We offer UV-Only cameras both with the Color Filter Array (CFA) and with no CFA (monochrome). Our UV-VIS-IR cameras with the CFA have about 1/6 the UV sensitivity of monochrome UV cameras. The CFA blocks most of the UV light, so putting a UV short pass filter in front of a camera sensor with a CFA makes getting UV shots much more difficult.
To understand UV cameras better, it helps to understand the way color camera sensors see light.
Front surface of a Canon 450D/ Digital Rebel XSi sensor
This picture shows the CFA arrangement on a Canon sensor. We took this picture with a front surface illumination microscope.
Pixels are arranged usually in a Bayer Red-Green-Blue-Green pattern. Green is used twice as much as red and blue in an effort to more closely mimic the human eye which sees green better than red or blue. Humans see green the best of any color.
The picture above shows the structure of a red pixel. A green pixel will have a green color filter, and a blue pixel will have a blue color filter.
Before the camera can see light at the photodiode, light must pass through the microlens and the color filter. Both the microlens and the color filter block UV light. LDP has the proprietary technology to remove the microlens and color filter without damaging the photodiode underneath. Since we are only talking about removing microns of material, this is a delicate operation to say the least!
Once we have removed the microlens and CFA, the camera becomes roughly six times more sensitive to UV light. In practical terms, this means you can shoot outdoors handheld versus needing a long exposure time and tripod. Removing the CFA also gives the camera much more resolution in the UV because the blue and green color filters block UV light more than the red filter. For a monochrome camera with no CFA, all the sensor pixel locations can see the UV light equally well which translates into a much higher resolution image.
UV-Only Camera with CFA. 1/25 second at f4.0.
UV-Only Camera without CFA. 1/160 second at f4.0
If we zoom into the picture and look at pixels at 100%, this is what we see.
UV-Only Camera with CFA. 1/25 second at f4.0 at 100%
UV-Only Camera without CFA. 1/160 second at f4.0 at 100%.
Clearly, the monochrome UV-Only camera with no CFA has much higher performance.