With some DIY work, imaging spider genitalia can be done on a budget. The key components are listed below, with the respective estimated costs in Singapore dollars.
- Camera that allows fitting of extension tubes (~S$1000)
Almost any camera body that allows interchangeable lenses, or more accurately the fitting of extension tubes, will work.
- Microscope objective (~S$30 per objective)
Surprisingly, cheap no-brand plan or semi-plan objectives bought online can have good results. Imaging spider genitalia typically requires 4x for large spiders to 40x for tiny spiders.
- Adapter ring to fit the objective onto the extension tubes (~S$5)
Most microscope objectives have RMS-mount screw threads. Some, e.g. Nikon objectives, use M25/C-mount screw threads. These adapter rings can easily be found online.
- Extension tubes of sufficient length (~S$20)
Most commonly found microscope objectives are made to cast an image 160 mm from the base of the objective (where the objective’s screw threads meet the shaft of the objective), so extension tubes are required to space the base of the objective that distance from the camera sensor. This distance does not need to be very accurate; slight deviations of a couple of cm in this length will simply result in small differences in the resultant magnification. Some microscope objectives cast an image an infinite distance away from the objective. These infinity objectives can be used just the same as the more common objectives.
- Focus rail that allows fine adjustment (or operates using a worm gear, ~S$30)
Fine adjustment is crucial, the setup must allow focusing at small enough steps. Depth of field for microscope objectives can be around ten microns or smaller, meaning the focus rail must allow focusing at such small steps.
- A means to fix the camera and focus rail such that it is unmovable (~S$50-200)
A camera tripod, an old microscope stand, or any solid, steady stand or frame will work. The most convenient configuration will be to fix the camera such that it is pointing straight down. Slide-mounted specimens with cover slips can sometimes be mounted vertically such that the camera can be pointing horizontally.
- Sufficiently bright light source to illuminate the subject (~S$30-400)
Shutter speed needs to be around 1/400 or faster in order not to have motion blur, and ISO needs to be around 200 in order not to have significant noise (these can vary depending on your particular camera and setup). High power flashlights, microscope lights, or camera flashes are all possibilities.
- Image stacking software (varies)
At high magnification, it will be challenging to have sufficient depth of field such that everything is in focus in one shot. Stacking images will likely be a necessity.
- Remote trigger for camera or tether software that can control the camera (~S$5 or included in software)
At high magnifications, even very small movements will significantly shake the camera or specimen, throwing things out of focus. It is therefore important not to touch the camera if possible. A remote trigger, or controlling the shutter through tether software are options for taking photos without touching the camera.
Compilation and photos by James W B KOH.