linearity of x-ray film/autorads

daj (David Johnston) daj at nhm.ic.ac.uk
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.
Cheers,
DAJ

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 nhm.ic.ac.uk)



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