[platz]

> Measurements taken in the '50s and '60s focused on the rate of growth of the fireball. These measurements were done manually by projecting each frame onto a grid, with an analyst jotting down the eyeballed measurement before the projector’s heat began to melt the frame.

What?

[eatbitseveryday]

>> before the projector’s heat began to melt the frame.

> What?

The projector uses a hot lightbulb to display the frame in the film onto a wall or screen. The film sits just in front of this bulb, and of course the heat can risk damaging or melting the plastic film if the film is not quickly accelerated past the bulb (as is the case for watching a video - a sequence of frames).

Keeping one frame visible on a wall is to measure the visible size of the fireball, but doing so means one frame stays in front of the bulb long enough to risk it melting.

[dsfyu404ed]

The grid on the photo, the camera field of view, the landscape, sounding rocket contrails, etc, etc are all of known size. It's like using a beer can for scale in a photo.

[platz]

Sure, I'm more interested in the "melting the frame" issue

[magduf]

You must be too young to have used a home film projector. Even in a little 8mm projector, the light bulb is very hot, to get the brightness needed. Any film that sits in front of the bulb will simply melt from the heat. The only reason it normally doesn't is because the film is being moved through the projector so quickly that it doesn't have time to get that hot, but when the advancing mechanism gets stuck, it only takes a few seconds for that frame of the film to melt away.

[implements]

Here's a good example - the film was loaded incorrectly and started to burn whenever it slowed down:

https://www.youtube.com/watch?v=aCNR6rnl8LQ