What Does All This Thermal Jargon Mean

Kirsch

Active member
I am not a camera or lens expert. I have played around with enough thermal to know what works and doesn't work for me. I used to be one of those people who said, "why doesn't XYZ company just have a base mag of this or FOV of this and it would be great. Well hopefully after reading this you will have a better idea of why.

Have you ever wondered why for instance the Pulsar XP line has a large field of view and low base magnification while the Pulsar XQ line has a smaller field of view and higher magnification. It is due to the 640 core vs 384 core. Or, why the new Pulsar Thermion and Axions have a high base mag and smaller FOV? It is mainly due to moving to 12 microns.

However, how this all works together is explained pretty well Here

Here are the keys to take from that post plus a little extra added by me:

Higher Focal Lengths mean higher magnification and less FOV. Larger diameter lenses will have higher focal lengths.
Pulsar XP50 (50mm focal length) has higher magnification (1.6x) and less FOV (12.4x9.3) than a XP38 (38mm focal length) with 1.2x base mag and FOV 16.3x12.3. The same is true of the XQ50 and XQ38 as well.

Flir PT536 (50mm focal length) has higher magnification (4x) and less FOV (4.5° × 3.5°) than a PTS233 (19mm focal length) with 1.5x base mag and FOV 12° × 9.5°.

Larger sensors increase FOV:
Pulsar Trail XP38 and XP50 which have 640x480 sensor have a larger field of view compared to the XQ line which has a 384x288 sensor. For example, the Pulsar XP50 (640 core) has a FOV of 12.4x9.3 while the Pulsar XQ50 (384 core) has a FOV of 7.5x5.6. Both the XP50 and the XQ50 have the same objective size of 42mm and the focal length of 50mm. It is only the sensor that changed.

Lower micron level (12 vs 17 for instance) equates to more magnification and less fov with same objective.
Pulsar Thermion XM38 (12 micron) has a 4x base mag and 5.8x4.3 FOV while the Pulsar XQ38 (17 micron) has a base mag of 2.1x base mag and 9.8x7.4.

Many people may ask why is Pulsar moving from the Trail 384 core 17 micron core and moving to a 320 core 12 micron with the Thermion and the Axion. 12 micron technology delivers more magnification from the same lens used on a 17 micron thermal core. This can lead to more magnification with less expense (objective size).

The number of the scope doesn't always equal the scope objective size:
Pulsar - Uses the focal length for their scope number. XP50, and XQ50 have objective sizes of 42mm and focal length of 50mm while the XP38 and XQ38 have an objective size of 34mm and focal length of 38mm. It is the f/1.2 aperture that results in a higher focal length number

Flir - Focal length and objective sizes are the same as they use a f/1.0 lens vs f/1.2, PTS233 (19mm focal length and objective size), PTS536 (50mm focal length and objective size) and PTS736 (75mm focal length and objective size)

What does a larger objective provide: Larger lenses (have higher focal lengths) are more sensitive at collecting light, IR etc. It leads to scopes that can see further and provide clarity at distance. It can also help combat things like humidity. So, does bigger always mean better, no. It typically means more expensive because the germanium lens is very expensive to build. A great example is a Flir PTS736. It has a very narrow field of view. It is a great 300 yard+ thermal scope, but isn't a great solution for someone hunting in a lot of cover with limited range.
 

Great information, Kirsch. That certainly helps better understand all the technical data. It is confusing sometimes and most of us have limited experience with these high dollar toys. Information like this can be a great help in trying to assess a hunter’s needs in the particular area where he / she hunts. Thanks for this.
 
Humidity is always the worst to deal with any uncooled VOx microbolometer.

Here in Florida, humidities may get down to 25% during a dry cold front during the winter, but rest of the time are 50-100%, much different in many interior Mid-West and Western states with humidities down to 5%.

In spite of the high humidities we experience here, I always go for a WFOV thermal since we are not shooting out past 200 yards 95% of the time and always want more FOV for picking up targets, especially after the first shot when they are on the run.
 
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