Thermal camera macro lens diameter

[paulc]

For a given focal length of 38mm or 50mm, is a 12mm diameter enough?
Will a 20mm diameter lens give much better quality/less distortion?
(Lens is ZnSe of course)

[Fraser]

What camera are you using ?

To avoid image vignetting the 20mm diameter lens is the safest option. You need to consider the cameras field of view and how far away from the cameras lens the close-up lens will be mounted. The laser focus lenses are not intended to be used with thermal Cameras so some image distortion is to be expected but is not normally an issue during use. By using a larger diameter close-up lens than the minimum needed you use mainly the centre of it where image quality is likely at its best.

Fraser