Tuesday, March 31, 2009

UV images exhibition - Hutter im Schloss, Weinheim, Germany

[click on image to see a larger one]

Well, in case you are around our wonderfull small town Weinheim, Germany, I invite you to pay a visit to our famous top class restaurant "Hutter im Schloss" http://www.hutter-im-schloss.de/

and to have a look at six of my UV works which are on display there now. 

The restaurant is wonderfully set as part of the historic ensemble of  "Schloss Berckheim" which forms the center of the historic center of Weinheim on top of a local hill and streches into the wondefully set "exotic park" which was the hobby of the nobles who lived there many years ago. So you will find 50 meters tall redwoods from the US westcoast, trees from China and all over the world. The largest Lebanese cedar tree north of the alps also grows here since 300 years.

Well certainly worth a walk and a nice rest at that fine restaurant with local foods and some inspiration from Spain (Perelada region), where the Chef, Jan Hutter, has worked many years and brought some nice recipes with him. 

Thursday, March 26, 2009

Multispectral UV+VIS+NIR in just one shot II

Now this is about multispectral imaging again.

Well, you know what an effort multispectral UV+VIS+NIR imaging is.Take three shots with different filters, modify them, transform them to bw and assemble them into one RGB image. Biggest thing actually is to take matching shots outside considering wind, changing light conditions etc.

So while I was playing around and doing tests using that FOVEON based Sigma SD-14, I had this idea if I could find a suitable filter, which would allow me to do it all in just one shot. I mean the following mapping: UV-> blue, Vis->green, NIR->red.

So after even more mumbling and grumbling, many calculations and stressing out my electronic spectrometer, I finally found a working filter combination. The issue to solve is, that the UV sensitivity is about 8...10EV lower than the visible one, the NIR is 1..2EV more than the visible one, so that filter has to stretch over 12 EV (!!!) taking into account that special sensitivity profile of that camera (internal filter removed, which can be done yourself in just 2 seconds!!). So in simple words, that needs to pass lots of UV, a bit of visible and just a tiny bit of NIR.

So 'nuff talked, lets see some results, using a daffodil (Narcissus jonquilla) as a target.

Camera used Sigma SD-14, unclipped internal filter, X35 lens, high power Xenon UV flash (unfiltered at 200Ws), 1/160sec at ISO 200 and f16.

This result came out of the Sigma SD-14 using a UV/IR blocking filter, i.e. the VIS shot:

This now is the (blue adjusted) UV-VIS-NIR result using my XUVIR filter:

and here the unadjusted UV-VIS-NIR image:

The RGB channels of that unadjusted UV-VIS-NIR image looks like this:

Plus a shot outside using sunlight, proving that these images may be achieved with reasonable exposure times. Lens used in this case: Pentax Ultra Achromatic Takumar 4.5 85mm at f11, 1/30sec, XUVIR filter, ISO200 :

Well, it may not be a perfect scientific mapping, but from an "artsy" standpoint it looks acceptable to me.

But the real idea behind that is to find a way to map "bee vision" in just one shot ... watch out here, more to come on that.

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

Monday, March 16, 2009

Carnivore plant shows UV pattern

A friend of mine, Dr. Andreas Wistuba, collects and breeds special forms of carnivore plants and we were both wondering if some would show some UV reflective patterns. Well indeed, some do on these "needles" which prevent their prey to escape!!

Shot using off the shelf D70, UV-Nikkor 105mm, SB-140 flash + 2" Baader U-filter (310-390nm) (resp. UV blocking filter for the fluorescence shot)
[click on image to see a larger one]
UV shot:

UV shot detail:

Fluorescence shot:

Not sure what caused that, but evolution surely had a reason to develop that UV pattern!

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

Normal 135mm lenses for UV?

