Thursday, July 19, 2007

A blue sun? How did that come?

So we humans see with our three channels, Blue, Green and Red. UV (less than 400nm) however we can't see [It has been reported that a few people can see UV and funny enough if I look into my spectrophotometer and turn the knob until I don't see any light anymore, it stops at 330nm?!].

So how would we now display shots we have taken with our expensive quartz lens, UV transmitting filter and UV sensitive digital camera? My idea now was to combine the UV and the visual shot into one image, i.e. to remap the UV "color" space into our blue-to-red visual space - we perform a translation so to speak. I usually map UV as violet/dark blue, just because it is at the "right" end of the spectrum, but that is just my personal preference - and it looks good, at least for me.

How that works, you might ask. We take a shot in UV and combine it with a visual shot in a way that we subtract the UV image from the visual shot after some suitable preprocessing, noise removal, sharpening, contrast enhancement - whatever it needs.

An example for that follows now. This shot has been done using some exotic lens, the 500mm focal length Makowsky Katoptaron TS-E 500 mirror only lens. Dr Makowsky developed that lens many years ago in 1968 using only two suitable Zeiss Schott Quartz (Zerodur) mirrors which project light in a Z-folded light path. A side effect of not using any lenses is the ability of that "lens" (optical system would be more correct) to record from UV to deep into the IR region (up to 4000nm as per data sheet).

Here now the visual shot of a sunset from my balcony:

The UV shot however looks very different, like that:
[the "color" you see just respresent the reaction of the built in chip - here a Nikon D70 DSLR - to UV exposure, it is no "real" color...]

So if we now apply the remapping procedure mentioned above, the result is:

So now also the mystery behind my logo has be revealed!

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site>