Re: [APML] TMax 400 Reciprocity Failure and Pre-flash Hypersensitization

["D. Kodama" <kodama@alumni.caltech.edu>]

Mike,

Very interesting results that preflashing actually harms the performance.

By coincidence last weekend I actually took some astrophotos on TMax 400
(120 format film).  The only reason I used this film is because that was
all that was available at the camera shop in 120 format.  This was for
some quick focus tests of a new (used) Schmidt camera I just got.  There
are two images here:

  http://www.eanet.com/kodama/astro/2004/0821a/

Both are 10 minute exposures with film developed for the recommended time
in TMax developer.  One shot is of the Double Cluster, where the lack of
H-alpha sensitivity is obvious since the nearby emission nebulosity is
absent, and the other shot is of M45, where it is starting to pick up the
blue reflection nebulosity.

This will certainly not be my choice of film for astrophotography in
normal circumstances.

Dave Kodama


> Hello!  I just completed my tests with 4x5 TMax 400 sheet film.  Using a
> Kodak gray scale, I used a 5000K fluorescent bulb and exposed the gray
> scale
> at 1/10 sec at f4.7 for the normal exposure.  Then, I exposed at f4.7 at
> 16min 40sec using a 10,000 ND filter to estimate the reciprocity failure.
> In order to eliminate the development variability, I developed each set of
> pre-flashed negatives together with a normal exposure and a unhypered
> exposure using the ND10,000 filter – so I developed 6 negatives at a time.
> I was then sure that I could compare each preflash hypered negative to a
> normal exposure and an unhyperred exposure that had been developed in
> exactly the same way.
>
>
>
>     I used two techniques of preflash hypersensitization.  For the first
> technique, I used my camera flash with a milk plastic diffusing screen
> over
> the lens for my 4x5 camera.  I calculated the distance from the film plane
> to a gray surface required to give a normal exposure, then I calculated
> the
> distance to give N-3, N-4, N-5, N-6 preflash hypersensitization.
>
>
>
>     For the second type, I metered the bright blue sky, used a milk
> plastic
> diffusion filter, and shot N-3, N-4, N-5, and N-6 preflash exposures.
>
>
>
>     I then used each preflashed negagive to exposure the Kodak Gray scale
> using a 10,000 ND filter at f4.7 at 16min 40 seconds.
>
>
>
>     I had the negatives scanned at the local photo shop with instructions
> to
> scan the negatives at the same settings and to scan without any
> “improvements.”
>
>
>
>     TMax had consistently about 1 2/3 stop speed loss after 16min 40
> seconds
> in the two batches.
>
>
>
>     No preflashed hypersensitized negative had improved speed compared to
> the negative that had not been preflashed.  In fact, each preflash
> negative
> appeared to have worse reciprocity failure than the unflashed negative;
> the
> most pronounced effects seen with the negatives that had the most
> preflash!
>
>
>
>     Preflash hypersensitization does not appear to improve the reciprocity
> failure characteristics of TMax 400 sheet film.
>
>
>
> Best regards.
>
>
>
> Mike
>
>
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