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UltravioletPhotography

White balance lens cap - any good for UV?


lost cat

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Has anyone had success getting good white balance in the UV using a white balance lens cap? I've read a few positive reviews on these for visible imaging, not so much for UV. The prices also range from a few bucks to about $100.

 

Sometimes you get what you pay for but in some cases - speaker wires come to mind here - a $2 generic wire performs just as well as a $2000 brand name wire. Will a cheap WB cap do the job well enough, is it worth spending the full Monty, or are external WB options the way to go?

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UV and visible can be very different animals. There is no reason to believe that anything appearing 'white' to the human eye also will be UV-'white' or UV-'grey' (ie. reflecting equally all wavelengths). It might happen, or more commonly, not.

 

Use a piece of white Teflon material PTFE. It will do well as a starting point for UV w/b.

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UV and visible can be very different animals. There is no reason to believe that anything appearing 'white' to the human eye also will be UV-'white' or UV-'grey' (ie. reflecting equally all wavelengths). It might happen, or more commonly, not.

 

Use a piece of white Teflon material PTFE. It will do well as a starting point for UV w/b.

 

That's been my strategy so far.

 

My thinking is a white balance lens cap may be better since it covers the entire field of view and - I'm guessing - is less likely to "blowout" as I find PFTE sheets tend to do.

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You can get a ptfe filter for this kind of WB effort.

 

1. Here is one such example: http://www.ebay.com/...HsAAOSwl8NVX5fU

2. Our member John Dowdy once had some of these also, but I don't know what is current with him. So PM him to ask.

 

I cannot say how they perform from my own personal experience because Nikon cameras will not perform a full in-camera WB through a UV filter due to some restriction of the software somewhere. So perhaps someone else will let us know if this kind of item works well.

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If you have access to a WB lens cap, you could test it against some known standard to see if it shows a color difference, e.g. photograph it against some target such as PTFE or fresh snow or whatever and see, after independently white-balancing the target area, if the light transmitted through the cap is rendered as neutral grey (pass) or colored (fail.)
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My DIY WB lens cap works nicely on my Lumix G3, here is a photo of it. The virgin PTFE is thick enough that the in camera WB doesn't give a "scene to bright" error message when pointed straight at the sun, although it will with a flash when I am to close. Usually when I WB with the PTFE lens cap and then take a photo of a spectralon reference and open the raw in PN the spectralon is usually within 1-3 degrees on the WB click on the spectralon.
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I have been using a virgin 3mm thick PTFE disc set in a 52mm threaded ring. It can double as a lens cap and is easy to keep around. I sometimes include these with filter orders.
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