Re: cyanotype question

Joe,

The problem is with interpretation of log scale or transmission density.
Maybe the following numbers will clarify:

If you expose for 100 units, step 1 receives 100 units, and doubling this
exposure means an actual exposure for 200 units.

But when you expose for 100 units, step 5 only receives 25% of the exposure,
so it receives only 25 units, doubling the exposure for step 5 means only an
actual exposure for 50 unit.

Now when you expose for 200 units, step 1 receives 200 units, and step 5
receives 25% of that, which is 50 units; so both step 1 and step 5 should
move up 2 steps.

Dave S

----- Original Message -----
From: "Joe Smigiel" <jsmigiel@kvcc.edu>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Friday, September 03, 2004 2:12 PM
Subject: Re: cyanotype question

> Dave,
>
> Can you cite the problem with my interpretation? I thought I was saying
> the scale would shift upward at both the lower and upper end, just
> moreso and faster at the lower end.
>
> If we look at the steps, their corresponding densities and transmissions
> this is what we have (approximately and I've rounded things a bit to
> simplify...step 1 is actually 0.03 density and <100% transmission,
> etc.):
>
> Step 1, 0.00 density, 100% transmission
> Step 3, 0.30 density, 50% transmission
> Step 5, 0.60 density, 25% transmission
> Step 7, 0.90 density, 12.5% transmission
> Step 9, 1.20 density, 6.25% transmission
> Step 11, 1.50 density, 3.1% transmission
> Step 13, 1.80 density, 1.6% transmission
>
> My thought was that if the 250 unit exposure was "correct" to get some
> tone, say, max print density at step 1, then another identical
> arithmetic increase unit exposure (250 units) would be sufficient to
> produce the same tonal value (i.e., max d) at step 3 effectively
> shifting the scale upward two steps at that point. However, up around
> step 13, that arithmetic unit increase has an insignificant effect on
> the resultant tone so that there is no perceived upward sliding of the
> tonal scale at that point. Its going up a bit at that end, but not
> enough to discriminate visually.
>
> In the example, to get step 5 to max d would require 250 + 250 + 500
> =1000 units.
> Step 7 would need 2000 units (=250+250+500+1000) to achieve the same
> tone, step 9, 4000 units, and step 11 would require 8,000 units. To
> match at step 13 would require 16,000 units. As a result, the low end
> is shifting much more rapidly than the high end as exposure is increased
> (regardless of whether you talk of arithmetic or geometric exposure
> units).
>
> If I'm missing something here, please explain it in a bit more detail or
> point me to a good reference so I can understand it better.
>
> Thanks,
>
> Joe
>
>
> >>> fotodave@dsoemarko.us 09/03/04 12:31 PM >>>
> Hi Joe,
>
> Your interpretation of densitometry or log scale is not correct (no
> offense
> intended). If you double the exposure, the scale should shift up on both
> lower and upper end. In hand-coated materials, sometimes it is not
> exactly
> like that because of many factors including mechanical factor
> (repeatibility
> issue) and visual factor (the low and high ends are toe and shoulder
> region,
> so when you shift, the change/difference might not be that visible).
>
> But looking at your original data, I think the problem is something
> else.
> Could it be the warming-up factor of the exposure unit/light? You could
> probably try warming the light up for about 5 minutes and repeat your
> test
> and see if there is any difference.
>
>
> Dave S
>
> ----- Original Message -----
> From: "Joe Smigiel" <jsmigiel@kvcc.edu>
> To: <alt-photo-process-l@sask.usask.ca>
> Sent: Friday, September 03, 2004 12:01 PM
> Subject: Re: cyanotype question
>
>
> > Hmmm. Actually the effect is beginning to make sense to me based on
> > what you've just said. The 2 step gain is on the low end while the
> > higher zones are not increasing as much. The lower densities'
> > transmissions are closer to 100% so an arithmatic unit increase in
> > exposure would have a relatively greater effect there than on the high
> > zones. In other words, if max density is reached on step 1 which has
> a
> > density of approximately 0.00 an additional 250 units would really
> flood
> > the adjacent steps with exposure effect. At the same time, step 13
> > transmits only about 1.5% so it would require a huge arithmetic
> increase
> > to make a geometric increase of 2 steps (1 stop density) at that
> point.
> > Part of the exposure effect is also probably masked by the printed out
> > image in both the low steps and higher ones, but more pronounced at
> the
> > lower end. Add to this a possible intermittency effect as well as a
> > dark or drying effect. I don't think I would be able to isolate the
> > variables enough to actully solve this dilemma.
> >
> > It really makes me see why the density range of the negative becomes
> so
> > important and why the negative density range needs to be tailored to a
> > specific process and set of materials. I guess the easiest conclusion
> > is that an additional unit of exposure isn't just going to shift the
> > scale along the stepwedge evenly (as I assumed earlier) and the degree
> > to which this is evident actually depends on where the unit print
> > exposure matches the overall negative density scale.
> >
> > I think I'll give this a rest now and fine tune a couple prints. I'll
> > post the images somewhere along with the stepwedges in a few days if
> > anyone is interested.
> >
> > Joe
> >
> > >>> Ender100@aol.com 09/03/04 10:13 AM >>>
> > Joe,
> >
> > That's what is sort of baffling.... two steps is equal to a full stop,
> > or
> > doubling the exposure. So you should go up 2 steps when you double
> the
> > time
> > from 250 units to 500 units....and that is indeed what happened.
> > However, you
> > reported that you got two more steps merging when you went from 500 to
> > 750
> > units..... that should have only happened if you doubled the time from
> > 500 units to
> > 1000 units.
> >
> > Mark Nelson
> > www.precisiondigitalnegatives.com
> > www.markinelsonphoto.com
> >
> >
> >
> > In a message dated 9/2/04 10:19:17 PM, jsmigiel@kvcc.edu writes:
> >
> >
> > >
> > > Yes. You have it right as far as the mergers are concerned but I
> > don't
> > > follow you on the question about 2 additional steps merging at 750
> > units. No
> > > steps merge at 250. Three steps merge at 500 which indicates the
> low
> > end was
> > > pushed up the scale 2 steps as an additional 250 units was given.
> The
> > same
> > > thing happened as the exposure was further increased by 250 units to
> > 750, i.e.,
> > > the low end was pushed up the scale another 2 steps. This is also
> > showing in
> > > how many steps solarized initially. The highest solarized steps
> were
> > 6, 8,
> > > and 10 for the 250, 500, and 750 unit exposures, respectively. The
> > low steps
> > > are acting in a consistent manner gaining 2 steps with each
> additional
> > 250
> > > unit exposure. It is the high end that is behaving strangely
> showing
> > a
> > > decrease in the rate that the tones print as exposure is increased.
> > >
> >
> >
> >
> >
> >
> >
> >
> >
> >
>
>
>
>
Received on Sun Sep 5 08:28:35 2004