Hello Bill,
Lens is the only option when you are targeting 30-40cm distances from an object that's 2-5cm wide. SNR depends upon how good of an optics setup you can achieve. When you mentioned "close enough" can ypu please give me a range? For example if you are ~2cm away getting accuracies of 1C for a 2-5cm object will not be a problem.
Please refer to the following posts and the attachment (Please visit the site to view this file)for more information on lens recommendations:
- http://e2e.ti.com/support/other_analog/temperature_sensors/f/243/t/117229.aspx
- http://e2e.ti.com/support/other_analog/temperature_sensors/f/243/t/116631.aspx
http://www.edmundoptics.com/ is also a good resource for such applications.
I hope this helps.
Regards,
Abhi