From experience I believe the opening for the ground glass for the 45D is about 2.5 millimeters shorter than others. I purchased a Yanke ground glass/fresnel/grid set from China on the auction site for $110. When I received the package, it consisted of two pieces: 1) a plastic plate that included the ground matte side that goes toward thew len, a fresnel, and the grid (all on one piece of plastic), and 2), a clear piece of glass. I trimmed the plastic piece on one of the short sides with a metal straight edge and a sheet rock knife. I took the piece of glass to a glass cutter/window glass store and they sanded down one long side for $5. This glass is white glass that appears to be untempered. The clear glass does not have its corners cut, but since it is not matte on one side, it really doesn't matter. I took the back of the camera to the glass cutter so they could sand it down until it fit.
Installation is to put in the plastic piece in first with the matte side toward the camera, and then put the clear cover glass over it. Be sure to loosen up the retainer springs for the extra thickness. Be careful turning the screws. The support standoffs for the ground glass are spread apart so if you tighten the spring in the middle, it will bend the glass and break it.
The results are stellar. I love using the camera now. I think the secret to the performance is having the ground matte and fresnel on the same piece of plastic.
Regards,
Steve Pituch
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