Archived posting to the Leica Users Group, 2004/01/31

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Subject: Re: ISO for B&W film speed was Re: [Leica] should be Tmax 3200 at 1600/was TriX at 800
From: Mark Rabiner <>
Date: Sat, 31 Jan 2004 22:45:20 -0800

snip> For what it's worth the 'real' ISO speeds of the superspeed films
currently on 
> the market are as follows:
> Fuji Neopan 1600 ~640
> Ilford Delta 3200 ~800
> Kodak TMax 3200P ~1000
> I use the ~ because these are rounded to the nearest third of a stop.  It's
> useful to keep in mind that these speeds mean more on the box that the film
> comes in than they do in your darkroom.
> Plenty of people have taken great photos without even knowing what speed their
> film was, so find a message from one Kyle Cassidy and read the last line . . .
> off you go . . . 
> Marty

I'm really put off by this ISO baloney Marty.

All ears to where these numbers came from and why you'd lay them in this
particularly glib manner.

Earlier you stated that iso's are determined by among other things how they
are developed in a particular standardized developer.
Which would that developer be?
And why would you assume that is the developer we are using?
Or close to it?
And why not tell us in the first place?

Also your statement that our exact method of agitation is going to
critically affect our film speed is just a wild one.

Is this from your own experience or did your friend from the ISO tell you
this or did your read this in a little Kodak thing?
Will I gain an extra half stop if I agitate every 30 seconds instead of
every minute? Or the other way around? If the music is playing a little fast
and I've had one extra cup of coffee am I going to gain a half stop?

I don't think so  Marty. A forth of a grade of contrast maybe at the most on
that kind of stuff. Not measurable film speed.

A really basic idea which I'm sure the ISO people are onto is that film
speed comes mainly from exposure. Not from development.

I think if one agitated once every 3 or 4 minutes instead of every 30 to 60
seconds one might pick up a small fraction of a stop in speed. Perhaps
alternating in water bath or a slight alkali solution with some fava beans
for desert. A series of alternations going on for 45 minutes to an hour. But
these are extreme agitation schemes. Not a critical change.

It sound to me like you've been subjected to a whole lot of information in a
very small time. You're read much more than you've actually done. A very
dangerous combination. I'd put more flying time in the darkroom before you
hand out such a large amount of smug off center fanciful advise like you are
Charten Hesston coming down with the tablets from the mountain.
The people on this list were not born yesterday.

Mark Rabiner
Portland, Oregon

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