Author Topic: Radiation and photographic film  (Read 13409 times)

Offline Bob B.

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Re: Radiation and photographic film
« Reply #45 on: March 29, 2016, 07:50:39 PM »
The issue is a Apollo proponent is arguing with a hoaxer along with myself, and he(proponent) believes all images have some radiation damage.  See above post, but here it is

I understand the general issue being discussed.  That's why I gave a general answer.  However, if I'm being asked to comment on some specific set of circumstances, then that's not clear to me.

Offline bknight

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Re: Radiation and photographic film
« Reply #46 on: March 29, 2016, 10:04:45 PM »
I could envision that cosmic rays might also penetrate the camera or magazine and hit the film, but I've never seen any evidence of that in the Apollo images. I'd expect them to leave white traces, but because the paths are random I'd expect random streaks, not just dots.
Either streaks or similar, but I don't remember seeing anything, but I may have glossed over minor radiation effects, I guess that is what the proponent if speaking about.
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Offline ka9q

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Re: Radiation and photographic film
« Reply #47 on: March 30, 2016, 03:41:50 AM »
If the individual particle energies are insufficient to leave streaks, then I can see how enough of them, over time, might cause a general fogging of the film.

Offline smartcooky

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Re: Radiation and photographic film
« Reply #48 on: March 30, 2016, 04:45:31 AM »
For anyone who is really interested in the effects of radiation on the photographic film emulsions used in space-flight there is this very interesting write up... "The Effects of Space Radiation on Flight Film"

http://ston.jsc.NASA.gov/collections/trs/_techrep/CR188427.pdf

"One of the most damaging effects of radiation on photographic film is an increase in base exposure*.  It produces higher minimum densities for negative films and lower maximum densities for reversal films.  Both types of film experience decreased contrast caused by the changes in minimum and maximum densities. 

Minimum densities experience proportionately higher fog levels than higher densities, resulting in an additional loss of contrast.*  Graininess in the shadow regions and compression of the useful density range are also apparent effects of radiation exposure.*  Colour films experience a colour balance shift because the separate emulsion layers in a colour film, which sensitivities are adjusted for proper recording of different spectral regions of visible light, are affected to different degrees by the energy released from ionizing particles. The most effected layers are blue and green."


Given that photographic processing has been a significant part of my profession for the last 20+ years, I consider myself have enough expertise to discuss this passage with some degree of knowledge.

*Base exposure and contrast
Ideally the film base of an unexposed negative film is clear, and that of a fully exposed film is black. This is what creates the contrast in a black & white film; varying degrees of exposure resulting in a varying of shades of grey. However, when the base exposure is compromised with fogging, instead of having a contrast scale that runs from clear to black, it runs from a shade of light grey to a shade of dark grey, so the gap between fully exposed and unexposed is closed, and it can be difficult  to get a true white or black in the prints made from that negative.

However, three are two very important things to consider here

1. Base fogging can be very, very difficult to detect. Even for an expert its not easy, and even then, that expert really needs to have direct access to the original negatives into order to see it.  Any mild base fogging can be compensated for to some extent in the darkroom, it can even be compensated for if duplicate negatives are made from the original negatives

2. Film & Print scanning. ALL the images of Apollo that you see on the web have been scanned, and as soon as you scan negatives or prints, you have the means of minimising the apparent effects of base fogging and restoring the image to something close to what it would have been like if the film base was not fogged.  Here is an example



This photo is an original, unaltered scan of a single 6 x 4.5 frame from a roll of 120 Tri-X Pan film shot in the 1970s (the roll was found still loaded in the camera in the basement of a house that was being cleaned out). I only processed a year or two ago. It exhibits even but severe base fogging with considerable loss of contrast and lack of detail in the image highlights. 



This is what it looked like after I used Photoshop's Levels, Contrast & Brightness and Tone Curves adjustments. The base fog is undetectable; if you didn't see the top photo, how would you ever know that the original negative was fogged.

There is also a third thing to consider...

3. The subject The moon would have to be THE most high-contrast environment of all to take photographs in. All the  subject material in the scenery runs from bright white in parts of the lunar surface to the inky-black sky. Its is stark landscape, with no diffusion.

The conclusion I must draw from this is that, even of the film base of the films used in Apollo were fogged by radiation it would be extremely difficult to detect even with access to the original negatives, and impossible to detect just from prints or scans from the films.   
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Offline bknight

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Re: Radiation and photographic film
« Reply #49 on: March 30, 2016, 09:56:18 AM »
An excellent report, but I wish it would have addressed the Apollo missions, instead of concentrating on the Shuttle missions.
Truth needs no defense.  Nobody can take those footsteps I made on the surface of the moon away from me.
Eugene Cernan