G'day Dan, and welcome to the BABB.

If the effect is the one I'm thinking of, then all that happened was that Buzz Aldrin inside the LM opened up the aperture on the camera to let more light in. He wasn't sure whether the camera would record Armstrong correctly, so he checked with Mission Control. They told him the correct settings, and Aldrin changed the settings on the camera in accordance with their instruction.

The Apollo Lunar Surface Journal is a record of all the activities of the astronauts on the Moon: http://www.history.nasa.gov/alsj/

If you go to Apollo 11, and read the section dealing with the first Moon walk, you can find this conversation as Neil Armstrong reached the base of the ladder (the numbers represent hours:minutes:seconds since lift-off):

109:22:28 Aldrin: Okay. Will you verify the position - the opening - I ought to have on the (16 mm movie) camera?

109:22:34 McCandless: Stand by. (Long Pause)

109:22:48 McCandless: Okay. Neil, we can see you (on the TV) coming down the ladder now. (Pause)

109:22:59 Armstrong: Okay. I just checked getting back up to that first step, Buzz. It's...The strut isn't collapsed too far, but it's adequate to get back up.

109:23:10 McCandless: Roger. We copy.

109:23:11 Armstrong: Takes a pretty good little jump (to get back up to the first rung). (Pause)

109:23:25 McCandless: Buzz, this is Houston. F/2 (and)...

109:23:28 Armstrong: Okay, I'm at the...(Listens)

109:23:29 McCandless: ...1/160th second for shadow photography on the sequence camera.

109:23:35 Aldrin: Okay.

{The ladder is mounted on the west strut and is, therefore, in the LM's shadow. The recorded image is fairly dark. Journal Contributor Markus Mehring notes that, as a result of the information from Bruce, Buzz changes settings on the DAC and the recorded scene brightens, "just in time to catch Neil and his historic step off the footpad."}

109:23:38 Armstrong: I'm at the foot of the ladder. The LM footpads are only depressed in the surface about 1 or 2 inches, although the surface appears to be very, very fine grained, as you get close to it. It's almost like a powder. (The) ground mass is very fine. (Pause)

{Just before Neil's next transmission, as a result of Buzz's changes to the 16-mm camera settings and Neil's position on the footpad, the film record shows the LEC attached to the front of Neil's suit. We can see reflections of what appear to be parts of Buzz's suit as he changes the camera settings and monitors Neil's activities out the window.}

109:24:13 Armstrong: I'm going to step off the LM now.

= = = =

Of course, I might have this wrong, so apologies in advance if you had something else in mind.