Surprising STEINHEIL f2.8/50mm lens for reflected UV photography III

I had mentioned in my previous thread, that a few years ago I got an older lens, which was made decades ago by famous lens maker STEINHEIL . It is a possibly single coated, well made 2.8/50mm lens which attracted me, since it showed some seemingly good UV transmission when shining an 365nm UV LED beam through it. The surprise came when I had it under my spectrometer, revealing its high and deep reaching UV transmission, no other normal lens so far showed. But some outdoor images taken with it revealed, that it cannot be used fully open at f2.8 due to lacking sharpness and definition. So here now some indoor shots done in a controlled environment, using a modified Xenon flash for high UV output.

[click on image gets you a larger image]

VIS image using UV/IR Cut filter:
 

UV image using Baader-U filter (approx. 320-395nm) at f4:
 

UV image using Baader-U filter (approx. 320-395nm) at f5.6:
 

UV image using Baader-U filter (approx. 320-395nm) at f8:
 

UV image using Baader-U filter (approx. 320-395nm) at f11:
 

UV image using Baader-U filter (approx. 320-395nm) at f16:
 

VIS and UV image side-by-side both at f8:
 

As I had mentioned before, it got pretty clear that this lens has a very high UV performance, at 365nm it transmits around 75%, very close to the Kuribayashi 35mm which has 80%. Its peak transmission with Baader-U filter attached is around 68% at 360nm.

At f2.8 however the resulting images did not look as sharp as wished for, but stopping down has improved sharpness significantly, especially in reflected UV light, which by its shorter wavelength in theory resolves approx. 1.6x more. It gets quite obvious, that this lens is a clearly excellent and very useful lens for reflected UV at optimal f8/f11, especially since the image size deviation between visible and UV image is a bare 1.3% only.

I will in the next thread show the deep(er) UV performance of this lens...

I have written more about this lens HERE.

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