Why does Apollo footage show a smaller, dimmer second image of Earth in the spacecraft window?
Asked 7/28/2019
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In some Apollo-era footage, Earth appears as a large bright image through the spacecraft window, with a second smaller, dimmer image of Earth nearby. The smaller image moves differently as the handheld camera shifts. What likely causes this duplicate image: the spacecraft window, the camera lens, or something else?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
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The windows of both the LEM and the CM were flat, but both were at least two sheets of glass: the LEM windows were two, some of the CM windows were two & an outer pane to deal with heat during reentry. See this document. At least some of them were coated.
The images are almost certainly from either from 16mm movie cameras or from the Apollo TV cameras: they certainly are not video cameras in any sense we mean that now. I now think this were from the TV cameras.
The artifacts have undergone an even number of reflections and at least one was from a curved surface.
I think, therefore that the second images are lens front-element-window reflections: although it's possible they are internal reflections in the camera lens system, this seems unlikely.
Originally by user82065. Source · Licensed CC BY-SA 4.0
user82065
6y ago
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The most likely cause is a reflection artifact—either between multiple window panes/coatings or, more likely, inside the camera/lens itself.
Apollo spacecraft windows were built from multiple layers, and some surfaces were coated, so bright objects like Earth could produce secondary reflections. However, the way the smaller image is clipped at the frame edge and seems to move differently from the main Earth image suggests the reflection may be internal to the camera optics rather than only from the window.
In practical photographic terms, this is a form of ghosting/lens flare: a bright subject reflects between optical surfaces, creating a smaller, dimmer duplicate that shifts differently as the camera moves. A curved lens element or filter can also change the reflected image size, which fits the smaller appearance.
So the duplicate Earth is not a real second object or a problem with Apollo imaging quality—it is most plausibly an optical reflection/ghost image caused by the window, the lens, or both.
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