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Location: UFOUpDatesList.Com > 2007 > Dec > Dec 7

Re: Skylab 3

From: Bruce Maccabee <brumac.nul>
Date: Fri, 7 Dec 2007 12:12:58 -0500
Archived: Fri, 07 Dec 2007 23:26:11 -0500
Subject: Re: Skylab 3


>From: James Smith <lunartravel.nul>
>To: ufoupdates.nul
>Date: Thu, 6 Dec 2007 12:48:17 -0500 (EST)
>Subject: Re: Skylab 3


>>From: Brad Sparks <RB47x.nul>
>>To: ufoupdates.nul
>>Date: Thu, 6 Dec 2007 07:48:34 EST
>>Subject: Re: Skylab 3

>>>>>Query: The second set of photos that we blew up we found
>>>>>on the filmstrip, but they didn't come out; they were
>>>>>underexposed. If I looked at the records correctly, they were
>>>>>approximately an f/4.5 and the others were approximately a f/8.
>>>>>They were also blurry so there might have been some movement
>>>>>although the shutter speed was 1/500 of a second."

>>>Could the 'structure' in the fourth be simply due to camera
>>>jostle since no astronaut mentions it?

>>If the exposure was 1/500 of a second then camera "jostle" would
>>be virtually impossible, as that would mean the camera was
>>jerked at a velocity of about 0.4 m/sec or about 1 ft/sec. The
>>Y-shape of the 4th photo red object is not a continuous motion
>>smear image. The camera motion would have to precisely retrace
>>one branch of the Y-shape then move back up the other branch
>>which is patently absurd.

>Does f-stop truly relate to the exposure time? I remember in
>Rutledge's book (Plate 9, 800mm lens, f/8 had a 1 minute
>exposure) that he had time exposure images with standard f-
>stops. I am a novice about photography. Is there some other
>setting to keep the iris open for time lapse? Does the f-stop
>affect over-under exposure?

Photography 101:

The "f stop" and shutter time are independent parameters which
can be adjusted to determine the exposure level. The f stop
number is related to the diameter of the aperture that lets
light into the camera to be focused onto the film (plane). The
size of the aperture is inversely proportional to the f stop (f
stop number is the focal length divided by the diameter of the
lens opening). The shutter time is independent of the f-stop. It
is literally the time that a shutter allows light to hit the
film. A simple equation for Exposure (energy captured by the
film) is E = (pi) BTt/4(f#)^2 (think I have that right; been
years since I thought about it). B is the "brightness" of the
light source (this has a technical definition I won't go into,
but is related to "brightness" as a physiological sensation), T
is the lens (glass) transmission factor (typically 80-98%), t is
the shutter time, and f# is the "f-stop" number (typically
between f/22 and f/1.8 or so). The point here is that t and f#
are different quantities that act together to determine the
exposure of the film (whether one wants to consider exposure in
lumens or joules).

The brightness of the final printed image produced depends not
only upon the exposure as calculated above, but also in the
"film speed" or film sensitivity. The sensitivity of a film is
given by its ISO (formerly ASA) number. The more sensitive the
film, the larger the ISO number and the less exposure is
necessary to make a usefully bright image.

To answer your questions: the shutter can be adjusted over a
wide range on cameras such as the Nikon. The longer the shutter
time the more the exposure. But longer shutter times mean
blurrier pictures in a dynamic scene (changing with time). So,
if you want to minimize the effects of motion blur you use a
short shutter time (and even try to pan with the motion, if that
is possible, but then the background is blurred) like 1/125,
1/500., 1,1000 or "faster" (less time open). If you need to have
a fast shutter to "stop" motion, then you may have "open the
stop" (decrease the f# ) in order to maintain good exposure.


>The f-stop (f/4.5) mentioned was for the prior blurred laser
>images. Of course, by my past logic it would make sense that
>they keep the same f-stop but then it is possible for it to be
>the f/8 (1/125 second). Seems pretty fast, but maybe slow enough
>to catch a jostle, I haven't measured jostle speed before. How
>much of a distance must the camera be jostled to replicate the
>image using a single red dot?

