Building a 35mm depth of field adapter for a digital video camera

The concept of a 35mm depth of field on a digital video camera is not a new one; there are many forums devoted to the subject, many people with their own working versions, and companies that sell high quality versions for money that the crew and I simply can't justify at the moment. Since we're enterprising people and have hacked things together before, why not build our own version with for little money as possible?

The Plan

What's an idea without a plan? More then likely a good way to the hospital or finding oneself flat broke. With so many different versions on the Internet involving everything from spinning CD's to custom pieces of ground glass, we came up with a sort of in between variant. The following is a layout I came up with to describe our configuration:

Step 1 - The layout of the device
  1. Canon 50mm f/1.4 lens - originally we were going to go with an FD mount lens, but since I had an EF type handy, we went with what I had.
  2. Canon EF rear lens cap - this is going to be our lens mounting point
  3. Pipe fitting #1
  4. Ground Glass - this is what the lens will project the picture on
  5. Pipe fitting #2
  6. Macro lens - I happened to have on old macro I used to use on my Epson 3100z, this will be used to manifiy the image to the video camera
  7. Stepdown ring - connects the macro lens to the video camera

The design is fairly simple, but relies heavily on a quality piece of ground glass that doesn't have much grain. With a great deal of grain, the picture the camera captures won't be so great and we'll lose a lot of light. With this design, we went forth to gather the parts needed.

The Parts

As I mentioned, one of the main goals of this project was to produce something good, yet on the low side of the cost scale. Now the following part list is simply stuff we bought because it just happened to work for us; we literally took a Canon rear lens cap and the macro lens and just started shoving it into pipe fittings and rubber joints until we found a match at the hardware store. We left with:

  • One (1) black PVC 2 inch pipe coupler - female
  • One (1) black PVC 2 inch pipe coupler - male
  • One (1) black rubber 1 1/2 inch to 1 3/4 inch coupler
  • One (1) black 2 inch O-ring

There are some things I should point out. One, we used plumbing parts which wasn't the smartest thing to do. Plumbing parts are built with large tapered threads such that as you tighten two pieces together they lock very tight which means you can't travel the length of the threads. This is important in our design as you'll see below, because we use the couplings to focus infinity on the ground glass. This ended up not hurting us, but a more reasonable choice would have been to use electrical parts which have finer threads which can be traveled all the way to the end.

Another thing you may notice is that there are no parts for the ground glass. Hang in there, we're coming to that hack of a hack in a second.

The Build

The picture below is a view of all the parts built yet disassembled. Lets walk through what each of the parts does, and how that part came to be.

Step 2 - The built parts

The Lens Mount: First, we cut a hole out of the Canon read lens cap, being careful not to ruin the actual mount the lens will be attached to. Second, we took the female PVC coupling, and using a hot glue gun proceeded to attach the rear lens cap to the coupling. This resulted in items #2 and #3 of the original design being connected:

Step 3 - The lens mount #1 Step 3 - The lens mount #2 Step 3 - The lens mount #3

The Macro Attach: Trying to attach the macro lens to the male coupling (item #5 in the design image) became something of a problem. There was just no good way to do it. It was for this reason that we purchased the rubber coupler (the macro lens just happen to fit snugly on the rubber edge), which we proceeded to cut and place inside the male coupling. In the pictures below you can see that it's a tight fit on the threads end, but just enough of a gap to allow us to attach the macro lens on the other.

Step 4 - The macro attach #1 Step 4 - The macro attach #2

The Ground Glass: Without a frosted white surface, you won't get depth of field that the 35mm lens offers. Since I didn't have time to make my own piece, and we wanted to see this thing work now, we did what we usually do. We hacked it. In the build parts picture above, you may have noticed a piece of white plastic and a piece of clear plastic. The white plastic happens to be from a grocery bag, and the clear plastic is cut for a CD blank they sell with recordable CDs. Put them together and what do you get? Ground glass:

Step 5 - The ground glass #1

The picture doesn't do it justice. We kid you not, this works for us. We're not saying it's perfect (we still have some grain) but it works suprisingly well (as you'll see in the demo videos).

The Device

Put together, the device looks very simple. Since we used threaded parts, we can easily set the infinity focus of the lens we attach or change out the ground glass with minimal work.

Step 6 - the device #1 Step 6 - the device #2 Step 6 - the device #3

The Mounting Bracket

We soon determined that we would have to come up with a mounting bracket to really keep things from moving around. We went out to Dad's shop, and picked up the following items:

  • Two (2) pieces of 1/4 inch UHWA (the white plastic looking stuff)
  • One (1) hose clamp
  • One (1) piece of 2'x4"x1" plywood (rough numbers...we just found a piece and used it)
  • One (1) 1/4 inch self locking bolt (little speciality item)

With the help of my Dad (who has designed and built just about anything and everything consequently between the farming and sheet metal) he helped keep in the spirit of this hack, by helping us hack together the following bracket:

Step 7 - the bracket #1 Step 7 - the bracket #2

Simple and to the point, we then mounted this onto the steadicam (which we built out of 1 inch pipe and fittings) to see how see faired. James Duvall took her for a spin with my 75-300 attached:

James Duvall in action

Video Demos

What's a camera hack without some quick, barely edited footage?

Note, we're aware that the first video is upside down. Did I mention we forgot to flip it over?