Re: [APML]: 37 films tested (was Gold Max)

[Robert Reeves <rreeves@connecti.com>]

At 07:26 PM 1/29/98 +0000, you wrote:
>
>A very nice study indeed,  and I must express my suprise at the poor 
>results of the Gold Max film.  I have a couple nice shots of albeit 
>bright objects that I took for 15 minutes.  I look forward to trying 
>the other films anticipating even better results!
>
>But could you explain the chart below a little more, and precisely 
>how you determined the values of stop speed loss?  
>
>> Kodak Royal Gold 1000    (One stop speed loss in two minutes)
>> Kodak PJ400              (2/3 stop   "        "       "     )
>> Kodak PMZ                (1/2 stop   "        "       "     )
>> Kodak PJC-1              (One stop   "        "       "     )
>> Fuji Super G 100         (1/3 stop   "        "       "     )
>
>Thanks for the useful study!
>
>Cheers,
>
>Scott
>---------------
>Dr. Scott Teare
>University of Illinois and Mt. Wilson Observatory
>Mt Wilson, California.
>
>
The f/stop speed loss was determined by photographing a Kodak gray
scale/color patch card under blue flood lights at 1/8th second and around
f/11 or f/16.  The lighting was varried to keep the f/stop in this range
regardless of film speed.

The same card was then rephotographed at the same f/stop for 128 seconds
through a 1000X neutral density filter.  This is a 10 f/stop difference,
requiring a factor of 1000 in additional exposure.  (On five of the films, I
repeated this for 256 and 512 seconds as well.  I think they were Royal Gold
400, Royal Gold 1000, PJ400, PJC-1 and PMZ)  The extended exposures were
repeated at 1/3 f/stop wider apertures until a full 3 f/stops had been covered.

The resulting negative strips showed the original 1/8th sec. baseline, or
control exposure at "normal" density while the time exposures showed a
progresive darkening as the f/stop was sequentially opened.  The strips
typically started off lighter than the baseline exposure, then got darker at
the 3 f/stop point.  The point where the additional extra aperture gave me
an image density EQUAL to the baseline 1/8th second exposure told me how
much speed in f/stops the film had lost in the 128, 256, or 512 seconds of
exposure time.

Since I didn't do all the films out to the 512 second point (life is too
short!), I just use the 128 second shots to compare them all.  It is more
than adequate to relate one film's reciprocity law failure against another.
But as a point of interest, off the five films I did take out to 512 seonds,
only Royal Gold 400 had a flat reciprocity loss.  It stayed at 1 f/stop for
2, 4, and 8 minutes.  The others kept progressively loosing speed so the
reciprocity figure was greater after 8 minutes than it was at 2.  I'll have
all the details when the web page is finished.

This speed test is separate from the LED color tests I was speaking of earlier.

Since I haven't finished the page on my web site about these film tests, I
posted a 120K .jpg showing the color sensitivity test for all 15 color
negative films I have done.  There is no link to it yet on my home page, so
use a URL of

http://www.connecti.com/~rreeves/cnegall.jpg

to access it directly.  I will soon post the results of 13 B&W films and 11
slide films.  The B&W is finished and being writen in HTML but I just
haven't had time to scan the slides yet.  Maybe it will all be there in a week.

Robert Reeves                Home page http://www.connecti.com/~rreeves
520 Rittiman Rd.             Email     rreeves@connecti.com
San Antonio, Texas  78209    Phone     210-828-9036
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