Limitations
A DOF adapter comes with a few limitations. First is the inherent light loss that comes with attaching the unit to the front of the camera. Using any one of these adapters requires that the scene being shot by the camera be adequately lit.
Static (non-moving) adapters suffer greater image degradation from low-light situations because texture on the focusing screen becomes more noticeable. The camcorder used in conjunction with the adapter must focus on the focusing screen inside the adapter which is used as a projection surface. As a result, the camcorder also picks up the pits, dimples and/or specks in the material that give it its translucent properties. The solution to this problem is to shake, rotate or otherwise move the focusing screen so that the texture of the screen is blurred. In a non-static solution such as this, the texture is only a problem at very high shutter speeds, where blurring is reduced.
Vignetting, barrel distortion and chromatic aberration are also problems that are difficult to eradicate. The optics within the adapter must be of high quality and at the correct distance from each other in order to minimize these issues.
Image orientation is also an issue. The adapter, like any other lens, flips the image upside-down. To help address this issue while filming, an external monitor such as a small LCD screen may be mounted upside down to view the image in its correct orientation. Some LCD screens feature both mirror and flip options that correctly orient the image (flip vertically and mirror horizontally). In either case, the actual recorded footage must still be rotated 180 degrees in post-production. The one exception to this is the option to mount the camera upside down. This will allow the camera to record an upright image. However the camera LCD will still flip the image, and an external LCD monitor is still required.
Another option is to use a flip module. A flip module is yet another addition to 35mm adapter construction set that is made up of a series of mirrors or prisms that literally "flip" the image while shooting. This avoids the burden of needing an external LCD monitor, but at the cost of additional light loss. Many adapters already have a flip module within them, so the filmmakers do not have to worry about flipping the image in post-production.
Read more about this topic: Depth-of-field Adapter
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—Raymond Chandler (1888–1959)
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—Lawrence Balter (20th century)