31 replies to this topic

[nfoto]

Just a few examples of recent experiments with photomacrography in UV. I have confined myself to the range 5-10 x, which is just doable in a studio setting, and have explored the potential of fairly ordinary lenses for macro work.

First example is the corolla of Lysimachia punctata (Primulaceae). Shot at 8X using the D600 (modified), 100 ISO, Baader U2"(Venus) filter, Canon 20 mm f/3.5 Macro lens head at f/5.6, and Broncolor Studio flashes (uncoated Xenon).





The conical cells here are formed in shape of elongated ridges with rugose crosswalls. The long dimension of these cells are along the length of the petals. Interspersed are short, stubby glandular hairs. These hairs make the surface rough and give rise to the vernacular names such as 'Dotted' or 'Spotted' Loosestrife'. The glandular hairs are particularly plentiful along the petal edges.

[Andrea B.]

Very interesting.

I have a stupid question. How do you know what magnification you are shooting at? Thanks.

[nfoto]

Simple: either measure by shooting a ruler, or, in this case better: calculate directly using focal length f. Just measure distance v from the aperture position of the lens to the film plane mark on the camera and get magnification m = v/f -1. This formula uses thin-lens approximation, but for these conditions that is more than adequate.

[Andrea B.]

Is that (v/f)-1 or v/(f-1) ?
I should just go look that up.

Added: Looked it up.
it is (v-f)/f = (v/f) -1, give or take a minus sign.

ok.

(v-20)/20 = 8
v-20 = 160
v = 160 + 20 = 180mm which is about 7 inches.

So the canon 20 is on a bellows?

[nfoto]

Given that m=>0 when v=>f (infinity focus is v=f), the equation should be self-explaining taking operator precedence into account. ( or maybe I'm too bound to programming languages and their inherent properties) .

I used a focusing helicoid in conjunction with a filter box to get rear filtration as no filter(s) would have room in front of the lens. Yes, total extension lens-film plane about 18 cm is correct.

[JCDowdy]

Can you get enough UV to image from your UV LEDs?

The narrower spectrum might raise additional detail.

[nfoto]

Probably, but not tempting as that will introduce lot of hassles with long exposures and vibration. I might try again with a narrow-band filter instead of the Baader. A breeze as I can just put another filter into the filter box.

Whether the quality of the Canon lens is sufficient to warrant these additional steps is another discussion for which the jury is still out.

[JCDowdy]

A filter box is very nice when one has the space.

[Andrea B.]

Hackers can make use of operator precedence, as I did for 20 years, in the various coding languages. But Mathematicians typically make operator precedence explicit with extra notation because operator symbols can have varied meanings in different mathematical systems. Here you're talkin' arithmetic operator precedence in the Real number system. So as long as spacing does not cause ambiguity - as it did here for my tired eyes - no parens are needed. Stray outside the Reals into a group or a ring or whatnot, and parens are de rigeur because rules of precedence may go pie-whackety for the same symbol set. Or should that be π-whackety?

[Sorry other readers. Bjørn and I sometimes have these conversations. It is the only chance I get these days to remember what it was like to be a Math nerd. Bjørn is kind to let me do that.]

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It is raking light which helps bring out detail.
But that is an interesting question as to whether a narrower spectrum would bring out more detail?
Probably depends on what the detail is?

[nfoto]

JCDowdy, on 18 August 2014 - 21:17, said:

A filter box is very nice when one has the space.

Even when subtracting the 46.5 mm required for flange-film plane of my Nikons, the remaining 130-140 mm extension leaves plenty of room for a filter box. My box (from German company Teleskop-Service) has a minimum length of 22 mm and normally extends to about 25+ mm with mount adapters attached on either end.

[Andrea B.]

Are such filter boxes still available from Teleskop? I've never used one. Sounds cool.

[nfoto]

Yes, visit http://www.teleskop-express.de/shop/ which is their online shop.

I think the site is in German only, but the pictures are self-explanatory. Besides, German is not that difficult to understand.

I can make a separate post on the filter box and how it can be adapted to our camera systems if you like. As it uses 42 mm threads on either side, adaptations is simplicity itself.

[JCDowdy]

Filter boxes, also called filter drawers or filter sliders, are available from several makers. For putting filters between the camera and lens they are very convenient if you have the room. Mine is from Starizona and I really like it. I am considering having custom mounts made to improve it.

Andrea & Bjørn, this will make a good addition to UVP's Technical Zone.

[Andrea B.]

Yes please do a little write up. Both of you. Good information.

