However, it is also expressively limiting, because it is difficult to blur objects that are closer or further away than the main object in a scene. Depth blur is a staple in the language of film. It is frequently used to isolate a character, to focus importance on a person rather than the surroundings, and to direct the attention of the audience. This control is particularly important to microfilmmakers, who desire the aesthetic appearance of 35mm film and the artistic control over depth blur.
There are a number of in-camera tricks that can improve blur control or simulate depth blur. For example, opening the iris and adjusting the exposure with filters or shutter speed can make the focus shallower; and moving the camera back and zooming in can simulate depth blur, but all these techniques are limited.
One solution is moving up to a camera with a 2/3” sensor and a much larger, more expensive lens. At current prices, that would be about a $15,000 to $20,000 lens.
Another option is shooting on film, but these options are beyond the budget of most of us.
Enter the 35mm adapter. The concept is simple. Take a 35mm still camera lens, such as a Nikon, a Pentax, or a Canon lens, (which can be had for $100-$500) and then attach it to the front of the video camera, yielding 35mm focus control at bargain prices. It sounds easy, maybe “do-it-yourself” easy, but the technology is much more complicated than it appears.
When I first heard of 35mm adapters I thought it was a glorified filter ring. I mean, what’s the big deal? One side holds a 35mm lens, the other side attaches to the front of the video camera, and you need a tube of the right length in the middle. Right? Wrong.
If you don’t understand the array of really tough technical problems that the Letus 35 Extreme solves for you, then you won’t realize what an incredible bargain it is. So before we look at the adapter and the results it produces, let’s spend a moment reviewing what the Letus35 Extreme is doing for you – the value you don’t see.
What does a 35mm adapter do for you?
If you focus the light from a 35mm lens down to a small sensor, you end up with almost the same depth of focus as the native lens. So just attaching the 35mm lens on the camera does not solve the depth problem. What you have to do to get shallower focus is to create an image on a much larger area. You need a screen where you can focus the light from the 35mm lens and, if that image is large enough, it will have the shallow focus you want.
Assuming for a moment that you have an image on a screen inside the adapter, you will need to be able to focus the video camera on the back of the screen. And most video cameras are not designed to focus on an object that is only one inch high and that is only three inches in front of the camera. To focus that closely, you need a super-magnifying close-up lens, variously called a condenser lens, a relay lens, or an achromat lens. This is the kind of close-up lens used to photograph insects.
Now the screen presents a number of problems. It has to be perfectly aligned with the camera sensors and the lenses. If it is off in any dimension just a tiny bit, then the lens won’t focus at the same distance everywhere in the frame (called edge-to-edge sharpness). The left side will be in focus and the right side a blur, or the top in focus and the bottom a blur. Therefore, alignment is critical.