going to the heart of the matter
Full Spectrum conversion basically allows your camera to capture a wider range of electromagnetic waves (light) than your eye can see, by removing the hotmirror that prevents infrared light to reach the sensor.
It is a pretty straightforward process: disassemble your camera down to the sensor slot, remove the hotmirror (a blueish filter just about the same size as the sensor) and put everything back together.
At this point, we can use IR filters to block out visible light and dive deeper down into the
Each sensor will have a slightly different response, mostly due to the algorithms that decode electrical signals to an image, but the chart on the right gives you a rough idea of how sensitive full spectrum cameras are to the NIR spectrum.
The white outer line tracks the overall response of the sensor, without differentiating between RGB colors.
The Red, Blue and Green curves plot the response of the sensor filtered by the Bayer matrix, which allows digital cameras to reconstruct color information (and will not be removed in the conversion process).
The pink curve plots the frequencies that can make it through the hotmirror so basically only the RGB lines under the pink curve are recorded by the sensor.
In our process, we are going to get rid of that pink line.
I strongly recommend that you check out their website.
Defiltered sensors only record the luminosity of an image.
The Bayer Matrix is a red-green-blue dotted pattern layered over the sensor that allows each pixel to only record the luminosity for one specific component of the incoming light.
Data is then processed within neighbor pixels to determine
the value of the filtered out components for each pixel, and from that, through more calculation, a full-color image is rendered.
Bayer matrix certainly reduces the sensitivity of each pixel, very much so for Green and Blue components but thanks to the matrix algorithm, luminosity is fully recovered, with the major advantage of having 2 color components (as Blue and Green NIR curves almost overlap) that can be worked separately in postproduction.
IR filters are almost completely opaque, so you cannot see through them with your naked eye.
This is not a big issue if you convert a live view camera (i.e. anything apart from oldest DSLR models), as the sensor will "shift" the IR image into the visible range on your LCD.
If you are working with an older DSLR model though, you will only have an optical viewfinder which goes through the IR filtered lens, becoming increasingly opaque as you cut deeper into NIR; you will still manage to see some contrast against the sky with filters up to 720nm (not all of them, depending on how quickly they cut off), but from then on the viewfinder becomes totally useless
My first two IR cameras had no live view but, at the end of the day, this turned out to be not too much of a problem,
as I shot stopped-down wideangle most of the time; LCD instant replay was enough to fine tune the shot.
Exposure measuring and AF system will keep working fine; White Balance will have to be manually recalibrated each time you switch to a different filter.
You can also operate a permanent IR conversion by replacing the hotmirror with an IR Filter of the same size and then recover the ability to look through the viewfinder, but besides the fact that you'll have to stick to one single filter, problems arise in terms of focus recalibration.
As far as my experience goes, I strongly recommend the
Full Spectrum conversion, especially now that most
"old cameras" have a live view feature.
© all rights reserved