Although there could be lateral motion of the camera, what
causes the displacement of the image is rotation of the camera
lens axis. If, while photographing the moon, you rotate the
camera by 1/2 degree during the shutter time you will get an
elongated image that is twice as long as the moon is wide
(because the angular size of the moon is 1/2 degree). If the
shutter were open for 1 second, then the rotation rate could be
1/2 degree per second to get that elongation. However, at 1/100
sec the rotation rate has to be 100 times faster (50 deg/sec).
Smaller blur amounts require less angular rotation. At 1/250 or
1/500 sec the angular rotation rate has to be even greater. But
there is one other thing, and that is angular acceleration that
is needed to get the rotation' rate up to some value. The
angular acceleration can be caused by the forces (torques on the
camera) of hand vibration, but they are opposed by the inertia
(moment of inertia) of the camera. So. one does not get
instantaneous changes in the angular rotation. In order to have
one ":dot" make the image in photo 4 as a result of motion smear
would require angular motions of several tenths of a degree up-
down and left-right during the shutter time. Not impossible,
but, as I pointed out in a previous email message, the
continuous motion of the camera while the shutter is open
generates "looped" images because of the interaction of the hand
vibration with camera inertia. IMHO there is no "loopiness" in
the image in the fourth photo.

>For this camera, out of the about 600 frames of the 10 film
>magazines, about 50 images were blurred (about 20 blurred images
>occurred in the UFO sequence film magazine +the one prior),
>about 10 out of focus (6 in the two film magazines), about 30
>underexposed (3 in the two magazines), and 3 over exposed. So
>blurred images seemed to occur more frequently for some reason
>during these final two film magazines. Due to the nature of the
>other blurred frames (not points of light in darkness, except
>for the immediately prior blurred laser frames), the kind of
>blur would be hard to see. Blur implies one axis of motion.

Linear blur, yes. If all the images are elongated in a certain
direction then this is motion blur during the shutter time.
However, to have image extension that is "left-right" as well as
"up down" one needs more than just one axis of motion. IN this
case one needs two axis motion and that requires accelerations
to change the rotation from around one axis to around another,
perpendicular axis, and that results in "loopiness" of the
photo. I should point out that in "loopy" motion one often gets
bright spots which signify (if the light itself is constant)
momentary slow-downs or stops in the angular rotation (bright
spots imply longer exposures at various portions of the "loopy"
image."

Another cause of blur in the astronaut's photos could have been
the window(s) they photographed through. (Photographing through
glass windows always introduces some small blur.)

>I know I have messed up alot of photos simply from pressing the
>button on the camera without holding still enough. The blur in
>my fouled up photos do not stand out as to the exact trajectory
>of camera movement due to the large amount of complexity in the
>image, but for a single point light source, it might be viewed.

>>If the 300 mm lens was used then according to Bruce's
>>measurement the image was only 2.9 milliradians or about 10
>>arcminutes or about 1/3 Full Moon. That is not a prominent
>>angular size, and given a 10-second cycle of brightening and
>>dimming (or rotation where the full Y-shape was only seen
>>briefly during the 10-second period) then there was not
>>continuous visibility of the Y-shape.

>If they looked through their camera to take the "structure"
>image, then I assumed they could see the object with its
>structure, even though it may not be visible to the naked eye.
>The lens would make it visible to the photographer, as he took
>his time to aim and shoot. But the photographer doesn't mention
>any structure in his account. If it was spinning much faster (<1
>sec/cycle?), then even looking in the camera lens would make the
>structure not visible, except on film when the quick camera
>speed captured the shape. But this is not the account. The other
>possibility was two cycles of rotation somehow superimposed,
>one, slow, which caused the general brightening and the other,
>very fast, making it seem a circular blob.

Possibly Garriott did notice structure at the time he took the
fourth photo, even though the image was still quite small in the
viewing aperture of the camera. But he may also have forgotten
that fact when queried about the event days later. THe
astronauts did say it was "big".



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