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UltravioletPhotography

Never-ending story: getting higher UV resolution


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I'm currently on a quest to get more UV detail in my documentary work. The main underlying reason is of course to come to better grips with these elusive conical cells we may get a glimpse of in our stock UV work, but rarely can observe in any detail.

 

As I already have the top-flight lenses such as Coastal Optics 60 mm f/4 APO and the 105 UV-Nikkor(s), more detail translates to higher resolving power of course. You can get some of that by using good technique in conjunction with a UV-capable camera of higher pixel dimensions, but in oirder to get a significant increase in detail, the magnification itself has to be hiked up from the standard half- to full life-size range our lenses typically provide. Photomicrography (shooting through a compound microscope) requires specialised UV micro lenses that are extremely costly and at this stage of the exploration 5-10X will do nicely enough. Thus we deal with photomacrography instead.

 

Why not just add extension to the UV-performing lenses I already have? It is a matter of practicability. Even in a studio, 50 cm bellows extension and all that this entails, is literally an awkward package to deal with. What you really need is a shorter focal length lens that will require less extension. alternatively, try to reverse-mount the existing one. The UV-Nikkor 105 still is stubborn and won't open up the true 'macro' domain for you, but the reversed 60 APO will, albeit the required extension is large and cumbersome to handle.

 

You also need passable UV performance and by that it is implied not only sufficient UV transmission (preferably as low as possible, but going toward 350 nm will serve many applications adequately), but an ability to 'draw' a UV image without too high loss of contrast and deterioration of image quality. The latter being in fact the bigger problem in my experience. It goes without saying that these issues do not apply to the Coastal 60 :D. This specimen is as good as it gets.

 

These days, I have narrowed down the experiments to deal with Coastal 60 APO reversed, 55 mm f/2 Ultra-Micro-Nikkor, Olympus 38 mm f/2.8 OM Macro, and a Canon 20 mm f/3.5 bellows lens head.

 

I'll keep this thread updated with pictures and more text on the topic, for now have to dash for an outdoor assignment.

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I regularly see UV lenses being offered on internet auction sites, but most commonly they are of high magnification, 20X–100X. The ones designed for 5X–10X magnification are much less common, but can still be found at relatively acceptable prices (much less than UV-Nikkor or Coastal 60).

 

How does the Canon 20mm f/3.5 bellows lens works for you? Have you posted any examples yet?

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I can get about 3x life size with my cheap DO Industries which has about the same transmission as El Nikkor 80mm. I took a photos this morning of an Asian lily. then used 100% crop of the jpeg file. not sure if these are conical cells.

 

post-41-0-21264300-1406731938.jpg

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Another option to get a bit more resolution is to use monochrome camera – I am sure you had already considered that, Bjørn?
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I keep trying to read the scale bars on the SEM images in Whitney et al without much success to try to find out how small conical cells really are. Here http://floweringhighlights.org/2013/03/05/how-flowers-excel-in-their-hospitality-the-evolution-of-papillate-conical-cells-in-petals-is-linked-with-accommodating-the-right-visitors/ is a more recent reference for RBG Edinburgh which has a SEM with a scale bar of 20 micrometres so we have a fair way to go before we can reach those sizes optically.
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20 micrometers is not a problem for a microscope. As I said above, the high magnification microscope objectives designed to work in near-UV are common.
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Bjørn,

 

You've probably already seen this (and it is a bit hackneed), but I'm wondering if this type of a "rig" would be right for what you are attempting to accomplish? I'm not certain if one can obtain quality lenses that pass the correct wavelength to create a rig like this, but it might be worth looking in to.

 

http://chaoticmind75.blogspot.ru/2013/08/my-technique-for-snowflakes-shooting.html

 

Ahr

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Bjørn,

 

I think I understand the direction you are taking.

 

This paper might be helpful:

 

A tandem-lens epifluorescence macroscope: Hundred-fold brightness advantage for wide-field imaging

Journal of Neuroscience Methods, Volume 36, Issue 2, Pages 127-137

Eugene H. Ratzlaff, Amiram Grinvald

 

My university library's digital subscription to this journal only extends back to 1995 so I do not have this paper.

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Bjørn,

 

I calculate ~2.6X for a 40mm EL-Nikkor reversed onto the front of a 105mm UV-Nikkor. That is not quite the 5-10X you are looking for but should be reasonably UV capable within the limitations of the EL. One of those UV-Rodagons would surely be a better UV match for the UV-105.

 

Question, would then a slight bit of extension tube behind the UV-105 increase the mag to within that range? You like to seclude filters behind the lens anyway.

