[MF3D.FORUM:65] Re: Apparent image size, MF verus

[Richard Rylander <rlrylander@xxxxxxx>]

Bill Glickman wrote:

> > There is a very interesting 'development' in film technology recently
> announced
> > by AGFA.  By adding formate to an emulsion, researchers at the University
> of
> > Paris-Sud claim they can capture every bit of light incident on a film.
> > Basically, the formate is supposed to stop electrons kicked out of AgX
> crystals
> > by photons from recombining with the crystal.  This has the potential to
> > increase film speed 10-fold and dramatically reduce reciprocity law
> failure.  No
> > word on when we can expect commercial products exploiting the effect.
>
>     Very interesting, and thanks for sharing this Rich... clarification
> please... are you saying in addition to speed,  this new technololgy will
> enable chrome films to have greater exposure latitude also...this of course
> is one of the most cumbersome aspects of chrome film, blown out highlights
> and black shadows... If so, Agfa will be a viable competitor to Fuji and
> Kodak!
>
>     Also this sure makes a good case holding off on the purchase of those f2
> mega $$ lenses for now... with 10x the speed, everyone can shoot fast... is
> that 10x the speed or 10 stops.... I assume 10x which would equate to about
> 3 stops... where did you read this?
>
> Regards
> Bill

Bill -

The speed increase (from what I have read in a news item from Photo Marketing
Association International - www.pmai.org) could be 10x (~3 stops).  This is all
still very much in the research stage.  One potential problem to be ironed out
is how the formate will affect spectral sensitivity (i.e., will it react with
the sensitizing dyes used to make a film panchromatic, or sensitive to a
particular color range).  I wouldn't wait too long to buy a new lens - this
research may take a while.  By the way, Kodak has also been researching
chemicals that do what formate does, but they haven't announced any related
commercial products.

Exposure latitude is a function of film contrast, not sensitivity.  It has
usually been the case that faster films have had more latitude, but that is a
consequence of their having lower contrast.  Most of a film's contrast
characteristics relate to the distribution of grain sizes.  The more uniform the
grain size, the higher the contrast (i.e., grains of the same size tend to
'switch on' at the same light level).

Lithographic films have extremely high contrast, extremely fine grain, and a
very narrow range of grain sizes.  It takes special compensating developers to
eke out a gray scale from these films (when a relatively small number of grains
in a given area are reduced to metallic silver, the local development
environment is changed by exhaustion of a very dilute developing agent and/or
release of by-products to inhibit the development of nearby grains just on the
threshold of changing to metallic).

High speed films undergo a longer AgX crystal growth stage to produce larger,
more sensitive crystals.  But growth rate is not uniform, so you tend to get a
broader range of crystal sizes - an lower contrast as a result.  If this new
'formate' process increases sensitivity without extended crystal growth (and
grain size distribution), special measures might be needed to tame the contrast
(the 'chrome latitude situation will probably not improve).  On the other hand,
current high-speed, moderate contrast films could become "ultra-speed", moderate
contrast films without grain increase or loss of exposure latitude.

Rich