[UV] Effects of calibrating a lens for UV use

Joined
May 30, 2006
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499
Real Name
Dr Klaus Schmitt
I have mentioned earlier that I made some tests after calibrating lenses for UV. This procedure has been done with candidates which showed satisfactory UV transmission. Here n6w some results. Reference lenses are the Nikon UV Nikkor 105mm and the Coastal Optics Micro Apo 105mm. Images cropped/scaled for comparison.

Nikon D70 + 2" UG11xx shot at f11 ISO200 UV: 2" Nikon+Coastal, 4" 135mm lens (ca. -1.5..2EV as compared to the Nikon/Coastal); VIS: 1/125s

1. UV Nikkor VIS
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2. 135mm calibrated lens VIS
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3) Coastal Optics VIS
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4. UV Nikkor UV
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5. 135mm calibrated lens UV
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6. Coastal Optics UV
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7. UV Nikkor Differential
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8. 135mm calibrated lens Differential
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9. Coastal Optics Differential
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10. UV Nikkor detail Differential
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11. 135mm lens detail Differential
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12. Coastal Optics detail Differential
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13. UV Nikkor detail UV in bw
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14. 135mm lens detail UV in bw
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15. Coastal Optics detail UV in bw
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I will withold my personal comments for now and would like the group to comment on the results.


Visual Reference Calibration: Macro
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Before UV Calibration: Macro
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After UV Calibration: Macro
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Klaus
 
Joined
May 30, 2006
Messages
499
Real Name
Dr Klaus Schmitt
Some less technical results using this calibrated lens (Aubrieta deltoidea), diameter of flower ca. 10mm/ 0.5":

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Details (100% crop):

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Cheers, Klaus
 
Joined
Nov 2, 2006
Messages
469
Location
Tyrol, Austria
It seems worth the effort to calibrate the lens :)

I suppose that there is the same post processing on all UV shots:

from the UV shots "out of cam" (?) (nr. 4 5 6) I like the Coastal Optics most closely followed by the Nikkor and then the 135mm lens, which has a much more reddish colour sheme (which is less usefull for post processing).

from the UV differential images the Nikkor and the Coastal Optics image look the same, but the crops show that the Coastal Optics lens seems to have more contrast and it looks a bit sharper too.
But it is very interessting that the 135mm lens is more likely to show the refelection of the roof in the window!

the flower is nice in UV! The little spines seem to reflect UV quite good.

greetings
 
Joined
May 30, 2006
Messages
499
Real Name
Dr Klaus Schmitt
Joe,

Same postprocessing applied. The UV shots (4, 5, 6) were auto whitebalanced only. I cannot follow your comment on the different colors since it does not correspond to my experience. Mainly I would guess, it is the outcome of the different wavelengths the lenses transmit. The 135mm lens does only 340nm with substantial fall off after 350nm, whereas the others are quite flat beyond 300nm.

The differentials have to be interpreted very carefully, since the embossed 3D effect simulates sharpness where it is not but shows deviations in focal lengths (UV to VIS) i.e. focus shift mainly. Sharpness and contrast should be judged on the UV pics (color or bw) ONLY.

This is the computed relative transmission of that 135mm lens (w/o coating effects):

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This is the result of the spectrophotometric test with that 135mm lens plus attached 2" UG11xx filter.
Peak transmission is at about 370nm with some 43%, useful range 335nm ... 400nm. [pls keep in mind
that my older spectrophotometer hasn't been clibrated for a while, so take these results more indicative]

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Klaus
 
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