gifs for Z-stacks?

I am gearing up for tests of a new iteration of my Lieberkühn reflector for 58mm diameter, f=35mm lens for macrophotography. This will be my first print in Shapeways bronzed steel material. In the meantime, enjoy some Lieberkühn enhanced macrophotography, in gif format.

The subject is the lovely Osmia aglaia, a beautiful blue solitary bee from North America. Compression for the GIF format does some fuzzy things to the photos, but it was still worth the experiment for a simple way to display z-stacks. Click for larger versions.

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I’ve also recently launched a new double threaded lens cap: stays on the lens when bumped or carried, and now each lens cap fits two standard lens diameters instead of one. They are available here in a variety of sizes, and you can see the firm attachment compared to squeeze lens caps demoed here . I have only tested this design out in the lens diameters I and a few friends own and use. I now need more photographers to try it out and provide feedback. With this in mind I will keep the Shapeways price as low as possible until some more theBilder threaded lens caps have had a run in the wild!

The advantages of parametric design

I work primarily in OpenSCAD when making designs for 3D printing (and 2D designs for lasercutting). This means that instead of a WYSIWYG interface based primarily on using the mouse, my designs are all scripted in a programming language that looks a lot like C. This might seem a bit more difficult at first (and it is certainly less than ideal for some situations) but it makes for a pretty simple way to generate repetitive structural elements in basic flow control, i.e. for loops. Even more important, it means that I can substantially change a design by modifying the variable values passed to a function (called modules in OpenSCAD). For the sake of an example, take Lieberkühn reflectors for macrophotography. Lieberkühn reflectors are a classic illumination technique that have mostly fallen out of style in favour of more modern illumination such as LED or fibre-based lighting, but remains quite elegant and offers a few unique advantages. I have been working with these in conjunction with a few different lenses, and mostly with the help of a macro bellows. The bellows makes for variable working distances as well as magnifications, so the focus of one Lieberkühn will be the most effective only within a narrow range of macro-bellows lengths. Parametric designs such as the ones I create and work with in OpenSCAD allow me to change attributes such as the nominal working distance without starting each design from scratch. For example:

LRWD35

35mm Lieberkühn focus

LRWD30

30mm Lieberkühn focus

LRWD25

25mm Lieberkühn focus

LRWD20

20mm Lieberkühn focus

This approach has proven highly useful for me in terms of both creating highly customisable design and iterating to get fit just right. I’ll post results of my latest exploration of Lieberkühn reflectors soon after I receive the latest realisation in Shapeways bronzed steel.

Quantitative comparisons of #macrophotography with and without Lieberkühn reflectors

In order to quantitatively examine the effect of the the 3D printed Lieberkühn reflectors I described previously, I came up with two image quality metrics relevant to their use, both measured on the “dark side” of the image subject. The metrics we will look at today are average intensity and, as a measure of contrast, the standard deviation of pixel values on a line trace.

I’ll be using the Megachile photo from the previous post for these analyses.

The first line trace begins at right eye and extends back behind the wing:

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RightEyeTraceValues

If we plot these values together, we see that the photo taken with the Lieberkühn (values in black) is brighter and brings out a lot more detail, while the photo taken without is relatively flat and dark. We see similar results for second and third traces, taken across the tegula and along the wing.

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If we compare the average values:

octave3.2:25> mean(RE523(:,2)) %with Lieberkühn, right eye trace
ans = 102.00
octave3.2:26> mean(RE524(:,2))%w/o Lieberkühn, right eye trace
ans = 54.093
octave3.2:28> mean(AT523(:,2))%with Lieberkühn, trace across tegula
ans = 81.553
octave3.2:27> mean(AT524(:,2))%w/o Lieberkühn, trace across tegula
ans = 51.288
octave3.2:29> mean(W523(:,2))%with Lieberkühn, across the wing
ans = 103.85
octave3.2:30> mean(W524(:,2))%w/o Lieberkühn, across the wing
ans = 53.045

We see that taken together, the averages of the plots from the photo taken with the Lieberkühn are about 80% brighter than those without.

