My new 'UV' Nikkor

[Bill De Jager]

I finally got the adapters to use a Teleskop-Express filter drawer with Baader Venus filter to test my copy of this lens, in particular the hypothesis that poor performance (that I had informally noted by holding a 48mm Baader Venus filter in front of the 122mm opening at the front of the lens in live view!) is due to chromatic aberration within the range of UV wavelengths that reach the sensor.  Other aberrations could also be a factor, of course.

First, in visible light. Sony A6000 with Sachtler ENG 2 CF HD and Burzynski ballhead for support.  ISO 1600, 1/1600 at f/11, electronic first curtain, 10-sec. timer, hands off entire assembly.  Taken indoors looking through a single-pane window.  Focused in magnified live view on the needles in the upper left.  This is a crop of actual pixels from near the center of the image.

Abies vis mono crop by Bill de Jager, on Flickr

Next, in UV.  Sony A6000 with Lifepixel broadband conversion and a Baader Venus filter. Same support, timer, and focus technique.  ISO 1600, 1 second at f/11 to attempt to reduce aberrations.

Abies UV mono crop by Bill de Jager, on Flickr

Poor performance in the latter photo wasn't just a support issue compounded by a long exposure.  It really did look that bad in live view, and no focus efforts on any subject in live view were satisfactory.

I reduced the second image to monochrome since I don't yet have a UV color profile for this camera.  So the first image is also in monochrome to match.  Due to the behavior of the die-based Bayer filters over the pixels, renditions of "color" in UV using standard sensors don't have the same direct mapping to wavelength that exists in visible light.

Conclusion: The lens should be tested with narrow-pass UV filters to see if better results can be obtained.

My copy is #410257.  The subject is California red fir (Abies magnifica).

[Andrea B.]

It's that extra layer of glass you added -- the window.
I'm not sure what lens you are referring to though? Is it the UV-Nikkor 105/4.5?
If so, then that lens is corrected and you should not see aberrations like this.
Unless shooting through a window.

Nevermind the crossed out stuff!!!!I now realize that you are talking about the 400-Q. 

But still -- don't test a lens shooting thru a window.

[Bjørn Rørslett]

Few (actually, none) suitable UV test subjects around here this time of the year. From what I learned so far is that the lens, 400 mm f/4.5 Nikkor-Q, is really sharp its vintage considered, and there is some CA that may or may not cause issues. For visible light shots, the CA mostly is not objectionable and can be cured in the processing. For IR, the lens shines and turns in very sharp images with no traces of a hot spot. However, for false-colour work where upper part of the visible range is mixed with IR, the difference in focus becomes a real problem unless one can stop down almost all the way.  Thus I'll continue to rely on my trustworthy 200-400/4 ED AIS instead for that line of work.

As I stated first, no real experience with UV so far. It might work.

[Bill De Jager]

It's that extra layer of glass you added -- the window.... don't test a lens shooting thru a window.

This was a quick test to look for gross problems.  I try to avoid using a very long lens in a residential area because it can create the wrong impression, so I shot into my very small back yard from inside my residence. 

But you're right - shooting through a window will cause aberrations for any kind of light, and now that I think about it I expect it would affect shorter (UV) wavelengths more than the visible ones.   What I should do it take the whole setup, the reference standards, and a suitable UV subject to another location.  That will need to wait for a bit.