Objective size on a thermal scope or spotter

[Cloudhopper]

Can someone tell what the effect is of a larger diameter objective on a thermal unit? Is it simply a larger field of view at a given distance?
CH

 

[sir-lamp-alot]

Im may be wrong but I think its just the magnification thats effected

 

[mealiejimmy]

The objective lenses on thermal are not specified by diameter, but by focal length.
So, an XP50 has an objective lens with focal length of 50mm and an XQ38 has an objective lens with a focal length of 38mm
The focal length of the objective lens influences both the magnification and field of view
For a given size of sensor, longer focal length lenses will give more magnification than shorter focal length objective lenses and shorter focal length lenses will give a wider field of view than longer focal length lenses
The focal length and the diameter of the objective lens are related by the aperture of the lens
So, a thermal with a 50mm focal length objective lens with an aperture of 1.2 will have a diameter of 50/1.2 = 41.67mm
If the aperture of that lens had been f1.0, then the diameter of the the lens would be 50/1.0 = 50mm
More and more thermals have f1.0 lenses, so the diameter and focal length will be the same.

Cheers

Bruce