I know you've gone through it before Bruce but could you give a quick guide on what to look for in a thermal scope, what the numbers mean basically! I'll be using it on CF for fox up to 250yds max, usually around 150yds.
Thanks
Sorry, it's taken me so long to reply.
As Ian says, the numbers don't tell you everything about a thermal scope.
Some scopes with what appear to be very good specs don't produce an image nearly as good as cheaper scopes with lesser specs
However, I'll give it a go based on foxing out to 250 yards.
The first part of the equation is the objective lens.
Bigger lenses (i.e longer focal length and lower f number) are always better for shooting small targets at long range and in your case you'll need a minimum of 50mm and more if you can afford it.
The f number (aperture) should be f1.0 and definitely no higher than f1.2
The second part of the equation is the sensor.
Sensors are more difficult to specify because different elements of a sensor specification have different effects.
There are 3 elements to consider:
Pixel size - 12 micron or 17 micron in the current market
Number of pixels (resolution) - typically 640x480, 640x512 (pretty much the same), 384x288, and 320x240
Temperature sensitivity (NETD) - 50mK is OK, but the best sensors are now down at 35mK and even 20mK - lower is better and will provide more in target detail and more importantly, give improved background detail in poor thermal conditions (high humidity/mist/fog)
The level of size detail (not temperature detail) i.e the smallest thing a single pixel can detect depends only on the size of the pixels and the focal length of the lens.
Pixel size and lens focal length are what effectively sets the detection range.
Smaller pixels and longer focal length lenses result in longer detection ranges
So, a 12 micron sensor with a 50mm lens will, in theory, provide a more detailed image of a target and have a longer detection range than a 17 micron sensor with a 50mm lens.
Note that the number of sensor pixels is irrelevant.
A Thermion XQ50 (17 micron 384x288 sensor)has exactly the same detection range and can show the same level of size detail as a Thermion XQ50 (17 micron 640x480 sensor)
However, the XQ50 has higher magnification and a narrower field of view than the XP50
Basically, smaller sensors lead to higher magnification and narrower field of view
The third part of the equation is the display.
OLED/AMOLED and FLCOS are the common types, with AMOLED/OLED generally regarded as superior.
Display resolution is typically 1024x768 for AMOLED/OLED and 1280x960 for FLCOS
The big thing that does not appear in any spec sheet is how the signal produced at the sensor is processed before it goes to the display.
Every manufacture has their own proprietary signal processing algorithms and may even have different algorithms for different models in their range.
It's also the case that 2 people can look at one thermal and one will like the image it produces, while the other person can look at the same image and dislike it intensely.
It's also the case that once you have used a thermal for a while you become accustomed to the image and when you look at another thermal with different signal processing you might not like the image it produces, even although it is a higher spec model.
OK, after that long preamble, I guess you'll want suggestions for a thermal scope for CF foxing out to 250 yards.
I don't know your budget, but there are several scopes that will do the job:
Low resolution (12 or 17 micron, 384x288)
Pulsar Thermion 2 XQ50
Rico RL42 (just)
Guide TS450 (400x300 17 micron sensor)
T Ceptor Pro 55-3
High resolution (12 or 17 micron 640x480/640/512)
Pulsar Thermion 2 XP50
HIK Micro Thunder TQ50
T Ceptor Pro 55-6
Cheers
Bruce
