>>4056678Aperture must be placed at a precise spot inside the lens for it to work correctly. Placed at front or rear element will cause visible vignetting at closed apertures. You can still try and check your luck. m42 to ef is small metal disk. Find one of these for EF to your mount. They exist for various mounts for canons EF lenses. Aperture on most EF lenses is electronic and wouldn't work when adapted via dumb adapters. They've since been replaced by electronic ones that control aperture of the lens.
>>4056655In some cases it's possible to use native lens hood, but it's rare, you can use screw in hoods instead on the filter. Ring places filter slightly further from the lens that it would otherwise occupy, in theory that means miniscule softness increase. In combination with larger filter on the lens, this may also effect how flares effect picture. Nothing major, just something to keep in mind if you're pedantic.
