It is about blemishes which gets visible, the deeper reaching the used UV transmitting filters are. Remember, mine are:
- Baader-U filter (approx. 320-395nm, effective peak approx. 375nm)
- Jupiter-U filter (approx. 280-385nm, effective peak approx. 365nm)
- Saturn-U filter (approx. 300-350nm, effective peak approx. 325nm)
What gets visible, is that the naked human eye does not see anything in the visible image, but already the Baader-U filtered image starts to reveal some dots on the petals, which get more prominently visible when using the Jupiter-U filter and best when using the Saturn-U filter. I have noticed earlier in outdoor shots, that reflected UV imaging reveals plant and specifically flower infections and detoriation much earlier than visible light images. But let's have a look at the following "plant forensic" images....
[click on image to see a larger one]
Visible light image (400 - 700nm):
UV image using Baader-U filter (approx. 320-395nm, effective peak approx. 375nm):
UV image using Jupiter-U filter (approx. 280-385nm, effective peak approx. 365nm):
UV image using Saturn-U filter (approx. 300-350nm, effective peak approx. 325nm):
Quadriptych of the above:
And now in more detail two quadriptychs:
This Gazania's outer petals reflect strongly UV around 365nm, all invisible to us humans, and the blemishes caused by an infection or deterioration (needs to be studied) get nicely visible in deeper reflected "plant forensics" UV photography.
Stay tuned, more will follow on that fascinating subject...
More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos