Odd shadow effect in Apollo 12 images

[Noldi400]

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.

Don't feel bad; you're not the only one who didn't know.
From the AS-17 Transcript:

117:23:44 Cernan: (To Parker) Hey, let me ask you. When I was behind the LM, I could look right into an area and see the bell of the ascent stage. I never realized that before, but I guess that's normal, huh?

[Echnaton]

Well I wasn't really feeling bad about it, but now I do feel better.  Funny how that works. 

[Echnaton]

II'm also beginning to wonder if the window, and film type, are combining to produce the effect.

Of course lets not forget scanning artifacts.  Black blacks against non-black blacks have been know to give HBs the Hebejebes.  Perhaps they could have a minor but easily reversed effect on the less credulous. 

[onebigmonkey]

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.

I did look for that and couldn't find it - I was surprised it wasn't there but obviously I was looking for the wrong information (slope in degrees rather than deviation from 0.

[ChrLz]

I would advise a little caution here - this area is obviously way, way down in the blacks and once you get there posterising can occur very easily, especially if we are talking jpegs or indeed any 16-bit image where tiny variations in sensor readouts, even amplifier and readout designs, may give little jumps in the RGB numbers, especially at both the bottom and top of the brightness range.

Plus, as has been raised above, once the image is a second or third generation these effects could come from how it was scanned (some scanners have an awful lot of light spill) and processed, and all sorts of other effects may be involved eg film/backplate halation, effects from the reseau plate or other internal lens design/flare issues...

It would take a lot of careful research (none of which I have done) to look at exactly how that image got from the actual scene to that image file, and to identify all the things that might cause such an effect..  If it were possible, the best thing to do would be to take density measurements off the original film, and even then some of the stuff I listed above still may have caused it.  I'd be extremely hesitant to offer any opinion on whether that is a real effect or not - I'd say it might be better to come at this from the opposite direction, namely an Nvidia-like analysis on the scene to work out how the light falls on that shadow, ie identify every possible light source and check the terrain (is it a slightly more raised area, etc?) and see if there is a reason why it might be a real effect...   Nvidia, wanna do another one?

[ka9q]

I did look for that and couldn't find it

Table 9-IV in the Apollo 11 Mission Report gives the PGNS surface Euler angles as yaw +13.2275 deg, pitch +4.44055 deg, roll +0.4614 deg. Not sure how yaw is defined.

[onebigmonkey]

I did look for that and couldn't find it

Table 9-IV in the Apollo 11 Mission Report gives the PGNS surface Euler angles as yaw +13.2275 deg, pitch +4.44055 deg, roll +0.4614 deg. Not sure how yaw is defined.

I'm going with 'Slopey'.

[ka9q]

especially if we are talking jpegs or indeed any 16-bit image where tiny variations in sensor readouts, even amplifier and readout designs, may give little jumps in the RGB numbers, especially at both the bottom and top of the brightness range.

Especially jpeg. It's a lossy compression scheme that actually uses only 8 bits per primary color, and lossy compression on top of that. An amazing number of hoaxers and especially UFO believers have convinced themselves that JPEG artifacts really mean something.

all sorts of other effects may be involved eg film/backplate halation, effects from the reseau plate or other internal lens design/flare issues...

I hadn't thought of the reseau plate, but I could easily see how some light might scatter between the film emulsion and the surfaces of the plate unless (or even if) it is very carefully designed.

...Nvidia-like analysis...

CGI-like ray tracing analysis is proving surprisingly useful in various spacecraft problems. A few years ago, a Portuguese group used it with longwave IR to show that the so-called "Pioneer anomaly" was just due to the radiation pressure of heat from the RTGs reflecting off the spacecraft structure.