I invested some time today and measured the spectral transmissions of some 135mm lenses I had around.
[click on graph gives a larger image]

Top to bottom:
1) Pentax Takumar f2.5 135mm, multicoated (white)
2) X135 f2.8 135mm calibrated for UV lens, coated (turquise)
3) Enna f3.5 135mm lens from the 50ies, single coated (violet)
4) modern M42 non-name japanese f2.8 135mm lens, multicoated (orange)
5) Steinheil Quinar f3.8 135mm lens, multicoated (blue)

[please ignore the dips and jitter of the measured curves, that comes from that setup/Deuterium lamp used, this can also bee seen on that red 100% line w/o lens...]
I took the 365nm line as the wavelength to decide about the usebility of such a lens, since it is the center transmission of that famouns 2" Baader U-filter I mostly use for UV photography.  The X135 @365nm reaches 73% UV transmission (and it transmits down to about 320nm which correlates fine with the end of the UV sensitivity of an UV sensitive camera such as the Nikon D790 or D70s), wheras the next best one has only 39% (Quinar). Lens No.1 is a good example of what could be expected from a modern, multicoated lens in terms of UV transmission - not much actually since the multicoating and internal cemented lenses efficiently block UV, thus leaving such a lens quite useless for UV photography as compared to #2!
Please bear in mind that a useful UV transmission is just ONE criteria (but an important one) for successful UV photography. Resolution, sharpness, contrast, stray light and flare control, lack of hotspots etc. and focus shift of course are other important factors to consider.

HERE is a list of all lenses good for UV photography.

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

Is there "life" below 350nm II ?

Here now some infinity tests I made using the same stacked filters to see if there would also be some useful response below 350nm, using sunlight as an UV source. Again both the mod. Nikon D70 (clear quartz glass >270nm) and the Sigma SD-14 without internal filter (which can be clicked out easily without need for a professional service)  were used.

Lens used was a X35 wide angle lens (f=35mm) in both cases (infinity mount conversion done for the Nikon, M42 version with adaptor for the Sigma), shot at ISO200. [In all cases please ignore the vignetting of the corners, this was caused by the experimental filter mount I used, which could be done much better to avoid that effect]

This (blurry) result came out of the Sigma SD-14 after 30 sec exposure and f4 used:

It is pretty obvious that only the blue channel of that stacked FOVEON chip responds to UV radiation (as the theory also says, since that chip does not use any dyes to filter, just the effect that silicon filters out shorter wavelengths the deeper light (UV, VIS, IR radiation) penetrates that silicon chip. (c) photoscala.de

The Nikon D70 result after 30 sec exposure and f8 used showed a much clearer image and two channels being stimulated (blue + red) by that short UV at 330nm peak. Not sure why the results is so much sharper, be it the stepped down to f8 or the infinity converted same lens used. The hue was adjusted so as to match the Sigma result.

That second image shows the result straight out of the Nikon D70 camera:

And NO, this is NOT infrared (IR), just because it is red! I checked with my spectrometer carefully that no IR passes. The color is caused by the fact that at these short UV wavelengths (nearly) only the red channel of that Nikon D70 CCD sensor has some useful UV response (maybe due to visible fluorescence of that red filter dye of the Bayesian filter used when expsosed to UV radiation)

To summarize my findings:

Cameras + exposure used:
1) mod. Nikon D70 (quartz glass filter >270nm) @ ISO200, 30sec, f4
2) Sigma SD-14 w/o int. filter @ISO200, 30sec, f8

It gets pretty obvious, that the mod. Nikon D70 has the much higher UV sensitivity of ca 2EV @330nm. I can only guess that the higher sharpness is due to f8 used and since the UV-infinity converted Noflexar 35mm version was used and not the off the shelf M42 version as for the SD-14. The Nikon image has been adapted to the color of the Sigma, but has pretty much red and a little bit blue channel response. The Sigma only gives some monochromatic blue channel response at much less sensitivity.

So in short the findings:

  • Sigma SD-14 w/o internal filter is about 2 stops less sensitive than a mod. Nikon D70
  • Sigma SD-14 only records UV in the blue channel, also down to about 320-330nm
  • Nikon mod. D70/D70s is about 2 stops more sensitive than a Sigma SD-14
  • Nikon mod. D70/D70s may be used down to ca. 320nm, but with much less sensitivity than 350-400nm
  • The X35 lens may be used succesfully down to 320nm

Some remark here: This has been done since I get many questions about how far a modern DSLR may be able to record UV. Although it has been proven experimentally now that there is some response, in terms of using that 300-350nm band I would consider that as not being much useful since it does not reveal much different information (at least from what I know today). Normal UV photography using the 2" Baader U-filter obviously records mainly in the 350-400nm band due to the steeply decreasing sensitivity of the camera chip with shorter wavelengths and this with 2-4sec exposure time at ISO200-400, f8-f11 for an unmodified Nikon D70/D70s i.e. 8-10 stops below a normal visual light shot (and 1-2 stops faster for UV using a modified D70 with clear quartz glass window) which is in a real outside situation anyway nearly too long. If you have ever tried to shoot a flower with a bee on it in UV, you know what I'm talking about!

