RE: [APML] Provia 100F - Overdeveloped

[Kirk Carbo <kcarbo@lobosservices.com>]

Pushing film is accomplished by increasing the development time.  The basic
idea is that the shadow areas or areas that received little exposure to
light are fully developed in the first part of the development cycle and the
highlights or denser areas on the negative take more developer and time to
develop fully.  So the highlights on your negative are increasing in density
right up until you stop the developer.  Increasing the time in the developer
will increase the density of the highlights.  It also increases the density
in all the other parts of the negative, just not as much, so you get an
increase in the overall density range of the negative.  The base + fog
density of the negative increases with increased development time, so even
an unexposed portion of the negative is affected by the increased
development time.  The density of your sky background does increase when you
push film, but you should be able to print through the increased density.  
Normally push processing is called for when photographing a low contrast
subject.  A high contrast subject, M42 being the classic example, calls for
pull processing to lessen the contrast range.  The problem with decreasing
development time is   like push processing it affects local contrast too.
So you may get the density of the trapezium down, but the contrast in the
surrounding nebula will be reduced also.


> -----Original Message-----
> From: Brian Larmay [mailto:astrobri@ameritech.net]
> Sent: Monday, May 12, 2003 7:04 PM
> To: Discussion of Film Astrophotography
> Subject: Re: [APML] Provia 100F - Overdeveloped
> 
> 
> I should probably know this now but I dont...
> 
> When pushing film, does it increase just the contrast, or 
> does it increase
> the sky background as well as the contrast  and faint stuff.
> 
> Brian
> 
> 
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