Re: [APML] Pushing Provia 400F - Actual Speed Gain?

["Chris Cook" <ccook@cape.com>]

Hi Wei-Hao -

I shot some 400F with a +2 push a few years ago and found it to have a
strong red shift.  From looking at your test results, you didn't seem to
record this shift.  Any thoughts on this?

Thanks! :-)

Chris

-----------------------------
Chris Cook Photography
www.cookphoto.com


----- Original Message ----- 
From: "Wei-Hao Wang" <whwang@gmail.com>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Friday, February 04, 2005 8:26 PM
Subject: Re: [APML] Pushing Provia 400F - Actual Speed Gain?


> Hi Wade,
>
> Please come to this directory:
>
http://www.ifa.hawaii.edu/~wang/chinese/articles/wide_field_astrophoto/tone_control.files
> There are five JPG files.  The file names explain themselves.
>
> These images were taken at the same night with the same lens, on Provia
> 400F of course.  The sky condition was not too perfect and there might be
> some background brightness and transparency variations.  Nevertheless, I
> believe it is fair to say that 20min nopush and 10min push+1 give very
> similar densities.  In other words, Provia 400 push+1 does have EI=800,
> which is what Fuji tells us.
>
> As I understand, in terms of film speed, the effect of pushing has nothing
to
> do with long exposures.  I believe here you are talking about
> reciprocity failure.
> Reciprocity failure controls how fast latent image forms on the
unprocessed
> film.  Processing controls how the latent image is transformed into
density.
> These two are pretty much independent.  You can do some pushing tests
> under short exposure times (no reciprocity failure), as the film company
does.
> The result should apply to long exposure times (with reciprocity failure).
>
> Cheers,
>
> Wei-Hao
>
> -- 
> ________________________________________________________________
> Wei-Hao Wang  :)
>
> Institute for Astronomy at University of Hawaii
>
> Address:
> 2680 Woodlawn Drive         Personal Website:
> Honolulu, HI 96822             http://www.ifa.hawaii.edu/~wang
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>


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