A British man has built his own lens with a super fast 35mm f/0. 4 equivalent bokeh that is constructed around an old episcope projector lens and a mechanical system for controlling focus.
DIYPerks is an amateur tinkerer and doesn’t purchase anything that he cannot build. On his YouTube channel, Perks has built everything from a DIY 4K home cinema projector to a DIY microphone for recording audio in his home-built studio with home-built video lights.
In this case, Perks turned his attention to a vintage episcope lens harvested from an old art projector. An episcope projector was very popular in the 1960s and 1970s and would fit over a piece of art or any object that a user would want to project onto a wall or screen. Because they were inexpensive and projected bright images, they are very popular among schools. The light is reflected from the housing of the projector, shining down on the subject. This would reflect the light off the mirror onto the wall through the episcope lens.
As Perks admits, episcopes have largely been left behind by the steady march of technology into the digital realm which he clearly sees as a real shame because the episcope lens offers a remarkable bokeh thanks to its incredibly large image field — on the order of 500mm. To put that in perspective, the standard smartphone camera image sensor has an image circle of roughly eight millimeters, or 0. 016 the size.
To achieve the goal of using the episcopic lens with his camera, Perks would have to create a huge housing and focusing mechanism from scratch. And even then, the largest impediment to capturing an image, is that there isn’t a digital image sensor made that is large enough to capture the entire image circle the episcope lens can offer.
One option is to take the image while it’s being projected onto a wall. However, this comes with its own image quality problems from noise to distortion. It would also prevent mobile usage.
The other option would be to project the image onto an opaque surface and then capture the image from that. This opened up the possibility of taking the array just about anywhere if the design was portable enough.
Perks used a diffuser sandwiched between two pieces of acrylic and then built around a pyramid-shaped aluminum housing as a custom light screen. Two, actually: one to hold the episcope lens, and one for his Canon R5 full-frame mirrorless camera. To eliminate any unwanted vignetting, he added the Fresnel lens between.
With an origami folded black bellows to block out as much adjacent light as possible, and a 3D printed joystick focusing mechanism to control the entire system, Perks was ready to test out his cumbersome, yet interesting array. It is more like an image captured from a mirror on an opaque surface than it does from a sensor.
The episcope lens optically produces a dreamlike image with incredible background separation. Perks discovered that the custom lens array he used has a crop factor 0. 08 and an aperture of f/0. 4, which Perks claims makes his rig twice as fast as a $200,000 Zeiss 50mm f/0.7. This array can be used with smartphones, creating an optical background that is more natural than what modern handsets create through computation photography.
The total cost to build his DIY “Perkiscope” episcope lens array is only $200. Perks has promised a download link for all the plans to build an episcope camera rig of your own, but at the time of publication, it had not yet appeared in the video description. Even armed with those instructions, the lens itself may be the hardest thing to source for the project due to its vintage nature.
Image credits: All photos by Matt Perks