I'm able to navigate a German site fairly well. Mike knows some German. Klaus has helped me out in the past.
I've ordered from Baader and from another place I like which always has good step rings in stock.

QUESTION_1: Aren't you adding to the lens extension with these filter boxes?

QUESTION_2: Can you slide the Baader-U into these without takiing it out of its fitting?

[nfoto]

Re 1: Yes, you do add about 25 mm extension with the adapters in place at either side. Thus, if you add the filter box in a rear position, you often cannot reach infinity focus unless the lens itself is fairly long and/or lacks its own focusing helicoid. Do note you can front-mount the box as well, provided the lens has a narrow enough field of view so vignetting is avoided. This works well with the UV-Nikkor.

Re 2: You screw the Baader U into the internal filter holder and thus can slide this holder in and out of the filter box. They provide an insert for smaller 1.25" filters. Or you can make your own adapter for small filters.

[nfoto]

Tried the Canon lens on petals of Dasycarpa (Potentilla) fruticosa. This is a species with dark to very dark appearance in UV, and initially believed to "lack" a UV signature. Which of course is plainly wrong and caused by insufficient methods.

First, a quick shot of the D. fruticosa pulled from my archive. Not the same flower as I shot with the Canon lens, but it is the very same bush (on my front porch, by the way, and it is now coming into full bloom).


Ultraviolet light: Nikon D40X (modified), Coastal Optics 60 mm f/4 APO lens, internal Baader U2" (Venus) filter, SB-140 flash.

With the high resolving power of the camera and lens in UV, one sees the petals aren't really featureless UV-dark, but has variegated areas due to the presence of conical cells.

Now, fast forward to this shot taken with D600 (modified), Canon 20 mm f/3.5 macro lens at f/5.6, Baader U2" (Venus) filter in filter box, Broncolor studio flashes (uncoated Xenon tube), m=10.5X. I selected to shoot at an incidence angle of 60 degrees in order to bring forth the 3D shape of the surface of the petals. Thus, focus stacking was required to gain adequate depth of field. I used 26 frames for this capture.



A small section of the petal shown in 100% (average m=10.5X) . Some stacking jitter adversely impacts the final sharpness, plus I'm not entirely convinced the Canon lens performs very well in UV. However, the orderly lines of taller and narrow conical cells amongst the smaller papillate surface cells are very evident. It should be noted these cells are much smaller than what was documented for Lysimachia punctata earlier in this thread. Also noteworthy is that either configuration of conical cell shape makes the cells to reflect UV brightly. The overall effect apparently is Nature's original version of optical brighteners: flower colours will gain clarity and appear more vivid.

[Akira]

The pin-like lugs look very interesting. Maybe the pollinators can "free-climb" the petals by holding these lugs?

[nfoto]

That is the 'Velcro' hypothesis, which obviously cannot be disregarded seeing these structures in more detail. I for one like to think in terms of 'optical brightening' effects as well. You do need to attract the pollinators in the first place and how can they utilise the 'Velcro' if the flower itself isn't detected?

[Alaun]

Smell and a feeling like going on velvet?

Nice work!

It reminds me to work with an SEM: You discover a world of is own, you never would dream it is there!

[nfoto]

Another example from Lysimachia punctata. D600 (modified), Canon 20 mm f/3.5 @ f/5.6, ISO 1600, Baader U2" (Venus) filter in rear-mounted filter box, Broncolor studio flash (uncoated Xenon tube), m(average)=10.1X, incidence angle 63 degrees.

I initially shot this as a stack of 53 single frames. However, stacking jitter destroyed much of the detail sharpness so I resorted to slicing 5 and 5 frames for separate short stacks. I also initiated measures to abate the adverse impacts caused by overheating of the poor specimen during the barrage of high-power flashes fired at close range. I drilled a hole in an aluminium block to provide a water reservoir with efficient cooling, and placed the cut flower into this hole. Apparently worked quite well. I have plenty of copper coolers (from discontinued PCs) so if the Al block is insufficient, the heat-dissipating area can be extended.

Here is an 100% crop from one of these stacks. The details now are better preserved.



We now see the sharply ridged long cells with an intricate cross structure along the ridge, and appreciate how UV is reflected off by these cells.

As to the Canon macro lens head, it is by itself not that bad in terms of sharpness. However, I do wish it had a better UV response as I'm forced to crank up ISO more than I really like. For the next runs, I probably use the lens at f/3.5 (wide open) to be able to lower ISO, and rely on focus stacking for adequate depth of field. I think one has to shoot these scenes at a slanted angle in order to appreciate how the petal epidermal topology is manifested.