How to measure switch bounce on a CRO?
I've done exactly what you're trying, back in the day. It's possible.

First, learn to use the single sweep function. Let's say your setup looks like







simulate this circuit &ndash; Schematic created using CircuitLab

Set your scope to trigger at 2 - 3 volts, negative edge. Set the time base for about 2 - 5 msec/div. Set the brightness fairly high.

Now turn off the lights. Leave only enough light to see the scope and switch, and using a keychain flashlight is a perfectly good approach.

Arm the scope, turn off the flashlight, and hit the switch. You should be able to get a pretty good idea of bounce.

In the old days, you'd use a polaroid camera set up with the shutter held open, then develop the film. That's not likely to be a useful approach these days. However, if you have access to a good digital camera with a B setting, you can use this on a tripod to do the same thing.