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

Monday, March 2, 2009

Multispectral UV+VIS+IR in just one shot?

After some days of mumbling and grumbling and finally designing some special filter, I got that and now had the chance to make some initial tests, to see if the idea works.

Maybe you remember some time ago I published my remapping method to compress two images (UV, VIS) or even three (UV, VIS, IR) into a multispectral one. Quite a cumbersome process esp. making sure that all the images match while screwing in and out filters etc.

The steps looked like this using an off the shelf D70, UV Nikkor 105mm, UVIR cut filter for the VIS shot, Baader U-Filter for the UV shot (these are the old pictures):

[click on image to see a larger version]

Visual (VIS) shot:

UV shot using Baader-U filter:

and finally the composite UV+VIS remapped into one image:

in detail:

Now the result of the one-shot-process, using a full spectrum mod. D70 (clear quartz glass window >270nm), Nikon UV Nikkor 105mm plus my "secret" XUVIR filter (300-1000nm) to allow UV+VIS+IR in just one shot:

and in detail:

For comparison the identical shot using a special compensating filter, which makes the modified D70 a "normal" one, just VIS (i.e. an external filter which has the same filter characteristics as the removed internal filter had):

Be careful comparing the images, since the remapped one seems to be much sharper. Due to that embossing effect when overlaying two images it seems to have more structure, but this is not really existing. Another reason for the lack of sharpness is simply the fact that the UV Nikkor is focus corrected for UV+VIS, but not for IR.Important however is the fact, that the tiles reflect IR very strongly, which is clearly shown in red and that the tin roof above that window very strongly reflects UV, which clearly shows as deep blue. 

Another comparison, a street scene, shot some time ago in individual shots and remapped:

and about the same one, now using the new XUVIR filter and just ONE shot:

And both is accomplished now in just one shot, no remapping, no filter fumbling.

If you need such a XUVIR filter, drop me a note, I had made a few more....

[Remark: This technique shown only works well, if the reflection pattern of the subject is quite different in UV and IR, otherwise there won't be a clear separation]

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

Is there "life" below 350nm?

A lot has been discussed a forums dealing with UV photography what the low cut off UV wavelength might be of modern DSLR cameras i.e. how deep into the UV one could reach. A common assumption was around 350nm.

Well for that purpose I found a special steep astronomy filter which transmits only the 300-350nm band. A modified Nikon D70 camera was used, which I had modified using a clear quartz glass filter built in, which itself transmits flat from 270nm onwards. A Nikon UV-Nikkor f4.5 105mm was used as taking lens, since that transmits flat from 200nm onwards.

[click on image to see a larger version]

This now is the transmission spectra of that BP350 filter taken using a Ocean Optics USB2000 spectrometer (185-850nm; ignore that ripple on the right, measurement inaccuracy only, caused by the used Deutrium lamp):

and here in detail the spectra if stacked with a Baader U-filter (310-390nm) to insure NIR >700nm is completely suppressed, since that BP350 filter starts to leak some NIR above 900nm. The resulting transmission peaks at about 333nm and stretches from 320-350nm.

Now to the really interesting part, will the mod. D70 be able to record some useful information below 350nm? The camera was set to ISO1600 and the working aperture was f8. As a UV light source I used one shot of my modified High Power UV flash set at 400Ws, with UV front filter. Image came directly from the camera, only resized, and obviously only the RED channel records some useful information in this waveband.

So yes, there is life below 350nm, actually to about 325...330nm I would say.

And just for comparison, this is the result if only the Baader U-filter was used at the same f-stop:

It is obvious that using the BP350 and the 320-350nm band causes some 2...3 stops less sensitivity, but shows different detail of that Phalaenopsis Hybride Orchid.

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