The hot shoe red dot sight adapter allows you to mount a red dot sight onto your camera's flash hot shoe. A red dot sight greatly facilitates taking pictures of birds and other fast-moving objects with a telephoto lens.
The window of the red dot sight shows a glowing mark (dot, cross-hair, etc. depending on the model) in a way that mimics a laser spot. You calibrate the red dot sight so that its mark corresponds to the center of your image frame when you use a high-zoom telephoto lens. Then, you no longer need to aim the camera with the viewfinder or the screen -- you just use the red dot sight.
Notes: The red dot sight and the camera shown in the pictures are not included with this item -- you provide them yourself. Also, I have not tested the White and Black non-polished materials. Surface finish with these materials may be a bit rough.
You can use any red dot sight with Picatinny or Weaver mount. The sight in the pictures is similar to this one on Amazon.com:
UAG Tactical 4 Reticle Red Dot Open Reflex Sight
The jet fighter pictures are from the Blue Angels air show in San Francisco a couple of months ago. Back then I used a flimsy red dot sight adapter that was the motivation for designing the sturdier one-piece version described here.