It could be the image in the camera is reflected of the mirror that is in front of the film or sensor. The film on the pentax is 35mm and the 50 D is 22.3 x 14.9 mm. The mirror is about the same size as the media that is recieving the image. So you are looking at a smaller image to start with and they did not see the need of making the view finder bigger. The again, it could be the 50D has lots of space requirments for the electronics that govern exposure, flash, data processing and storage, Auto Focus, etc, that they had limited space for the optics to the view finder. If you needed to see a larger image, then you have the live view option on the LED display.