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UltravioletPhotography

BUG Impression of Marsh Marigold


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This contribution is meant to describe various ways of making UV photographs appear with diversified colours. Please do not read any intention of producing any kind of "bug vision" or "bee vision" into it. In this vein, let the BUG designation simply be an acronym for Blue-Ultraviolet-Green filter. I am deliberately using this label as the filter is sold under this name on eBay (seller handle 'uviroptics') and elsewhere.

 

The BUG filter basically is a filter stack comprising Schott UG5 and Schott S8612 in various combinations of thickness. The BUG filter I purchased has UG 5 of 1.5mm and S8612 of 2mm thickness, so the overall stack is fairly thick and thus will change the focal plane a bit. Accordingly LiveView (LV) focusing is highly recommended. Of course, the electronic finder ( EVF) of a mirrorless camera doubles as an LV at the same time. As the filter components of the BUG unit are not dichroic, there is no variation in transmission across the photographed frame, which of course is a benefit when you shoot with wide-angle lenses.

 

The idea behind the BUG filter is to allow a limited part of the visible range of the spectrum to pass it, in addition to UV. The underlying philosophy of such a filter bandpass is left out here as I simply am not interested. What is more important is of course that any visible component has to be attenuated strongly lest they overwhelm the visual outcome, because UV levels are so much weaker than the visible.

 

Here is the transmission curve for the BUG filter (Source: eBay: uviroptics),

bug_u5.JPG

 

Compare this to the ubiquitous Baader U ("Venus") filter of the latest generation to see the massive difference in the blue and green range of the spectrum. (Source: web: baader-planetarium.de)

 

gross_ufilter_spektrum.jpg

 

For this informal shoot-out, I selected Marsh Marigold (Caltha palustris; Ranunculaceae) as a suitable target. In common with many members of the Buttercup Family, it has yellow flowers that exhibit a strong classic bull's-eye pattern in UV. C. palustris is a variable species with a wide distribution in the Northern Hemisphere and the taxonomy of these races is, as usual, quite confused. All material in this article was collected at Maridalsvann, a lake on the outskirts of Oslo, Norway, and as it happens, very close to where I live.

 

In visible light, the flower is yellow all over. The basal parts of the sepals have tissue rich in fat and carry a nectarium. This and next picture are taken with a Panasonic GH-2 and the Coastal Optics 60 mm f/4 APO lens.

 

CALT_PALI1205290232_VIS.jpg

(Broncolor studio flash, uncoated Xenon tube, Baader UV/IR Cut filter, custom colour profile in PhotoNinja from Colorchecker Passport)

 

In UV, taken with a standard Baader U 2" ("Venus") filter, the strong bull's-eye pattern is visually dominant.

 

CALT_PAL_I1205290224_UV.jpg

(Broncolor studio flash, uncoated Xenon tube, custom colour profile against white PTFE standards)

 

Now, a few BUG-based captures obtained under field conditions. These are taken with the same Panasonic GH-2 (modified) camera and a Petri 35 mm f/3.5 lens with BUG filter. All used f/11 and ISO 160, 0.6sec. in late afternoon light. The treacherous bottom in the swamp where I found the Marigolds kept me at a distance to the motif, and my UV flash (SB-140) thus wasn't very efficient in cutting down wind-induced movement of the plants. I decided to use a longer shutter speed (0.6 sec instead of 1/180 flash sync) and let the flash run with rear sync. This approach should at least render the flowers with a core of sharpness.

 

Here is the straight-forward output from the BUG filter, using the w/b preset from a white Teflon disc.

 

BUG_standard_T1505150262.jpg

 

It is immediately evident that the visual impression is quite confusing and lacks the inherent clarity seen in the traditional Baader U depiction. Partly one could explain this by the UV response of the camera that clearly is not strictly confined to a single channel (red). Instead, the broad UV band encompassed by this filter means more false colours are triggered in UV and these mix up with the visible light response in blue and green to produce a colourful yet very bland overall rendition. We surely can do better than this.

 

A first try is to make the green channel much darker and desaturated simultaneously. This swings the flower appearance towards the pattern exhibited by the Baader U capture yet keeps much of the colour diversity elsewhere.

 

BUG_Black_T1505150263.jpg

 

A second try is moving the greens to become red instead. We then attain the greatest colour differentiation of this particular flower.

 

BUG_Redhanced_T1505150264.jpg

 

I am going to experiment further with the BUG filter in order to learn its characteristics better. Obviously this kind of filtration holds promise if one wishes for more pleasing and colourful false-colour UV images. Perhaps the BUG can attract landscapes as well.

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I really like the artistic potential of the BUG filter. Steve produced some nice false-color pictures with different stacks.

However, I am still not decided as to what colors I prefer among the ones you produced.

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That last one is spectacular and delightful !! Or should I say delightfully spectacular. Wonderful!

I enjoy these filters also for their interesting UV false colour possibilities.

(I happen to also like the green version in #3, too.)

 

I really want to see how a BUG UV signature is rendered for a flower which would typically give a dark false blue with no yellow. Some coreopsis or chrysanthemums for example? Do you have anything handy like that to use as an example? Maybe some violas? I'm guessing such a flower would go dark green in BUG (or red with your last colour twist). I don't recall what Steve had for such a flower, but I think it was dark green as I remember his dark green centered Rudbeckias.

 

It is useful to try to pull these non-BaaderU filters towards the typical "documentary" look (as you did in #4) so that we can accept UV floral signatures from folks using non-BaaderU filters.

 

(BTW, it is nice to add these alternate versions to an existing documentary post. You could add that red one, #5, to your existing Caltha post, maybe??)

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Wood Anemone Anemone nemorosa is plentiful around here and would fit your description, Andrea. Warming up to the National Day 17 May tomorrow so will try this species over the weekend.

 

I saw a few specimens of Omphalodes verna (Boraginaceae) not far away earlier today and they will be included as well.

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Happy National Day, Norway !!!! I still have my Ribbon Pin, so I'll display it tomorrow. :lol:
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  • 2 weeks later...
"A second try is moving the greens to become red instead. We then attain the greatest colour differentiation of this particular flower." -- how can the green of the leaves were not affected and also became red?
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Because "green" (seen in this photo) is not a spectrally pure (narrow-band) colour.
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