The main mirror of my Canon EOS 5D Mark I / classic fell off - what to do?

Here images how the EOS 5D DSLR looks like after the mirror fell off and I took the lens away:

For me this was nearly no question - no sending to Canon for repair!
This problem is common, and Canon repairs normaly for free this defect - see the Canon 5D mirror fix homepage.

But I do not use this - because I planned to replace it with a 100% silver mirror of an old film camera - to get ~2/3 f-stop more viewfinder brightness.

The normal Canon EOS 5D mirror has only 60% reflection, and 40% transmission for the autofocus system.
So with the 100% mirror there is no more autofocus! Cause I use manual lenses, this is no problem for me. Furthermore the exposure measurement may be off (this could partly be solved with screen mode and EE-S screen)

Here you see the camera without the main mirror:

And here the 5D classic main mirror, with the "adhesive" points and the plastic masking.

As a first preliminary fix I taped the old mirror inside the camera with small Gaffa tape slices - and this I did with the 100% mirror for the first tests too (this is when I made these images). The end in the front is easy, the mirror end near the shutter is hard and a bit dangerous to tape.

I had some defective old cameras. I think the Pentax ME super was the one with a big enough mirror and fitting mirror.

I disassemblend the camera (to get parts for my other photo DIY work). The mirror was glued to its frame. I could take this apart with a sharp knife.

The donot mirror with ~100% reflectivity was a bit too widht. For the grinding I used a Dremel tool. And to stabilize the ~1mm thick surface mirror I presses it bewtween two clean UV filters (a good job for these filters).

Here the original EOS 5D mirror and its intended replacement:

Now the plastic mirror frame needs a "close shave". OK, the mirror frame needs grinding too, to get additional room for adapted / converted lenses - their back lens sometimes protrudes too much. And some users of old manual are shaving the Canon EOS 5D mirror to make some lenses usable. I want to use the Carl Zeiss 18mm f/4 for Contax super wide angle lens.

For grinding inside the camera it is absolutly neccesary to keep the dust and chips away from the camera shutter and mirror mechanism.
I did this with some tape.

The grinding I have done the grinding again with the dremel tool - very carefully.

I used this slower hardening super glue to glue the new mirror inside the camera. But there are doubts regarding super glue because of the solvents inside the camera.

I have no 1:1 viewfinder brightness comparison, but I am pretty sure that it has 2/3 f-stop more viewfinder brightness (from theory).
No problem focussing my Minolta Rokkor 58mm f/1.2 lens or Canon FD 85mm f/1.2 wideopen.

Please visit my other tinker work, or my DIY directory with ~1700 DIY links to other photo tinkering sites.