[UV, VIS] Cerco 28mm multispectral lens

Today about a CERCO 3.5/28mm multispectral lens, made of fluorite / quartz and a big CAVEAT upfront, as I'm using this lens way outside its defined range, which has been made to serve as a lens for an image intensifier system originally with a 18mm image diameter - I'm using 21.6mm, because that's the sensor diameter of my UV sensitive camera. So what has to be expected is a sharp and contrasty center, but most likely quite some fall-off outside that central area.

Mechanically this lens is very tiny, about half the size of my thumb, c-mount and has a rare front filter thread. Register is quite short due to its defined use for an image intensifier, but meets c-mount lens standards and even focuses from beyond infinity to about 0.5m (so it cannot be used on Nikon bodies, to make it clear).

[click on image to see a larger one]

Transmission is quite good and as expected:

[measurement valid from about 315 - 750nm]

That said, now to the UV and VIS test results. All shots done in sunlight, ISO640, f5.6, focus set in visible light, no focus adjustments done. ReflectionDisc in camera whitebalance, reduced to 1280pix, sharpened for web, contrast enhanced (UV).

1) Rudbeckia fulgida flower close-up (same camera position as in my shots shown in other thread here)

VIS:


UV:



2) Shot down to the city (infinity):

VIS:


UV:



3) Shot of our neighbors house (ca 30m):

VIS:


UV:



Especially from the last two shots it gets quite clear, that this lens was used outside its defined image circle and the loss of sharpness is evident. The close-up shots are much better (as could have been expected due to the much larger projected image circle). The image center is actually quite sharp and contrasty for such a lens and esp. when compared with a Noflexar 35mm, which it certainly beats in resolution and transmission (but the Noflexar 35mm has the benefit to cover a FF sensor). This lens was made for very faint light intensities, so no wonder that it shows some signs of flare if used at high light intensities (although proper shading was used), but I could not detect a prominent hotspot (which its brother, the Cerco 94mm has).

Overall a nicely performing lens for UV-VIS (I haven't tested it for IR) if used inside the specified range, but also quite an expensive one (UV-Nikkor range).


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

[UV, VIS, BV] first Rudbeckia flower unfolding

Today shots of my first Rudbeckia flower this year, using UV sensitive camera, Cerco 94mm lens, Baader-U resp. UV/IR Cut filter

[click on images to see larger ones]

UV shot:


Bee Vision (simulated using filter):


VIS comparison shot:


The idea is to see, how the UV pattern emerges within the next days when the flower totally enfolds ...


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

[UV] Hungarian Parliament building in reflected ultraviolet light

From a recent trip to Hungary, here a shot of the famous Hungarian Parliament building as seen from the Buda castle on the opposite side of the Danube river.

Shot using my UV sensitive camera, Cerco 94mm lens, Baader-U filter and preset UV WhiteBalance using my ReflectionDisc.

[click on image to see a larger one]




Reflected UV "colors" are according to the previously described "UV color palette" related to wavelength:


A visible comparison shot taken a few minutes from the one above looks like that:



Note the very different colors and especially the fogged background due to Rayleigh scattering of UV light which is much stronger for UV light than for visible or even IR light (this is why IR is so often used to penetrate clouds = make them transparent).

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

[UV] Hungarian Puszta flowers in reflected ultraviolet light

From a recent field trip to Hungary, a few flowers shots from the Kiskunsagi Nemzeti Park in the Hungarian Puszta.

Shot using my UV sensitive camera, Cerco 94mm lens, Baader-U filter and preset UV WhiteBalance using my ReflectionDisc.

[click on image to see a larger one]














A few butterfly shots in UV:




and the reminders of a predator:


Reflected UV "colors" are according to the previously described "UV color palette" related to wavelength:



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

[UV] on wide angle lens whitebalance using a GH1-UVIR

In previous posts on whitebalancing using my ReflectionDisc I warned about generalizing results and stated that it is only valid for that camera, that lens, that filter and that lighting situation. Well, I was curious, how much would change if two parameters were changed: a) using a wide angle lens (with substantial less UV transmission), b) lighting situation
So, using my GH1-UVIR, a Cerco 94mm lens, Baader-U filter and sunlight, I had preset a whitebalance for a similarely lit situation using my Reflection Disc, call that WB1 for now.

The weather today was very overcast and no sun, just about 250 microWatt/cm² UV-A (as measured using a calibrated Minolta UV-A meter).
The lens was changed, from a color corrected, flat transmitting (<300nm) quartz / fluorite lens to a non-color corrected not that much UV transmitting conventional wide angle lens, a 2.8/28mm in that case, which barely reaches about 350nm, to see which impact that would have. A set WB was done for that 28mm wide angle lens, call that WB2.
So what we see here is:
1) top left: previously set sunlight WB used (WB1)
2) top right: correct WB for that lighting situation set (WB2)
3) bottom left: previously set sunlight WB used (WB1), bw version with histogram
4) bottom right: correct WB for that lighting situation set (WB2); bw version with histogram
[click on image to see a larger one]




Here now quite some difference in whitebalancing may be noted; the preset WB1 was quite different from the correct WB2 for that lens (and lighting situation). Major impact had the lens change, not the changed lighting. As may be seen on the histogram, the correctly whitebalanced image is about 1/4 - 1/3 stop less exposed than the incorrectly one (both images were identically exposed at 1/1.6sec, same ISO) , so consequently using the correct WB at shooting time would require a somewhat higher exposure.

SUMMARY: UV whitebalance, for lenses having very different spectral (UV-) transmission, should be correctly set at exposure, not later in post processing and properly exposed (a tad more).
P.S.: I have tested at different exposure values (higher + lower) but the principal result remained the same.


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

[UV] on whitebalance tolerance using a GH1-UVIR

In previous posts on whitebalancing using my ReflectionDisc I warned about generalizing results and stated that it is only valid for that camera, that lens, that filter and that lighting situation. Well, I was curious, how much would change if two parameters were changed: a) lens in use, b) lighting situation

So, using my GH1-UVIR, a Cerco 94mm lens, Baader-U filter and sunlight, I had preset a whitebalance for that situation using my Reflection Disc, call that WB1 for now.

The weather today was different, quite well lit, but overcast and no sun. A set WB was done, call that WB2.
Also the lens was changed, form a color corrected, flat transmitting (<300nm) quartz / fluorite lens to a non-color corrected suitably UV transmitting conventional enlarger lens, which reaches about 350nm, to see which impact that would have. So what we see here is:
1) top left: Cerco 94mm lens, correct WB for that lighting situation set (WB2)
2) top right: Cerco 94mm lens, previously set sunlight WB used (WB1)
3) bottom left: 95mm enlarger lens, correct WB for that lighting situation set (WB2)
4) bottom right: 95mm enlarger lens, previously set sunlight WB used (WB1)
[click on image to see a larger one]



Interesting to note, that only the blue and red channels are shifted just a bit, which can easily be corrected afterwards in post processing, but the image out of the camera is still quite close to the "correct" one.

That's important if you're out in the field and the lighting situation changes and / or different lenses are used (as long as they are suitably UV transmitting; this may not work for white angle lenses having hardly any UV transmission). For critical scientific work I would of course always do proper whitebalancing upfront.

SUMMARY: UV whitebalance, once correctly set, works suitably well also under changed situations (light, lens)


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

[UV] An attempt to standardize UV colors

(currently being reworked)