After running into several problems with my iPhone DSLR Lens Mount Prototype 1.0 I decided to find some solutions.
One major problem was that the back of the DSLR lens had such a small image that it was impossible to get a useful image cast unto the iPhone camera. So what was the solution? A Depth of Field (DOF) Adapter.
DOF adapters are used on video cameras that have lenses that can’t produce the depth of field effect. The term 35mm adapter comes from the fact that most common designs use a focusing screen the size of a 35mm film frame (24×36 mm) and interface with lenses designed for 35mm cameras.
Focusing Screen
The major component of a DOF adapter is the focusing screen. Generally the screen is made of ground glass. The screen is where the DSLR/photographic lens image is projected. Using the adapter creates a much more reasonably sized image for the iPhone or video camera to focus on. As you can see here:
Macro Lens
A macro lens is needed when the device does not have adequate macro capability. As a stand alone camera, I’ve found that the minimum focal distance on the iPhone is somwhere between 50-60mm. But by using intermediary optics to increase magnification, minimum focal distance can be significantly reduced.
Achromatic Lens
As light passes through lenses color is refracted at different wavelengths, a lens can fail in focusing all the colors into one convergence point and the resulting image can be distored. This is called chromatic abberations.
Additionally, light is refracted differently when it passes through the center of a lens vs when it passes through the edge of a lens. This this type of distortion is called spherical abberations.
- A perfect lens (top) focuses all incoming rays to a point on the optic axis. A real lens with spherical surfaces (bottom) suffers from spherical aberration: it focuses rays more tightly if they enter it far from the optic axis than if they enter closer to the axis. It therefore does not produce a perfect focal point.
An achromatic lens is can can optionally be used with a DOF adapter to reduce chromatic and spherical abberations. In other words, it makes images look less like they came out of a fish eye lens and puts the colors back together.
Limitations
DOF Adapters do not come without their limitations. One inherent limitation is the loss of light. I’ve found that when using the depth of field adpater I loose about 1-2 F-stops of light. So shooting with it requires that the subject is adequately lit.
Another limitation I found was that it is very difficult to keep all the optics in the DOF adapter free of dust. If there is any dust on the ground glass, on the macro lenses, or on the achromatic lens it will show up on the image.
Image orientation is also a limitation. when shooting with a DOF adapter, the image will be flipped upside down. When shooting with an iPhone, this problem can be addressed by using an app called ”almostDSLR”
Cost is another limitation. Getting a professional quality DOF adapter can cost you anywhere between a couple hundred to a couple thousand dollars. You could make your own… Which is a difficult undertaking (trust me). Or you could do what I did and buy one online. I got the EnCinema 35mm DOF Adapter from Vid-atlantic for great price.
With the DOF adapter and intermediary optics, I’m naming this model “Prototype 1.1″. I’ll post some the photos I took with it shortly.
[UPDATE 8/16/2010]
You can find photos I took with “Prototype 1.1″ here: Sample Shots from iPhone DSLR Lens Mount Prototype 1.1
