Jump to content
UltravioletPhotography

Cornus florida [Flowering Dogwood]


igoriginal

Recommended Posts

Butorsky, I. (2014) Cornus florida L. (Cornaceae) Flowering Dogwood. Flowers photographed in ultraviolet and visible light. http://www.ultraviol...wering-dogwood/

 

Trussville, Alabama USA (Google map: https://maps.google....=m&z=11&iwloc=A)

20 April 2014

10:14 Central Standard Time

Wildflower

 

Common Names:

  • Flowering Dogwood[1]

Comment:

C. florida is native to the North American continent, and has been found to inhabit a good portion of the eastern half of the USA, as well as the eastern Canadian province of Ontario[1].

 

Commonly known as "flowering dogwood", this small deciduous tree typically grows 15-30 feet tall, with a low-branching, broadly-pyramidal but somewhat flat-topped habit.

 

The true dogwood flowers are actually tiny, yellowish to yellowish-green and insignificant, being compacted into button-like clusters. However, each flower cluster is surrounded by four showy, white, petal-like bracts[2] which open flat, giving the appearance of a single, large, 3-4” diameter, 4-petaled, white flower.[3]

 

UV-A Appearance:

When custom-white-balanced against PTFE ("virgin-white Teflon"), the four petal-like white bracts of C. florida clearly exhibit uniformly strong UV-dark / absorptive properties (although there is evidence of subtle "iridescent" shifts showing up as uneven patches and bands of mild coloration amid the generally UV-dark properties, depending on angle of viewing, and angle of UV light source), while the normally yellow flower clusters (at center) also seem to indicate generally strong UV-dark / absorptive properties (although the "stamens" upon which the flower clusters are perched seem to suggest some increased UV reflectivity in relation to the rest of the surrounding structures).

 

References:

1. Plants Database of the USDA http://plants.usda.g...le?symbol=cofl2

3. Britannica http://www.britannic...pic/76726/bract

4. Missouri Botanical Garden http://www.missourib...kempercode=c280

 

-----------------------------------------------

 

- Camera: Panasonic Lumix G2 (full-spectrum converted)

 

- Lens: Argus Sandmar 35mm F/4.5 (Enna-Werk made, out of U.S. zone/occupied München, Germany - post World-War II); 34mm threaded screw base / mount; Serial # 38174; Mounted on two step-down rings (first fitted with a 37mm-34mm step-down ring, then fitted with 42mm-37mm step-down ring), then in turn adapted to Micro-4/3 camera via two-in-one M42-to-Micro-4/3 / macro helicoid adapter (See this for example: http://www.ebay.com/...=item33842475db)

 

- Settings for visible exposure: ISO 100, Aperture F/11, Shutter 1/320 sec, BG40 (2mm thick) filter, in-camera CWB (custom-white-balance) set to 18% neutral gray target, color-cast further corrected in post-photo editing.

post-34-0-81205300-1398456568.jpg

 

- Settings for UV-A exposure: ISO 100, Aperture F/11, Shutter 3.2 sec, B+W #403 (roughly equivalent to 2.5mm-thick UG-1) and BG40 (2mm-thick) filter stack, in-camera CWB (custom-white-balance) set to PTFE (virgin-white polytetrafluoroethylene / Teflon).

post-34-0-04431500-1398456580.jpg

Link to comment

Also note: This formal post serves to confirm my most recent discovery of the Argus Sandmar 35mm F/4.5, as being quite UV-capable. Although contrast gleaned from original UV exposure is significantly low (lower than what is observed with some other UV-capable lenses), and hence requires some heavy post-photo editing of image to enhance contrast to a more pleasing presentation quality.

 

Focus shift is also quite substantial, but decreases considerably (to a more manageable degree) when stopping down the aperture to F/11 or greater.

 

As for actual UV transmission, I suspect that this lens may transmit UV down to about 325nm or possibly even 320nm (given initial impressions of this lens's results compared to other known lenses in my possession with the same transmission properties, and the fact that in-camera white-balance does not need to be recalibrated when swapping this lens with another lens of known UV transmission down to 325 / 320 nm). However, this is just speculation, until actual transmission testing is undertaken.

 

Finally, it is of most tantamount importance to be aware that my discovery of the UV-capable properties of this lens concerns the first variant of the Argus Sandmar 35mm F/4.5 (in shiny aluminum), and not the second (black-colored) variant. I have not tested any other variants (as of yet) for their UV-transmissive potential.

 

See link here, for visual comparisons: http://www.arguscg.o...lens-c-wa.shtml

 

Front filter threading is 34.5mm (which also coincidentally happens to be the front filter threading of some of the El Nikkor enlarging lenses). Technically, this front threading was specifically intended to accommodate the matching, shiny-aluminum hood that was originally included with this lens. But, of course, can be removed, and the lens can be fitted with a step-up filter ring to accommodate various filters, instead.

 

(UPDATE: It has also been brought to my attention that the coatings on the first-variant Argus Sandmar 35mm F/4.5 had undergone several changes, throughout its serial number-linked manufacturing period ... and that these changes in the coatings may or may not exhibit variability in UV results. I am therefore currently in the process of acquiring three more copies of this variant - deliberately selected for spread-out serial numbers - in order to test for possible deviations in UV results across the entire production period of this lens.

 

For the time being, the serial # of the lens which was used to obtain the UV results - as seen above - is etched on the body of the lens as "Nr 38174." The appearance of the coatings, when looking at the front element under a strong light source, appear to reflect predominantly whitish-gold colors, with only a slight trace of blue hues.)

Link to comment

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now
×
×
  • Create New...