From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


>From: "Fabio Pettinati" 
>
>
>On Thursday, January 23, 2003, at 03:52  AM, Vladimir Galogaza wrote:
>
>> it is well defined. So the question is how to calibrate deformations.
>> Can it be done by photographing well known dense star fields and
>> compare
>> measured coordinates on the film with known coordinates of imaged
>> stars...
>
>
>Take a look at this site:
>http://home.arcor-online.de/axel.mellinger/mwpan_web/mwpan_web.html
>
>It pretty much provides all the information needed to address the
>problem.
>
>Please note that instead of photographing star fields, one could
>photograph a target of known dimensions at a sufficiently long distance
>and accomplish essentially the same result in terms of deriving the
>mathematical transformations. The target could be as simple as a sheet
>of paper where you print horizontal and vertical lines at the same
>distance (i.e. a square grid) using a laser printer. You could
>photograph that sheet during the day, or you could print a negative
>image (i.e. white grid on a black background--toner is cheap) and
>photograph it at night with proper illumination (sideways).
>
>If the target is sufficiently far away the distortion seen on the
>photograph is essentially the same as when you photograph something at
>infinity. The closer the target to the camera (or telescope) the more
>different the distortion.
>
>Fabio
>San Jose, CA

Hi Fabio
 Part of Richard problem is that without something on the
film to locate the exact center of the particular piece of film he has, he
would not know how to overlay such grid. I'm sure he can handle the math,
it is just finding a way to find the center of a particular piece of film.
Dwight

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