Also any experience with any replacement lens shade/hoods for a 50mm f1.8 Canon lens -- it's the odd 40mm thread size. I have a generic that I think is made for a Fuji digital camera which fits fine but is 58mm at the front end and blocks a big hunk of the viewfinder. I would love to find something narrower if that exists -- or do all the hoods block the finder significantly.
My below comments are made with the black anodized version of the 50/1.8 in mind, I have no idea about the older full chrome version.
A lens hood has to have a certain length to be effective; and the longer the hood the wider it has to be at its end to avoid vignetting and the worse the finder blockage will be. The original Canon lens hood for the 50mm f1.8 measures about 58mm in diameter at the wide end. You do not give the length of the generic hood you use now, so I can only assume it is about the same length as the original hood (25 mm). Any lens hood with a smaller diameter at the long end would have to be shorter allover to avoid vignetting, which would make it less effective. As the original Canon hood is not so terribly long to begin with, I suspect that it doesn't make a lot of sense to use anything shorter and narrower.
As mentioned, Canon made a dedicated clamp on shade for this lens (fixed via a small screw and spring). You should be able to find it on Ebay with a bit of patience, but I fear it will be similar when it comes to finder blockage. One thing you could do is use the Leica clamp on hood 12585 (several versions exist, early metal, later plastic), which has cut outs to help with finder blockage; it will fit nicely on the 50/1.8, but I would not recommend to keep it attached to the lens permanently, as the Canon lens misses the groove into which the spring loaded fingers of the hood grab, so it will not sit as securely on the Canon as it would on a Leica lens.
If you cannot find the original Canon push on plastic cap, an older Leica push on metal cap for the 39mm filter size fits snugly on my 50/1.8.