This is a viewfinder LCDVF that helps videographers to focus better with its magnifying properties when used on a DSLR 3 inch LCD screen. This feature is crucial especially when using fast lenses to get pin-point accuracy in determining where the focus point is.
This viewfinder also allows videographers to shoot outdoors under the bright sunlight which has been a huge problem as glare makes LCD screen very difficult to use when making movies in the afternoon in sunny areas.
Nikon D90, D300s, D3
Canon 1D to Mark IV, 5D Mark II, 7D, 500D, S90
and all other cameras with an LCD display 3.0”
How about 550d with it's 16:9 ratios? It does not fit 'perfectly' but it is completely usable.
(Using it on my own 550d) There will be about one mm margin of viewing area cut off for the sides.