Fotodiox just released a pretty cool accesory called the Excell+1. The Excell+1 is a lens booster which means that it has internal optics to concentrate the light coming from a lens into a smaller area.
now, why would you want to do that?
What is a lens booster
A lens booster is a small device that goes between the lens and the camera’s native bionet. If the camera lens combo is such that the lens is a full frame lens while the body is using a crop factor sensor, some of the image from the less “spills” around the sensor.
A lens booster manipulates the light coming from the lens so it only overlaps the needed sensor. So basically a lens booster uncrops a lens/camera combo.
There are two effects to this uncropping, the obvious one is that you loose the ‘zoom’ factor crop sensors create. So a 100mm lens will actually perform as a 100mm lens even if you are using a smaller sensor. (on a Nikon DX sensor, it would appear to be 150mm for example)
The other effect is that you are getting more light into the sensor, so whatever f rating the lens has gets a +1 upgrade. Kinda like in the Mario brothers arcade. Here is what you gain:
When can you use a booster?
Since the booster depends on the camera bionet, the lens bionet and the crop factor, the boosters are camera/lens specific.
The Excel+1 comes in two flavors: Nikon F-Mount G Lens and Canon FD Lens both build for the micro four thirds on the camera end. That means that those specific ones will work with the pocket BMCC as well as any m43 camera.
I have not tested those personally so I am not sure what the optical impact is, but it would sure be an interesting experience, and if you consider the price shift from an f/1.8 to an f/1.4 lens the $160 may be absolutely worth it.