Odd shadow effect in Apollo 12 images

[onebigmonkey]

Having started looking at changes in shadow length in Apollo surface images I started to look at Apollo 12, and noticed a weird effect in the post-landing shots of the LM shadow.

Here's a close up of one of them http://www.lpi.usra.edu/resources/apollo/images/print/AS12/48/7026.jpg:



In case you don't see it, it's as if there is a central region of truly dark shadow, with a lighter shadow around it.

My theory is that as the shadow is falling into a crater, light is being reflected by the crater walls into the shadow, causing it to be less dark.

Sound reasonable?

[Echnaton]

Penumbra? Light diffusion in the window?  Bleed on the film?

[smartcooky]

Having started looking at changes in shadow length in Apollo surface images I started to look at Apollo 12, and noticed a weird effect in the post-landing shots of the LM shadow.

Here's a close up of one of them http://www.lpi.usra.edu/resources/apollo/images/print/AS12/48/7026.jpg:



In case you don't see it, it's as if there is a central region of truly dark shadow, with a lighter shadow around it.

My theory is that as the shadow is falling into a crater, light is being reflected by the crater walls into the shadow, causing it to be less dark.

Sound reasonable?

Penumbra? Light diffusion in the window?  Bleed on the film?

The Sun is not a point light source; it has an apparent diameter of about ½°, therefore, any shadow it casts is not sharp.

[onebigmonkey]

I've outlined the dark bit to make it clearer:

[ka9q]

BTW, these pictures of LM shadows demonstrate very well the opposition effect that scatters a great deal of light onto the front of the LM to illuminate Aldrin in that picture of him descending the ladder.

[smartcooky]

I've outlined the dark bit to make it clearer:

OK, I have enhanced the area by driving up the shadow contrast in Photoshop





Definitely see what you are talking about now. That has to be some kind of reflection into the shadow although I notice that the dark shadow still follows the general outline of the LM

[Echnaton]

That seems to rule out penumbra.  Light diffusion in the window seems to be at least speculatively still in play and an alternate cause.

Looking at the light blob near the bottom of the blow up, it seems to be the lunar surface.  Any idea where that light came from.

[Allan F]

The blob in the bottom looks more like a lens flare - or perhaps some reflection in the window it was shot thorugh.

[onebigmonkey]

I believe the 'blob' has been identified as from light shining through a gap between the ascent and descent modules.

I'm also beginning to wonder if the window, and film type, are combining to produce the effect. It doesn't seem to be present in B&W images taken of the LM shadow outside (although the angle of the photograph doesn't help there), and it doesn't seem to be present in the colour ones taken inside.

Later views in B&W of the LM shadow do not have as pronounced an effect.

[ka9q]

A lot of the B&W images from Apollo 12 have a "halo" effect. I had thought it was from dust on the lens but that is unlikely to be the cause here because they were taken before the first EVA.

Another possibility here is that the film anti-halation backing wasn't completely effective. This is a dark dye, visible on undeveloped film, placed on the non-emulsion side of the film to minimize light scattering. It dissolves during development.

I still wonder what was on the magazine they accidentally left on the surface. We'll never know; I'm sure the film disintegrated from thermal cycling long ago.

[ka9q]

Looking at the full image on the ALSJ, I see what looks like the out-of-focus shadow of the LPD (landing point designator, inscribed on the commander's window) on the right side of the image. The top (horizontal) part of the scale seems to project onto the right edge of the LM shadow.

This doesn't explain the entire effect, but it might explain the shape of it on the right side.

[Echnaton]

I believe the 'blob' has been identified as from light shining through a gap between the ascent and descent modules.

That is what it looked like to me.  I did not know there was a gap, so there is something new in the photo for me.

What window was it taken out of?  A reconstruction of the camera position relative to the glass might give a clue. 

[ka9q]

I believe the 'blob' has been identified as from light shining through a gap between the ascent and descent modules.

That is what it looked like to me.  I did not know there was a gap, so there is something new in the photo for me.

Note that Apollo 12 landed yawed well to the right relative to the sun line; this partly explains the asymmetry of the shadow (e.g., the prominence of the RCS plume deflector on the right) and also the nature of the spots where the sun could shine through between the two stages. Of course the LM itself is rather asymmetric, with the ascent stage fuel tank jutting farther out to the -Y (CDR, left) side than the heavier oxidizer tank on the +Y (LMP, right) side.

What window was it taken out of?  A reconstruction of the camera position relative to the glass might give a clue.

Pete Conrad's, i.e., the commander's window. The LPD is only present on that window, on the right side.

[Echnaton]

I see what you are saying about the LPD.  That answers the question.

[ka9q]

Having started looking at changes in shadow length in Apollo surface images

In your webpage you wonder how level the LM was on the surface. Each mission report gave the landed orientation in terms of pitch, roll and yaw.