Good luck with that. Phosphor decay might be in the orders of microseconds to milliseconds. How much signal will the camera register from a dim CRT in that time? For single shot, they used lenses with apertures up to f/1.2 and film speeds up to ISO 20,000. This will cause issues with bulb mode, however, that film would probably be overexposed from ambient light and graticule illumination before you could trigger the scope. Bulb mode might be ok for slow signals that occur frequently, but not for ns pulses that might occur once every few hours.
Agree, its not easy and mostly it will fail if the "blip" is too fast for your camera to capture even in perfectly dark room and with the graticule illumination turned off.
Example my setup below, using the camera's remote to take the shot of a steady repeating signal only at my 400Mhz analog scope, not for capturing single shot, while for that I used my cheap dso.
I have a sealed room from external light, and with this remote is quite handy since I have the room's lightning switch within my arm's reach. So to start taking shot, the sequence is turn off room light and it will be totally pitch dark, press the camera's remote to open the shutter, once finished, turn on the room light again to prevent me from knocking out things around in the dark.
PS : This picture is originated my other post from other thread discussing how to capture a good repeating signal at analog scope ->
w2aew's excellent scope training thread