mean(Lieberkühn)/mean(no Lieberkühn) = 1.8142

octave3.2:56> std(RE523(:,2)))%with Lieberkühn, right eye trace
ans = 20.316
octave3.2:55> std(RE524(:,2))%w/o Lieberkühn, right eye trace
ans = 7.3926

octave3.2:54> std(AT523(:,2))%with Lieberkühn, trace across tegula
ans = 17.737
octave3.2:53> std(AT524(:,2))%w/o Lieberkühn, trace across tegula
ans = 13.227

octave3.2:52> std(W523(:,2))%with Lieberkühn, across the wing
ans = 12.746
octave3.2:51> std(W524(:,2))%w/o Lieberkühn, across the wing
ans = 8.2902

Using standard deviation as a metric for image detail, we get an increase of about 75% in standard deviation over the dark photo by using the reflector.

octave3.2:30> (20.316+17.737+12.746)/(7.3926+13.227+8.2902)
ans = 1.7572

The averages, standard deviation etc. may seem a bit redundant at this point; you don’t need to plot a pixel-value profile to see that the image with the reflector is much brighter and more detailed than the photo taken without. Rather than “proving” that the Lieberkühn photos are better, these notes will serve as a baseline for future iterations of the reflectors made with different materials and/or with the addition of a reflective coating.

First tests of 3D printed Lieberkühn reflectors

Here I will report my initial tests of my Lieberkühn reflector designs, “hot” off the 3D printers at Shapeways. DSC_0503

I am testing a squeeze-to-attach Lieberkühn that roughly fits a Canon f/3.5 20mm focal length macro lens (above), and a 58mm threaded version (below), tested with a Canon 35mm f/2.8 manual tilt shift lens. I used a Canon auto macro bellows and a Nikon D5100 with an adapter for all test images.
DSC_0512 I haven’t added any reflective material to them yet, so they are essentially “Lieberkühn diffusers” for these tests. I used a domestic desk lamp with a 750 lumen halogen bulb to illuminate the specimens, for slightly off-axis trans illumination.

DSC_0528These are the legs on a cicada molt from last year’s 17-year brood. The photo was taken with the 35mm Canon tilt-shift lens at about the shortest macro-bellows distance possible.

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And here is a shot of the same view with the reflector attached. I used a 1/13 second exposures at ISO 1600 and f/5.6 for both shots.

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The large claws up front with (below) and without (above) the reflector. Again this was taken at f/5.6, an ISO 0f 1600, and 1/13 second exposure time. I increased the bellows distance slightly for this shot, increasing the magnification.

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Although the fill light is definitely better in the shots with the reflector, in some cases a photographer may prefer the image without using it, e.g. to bring out the small details with shadow. The cicada molt is partially transparent, giving a nice effect to the light transmitted through the subject.

I took the two photos of a leaf-cutter bee (Megachile genus, female) below with the same setup. The difference in lighting with and without the reflector is pretty drastic.

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I made the next two pairs of photos using the 20mm macro lens and the squeeze Lieberkühn reflector. The photos contain some apparent lens flare resulting from the off-axis light source, manifesting as a slight general brightening (and resulting loss of contrast) in the middle of each image. I am not sure if the aberration is reduced with the addition of the reflector or if it just looks that way due to the rest of the image being brighter. Looks like a job for some quantitative comparisons, for the next post.

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The position of the lamp and bellows stand were maintained for each pair of images. The bellows was set at the same distance but displaced between exposures to make room to attach the reflectors without disturbing the subjects, so the comparison images may be focused ever-so-slightly at different depths.

The lighting was definitely improved by the use of reflectors for these (mostly opaque) subjects. The images above were intended as a qualitative investigation, I will be looking into the performance and useability of the designs further.

As a final note, compare the print of the 58mm threaded reflector with the render from the STL file. The consistency is inhomogenous, with some bulges introduced during manufacture that were not part of the design file. Can’t say that I’m impressed with the print quality.

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render58mmLR