The Pentax Beam Splitter is an ingenious device which allows 3D images to be taken instantaneously on a single frame. Primarily aimed at 35mm SLR users it is still perfectly usable on a modern DSLR. The image shows my Pentax Beam Splitter fitted to a Nikon D3000 DSLR.
The Beam Splitter is designed to work with a lens that matches the standard focal length for the sensor of film size. For full frame or 35mm film this would be 50mm but for my Nikons with DX size sensors this would be about 32mm. It is important that the front element does not rotate during focussing so my 18-55mm zoom is unsuitable but my 35mm F1.8 Nikon lens is perfect. As the device creates both left and right images on a single frame the pixel count is therefore halved. For example a 24mp sensor will produce in effect approximately 2 x 12mp images. (Note there is a loss of image area at the join in the centre of the frame). The Nikon pictured is 10mp and this will produce 2x 5mp images which is why I prefer to use my 24mp D7100 when using the Beam Splitter.
This is a typical image taken with the Beam Splitter. The central join is dependent on the aperture used. I use approximately F4 which gives this soft transition. Smaller apertures will give a sharper join but can cost image space. I crop each half of the image to separate the left and right views before creating my final 3D/stereo image. Click here to see more examples of images taken with a Pentax Beam Splitter