Wednesday, July 22, 2020

Got a rare U.V. lens donated

Well, sometimes something really special happens! As I am into special optics and filters, as you may know by now, a member of some forum I am in informed me, that he found a special lens while cleaning up his house. He told me that it was labeled "U.V. Lens", so he thought of me and my UV and multispectral work and offered me that U.V. f4.3 lens with approx. 172mm focal length for just postage, which certainly was very kind of him!

So now on to the lens, which has a built in blue filter in its rear [these are not my images, but from the donating member here...]

U.V. Lens, pictures from the Donor

Now these are some quick test shots hand-holding filters in front of the lens: blue image is what seemingly it was made for (projecting images to a fluorescent screen I'm guessing), then I took that internal filter out and did an UV shot using a 365nm UV LED (quite sharp image) using the Baader-U filter and then a visible light image with suitable VIS-filter (which shows the lens was not computed for that) - all shot wide open at approx f4.

Here now the transmission of that lens: The RED line is the filter alone, the GREEN the lens alone, the BLUE as it came assembled with filter inside. Most likely it was designed to project images onto a fluorescent screen. That built in short pass filter makes me believe that. It is not really UV, but short wave blue, enough to stimulate visible fluorescence.

So it has to be seen what this lens can be used for, guess it will work well for reflected UV!

My thanks and well wishes go out to the donor!

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

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