Ultraviolet Hidden Markings, Are Very Good At Hiding?

YouVIart

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Cheers, there isn't much leakage, even a BG38 can deal with it. The evening atmosphere, was acting as a weak UV-block/IR-pass filter.
 

kds315

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Dr Klaus Schmitt
You don't mention which lens your using, this makes a huge difference in UV images, My panasonic kit lenses both show less than 1% transmission below 350nm, while several others give ~50% at 350nm...
For those interested my lens transmission results are on the IR forum here: http://infrared-photography.freeforums.net/thread/392/lens-transmission-wavelength
Of course this lens is not suitable for recoding UV."Scattering effect" of a lens? Are you joking in that IR thread, it's simply the glass absorption and the coating which causes transmission losses.
 

Petrochemist

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Of course this lens is not suitable for recoding UV."Scattering effect" of a lens? Are you joking in that IR thread, it's simply the glass absorption and the coating which causes transmission losses.
No Joke, Klaus just badly worded.
The lenses were not aligned with the spectrometer beam, so with wide angle lenses the beam will be bent more than for longer focal lengths. With many lenses this still means the light beam totally hits he spectrometer sensor, and gives good results.
The Olympus 17mm has much smaller target and bends the beam significantly, 'scattering' the beam beyond the instruments sensor, giving transmission reading below what actually would be transmitted by the lens..
I'd be very surprised if the 17mm lens doesn't actually transmit more than twice what I was able to measure in the visible part of the spectrum at least.

Those measuring lens transmission commercially will have an optical bench to align the lens exactly with the light beam. I had to make do with propping it so as to be as near center as possible.
Although the deflection of the light beam will vary with wavelength in most cases, I'd expect this to make fairly little difference to the relative transmissions.
 

kds315

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Dr Klaus Schmitt
It is even more complicated than that, took me a while to figure that out. A normal spectrometer just has a straight beam and lenses disperse that, especially wide angles. Really tricky to get those measured correctly, aligning the beam is just one aspect ;-)
 
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