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UV/IR Thermal or Xray Photography Humans happen to use visible light naturally but now we can go beyond the usual wavelengths we appreciate, to find out more about our world and ourselves.

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Old January 11th, 2013, 07:14 AM
Dr Klaus Schmitt Dr Klaus Schmitt is offline
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Join Date: Jul 2010
Location: Weinheim, Germany
Posts: 1,185
Default Using a quartz lens for UV ? Quartz Takumar 85mm

Today on some astonishingly sunny day, I took the Quartz Takumar f3.5 85mm out of my "lens vault" and made a few shots with it.

The questions was, how the image quality would turn out, knowing that such type of lenses should only be used for a quite
narrow wavelength band (literature states between 10nm and 20nm depending on source), as these lenses are not chromatically
corrected. All shots were done stopped down to f8, which is a usual working aperture to get enough DOF and sharpness.

Here some results:

visible light image using UV/IR cut filter:


multispectral image (i.e. unfiltered) and sunlight:


UV image using Baader-U filter and sunlight:


UV image using Baader-U filter and sunlight + 365nm UV LED:


Findings:
1) There is a substantial focusing difference, here 5mm between the UV (95mm) and the VIS image (100mm between front and
camera mount), resulting in a 5% different image size when focused both (UV image is smaller). Distance orchid - camera was
700mm.

2) When white light is being used for visible photography, the 400-750nm band is quite broad, i.e. 350nm, which leads to quite
visible CA (around edges), soft image and loss of contrast.

3) When white light is being used for multispectral (i.e. unfiltered ca 300-1100nm) photography, that band is even broader,
leading to even softer images and loss of contrast.

4) Also the UV image taken in sunlight using a Baader-U filter (320-395nm i.e. 75nm bandwith) leads to rather soft images,
but a bit better as the band is narrower, only 75nm wide.

5) The UV image taken in UV LED light at 365nm (ca 20nm bandwith) using a Baader-U filter leads to the best image, as here
only the narrow 20nm bandwith of the UV LED around 365nm plays a role. The image is crisp, sharp (see structures on petals)
and has a rather high contrast.

Conclusion is, that only if quasi monochromatic photography is being done (either using narrowband UV filters or narrowband UV
light), acceptable results can be expected. For broadband UV photography, chromatically corrected UV lenses are required, such
as quartz fluorite lenses.
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Klaus
https://www.flickr.com/photos/kds315/ my normal photographic work
http://photographyoftheinvisibleworld.blogspot.com/ my ultraviolet (UV) work
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