Question about matching the lens to the detector

[a***@gmail.com]

I am designing an infrared lens to work at 10 microns. I have a detector with a 12 micron pitch and a system maximum aperture of 95 mm. What would be the optimum focal length for this lens?
I realize that it is best to have two pixels across the Airy disk, which would mean this system should a focal length of 80 mm.

However, the customer wants the resolution equivalent of a diffraction-limited system with a focal length of 200 mm, which of course is not happening with this aperture and this detector pitch, but I was wondering if there is some optimum value for a mismatch between the lens and a detector? Some focal length which would allow the unresolved details of the scene to best be extracted?

The system will be taking several images of the scene, and they could, theoretically, be combined to increase the level of detail.

Thanks in advance for your replies.

[Phil Hobbs]

Post by a***@gmail.com
I am designing an infrared lens to work at 10 microns. I have a
detector with a 12 micron pitch and a system maximum aperture of 95
mm. What would be the optimum focal length for this lens? I realize
that it is best to have two pixels across the Airy disk, which would
mean this system should a focal length of 80 mm.

At some point the FOV has to come into the equation. Otherwise you can
oversample the image as much as you want.

Post by a***@gmail.com
However, the customer wants the resolution equivalent of a
diffraction-limited system with a focal length of 200 mm, which of
course is not happening with this aperture and this detector pitch.

Why not? The FL just determines what the angular subtense of each pixel
is. The image-side numerical aperture is what determines the maximum
available resolution for a given wavelength.

Post by a***@gmail.com
but I was wondering if there is some optimum value for a mismatch
between the lens and a detector? Some focal length which would allow
the unresolved details of the scene to best be extracted?

Professional astronomers with relatively deep pockets often use four
pixels per cycle at Nyquist. Amateurs have to trade off the diameter
and FOV of the scope (which determine the image NA) vs. the available
budget.

Post by a***@gmail.com
The system will be taking several images of the scene, and they
could, theoretically, be combined to increase the level of detail.
Thanks in advance for your replies.

Cheers

Phil Hobbs