Author Topic: Apollo 16 camera exposure  (Read 1228 times)

Offline frenat

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Apollo 16 camera exposure
« on: March 18, 2018, 12:19:22 PM »
In this clip

you can see the lighting change as the camera is pointed near the sun.  Is this automatic to the camera and if so does anyone have a reference for it?  Or was it controlled remotely from Houston?
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Offline onebigmonkey

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Re: Apollo 16 camera exposure
« Reply #1 on: March 18, 2018, 01:41:49 PM »
Not sure if it answers your question, but this document has references to 'Automatic Lighting Control'

https://www.hq.nasa.gov/alsj/WEC-ColorTV-Manual.pdf


Offline raven

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Re: Apollo 16 camera exposure
« Reply #2 on: March 18, 2018, 04:29:53 PM »
Not sure if it answers your question, but this document has references to 'Automatic Lighting Control'

https://www.hq.nasa.gov/alsj/WEC-ColorTV-Manual.pdf
I think that manual refers to the one that ended up getting fried on Apollo 12, and not the RCA camera used on Apollo 16.

Offline onebigmonkey

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Re: Apollo 16 camera exposure
« Reply #3 on: March 18, 2018, 05:05:50 PM »
Not sure if it answers your question, but this document has references to 'Automatic Lighting Control'

https://www.hq.nasa.gov/alsj/WEC-ColorTV-Manual.pdf
I think that manual refers to the one that ended up getting fried on Apollo 12, and not the RCA camera used on Apollo 16.

Ah right. ALC is also mentioned in passing in this one from RCA

https://www.hq.nasa.gov/alsj/GCTA-Final-Report.pdf

which does mention it can be remotely controlled.

Offline frenat

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Re: Apollo 16 camera exposure
« Reply #4 on: March 19, 2018, 09:49:27 PM »
Not sure if it answers your question, but this document has references to 'Automatic Lighting Control'

https://www.hq.nasa.gov/alsj/WEC-ColorTV-Manual.pdf
I think that manual refers to the one that ended up getting fried on Apollo 12, and not the RCA camera used on Apollo 16.

Ah right. ALC is also mentioned in passing in this one from RCA

https://www.hq.nasa.gov/alsj/GCTA-Final-Report.pdf

which does mention it can be remotely controlled.
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Offline TexMex

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Re: Apollo 16 camera exposure
« Reply #5 on: April 24, 2018, 01:37:35 AM »
Something to keep in mind here is the the dimming could have been caused by adjusting the camera's aperture to allow in less light.  The camera had an adjustable aperture.  And if the automatic control was being used, maybe it was hunting.  If manual, maybe someone was adjusting.

But the dimming could also be any number of other things. This is a signal being transmitted 250,000 miles to a rotating planet with a few radio telescopes picking up the signal. And from there retransmitted via satellite to NASA in Houston.   Was the dimming caused by shifting from one receiver to another? Did the receiving antenna get a little out of whack?  Was someone adjusting the gain trying to get a better pic?  Did the satellite have an issue?  We don't really know.

Offline Allan F

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Re: Apollo 16 camera exposure
« Reply #6 on: April 24, 2018, 07:16:23 AM »
It looked more like the aperture was closed about 3 stops remotely. It stopped down before it moved significantly towards the sun.
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Online Kiwi

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Re: Apollo 16 camera exposure
« Reply #7 on: April 24, 2018, 08:00:36 AM »
Does anyone recognise the exact scene?  I don't from the still photography and I've yet to view all of the video on the Spacecraft Films' Apollo 16 DVDs. Of the EVA TV from all missions that I have seen, I don't recall the same thing happening. If similar darkening is caused by pointing the camera close to the sun, it's common to see a lot of lens flare first, but I've not seen a scene go so dark because of that.  If the darkening is caused by the camera, it looks like the aperture was simply stopped right down then opened up again, and that it was not due to the sun catching the lens.

Once we have the scene and/or the GET, we can look up the Apollo Lunar Surface Journal to see if there is a comment about the darkness of the TV image. The guys' suits look pretty grubby so I'd guess second or third EVA.

On the other hand, can anyone who's playing with video deliberately darken a scene like that then post it online?

I've gone right through the Apollo 16 ALSJ and had no luck finding the scene by searching for "dark, "black," "exposure," "aperture," and "Fendell" to see what Ed Fendell was doing with the TV camera from Houston. His name occurred 526 times.
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Offline dwight

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Re: Apollo 16 camera exposure
« Reply #8 on: June 21, 2018, 07:49:18 PM »
It is AGC circuitry which was designed specifically for the inadvertent pointing at the sun. Additionally the GCTA had a modified plate over the image sensor in the camera which would prevent over heating and subsequent burnout in such a situation. From "Live TV From the Moon", by yours truly:

Apollo 14 WEC Camera: p179  "The burn-proof image sensor which had been successfully used to transmit live launch tower perspective pictures of the Apollo 13 launch was added to the
lunar surface camera. The new tube was Westinghouse’s Electron Bombardment Silicon (EBS) sensor. It had the benefit of being able to “see” in extremely low light conditions, yet would not burn out if accidentally pointed at the sun. Due to a wire mesh covering the image sensor, any heat build-up as a result of the sun’s highly intense brightness being focused on the senor would be dissipated, leaving the camera undamaged. The ultra sensitive sensor could amplify light ten to twenty times greater than the SEC tube built into
the Apollo 11 black-and-white TV camera.

As an added precaution, a lens cap was also implemented which would be put over the lens any time the camera was relocated from one location to another."

For the Apollo J Missions GCTA: p 192: "Early in September of 1970, a preliminary design and system interface review was held by RCA. Recommendations were made to incorporate a thermal sensor on the Vidicon faceplate to provide an indication of faceplate temperature. Further thermal and de-emphasis considerations were recommended to be given further tests over a 20 month period. In October senior RCA engineers reviewed the design of the camera and with additional systems management support, worked to improve the overall video quality of the camera."

p 195: "Testing of the internal circuitry and mechanical functions of the TV system were conducted through to the end of 1970. Thermal considerations continued to be the main
focus of physical design attributes of the camera. It was determined that thermal blankets covering the camera would be required from the first EVA. Automatic Light Control and Automatic Gain Control functions were added to the system to facilitate in an improved TV picture. According to Sam Russell, the picture tube had to undergo tests where it was pointed at the sun for extended periods of time and not be burned out because of it. NASA was adamant that a repeat of Apollo 12’s TV problems would not occur with the GCTA."
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