linearity of x-ray film/autorads

daj (David Johnston) daj at
Mon Jan 24 04:07:50 EST 1994

On Fri, 21 Jan 94 18:17:18 GMT,
  DAVID SCOTT writes:

>We qould like to know across what range x-ray film (autorads) are
>going to be linear in signal. Example. We are looking at differant
>methods of scanning autoradiograms, and quantitating signal. We are
>looking at northerns and genomic southerns. Scanners can handel from
>1.7 to 4.0 O.D. (depending on method of scanning, $ spent), so
>we are wondering what the film can handle. Buying a scanner that is
>more accurate than the film seems like a waste of money. Comments 
>or answers would be greatly aprecciated.

You can test this directly. Make a thick cardboard mask to cover a piece of 
film. Cut numerous openable windows in it, hinge and seal with tape. In a 
dark room, expose different windows to different numbers of flashes from a 
MANUAL flashgun (identical distance and duration). Develop the film and put 
pieces from the windows through a spectrophotometer. Plot "exposure" 
against adsorbtion.

David A. Johnston
Dept of Zoology, The Natural History Museum, Cromwell Road,
South Kensington, London SW7 5DB.
(tel 071 9389297, fax 071 9388754, email daj at

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