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Location: UFOUpDatesList.Com > 2007 > Jul > Jul 19

Re: The 1952 Tremonton Utah 'Seagulls'

From: Michael Tarbell <mtarbell.nul>
Date: Wed, 18 Jul 2007 13:01:52 -0600
Archived: Thu, 19 Jul 2007 10:26:07 -0400
Subject: Re: The 1952 Tremonton  Utah 'Seagulls'


>From: Bruce Maccabee <brumac.nul>
>To: <ufoupdates.nul>
>Date: Tue, 17 Jul 2007 18:35:59 -0400
>Subject: Re: The 1952 Tremonton Utah 'Seagulls'Confirmation?

<snip>

>I discovered, or more accurately, rediscovered the image size
>vs brightness relationship while I was analyzing the New Zealand
>(Dec. 31, 1978) film oh, so long ago!
>I carried out experiments which showed the following:

>Let "geosize" be the geometric sized image which depends
>upon the focal length, F, the distance to the object, D and the object
>size (transverse to the line of sight), O. Then

>geosize = F (O/D)

>This is simply the equivalence of two ratios: geosize/F = O/D.

>However, this has to be modified when brightness becomes very
>large. Light travels sideways in the film thereby increasing
>the size of the image beyond its geosize according to the
>relation, where I = image size including brightness effects,

>I = geosize + K log (Exposure)

>K is a function of the film and its development. Exposure is the
>amount of light energy hitting the film (the illuminance on the
>film multiplied by the shutter time, or the irradiance in W/cm^2
>times the shutter time). Exposure depends upon how much light
>falls on the film while the shutter is open and this also
>depends upon the area of the the lens aperture which is
>proportional to the square of the f#. If one had film identical
>to what Newhouse used, and if it were developed in the same way,
>it would be possible to determine from the test film what the
>constant K is. (I did this years ago for the New Zealand color
>movie film by photographing back-illuminated apertures of
>various sizes using various exposure settings.) Since he changed
>the f# it might be possible to deduce or approximate K from the
>film itself if one had the original (sorry about that!) or a
>good copy. It would be necessary to measure the sizes of the
>images before and after the f stop change. IF there was very
>little change then probably there was little image growth due to
>exposure. If there was a large change (e.g., 30%) then the image
>sizes at f/16 would probably still be "inflated" somewhat by
>brightness.


Hello Bruce,

This is an interesting and handy relationship. I am still not
sure how to interpret the Exposure term. Typically the argument
to the logarithm function is a normalized (dimensionless)
quantity. For example, if E0 were the exposure that gives
exactly the true 'geosize', then the expression might take the
form

I = geosize + K log(E/E0)

However, this can't be right, since it suggests that
underexposing (E < E0) can make the object appear smaller than
its geosize. What do you actually use as the argument to the log
function?


Thanks,

Mike



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