Thread: Thermals. Whats the point of no return.

I am not familiar with thermals but I believe it works the same way as digital cameras. That I have plenty of experience.

Width FOV is basically the reverse of optical magnification (ignoring hardware digital magnification for a minute). The number in Pulsar's model name appears to be focal length, which is one of the two things that affect FOV. The bigger this number the longer the focal length and narrower FOV / larger magnification. Vice Vesa.

The second thing that affects FOV is sensor size. For a given focal length, the larger the sensor, the wider the FOV. Pulsar dont directly state the sensor size of their products but it gives you resolution and pixel pitch. So you can get a idea of how big the sensors are relative to each other. For example XP50 is 640x480 at 17um, same with XP38. Therefore, XP38, with shorter focal length, must have wider FOV but less optical magnification compared to XP50. XQ50F has 384x288 pix. @ 17 µm, the sensor has same pixel density but few pixels therefore it is way smaller. This must mean XQ50 has narrower FOV compared to XP50. But because it is the same focal length, it does not have better optical magnification. (And because it has the same pixel density it also doesnt have better hardware digital magnification either.)

Aperture size does not affect either FOV or magnification. Aperture affects how much light is let in. The larger the aperture the more light comes in, resulting in better image. However, aperture works in cohort with focal length. It is the ratio of focal length vs aperture that affects how much light is focused/projected onto the sensor. XP50, XQ50, XP38 all have F ratio at 1.2 so they should all pass on same amount of light to the sensor plane. It should be noted that XP38's aperture is indeed smaller at 38/1.2 = 32mm, vs XP/XQ50's 42mm. It should also be noted that XQ50 has a smaller sensor to receive light compared to XP50 even though their optics were able to deliver the same amount of light. XQ50s' sensor, being about 35% the size, only receives about 35% as much light as XP50.

There is yet another thing that gets added into the equation. The new XM line uses sensor with smaller pixel size - 12um. This increases hardware digital magnification by putting more pixels on the same given area of projected optical image. But because the sensors have even less overall pixels, there is a significant sacrifice of FOV. XM's 320x240 12u sensors is about 1/8 the size of XP50's 640x480 17u. You can imagine how much FOV is cropped off.

Ideally you want a sensor that is large physically and have small pixels, thus have high resolution. If they can make the XP50 sensor go from 17um to 12um, it would end up with about twice the resolution around 960x640. As to why we dont have something like that, my guess is that: 1. the fabrication technology for large high density thermal sensor is still expensive. 2. more pixels = more circuitry = more heat = worse image.

Maybe it is the security concerns involved with thermals, thermal tech development seems to have been limited to only a few small time players. It has been quite slow compared to other similar areas where expanding size and density has been the goal. For example CPU, GPU, bayer CMOS sensor, OLED, AMOLED, etc. Just compare the image quality from your phone today to what it was 5 years ago or 10 years ago. in comparison thermal scopes seem to be stagnating. they just change around different trade-offs.