HDV Camcorders and Film Lens Adapters

Cinevate Brevis35

Those who shoot 24p with camcorders that have small imagers—less than 1/2in.—have long used various types of adapters to overcome their camcorders' far-too-large depth of field (DOF). Those shooting with JVC ProHD camcorders now have a new option: the JVC HZ-CA13U. Before looking at JVC''s adapter, we''ll look at alternative solutions.

There are several non-JVC options to reduce DOF. These include the Cinevate Brevis35, Redrock Microsystems M2, and the P+S Technik Mini35.

Redrock Microsystems M2

All of these operate in a similar manner. A 35mm still camera lens or a 35mm cine lens is mounted on the front of the adapter. The attached lens projects an upside-down image on a ground-glass screen exactly as it would on 35mm film. You set the aperture and focus with the attached lens. The inherent DOF of the attached lens becomes the DOF of your video camera.

P+S Technik Mini35

The ground-glass screen has texture, which has several consequences. First, the texture could be visible. To hide the texture, the ground glass is spun at high speed or rapidly shifted side to side. This requires battery power and may create audible noise. Second, the ground-glass screen can cause up to over two stops loss of light.

Mini35 used with a Sony Z1

The Brevis35 system is inexpensive, at about $1,000. Because it is lightweight (9.2oz.) it is ideal for use with small camcorders such as the Sony HVR-V1U or Canon HV20. According to Cinevate, the Brevis35 has only a 0.5 f/stop-to-0.7 f/stop loss of actual measured light with an F1.4 50mm attached lens.

The Redrock M2 is also inexpensive, at about $1,300. A more expensive version, at about $1,750, provides an Arriflex PL lens mount. This enables cine lenses with an Arriflex PL lens mount to be attached. They can be prime (non-zoom) or zoom lenses. Redrock also offers a DIY kit with a Redrock ground glass for $45.

For about $650, you can purchase a microFollowFocus Indie Bundle from Redrock.

Mini35 Compact

The P+S Technik Mini35 comes in two flavors: the original Mini35 and the newer Mini35 Compact for 1/3in. CCD cameras with a detachable lens.

The P+S Technik adapters feature the company's Interchangeable Mount System (IMS) for shooting with Arri PL, Nikon, Panavision, Leica, Carl Zeiss-Contax, or Canon EF 35mm lenses. The Mini35 is relatively heavy at 5.62lbs., while Compact is lighter at 3.97lbs.

JVC HZ-CA13U

Angenieux/Zeiss, and now JVC, have designed and built adapters that use no ground-glass screen. This eliminates the need for both motors and batteries, plus introduces minimal light loss. The JVC design uses 11 optical elements to focus an aerial image on a "virtual focal plane" at a standard 52mm distance from the lens seat.

JVC showed the HZ-CA13U at NAB 2006 and spent a year refining its design with input from filmmakers. During the last year, encouraging reports emerged from these early testers. At NAB, JVC showed the final version that sells for $4,395. At NAB 2007, 200 series camcorders were available with a HZ-CA13U adapter, which made it possible to get some hands-on time. (This was critical for me because it was the last necessary step before I could release the second edition of my ProHD Handbook, which is now available at http://www.knowledge-download.com/JVCHDV.)

JVC HZ-CA13U

The HZ-CA13U adapter has a 1/3in. bayonet mount that allows it to be mounted easily on a JVC ProHD camcorder. The adapter is 132.8mm long. The adapter weighs less than 2lbs.

The optical elements in the CA13U reduce the size of the aerial image to that of the 1/3in. CCDs. Amazingly, the 11 elements reduce the light transfer by only 0.5 stops while maintaining the angle of view as well as the circle of confusion (0.0015mm) and DOF characteristics of 16mm film camera. Thus, to any mounted lens, a JVC ProHD camera functions as though it were a 16mm film camera.
The adapter has an industry-standard Arri PL mount. You can use either prime or zoom lenses. These can be 16mm, Super 16, 35mm, and Super 35 lenses. When mounted on the HZ-CA13U, each provides approximately the same field of view they would when mounted on 16mm camera.
The chart below shows field of view ordered by focal length (5.9mm to 135mm) for these four types of lenses.

Click here for a larger image

Assuming the PL-mount lens you want to use is in excellent condition, you must first set the backfocus for the HZ-CA13U. Be sure to allow the camera to warm up before setting backfocus. This following procedure must be performed with an HD monitor.

• Begin by mounting a Siemens star to a wall.
• Attach a prime lens with a focal length of 50mm to 85mm to the CA13U.
• Fully open the iris.
• Set focus on the prime lens to an exact distance marked distance on its barrel. (For example, 5m.)
• Now, place the camcorder so the marked focal plane on the CA13U is exactly 5m from the star.
• Next, use the backfocus knob to adjust the backfocus.
• Adjust the camcorder''s white shading for the lens you shoot with.
• The camera mount and adapter are sensitive to temperature changes, so you must check backfocus when you change locations to account for changes in temperature.
• Adjust focus via the focus ring on this lens. You can use a measuring tape for maximum accuracy. Use the lens iris to set exposure. The wider open the iris, the less DOF.
• As you open the iris, you will find image brightness increases until it reaches f/2.8. Then, no matter how much more you open the iris, brightness will not increase. This occurs because of the Lagrange invariant: m=NA/NA‡ where NA is the aperture on the object side (9.35mm for 16mm film) and NA‡ is the aperture on the image side (4.8mm for 1/3in. CCDs). Therefore, m=1.94791.
  NA=mxNA‡ where NA is the maximum aperture on the attached lens side and NA‡ is the camcorder''s maximum aperture (f/1.4). Therefore, NA=1.94791x1.4, which yields 2.727, or f/2.8.
  Even if you can open the lens wider than f/2.8, do not do so because not only will the lens not produce brighter video, image quality falls the wider a lens is opened.
• Because the image is upside down, you must switch your ProHD camcorder to either flip the viewfinder image (GY-HD110) or flip the image coming from the CCDs (GY-HD200 and GY-HD250).