I have been looking to buy yet another thermal. What is the advantage of the larger objective when it comes to thermals? What does getting a 35mm get you that a 25mm doesn't?
The larger objective helps under a similar theory as a day scope: the larger the objective, more return is allowed to reach your sensor plate for processing. Where it differs is that the pixel pitch of that plate (all else being equal) has as much to do with what gets processed and seen at the eye end. In this case, SMALLER pixel pitch (12um vs 17um) is better, as there are more sensors on the same sized array, if they’re smaller in size. More sensors is a good thing. 12um in a 25mm device often detects and resolves as well or better than a 17um, 35mm device. A 12umx35mm will perform as good or better than a 17umx50mm objective device. It becomes more evident when conditions aren’t ideal: high temps, high humidity, fog, etc. What’s interesting is that until Pulsat started using 12um on some of their 384 devices, they trash talked other makes using the smaller PP ‘as nothing but a way to reduce cost by reducing germanium objective sizes’. While smaller PP can make smaller objectives perform like larger objectives, the truth is that smaller PP just works better.