This is a two-part adapter to take commonly available laser modules and heatsinks found cheaply on Ebay (just one example: for under $15, many also available https://www.ebay.com/itm/Red-Diode-Lasers-650nm-Module-Dot-Line-Cross-LED-5mw-Focusable-with-Heatsink/262203403699?hash=item3d0c8a6db3:g:IJ4AAOSwHPlWeRlU ) and hold the module precisely in place at the camera eyepiece.
Why would you want to do this? In photomacrography, one often works at magnifications high enough to make aiming the camera at a particular feature challenging - anything above about 2x life size but especially above 5x. However, you can use the optical system of the DSLR in reverse with the mirror down and a laser at the eyepiece; it will illuminate the subject precisely at the point of focus making it much easier and simpler to align the camera with the tiny feature of interest. Additional details with many images on this at https://www.photomacrography.net/forum/viewtopic.php?p=155824#p155824
Most people previously used homemade adapters to hold the laser in place, but this is my attempt to standardize and distribute a model which hopefully is useful and adaptable. This model allows alignment of the laser and eyepiece in 3 axes. It is a two-part model; part 0 mounts to the camera and has two slots which part 1 connects to via 3 mm screws to control height; part 1 then has four aligned slots to mount the laser heatsink which allow a few mm of horizontal translation of the laser module. The heatsink itself has set screws which allow forward/back translation.
As provided this model works on Nikon DSLRs, tested on D7000 and D200. Other manufacturers would need to model a replacement for part 0.
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