Sphaeralcea ambigua [Desert Globemallow]

[Andrea B.]

Blum, A.G. (2013) Sphaeralcea ambigua A. Gray (Malvaceae) Desert Globemallow. Flowers photographed in visible, ultraviolet and infrared light. http://www.ultraviol...rt-globemallow/

 

Other Common Name:

• Apricot Mallow
  

Comment:

Characteristic of all Malvaceae are the fused anthers which in S. ambigua flare out around the eventually protruding central stigma. S. ambigua is easily found in the Southwestern US deserts and Baja California. The UV appearance of the flower is bright with UV-dark petal bases and primarily UV-dark central parts. The filaments are only moderately UV-dark, and there is a UV-bright accent on each anther.

 

Reference:

1. Morhardt, S. & E. (2004) Sphaeralcea ambigua, page 201. California Desert Flowers. The U. of Cal. Press, Berkeley, CA.

2. Jepson eFlora (2013) Sphaeralcea ambigua. Jepson Herbarium, U. of Cal.-Berkeley, Berkeley, CA. http://ucjeps.berkel...JM.pl?tid=45130

 

Set 1

Death Valley National Park, California, USA

29 Feb 2012

Wildflower

 

Equipment: [Nikon D300-broadband + Nikon 105mm f/4.5 UV-Nikkor]

 

Visible Light [f/4.8 for 1/2000” @ ISO 200 with Nikon D3S]

 

Visible Light [f/4.8 for 1/8000” @ ISO 200 with Nikon D3S]

 

Visible Light [f/16 for 1/200” @ ISO 200 in Sunlight with Baader UVIR-Block Filter]

 

Visible Light [Detail from preceding bud showing stellate hairs which cover sepals and leaves.]

 

Ultraviolet Light [f/11 for 1/250” @ ISO 200 with SB-14 UV-modified Flash and Baader UV-Pass Filter]

 

Infrared Light [f/11 for 1/160” @ ISO 200 in Sunlight with B+W 092 IR-Pass FIlter]

 

 

Set 2

Boyce Thompson Arboretum, Superior, Arizona, USA

24 April 2013

Wildflower

 

Equipment: [Nikon D600-broadband + Nikon 105mm f/4.5 UV-Nikkor]

 

Visible Light [f/3.5 for 1/1600” @ ISO 200 with Nikon Coolpix A]

 

Ultraviolet Light [f/8 for 1/60” @ ISO 400 with SB-14 UV-modified Flash and Baader UV-Pass Filter]

[nfoto]

So, basically, the two different cameras yielded the same UV signature. Evidence that the profiling works.

[Andrea B.]

Well, she said, perhaps we can conclude that standardized profiling seems to work for Nikon DSLRs when the Baader-U Filter, Labsphere Standards and Photo Ninja are used.

 

I suppose we should remain open to the possibility that our current process could yield a different look if Nikon ever changes their Bayer filter or if sensors change from CCD or CMOS.

 

Of course, we already know that the "look" changes a bit if other UV-Pass filters are used. At some point we should try to develop a standardized profile for the Precision-U or for something like the UG11+8612 Stack which I just got to play with.

[nfoto]

The profiling also works for Panasonic (GH-2) and Fuji (S3PRo UVIR) so appears to be pretty universal. More to the point, it works across CCD and CMOS sensor types (Nikon D40X and D200: CCD; Nikon D300; D3, D600: CMOS).

 

As we are unshamedly "abusing" the out-of-range spectral response of the Bayer dyes, there is no guarantee the profiling is set in stone for eternity and thus we should always try to retest our equipment once in a while.

[Andrea B.]

So far, so good - as they say.

 

But I would again remind anyone reading here that these profiles are made using a Baader-U.

 

Interestingly, it turns out that you can UV profile 95% of the time by white-clicking on anything Magenta in UV fotos made with an Incandescent white balance setting. Then you refine the result, if needed, by clicking on areas you know will be "UV-neutral". But white-clicks are not always a sure thing, so properly prepared profiles need to be at hand to ensure best results.

 

It is the Visible colour which is the most difficult for me to recover. Even with the white & grey Labspheres and the Colour Checker Passport, I sometimes feel that the Visible colour result is not quite right. Close enough, however, for all practical purposes. :)

And I make it a habit to make a Visible reference foto of the flower with an unconverted camera such as the D3S or the Coolpix A.

[nfoto]

That is why I prefer to use a separate camera for the reference shots. Makes processing easier and less prone to variation.

 

The best combination I have found so far is the D300 with the 120 mm f/4 Medical-Nikkor. The lens is sharp, but so are other Nikkors (and third-party lenses for that matter). However, the ring flash built into the 120 Medical does make minute surface details such as hairs come out very clearly and such characteristics are frequently required when a specimen is to be identified. My Medical is heavily modified though, largely because the philosophy behind Nikon's design is not optimised for the digital era. So the lens is modified to have the linkage between focusing and automated aperture setting broken and replaced by a CPU chip. This means you can dial in the aperture you want largely independent of the actual focused distance. The strength of the flash output can be chosen as well.

[Andrea B.]

Sounds very nice.

The ring flash is built in??

[nfoto]

Absolutely. I will probably write down more on this lens in the Methods section later.