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UltravioletPhotography

Pasque flower, with different filter stacks, 2017


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In the end of May last summer I found some Pasque flowers, still in bloom.

Here in southern Sweden they are blooming quite early and I wasn't I wasn't sure I'd find any.

 

The Swedish name of this flower is Backsippa, Here it is a rather rare, protected plant.

 

My filter collection at the time was rather small, resulting in only four different image versions.

 

I tried and failed using a PTFE-target for white balance. The target in the images was overexposed.

White balance to taste, by clicking around in the images until a reasonable balance was found.

 

All images reduced to 22% from the original raw-files. The big images has a lot more details.

 

Camera: Canon EOS 60D, ISO100 .

Lens: EL-NIKKOR 1:3.5 80mm Nippon Kogaku Japan, the first version of the old metal-type lens.

 

VIS. Filter: S8612, 2mm. Exposure: 1/50s, f1/22:

post-150-0-15110400-1525016649.jpg

 

UV + B. Filter: S8612, 2mm + BG3, 2mm. Exposure: 0.4s, f1/22:

post-150-0-00535400-1525016670.jpg

 

UV + BG. Filter: S8612 + UG5, 1.5mm. Exposure: 0.8s, f1/22:

post-150-0-35627500-1525016689.jpg

 

UV. Filter: Baader U. Exposure: 4s, f1/22:

post-150-0-69048300-1525016710.jpg

 

In the second image the golden hues at twi the petals at the bottom is not due to saturation. The raw files was not saturated in any channel.

Could it be conical cells? I have no idea what such cells are. Please explain. I want to learn.

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Ulf, this is a lovely series, and I hope you will please consider entering it into our botanical section. I will help you with the formatting.

 

Conical cells are surface cells usually found on a flowers petals or rays. These cells both transmit and refract light to aid the plant in various plant metabolisms. Strictly speaking, the cells may are not actually conical (IIRC) but the top surface is curved is such a way that we often see see specular reflections or iridescence when photographing them in strong light whether visible, UV or IR. I have a link to a paper somewhere which has photos of conical cells. I'll look for that and put it here. The paper is a downloadable PDF which has some great photos of conical cells and lots of info about them.

 

Whitney HM, Bennett KM, Dorling M, Sandbach L, Prince D, Chittka L, and Glover BJ (2011) Why do so many petals have conical epidermal cells? Annals of Botany 108: 609-616

Full text: http://chittkalab.sb...20Ann%20Bot.pdf

 

The conical cell iridescence effects can cause color changes (by definition). The specular reflections, which are probably what is shown in your photo #2, cannot always be recovered with highlight tools back to the basic petal color. That's ok, of course, as specular reflections are a well-known part of photography.

 

Usually a blown highlight in 1 or 2 channels can be recovered, depending on the converter used. Recovering 3 blown channels (specular white) depends on the dynamic range of the camera and how much it permits pushed exposures ("the headroom"). Sometimes applying white balance to false colors can wrench the colors in such a way that bright areas which are blown become oddly colored. I often see green or cyan false color in blown areas of UV photographs after white balancing the false colors.

 

Some of this I know you already know :), but I try to err on the side of complete answers.

 

PTFE is easy to blow out. Have to dial back the exposure. Try putting your camera into black & white mode and keep the histogram off the right-hand wall.

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Andrea, Thank you for your kind words and an interesting document. I just had a quick peek now, but will read it later when I have more time.

 

I didn't think my pictures was good enough for the botanical section, as they are not white balanced against a well-defined reference.

I would like to enter them, as you say they are OK and will help correcting the format errors I will do.

 

The pasque flower was my main objective the other day, when I finished off with the anemone nemorosa I posted about recently.

 

I have more images of the pasque flower taken with several different new filters.

It will be a long post with many images.

 

This year the flowers look slightly different, possibly due to individual differences or because it is one month earlier than last year.

This winter also lasted longer this year.

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Ulf, the white balancing you are showing for the UV photograph is good. We are simply looking for that blue/yellow/grey/white/black palette in the UV photograph. (The blue does become blue-violet or grey-blue sometimes. That is OK.) There is no requirement for white balance with other filters such as the BG3 you used. So think it over and if you have time, make a botanical post. :)

 

Here is a good botanical reference website for you.

Den virtuella floran

 

The Pasque Flower is here:

http://linnaeus.nrm.se/flora/di/ranuncula/pulsa/pulsvul.html

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