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Development Time Constants



 
 
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  #1  
Old March 17th 06, 01:22 AM posted to rec.photo.darkroom
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Default Development Time Constants

This question is within the context of the subject title.

ALL things being equal, if HP5+ is given X minutes to
develop, what is the value of the constant K in the equation
X times K equals Y. Y is the time needed to develop Delta 3200.

I think the value of K may hold steady for all films in the same
developer. If so, some film, Plus X perhaps, may be used to
establish base times and a constant K applied to each
of any other films in that same developer.

To the point, I've from the woods ONE roll of Delta 3200 to
develop. If ten minutes will do for a roll of HP5+ how many
minutes should I give the Delta? Or, by what factor should
I multiply the ten minutes? Dan

  #2  
Old March 17th 06, 02:26 AM posted to rec.photo.darkroom
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Default Development Time Constants

wrote:
This question is within the context of the subject title.

ALL things being equal, if HP5+ is given X minutes to
develop, what is the value of the constant K in the equation
X times K equals Y. Y is the time needed to develop Delta 3200.

I think the value of K may hold steady for all films in the same
developer. If so, some film, Plus X perhaps, may be used to
establish base times and a constant K applied to each
of any other films in that same developer.

To the point, I've from the woods ONE roll of Delta 3200 to
develop. If ten minutes will do for a roll of HP5+ how many
minutes should I give the Delta? Or, by what factor should
I multiply the ten minutes? Dan


The factor will depend upon the developer, film, EI and temperature. I've went
through this in detail when I wrote a program to calculate development times for
films plugging in the following variables: developer, desired contrast index,
temperature, and film EI. However, it was written before Delta 3200 was on the
market, so I didn't include data for that film. Just about every estimate of a
"constant" required non-linear regression (500+ combinations).

If you're trying to estimate a time for Delta 3200 based on a known HP5+ time
for a certain temperature, EI and CI, check the Ilford film PDF's for both films
and the developer you intend to use. If there's a problem, post your HP5+ EI,
developer, time and temperature.
  #4  
Old March 19th 06, 07:51 PM posted to rec.photo.darkroom
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Default Development Time Constants

One other variable that may need to be considered (based only on my empiric
data). You may need to group films into "families" to get anything like an
easy "k" factor. Perhaps grouping films by characteristics:

High resolving microfilm types perhaps including TechPan
Slow speed fine grain films like Pan F and Panatomic-X
Medium speed conventional films FP-4
Medium speed tablet grain films Delta 100 TMax 100 Acros(?)
400 speed conventional films Tri-X, HP-5 plus
High Speed T-grain films TMax 3200, Delta, etc.

Kodak's Darkroom Data Guide once had a dial used to figure time and temp for
all their films, by extrapolation I included films by other makers but ran
into problems when the TMax films came out.

--
darkroommike
wrote in message
oups.com...
REUC wrote:

There is no such universal 'constant'. Each developer
will react differently.


Time and temperature compilations are taken by most
to be ballpark figures. A not too inclusive compilation might
be worth while. A type of developer and perhaps eight or ten
films might be accurate enough across the board. Dan



  #6  
Old March 20th 06, 01:42 AM posted to rec.photo.darkroom
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Default Development Time Constants

wrote:

Michael Gudzinowicz wrote:

wrote:

To the point, I've from the woods ONE roll of Delta 3200 to
develop. If ten minutes will do for a roll of HP5+ how many
minutes should I give the Delta? Or, by what factor should
I multiply the ten minutes? Dan


If you're trying to estimate a time for Delta 3200 based on a
known HP5+ time for a certain temperature, EI and CI, check
the Ilford film PDF's for both films and the developer you
intend to use.


The developer is ACU-1 and the films are the HP5+ and
Delta 3200. ACU-1 and the Delta is not a combination listed
in the Massive Chart. For a K I'll check the two films in D-76
and likely another developer or two in which both films
have been processed. Dan


If some data was available, I guess you wouldn't have asked.

I assume that you don't have more D3200 to run a clip test,
or a developer for which Ilford provides data.

There is a "constant" called the Waller coefficient which varies
markedly for different developers, but is fairly "constant" for
similar types of films. The coefficient is the ratio of the required or
total development time to the time of emergence of the image. That
observation is the basis of "factorial" development of paper.

And of course, we don't know the value for Acu1, and apparently
there's no D3200 film to waste. What I would do, would be to clip
a section of leader from HP5+ or the last 1/4" of the tail of 120
film, and reroll it. Expose to light and develop in a tray and note
the emergence time for a light gray image. I'd let development
continue for the same period of time (2X emergence time total), stop
and fix the HP5+. The film should be underdeveloped to a grey tone
rather than opaque black.

Divide your known development time by the time to emergence, and
use this as your constant. Get a scrap of D3200 film from the leader or
non-image area of 120, in light determine the emergence time, and
stop at 2x that time as with HP5+. Compare the fixed films and see
if the densities are the same. If they are identical, use the factor to
calculate a D3200 development time. If they are "close" (within 10% using a
densitometer), use the optical density ratios to tweak the time calculated with
the factor. If they are no where near agreement, try again with scraps you've saved.

This is a rather oblique approach, but it avoids the comparison of
two films in different developers where the ratios of development times
will differ. In those situations, the ratio of emergence times differs.

If you don't post, let me know where this goes by email.
  #7  
Old March 20th 06, 03:36 AM posted to rec.photo.darkroom
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Default Development Time Constants

Mike King wrote:

Kodak's Darkroom Data Guide once had a dial used to figure time and temp for
all their films, by extrapolation I included films by other makers but ran
into problems when the TMax films came out.


The dial works (in my not very well tested experience) for time
versus temperature, while film and developer are held constant.
That is, if you know the right time at 68 F, you can predict a
reasonable time at 72 F. But you already need to know a right
time for your film+developer combination. For Tmax, I used the
film box or datasheet value as a starting point. The dial is basically
just a convenient version of a time/temp chart like this:
http://www.digitaltruth.com/chart/timetemp.html

Dan wants a formula that lets him convert times from one developer
to another, or one film to another. I don't think this is possible
with a simple conversion. If this were possible, the time for film X
would always be a constant factor times that for film Y, and
some study of a dev chart will show exceptions.

For example, a very small amount of data from the
Massive Dev Chart:

35mm,20C HP5+(400) FP4+(125) Tri-X(400)
Acufine 4.5 4 -
D-76 7.5 8.5 7-8
D-76 1:1 13 11 10-11
HC-110 B 5 9 4.5-6
Rodinal 1:50 11 15 13

Now, maybe these times are all crap, although I think some
of them are from manufacturer's datasheets.
But my point is you can't come up with blanket statements
like FP4 takes 50% as long as HP5, or HC-110B takes
2/3rds as long as D-76. And I deliberately picked three
films that are fairly similar, so the difference isn't
regular vs T-grain or anything like that.

  #8  
Old March 22nd 06, 01:39 AM posted to rec.photo.darkroom
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Default Development Time Constants

wrote:

Dan wants a formula that ...


I've the formula. What's needed is a method of
establishing the values of k.
I think I've Got It! All films through the STD
developer and the STD film through All developers.
The chart looks like this:

Films
l--------l---------l----------l-------
D l--------l---------l----------l-------
E l--------l---------l----------l-------
V l--------l---------l----------l-------
l--------l---------l----------l-------

Top row STD developer, Left column STD film.
Fresh off the top of my head. I think it makes
sense. What do you and ... think of it? Dan

 




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