Here is a bur from the Medicago polymorpha plant, known by common names including smooth burclover. A botanist friend of mine collected if from Barry County, Michigan (USA), where it has not previously been reported. His discovery of it there did not especially surprise him, as this Eurasian plant has become an invasive throughout much of the USA. But it has so far only been reported in two of the 83 counties in Michigan. My friend asked me to document the bur it before he reported it to state and federal agencies. Particularly, he noted that the curved spines are not generally well represented in photographs, and seem to be well adapted for dispersal via the fur of animal feet and legs. He found this plant growing on a horse trail, and conjectures that it traveled there on the legs of horses.
This is my first use of the Nikon M Plan 2.5x NA .075. In direct comparison during this shoot, I found it markedly superior to my reversed EL Nikkor 50mm f/2.8 enlarging lens (set between f/5.6 and f/8 ), other than the fact that the M Plan vigetted at the edges (which I cropped out.) I have a suspicion that a Nikon micro lens, reversed, might perform better at this low magnification, but have not directly tested that conjecture,
This was shot with a Nikond D200, 191 images at 20 micron intervals, stacked with Zerene Stacker. Yes, probably more images than I needed--am going to have to do some direct testing, as am not sure I trust the calculated approaches, which rely on aspects such as what the photographer considers acceptable. And I really should do a little more cleaning up at the edges--though for my friend's purposes in documentation, this image will likely serve as is.
As always, comments, criticism, adulation or flagellation welcome and invited.
On the downside, from this particular picture I think I get the wrong impression of overall shape. I'm seeing it in this picture as basically a sphere with hooks popping out all over the surface. But from other pictures at the link you gave, I think the structure is actually a tight spiral with hooks on the outer margin. Is this correct?
Presumably the structure would become clear from an oblique or sideways viewing angle.
But since this is a deep stack, you might also try making a stereo pair from the images you already have, using Zerene's synthetic stereo tool. See HERE and HERE for some more info about that. Whether stereo would help for your audience, I have no idea. It does for some, does not for others. HERE is an older true-stereo pair of a spiral seed head that might give you an idea of whether stereo would help for you.
Thanks for your comments about the lenses. That's useful info. From the standpoint of aperture, your two lenses are not much different. The objective at 2.5X and NA 0.075 is equivalent to an ordinary lens set at f/4.8 and also running at 2.5X. So it must be that the objective has less aberration or flare. Can you describe more precisely what "markedly superior" means?
--Rik
Edit: to correct a grievous error in calculation.
Last edited by rjlittlefield on Thu Sep 17, 2009 9:18 am, edited 1 time in total.
Andrew, the working distance is listed at 11mm. I haven’t directly measured it myself, but that number feels about right.
Rik, agreed, a side view of this bur shows something that an end view does not, and vice versa. Under the dissecting scope, I get the impression that there is a central seed, and that the spines come off a tendril-like structure that spirals around it. Ideally, I think three separate views would be nice: End on (such as this) to best illustrate the hooks, side on (as you’ve suggested) to better illustrate the spiral nature of the hook-covered tendril-like structure, and some sort of dissection that shows us what the underlying structure really is.
I’ll probably do the side view, but alas, I can’t dissect this bur, as my botanist friend intends to plant it for his herbarium. Where people of more limited abilities, such as myself, need to see many plants flower or fruit in order to identify them, my friend can generally identify them at any stage of the plant’s life—and he does this by minutely studying each plant from the time it first sprouts through the point where it is nothing but desiccated, wind-blown winter remains. With an invasive such as this, he’ll harvest the specimen before the seeds become viable—but he’ll minutely study all the earlier stages, and the harvested specimen will be pressed, mounted, and join many tens of thousands of others in his herbarium.
When I lit this image, I found that even from the end-on view, if I used enough diffused light, I could show something more of the spiral nature. But when I did that, the curved spines showed up much less starkly, and that was what my friend had particularly asked me to document. To emphasize the nature of the spines, hard side-light worked better, to which I did add some diffused fill, though trying to keep it low enough not enough not to draw attention away from those spines.
Admirable stereo pair of yours, Rik. Of course, now I’ll be seeing double for an hour or so.
As for what I meant by “markedly superior,” I wish now that I’d kept some of the comparison images. Using about the same magnification, I focused each lens on a particular spine near the center of the image, in a spot where the spine ran fairly parallel to what we used to call the “film plane.” I took a series of images, slightly adjusting focus each time, and compared the best such image from both optics. The 2.5x M plan showed me quite a bit more detail. The difference was not subtle. I was in a hurry to get the image shot (was borrowing time from a project I’m supposed to be working on right now) and didn’t consider the matter further. It would be pretty easy to arrange a more authoritative test at a later date, though.
I’m yet satisfied with the sharpness or detail I’m getting at this range. Rik’s bur looks quite a bit better to me. Olympus 80mm bellows lens, hmm?
Chris R, I did use a hood on the reversed enlarging lens. I used a ring of black paper—not a pointy cone, but a simple cylinder. However, I wrapped it not around the entire lens, but around the small area from which the glass itself protrudes. In past tests, this has given me the best results.
Chris S. wrote:Rik’s bur looks quite a bit better to me. Olympus 80mm bellows lens, hmm?
Be careful to note that 1) my seed head is about twice as big as your bur, and 2) all of these images are being posted at a reduced size where lens resolution should not be an issue.
What you're seeing is probably some combination of lighting, differences in surface texture, and post-processing such as sharpening.
I am very fond of the Olympus bellows macro lenses. But I have not tested them head-to-head against other high quality lenses. Offhand I have no reason to believe that the Olympus 80 mm f/4 I used for my seed head would be significantly sharper than an EL Nikkor 50/2.8 at same magnification and optimum f-stop.
