Sunday, May 6, 2012

[UV] filters for recording deep(er) reflected UV for peak 375nm, 365nm, 350nm, 325nm

Here a comparison of the false UV colors to expect using the Baader-U white balance setting when using specific short wave filters for deeper reflected UV recording with the effective [*] peaks: 375nm, 365nm, 350nm, 325nm. It includes that new Jupiter-U filter of mine.

[click on image to see a larger one]

The UV images here also uses my standardized false UV color normal + high intensity palette:

top left: Baader-U (effective peak approx. 375nm), top right: Jupiter-U (effective peak approx. 365nm)
bottom left: filter stack I (effective peak approx 350nm), bottom right: filter stack II (effective peak approx. 325nm)
[ignore quality issues please, these latter three are experimental versions]

Interesting to note, that the red channel looses on intensity when the wavelength gets shorter, the green channel stays about constant, the blue channel declines first, then later on (325nm) recovers slightly.

Note that the exposure of these 4 images are not the same; I tried to get about equal exposed results.

[*]In that context "effective" means what the combination of filter, lens, sensor results in (for a given light source: sun / Xenon in that case) as a peak wavelength for that combination (lens is a flat transmitting quartz fluorite lens, Cerco 94mm in that case) as per my simulation system.

So, now the question arises of course, if such deep UV explorations is only for the the priviledged owners of a quartz fluorite lens. Well, have a look at that following test result using a common 35mm lens and the same filter sequence as above.

Of course there are differences, especially in exposure, but in principle, it seems doable. Don't get too excited, please, the exposure difference is a massive one.

I will reveal more about these experimental filters of mine here later, once they have proven their usefulness and when acceptable photographic quality has been achieved.

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

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