Calibration / Thermal gradient due to add on lenses on the Flir Exx series

[hikanio]

I've been experimenting with the 45 degree wide angle add on lens on my E30 and was wondering how big the differences in temperature measurements (thermal gradient) would be due to the additional lenses.
So I tried certain reference measurements with and without the add on lens but without setting the camera configuration for this add on lens, because it seems to have no valid calibration anyway.
To my surprise I could not find any difference in any temperature reading (tried between 0-300 degrees Celsius), neither in the center nor in the outer frame of the picture.

Anybody else having an explanation because I was expecting at least a slight difference here?

Cheers
Hikanio

[hikanio]

Moved this question to an existing thread:

https://www.eevblog.com/forum/thermal-imaging/swapping-lenses-on-a-e30/msg1156540/#msg1156540