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UltravioletPhotography

Lots of dandelions


Stefano

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I have a lot of dandelions growing in my garden. Today they are not fully open because of the overcast weather, but the pattern still shows up. This is just a quick photo I took, this topic is intended to be informal.

 

Do I need to post the settings?

post-284-0-04711100-1585228007.jpg

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Stefano, here is something interesting to look for. When the dandelion flower fades and closes up, an IR photo will show the closed involucre ("cup" in which the dandelion grows) as IR-dark.

https://www.ultravio...&attach_id=5163

 

I never really appreciated the intricacy and beauty of dandelions until I photographed them in UV and IR. :cool:

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Stefano, here is something interesting to look for. When the dandelion flower fades and closes up, an IR photo will show the closed involucre ("cup" in which the dandelion grows) as IR-dark.

https://www.ultravio...&attach_id=5163

 

I never really appreciated the intricacy and beauty of dandelions until I photographed them in UV and IR. :cool:

I remember noticing it too. It is one of the very few examples of dark plants in IR (not considering bark).
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Today there was more sun and the flowers (or better flower heads, right?) fully opened.

 

post-284-0-72715900-1585339709.jpg

 

post-284-0-76963200-1585339731.jpg

 

post-284-0-09656800-1585339738.jpg

 

Bees doing their job:

 

post-284-0-40254700-1585339753.jpg

 

post-284-0-66410300-1585339722.jpg

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And it looks like some bees or flies are also enjoying the Dandelions. :grin:
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Dandelions always attract a lot of pollinators. However that's smoke and mirrors as the plants don't *need* the pollinators at all ! All the microspecies of Taraxacum are apomictic (or to use an even more fancy word from the language of botany, agamogenetic).

 

If evolution was driven by easily understood forces we wouldn't expect such a strategy as making the flower parts surely "cost" the plants a lot of the photosynthetic energy they harvest. A number of the smaller microspecies of Taraxacum have taken this lesson to heart and produce little or no pollen at all. They still need having to flowers in order to set fruit and thus ensure their dispersal, though.

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  • 2 weeks later...

Taken two days ago. We are having a lot of sunny days in a row here (almost a week).

 

F-stop: f/2.8, ISO 400, 1/8 s exposure.

post-284-0-19899500-1586371780.jpg

 

I was lucky, but this was the best one out of 14 images taken in a row, keeping the button pressed.

 

Also notice how my camera probably "clipped off" blacks, those nectar guides are really dark.

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  • 11 months later...

And now, the updated version:

 

Camera: Full spectrum Canon EOS M

Lens: Soligor 35 mm f/3.5

Filter: ZWB2 (2 mm) + Chinese BG39 (2 mm)

 

f/3.5, ISO 3200, 1/30 s exposure.

post-284-0-11696300-1616191239.jpg

 

f/8, ISO 3200, 1/2 s exposure.

post-284-0-97072500-1616191343.jpg

 

f/8, ISO 3200, 1/2 s exposure.

post-284-0-10501300-1616191489.jpg

 

The apertures can be incorrect, the values I put are those I think I used. I didn't use a tripod, but the last two images were taken with the lens resting on a wall (first) and a rock (second). Beware, not the bare lens, but the filter, where there is the black tape. I would never put the lens on those surfaces.

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Wow you have dandelions already. We still don't have flowers yet.

This morning we even had a bit of snow, that melted after an hour or so.
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Also notice how my camera probably "clipped off" blacks, those nectar guides are really dark.

 

I'm not sure that your camera clipped blacks? It looks more like some minor contamination from vis or ir???

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How can darkness indicate a leak, in this case? I would expect the nectar guides to be lighter instead.

 

To me it seems like my camera clipped the blacks and those pixels became 0, 0, 0.

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The dandelion centers are a bit light or bright or whatever the appropriate term is when compared to most dandelion photos I've made. But not by much, so don't read too much into my remark, OK?

 

In the first photo in Post #16, the centers of the dandelions range from threshold 16 to threshold 64 which is an approximate brightness range between 6% - 25% 6.25%-25%. If we assume brightness can serve as a proxy for UV absorption, then this seems to be "dark enough" for all practical purposes of finding UV signatures. :grin:

 

I could not find any (0,0,0) pixels in the centers of the dandelions in that photo. I ran a threshold of 8 over the photo. This represents a 3.125% brightness or pixel value of, obviously, (8,8,8). The magenta areas are 0 - 3.125% bright (well, dark in this case). No magenta areas are in the center of the flowers, so no (0,0,0) there.

threshold8.jpg

 

 

It is probably totally WRONG to evaluate tonalities on a JPG. But maybe we are in the ball park.

Right now I would like to be in a ball park on a nice spring day.

 

 

A Ramble:

But I'm thinking that we don't really know just how dark those dandelion centers are "supposed" to be because we look at our UV photos with a brightness curve applied for human eyes. Although if we set up a photo using a range of UV standards next to one of the flowers, we could make a better determination of the absorption of the dandelion center. Even though the brightness curve would have been applied also to the standards, one could still compare the dandelion center to the standards. That seems like it would be a reasonable approximation of the actual UV absorption measured spectrometrically. However, this "eyeball" comparison of darkness would not have good granularity because some tonality is squished when the curve is applied.

 

"squished" is a very useful scientific term.

humor alert

 

 

 

Edit: typo in values.

 

Ah well....Stefano forgive me for rambling on. I don't want to go clean the house which seems to be terribly full of dust from the recent winds here. It is a LOT more fun to play around with thresholds of dandelion centers.

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Andrea, keep in mind that the images were taken with two different cameras. The image you were initially referring to, I think this one, was taken with my old point-and-shoot.
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No, I was referring to the one I posted above with the Canon and the ZBW stack.
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