 

I have never done this before, but I reversed a 50mm EL-Nikkor onto a 135mm Takumar out of curiosity. I photographed a ruler and got a ~6-7mm wide frame on my G3. 135/50=2.7 so that is about right for a 17.3mm wide µ4/3 sensor. It was really hard to focus with such razor thin DOF, no problem for a master such as yourself!

 

As usual following you educates me, thanks!

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A very short progress report: some of the tested lens combinations do work in the 5+ X range, also for UV. However, there is a practicality issue here such as getting higher and (presumably) better quality clashes rapidly with the reality of field photography. Thus, I limit myself to 3-4X as this seems to be what one can acquire in the field without so much hassles and troubles to lose whatever hair you have left. Higher magnification than that is studio work exclusively. Plus you really need the more powerful output provided by studio flashes run on A/C.

 

For the in-field 3-4X range, I can scrape by using for example the Olympus OM 38 mm f/2.8 macro lens head in conjunction with a moderately sized focusing extension, and my SB-140 flash used at close range can give pretty decently exposed UV images at f/11 200 ISO with the Baader U2" (Venus) filter. Focusing has to be conducted using the optical viewfinder on my D3200, which just barely is acceptable at these small effective apertures. Fortunately, the Olympus lens seems to have little focus shift from visible to UV.

 

An example of what you can get in terms of added detail at 4X with the Olympus 38 mm lens. This is 100% crop of the upper lip of a Common Cow-wheat (Melampyrum pratense; Orobanchaceae). The camera rig + flash was used hand-held (not recommended unless you are as stubborn as me), and the crop is just a tiny section of the 24 MPix frame.

 

MELA_PRA_I1408052130_UV_upper_lip_100pct.jpg

 

One can readily discern different kinds of conical cells of the corolla here. There are streaks of larger extending cells alternating with shorter, papillate ones. The corolla of this species previously was thought to have "no UV pattern" at all as it will photograph quite dark and without much detail unless you have adequate resolution available.

 

Other captures, not provided here, indicate that the conical cell structures are as diversified as the flowers themselves. Some flowers (e.g., Lysimachia nummularia) have petals with structures shaped as parallel oriented ridges (striations). These cause an intense shimmering play of light.

 

Better definition would require 8+ X magnification and the use of stacking methods, not just the single-shot approach demonstrated here. However, we then are well and truly confined to studio settings.

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Forgive me if this comment just complicates the issue. As the magnification is increased doesn't the effective aperture become even smaller so that the dreaded Airy disc diffraction effect softens the image much more than you would think by just reading the aperture set on the lens. So, doesn't that lead to a point where even at maximum lens aperture the results are suffering from diffraction-induced softening?

 

Dave

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That is the pessimistic version of the matter. In reality the situation is not equally bad as you have much more headroom than so.

 

Do remember diffraction while unavoidable, is not similar to running into a brick wall. It is a gradual softening of the image that can be combated by optics better corrected for high magnification at wider aperture, using stacking to gain more depth of field than by stopping down alone, by lighting the scene with more contrast and using shorter wave lengths, and by using higher resolving media for the final capture.

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And also a little judicious application of sharpening tools in the editor can quite often tighten up the diffraction softening in those areas where detail has not been lost.

 

Bjørn, your Melampyrum photo is more like a map of the surface cells on that portion of the petal. I cannot get a sense of depth from it. [bTW, kindly take this as an observation and not a negative comment.] So I was wondering if you used a UV polarizer you might be able to control that white blowout from the conical cell refraction? We have never investigated the use of a UV polarizer. I think it would be a useful experiment. So, ha-ha, who is going to spring for one first?? They are likely to be pretty pricey!

 

Also this is a case where you should, in my opinion, use the D600 for its better handling of dynamic range. The ADL setting is so very useful in these situations because even though it does lower exposure, it does provide 1/3 EV gain in the shadows and between 1/3-1 EV gain in the Highlights when used between the Normal to Ex High settings. Of course, you would have to make a conversion in View or old Capture to preserve that. But surely the occasional conversion in View or old Capture can't be too tough. "-)

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Seeing a bigger portion of the frame would help ...

 

For field use, D600 will not do. I need visual focusing.

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I'm also interested in getting as close as I can to the texture of the UV images, which presumably means conical cells.

 

Here's a 100% view of a recent image of Eucalyptus nicholli

(yet to be formally posted)

 

post-28-0-30663900-1407457630.jpg

 

Do you see lines of conical cells in your images?

 

Dave

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