A Depth of Field (DOF) adapter allows a standard camcorder to capture a more film like view of the world. With film cameras you are able to focus the lens at a point in space and have other areas go out of focus. Videographers that are using commercial grade equipment end up with the entire frame in focus. This is due to the nature of the optics that are included on the commercial grade equipment. A good description of depth of field can be found on wikipedia.
A DOF adapter works by focusing the image from the camera lens onto a piece of ground glass. A lens with a good amount of light gathering capability is required since this arrangement leads to loss of light during the process. The video camera then focuses on the ground glass and captures that image. A macro lens may be required to focus on the ground glass since it is so close to the ground glass.
For more information on Depth of Field adapters see wikipedia.
There are several DOF adapters available that are designed for manual focus 35mm lenses. A few of them are relatively affordable like the equipment available from www.jag35.com.
These adapters would not work for me, since they are designed 35 mm lenses and I had access to a very nice medium format Mamiya lens that I wanted to use.
The 35 mm lens has a film size of 24mm x 36mm, the Mamiya 645 lens has a film size of 42mm x 56mm. This is approximately .79 inches larger in width and .71 inches larger in height. So in order to capture the entire focus area a larger depth of field adapter must be built.
- Camera – Sony HDV-HC7 – 37mm ring
- Lens – Mamiya 45mm f2.8
I had two plates machined with 58 mm threaded holes in the center. On the Mamiya lens side of the DOF adapter a Mamiy M645 reversing ring is attached with 58mm thread is inserted into the hole in the plate. The Mamiya lens will now fit into the filter adapter. The adapters run between $30 and $50 US dollars.
On the other plate a 37mm to 58mm adapter is inserted so that the Sony video camera can be attached. These adapters run between $5 and $10.
The frame of the adapter is built from 8020 extruded aluminum stock. The faces are plastic.
I used a 100mm square piece of glass that I obtained from Edmunds Optics, that was sandblasted with 220 grit sand. The result was an image with noticable grains. Many DOF adapters have a vibrating motor, or rotating piece of ground glass to reduce the visibility of the grains. I have a pancake vibrating motor from Hobby Engineering but opted not to install it in the first version of my adapter. The flaws in the design didn’t make it seem a good use of time.
The fully assembled Depth of Field adapter.
There are a couple of major flaws with my initial design.
- The entire assembly is very much over engineered.
- Too heavy
- Too big
- The Mamiya lens is not light, and is very hard to support due to the size.
- The Video camera is also not easy to support
The next version will be designed to reduce the size of the design. I am going to reuse the adapter plates though as they work very well, and their size isn’t too large to make them a problem.
|Since the lens inverts the image when projecting it on the ground glass, it is easiest to mount the video camera upside down so that the recorded video will not have to be flipped over in post processing.|
|All pieces in the initial version of the DOF adapter.|