a continuous process programmed into the firmware - and that's about as much as I know of the detail of how it works
In practice, shutterless clearly has the advantage that you never hear that annoying click and the image never freezes, so there is no possibility of a shot being lost or missed because the thermal decided to calibrate.
The downside to shutterless is that the image quality is not as good as a thermal which has just calibrated.
However, the image quality on a thermal that calibrates, degrades with time, while the shutterless image quality does not change
I own and use thermals which NUC using both methods, and I really don't have a preference for either method and I certainly would not make it a deal breaker when choosing a thermal.

Cheers

Bruce

Sensor cost is identical nearly for both options, 90% of the large manufacturers choose the shuttered option for monoculars and rifle scopes for a reason, It produces a better quality image rather than a software based approach like you say Bruce.

 

[RichardAllen]

To summarise, thanks to mealiejimmy I have found that if you want the step change thermal scope, you can get it in the shape of the FXG50 add-on. I have a F455 NV add-on and although add-ons are a bit cumbersome, they are flexible if you don't want a dedicated rig.

There is a Thermion XG50 dedicated scope, which would be my preference for a dedicated night shooting rig, but that Thermion is currently only available in the US, apprently due to export restrictions.

 

[RichardAllen]

Should have added, many thanks to Clive too.

 

[Clive Ward]

I've done the comparisons with current shuttered and shutterless cores in mass produced thermal rifle scopes.

The shuttered core exhibited noticeable and increasing noise almost immediately after fresh calibration, whereas the shutterless core exhibited almost no noise at any time and had a much better image.

With the higher end shutterless thermal cores used in our own scopes such as the T-Ceptor...there is no noise.

In terms of cost. Shutterless cores are more expensive. this is mainly due to the licence fee that has to be paid to the patent holder and also the increased value of the finished core due to the feature.


Cheers





Clive

 

[Freeforester]

Sensor cost is identical nearly for both options, 90% of the large manufacturers choose the shuttered option for monoculars and rifle scopes for a reason, It produces a better quality image rather than a software based approach like you say Bruce.

Some context, courtesy of Bruce (himself also a shutterless scope user) in case anyone missed the nub of the matter:

"In practice, shutterless clearly has the advantage that you never hear that annoying click and the image never freezes, so there is no possibility of a shot being lost or missed because the thermal decided to calibrate.
The downside to shutterless is that the image quality is not as good as a thermal which has just calibrated.
However, the image quality on a thermal that calibrates, degrades with time, while the shutterless image quality does not change
I own and use thermals which NUC using both methods, and I really don't have a preference for either method and I certainly would not make it a deal breaker when choosing a thermal."

Cheers

Bruce"

 

[Freeforester]

I've done the comparisons with current shuttered and shutterless cores in mass produced thermal rifle scopes.

The shuttered core exhibited noticeable and increasing noise almost immediately after fresh calibration, whereas the shutterless core exhibited almost no noise at any time and had a much better image.

With the higher end shutterless thermal cores used in our own scopes such as the T-Ceptor...there is no noise.

In terms of cost. Shutterless cores are more expensive. this is mainly due to the licence fee that has to be paid to the patent holder and also the increased value of the finished core due to the feature.


Cheers





Clive

You better tease out 'noise' in this matter, Clive, in case someone doesn't understand?

 

[Clive Ward]

You better tease out 'noise' in this matter, Clive, in case someone doesn't understand?

Noise as in fixed pattern noise.

On a shuttered thermal this presents as static often vertical lines. It's often referred to as the net curtain effect. If you are in manual mode it will gradually increase until the image is completely unuseable and obscured by the noise.

On a shuttered thermal the fixed pattern noise is seen as slight differences in adjacent pixels, so looking at a uniform background, pixels might not all be the exact shade of grey. On the latest shutterless cores, this difference in pixel values is almost or completely undetectable, hence no noise. Even if there is some noise in a shuttered core, against a normal image then again it's impossible to see.

I personally much prefer a shutterless core. I have used a rifle scope with a shutter calibration. I had to turn off the automatic calibration for obvious animal welfare reasons and use the manual calibration. It soon got very very old to have to press a button on the scope to calibrate it for every shot. A bit like using NV and having to turn your IR on every time. Not a massive thing, but soon gets tedious when you are used to not having to do it.

I even use a shutterless spotter now. When there is a lot of ground to cover, again a freezing thermal gets tedious having to rescan an area.


Cheers





Clive

 

[Mr. Gain]

My buddy and I have been thermal spotting for 4 years and ID is still an issue over 100 yards unless you can wait for ages for definitive movement. Our best one was a certain sighting of a badger at approx 120 yards moving gently along. When we moved up to about 80 yards, it stuck it's head up - we had been spotting the arse end of a fallow buck grazing in a dip ! Still not a fox though.

Well that was a learning experience right there! Admitting your limitations when it comes to IDing animals with thermal is a valuable thing. To be fair, my comment was about riflescopes, and riflescopes tend to set the bar higher than spotters in any case, since the primary role of a spotter is detection, not identification. Moreover, "not top-end" is not the same as "any spotter". All that said, however good your gear, when you can't see the whole animal, sometimes you just have to wait, or move, until you can.

 

[Cyres]

I have been using an XQ38F for 5 years and if the animal is moving then with experience its possible to make identifications. Issues are when something is still and clamped down. Using my Zeiss and red LED does help but even that at times does not provide adequate visulisation. Recently I upgraded to a Yukon N470S Sightline. This has been a revelation and foxs at 200 yds are clearly visible with the on board IR. In the last cople of months two cats have had lucky escapes as correct identification was possible through the the NV. I have looked through a Thermilion and was mighty impressed with the image quality but they are very serious money and I rather upgrade my spotter and stay with the Sightline.

D