Scales Fringing the Eye of a Male Giant Predatory Mosquito

© Geoff Thompson

I am a Collection Imager at Queensland Museum (QM), Brisbane, Australia, with 41 years of service at this institution. I started illustrating insects by hand in 1975, at University of Queensland and continued illustrating this way till 2004. In 2005 I won a Queensland-Smithsonian Fellowship to work for 15 weeks at the Smithsonian’s National Museum of Natural History in Washington DC. There I learned to illustrate digitally and evaluated imaging systems in use at the time. In 2011 I won a contract, worth over $260,000AU, with The Atlas of Living Australia (an Australian Federal Government initiative) to purchase imaging equipment and supply images of the QM collection.

The Visionary Digital imaging system purchased at that time has been well maintained and greatly improved by QM and can produce images of tiny invertebrates in stunning detail and natural colour. Its main purposes are firstly to share images of definitive, type specimens, of both new and already known species, with scientists all around the world and secondly to produce spectacular images for display and popular publications.

The system uses a patented lift to move the camera with the focus set to manual. The software that controls the camera lift has built-in settings for the system’s suite of lenses, at various marked magnification points, where this is an option. Once points of top and bottom of focus are set, the system takes a series of photos from top to bottom, at regular intervals, precalculated so focus overlaps from one image to the next. Profoto studio flashes, carefully angled, reflected and diffused, fire at each shot. Magnification stays the same.

In 2017, after a major upgrade, we started using Mitutoyo objectives on a 200mm telephoto lens. This setup was researched and recommended by Roy Larimer, who supplied and built the system. Sadly, Roy has now retired and no longer builds or supplies these fabulous systems.

The telephoto lens acts like a tube, when focussed on infinity. This setup allows the beautiful Mitutoyo objectives to fill the larger, 50-megapixel sensor of the Canon 5DS camera, without any apparent loss in quality. The lens must be used wide open, otherwise bad vignetting is evident.

In May 2022 we took delivery of a new 50X Mitutoyo objective, purchased with exhibition funds. I wanted to take some spectacular images that could be used for a planned insect display, opening later in 2023.

The objective can resolve 0.5 microns and more than doubled the maximum magnification possible on our system, but the increased magnification comes at a cost. The camera moves in tiny one-micron steps, requiring many more source images. This means consequent increases in wear and tear on the camera and flash units, as well as significant increases in both photographing and processing times.

This image was my first serious attempt with the new objective. After keying in step size values and calibrating a new scale, I tried it out on a new specimen of the Giant Predatory Mosquito, Toxorhynchites speciosus. This is a beautiful, non-biting species which has larvae that eat other mosquitoes. Colleen Foelz kindly collected three pupae, which emerged the week before and I pinned them out carefully for possible 360° imaging. I pined the specimens from underneath, avoiding piercing the upper surface of the thorax.

This stack from over 240 source images has revealed incredible detail in the beautiful, coloured scales fringing an eye and amazing columnar ommatidia in part of the eye itself.

Each 55-megabyte Camera RAW image was exported as a 16-bit TIFFs, each about 290 megabytes in size. This required 83 gigabytes of disc space before Zerene Stacker software could begin the actual focus stacking. The final focus-stacked image is about the same size as one of the source images and of course we discard the source images after the process is complete. The composite image was then edited with Photoshop and sharpened with Topaz AI software. Calibration of the whole system’s set magnifications allowed a digital scale to be easily added with Photoshop.

Single-shot depth of field at this magnification is tiny. So, I had no idea what the resulting image would show until focus stacking was complete. I was absolutely astounded by this first result, despite over a decade working with focus stacking technology. I feel enormously privileged to be able to explore this tiny, beautiful world and show it to others.