Well, I’m back from vacation, the fires are over, it’s below freezing at nights, and we had our first small snowfall. I have a feeling fall is here.
To celebrate(I originally put ‘mourn’ here, but with the fire season, I’ll stick with celebrate) the death of summer, I thought I’d look at some more flowers. Not just flowers, but sunflowers.
I took this photo back in July. The sky was smoky, so there is a red tinge to the photo. I thought about correcting it, but if I’m looking at the spectra, it seems counterproductive to start altering it. I try to keep my white balance set to match a piece of white paper on a clear sunny day; if the colour of the sky is changing, the camera won’t adjust the photo to make it less noticeable.
Sunflowers are named because they turn to follow the sun, but the bright yellow colour MUST have something to do with it too, in my opinion. Anyways, these sunflowers must have been defective- I haven’t seen them follow anything yet, and they’re at the end of their life…
So, it’s a sunflower. Pretty, but there’s nothing special in the normal photo. Broken into the red, green, and blue channels, the usual trends can be seen. Like last time, the border around the photo indicates the colour channel.
As normal, red and green are fairly similar. The outer petals are similar shades, while the centre(apparently consisting of something called disc florets, as it was too early for seeds to form) is noticeably darker in the green channel than the red. Black spots form a regular pattern in the florets in both channels, as well as the visible spectrum photo. The leaves, grass, and pavement in the background are all similar in both channels.
The blue channel is… not as similar. It is normal for foliage to be very dark in the blue channel, but the flower is much darker than even the leaves or grass. As it is, the channel is so dark that it is hard to distinguish much detail from the flower. The divisions in the centre are most noticeable, with light and dark rings, but more on that later.
Near infrared(With a Zomei 760 nm filter) looks similar to the red and green channels.
The disk florets seem more clearly defined than in either visible channel photo. The background sunflower on the lower left shows this especially well. The leaves and grass in this photo are brighter compared to the pavement, but that’s not really a surprise. I should mention that due to the properties of the smoke in the sky and the fact that foliage appears much lighter in infrared, the infrared photos were taken at a much faster shutter speed than the visible photos. It’s not something that is apparent when viewing the photos, but it matters when taking them.
My Schott UG11 filter also looks similar to the red and green channels.
This filter allows a small amount of near infrared light through, and a large amount of ultraviolet light. As my camera isn’t too sensitive to ultraviolet, the end result when taking pictures of plants is often more similar to infrared; the smoky skies probably help with that. Normally most plants are pale green, the sky is a deep indigo, and almost everything else is grey.
On to pure ultraviolet, things get more interesting. I’ll start with my triple stacked UV filters (The UG11 filter to black visible light, than both my Schott BG40 and my homemade short pass filters to block infrared light). Once I do this, the laws of floral/stellar evolution become clear. It turns out that the regular old sunflower…
.. becomes a black hole flower!
I’m keeping that joke, by the way. I’m proud of it.
Yeah, in the shorter wavelength, a noticeable dark ring appears in the petals of the sunflower. It is actually visible in the blue channel photo…
… or at least it is if I bump up the brightness and contrast A LOT.
In ultraviolet, the haze is detrimental- exposures take much longer. In this case, the triple-stacked UV photo above took 1/5 of a second, once I went to the maximum aperture size(f 1.8- the other photos were taken at f 3.2). It wasn’t too bad, but the barely noticeable wind did slightly blur the flower in the triple stacked photo.
The dual stacked UG11+BG40 filters show are very similar(a minuscule amount of infrared light leaks through, according to other sources, but I can take UV photos much quicker with this combination than with the triple stacked filters)
The colours are different from the triple stacked filter, but as they’re both false colour anyways, it doesn’t really matter to me. I’d assume that the colour variation is a result of IR leakage, as mentioned above, but I never looked into it.
The short pass(UV, violet, and some blue light) filter I use was much quicker than either other UV combination, and the patterns were still clear to see even with the visible light entering the camera.
Like the blue channel, the the outer edges of the petals are brightest, getting darker about half way in. The disk florets are all darker, but an especially dark ring exists in the middle. I THINK that the centre of the flower has been pollinated and is starting to transform into seeds, which might explain why it doesn’t look as dark. As for the difference between the middle and outer florets…I have no information to explain this, but perhaps the outer ones are newer than the middle ones. If they’re like some other flowers, they may change colour as they age, perhaps when they are pollinated? The blue channel shows this too, as does the triple stacked photo.
I might have to look into this next year farther. Right now, all the sunflowers are the colour of ‘dying’, so it’s a little too late to do a day by day comparison.
To sum up, If you could see into the ultraviolet range, sunflowers would look completely different. The dark ring would change the colour significantly. Here is a false colour photo I played around with. The red and green channels are unaltered, but the triple-stacked filter photo is replacing the blue channel.
The contrast in UV results in the outer edge of the petals of the sunflower being almost white; as it gets closer to the centre, the flower gets darker and more colourful.
Another way of visualizing it might be by thinking of evening sun sunflowers.
(photo taken from Wikipedia )
It seems like these flowers have a similar pattern, but in longer wavelengths. Instead of the dark bullseye in UV, it seems to be present around the green wavelength. I’m not going to ‘dissect’ this photo into the colour channels, as I’d rather do that with my own pictures. I’ve seen a few of these sunflowers around, but never taken a photo of them. I’ll have to look around next year to see if I can do any UV comparisons of them.
That’s for next year, though. This year, the flowers are finishing up, and autumn is around the corner.
I should be back to doing weekly updates for a while- no trips or interruptions planned. I have a backlog of photos from my trip, so probably won’t get around to posting them for a while yet.
The above photos were taken with a modified Canon Rebel T3i camera.