This question applies to the legacy Photon camera models. The Photon product line and its accessories have been discontinued. The information here is provided for historical purposes. FLIR describes the range of focus to mean the hyperfocal range, that is, the range between infinity and some point less than infinity through which the lens remains in focus. All legacy Photon cameras with lenses were factory-calibrated with the lens locked at infinity focus.
All of the Photon 320 lenses used a screw-thread mount. The lens focus was locked by a small setscrew. All of the Photon 640 lenses also used a screw-thread mount, however the Photon 640 lens adapters used a collar with a socket-head cap screw instead of a setscrew.
To adjust the lens focus to something other than infinity focus, or to achieve the shortest possible focus, required that the setscrew or socket-head cap screw used to secure the lens to the lens holder be loosened. Care was advised to avoid cross-threading the lens in the lens adapter.
Although Photon lenses were capable of focusing to shorter object distances than specified, it is important to note that they were not designed, calibrated, or specified for this purpose. Image space f/numbers can change under extreme finite conjugates. Very close focus applications using a Photon calibrated at infinity focus could evidence possible image anomalies, non-uniformities, and/or degraded performance. Customers should be aware of these limitations and evaluate the images for issues.