Calibration in infrared camera conversions is very important. The infrared converted camera must focus the infrared light. Infrared light bends a bit different from visible light so we need to adjust cameras focusing system.
Compact cameras and compact system cameras (Fujifilm S2980, Canon EOS M, EOS M3) usually do not require recalibration but some models require sensor leveling.
The sensor leveling is needed to achieve even focus throughout all the image.
If the sensor is not leveled properly, the image will not even have a focus plane. Basically, this not always will be noticeable and probably will show itself if we take a picture of a flat surface i.e. a wall.
If the compact camera or compact system camera can’t focus we move the sensor to the back. Usually, a 0.5mm distance is enough.
DSLRs require recalibration (a sensor shift) and some DSLRs also require sensor leveling.
For example, the IR converted Canon 1200D will require a sensor shift to the back 0.5mm and sensor leveling.
The Canon 1100D will not require sensor leveling because the sensor is not fitted on springs and will need only sensor shift to the back (done with 0.5mm washers).
How sensor shifting is done. For sensors that are fitted on springs, we simply increase sensor distance from the chassis for about 0.5mm.
For sensors that are without a spring fitting, we use simple washers (0.5mm).
This sensor shift will allow us to use any lens on 50mm focal length with the quick focus feature.
What about full spectrum conversions? Full spectrum conversions do not require focus recalibration. It does, however, require sensor leveling on cameras with sensors fitted on springs.
If a full spectrum DSLR is used for infrared photography then an IR filter is placed on the lens and we can’t use quick focus because we can’t see anything. So Live View mode is used and the camera focuses perfectly all the time.
Some cameras like the Fujifilm X Pro require additional clear glass to be fitted in full spectrum conversions because they can’t focus otherwise.
Some digital compact cameras like Fujifilm S2980 require sensor shift to the front. This can be done adjusting three screws that the sensor is fitted with.
If the camera still can’t focus we simply remove those springs and the sensor then shifts a bit more to the front and the camera is able to focus.