Color processing myths dispelled

Editor’s Note: Thank to the photo.net members who were kind enough to lend their color film images for this article. Be a pal and go check out their portfolios when you are finished reading the article. -Josh

  1. Eastman-Kodak RA chemistry cannot be used except at relatively high
    temperatures. You must use a special kit.
  2. You can use a BLIX (Bleach Fix) for C41 and E6 films.
  3. You can use a ferricyanide bleach with modern color films, after all the
    old color films used them. (or quinone or persulfate)
  4. Color fixes are basic.
  5. You can’t mix color chemistry from scratch.
  6. There are good published color formulas.
  7. You can process Fuji, Agfa, and Eastman-Kodak films together in the same
    process.
  8. 8631345
  9. You can push / pull E6 and C41 films to get a higher / lower speed.
  10. Stabilizers stabilize film
  11. Color fixers are different / the same as B&W fixers.
  12. Kodak had a C21, C42, E5, E7 etc, process.
  13. You cannot cross process C41 films in E6 processes.
  14. E6 films cross processed in C41 require heavy filtration for printing.
  15. Tungsten films are daylight films with a filter layer (or vice versa).
  16. Freezing will preserve film almost indefinitely.
  17. Fuji and Kodak negative films don’t print on each others papers.
  18. Contrast has no effect on printing color slides / negatives
  19. Prints from slides are equal to or better than prints from negatives.
  20. Film has no speed limit / has a speed limit. Digital has no speed limit /
    has a speed limit etc. ad nauseum.
  21. Professional vs Consumer films, wow what a mess. People say they are the
    same others say they are different, others say they are selected etc.
  22. Color processing at home is hard / expensive.
  23. Color chemicals spoil fast.
  24. Color paper spoils if you keep it at room temperature
  25. Color chemicals are more toxic than B&W chemicals, and are vastly more
    toxic than digital imaging.
  26. Color films of different speeds have those speeds by virtue of having
    different emulsions with different speeds in them.
  27. Plotting an H&D curve of a film will give you an idea of its contrast
    in-camera compared to another film.
  28. I have a developed film with H&D curve that matches the aim of the
    film, so the process was ok.
  29. 9120553
  30. My H&D curve shows me that this film is lower / higher in contrast
    than that film.
  31. Most color films reproduce colors accurately.
  32. Magazines prefer transparencies.
  33. Color transparency film is sharper, finer grained than negative film.
  34. National Geographic photos are made from Kodachrome transparencies or at
    least some kind of transparency.
  35. Only transparency film can give you the vibrant colors you see in a
    magazine.

Introduction

After reading this and other forums, I have found a lot of myths presented as fact
about color products and processes. I thought I would list a few and dispel or affirm
their truth AFAIK.

Myths

1. Eastman-Kodak RA chemistry cannot be used except at relatively high
temperatures. You must use a special kit.

Fact: Eastman-Kodak-RA chemistry works down to 68? F (20? C) with only a change in
time and color balance needed to get a good print. I use 2 minutes at 20? C.

2. You can use a BLIX (Bleach Fix) for C41 and E6 films.
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Fact: You can, but you stand a very high chance of getting silver retention. In fact,
designing a blix for color films is one of the most difficult solutions to design, and
useful ones often can damage film if time is too long, or they contain some nasty
chemicals. Sometimes shelf life is poor due to oxidation of the fixing agent(s).

3. You can use a ferricyanide bleach with modern color films, after all
the old color films used them. (or quinone or persulfate)

Fact: If you go directly into a ferricyanide bleach after the color developer, you
oxidize the color developer and cause an overall heavy fog. You need a clearing bath and
wash before going into a ferricyanide bleach. In addition, modern couplers and dyes are
not routinely tested with these strong bleaches. Therefore, the couplers or dyes may be
harmed. Other bleaches recommended by the manufacturers will work as long as the process
cycle is modified appropriately, such as using the clearing bath mentioned above.

4. Color fixes are basic.

Fact: Color fixes and bleaches tend to be slightly acidic, around pH 6 – 7, and are non
hardening.

5. You can’t mix color chemistry from scratch.

Fact: You can. It is not much harder than mixing some B&W chemistry. But, you cannot
do it economically, at least not with the prices I have seen.

6. There are good published color formulas.

Fact: Every formula that I have seen published deviates substantially from the actual
Eastman-Kodak formulas that I have personally seen. (I have not seen all published
formulas, but I have researched a lot including patents) The missing or incorrect
chemicals generally tend to be those that affect microdensitometry (sharpness) and
granularity, and therefore you may get a pleasing picture with the right speed, but not
the right sharpness and grain as specified by the manufacturer. In addition, these
developers would tend to ‘season’ improperly and therefore would only be useful in a one-
shot situation.

7. You can process Fuji, Agfa, and Eastman-Kodak films together in the
same process.

Fact: Yes and No. All three families of films of either negative or positive type use
different chemistry to achieve the same end result. Therefore, as a developer seasons in,
it accumulates the leached out chemistry of the most prevalent film being processed. Each
manufacturer balances their own films against each other because they use similar
chemistry. They cannot balance against the films of other manufacturers due to the fact
that the ratios of chemicals change with the mix of film being processed. Therefore, you
stand a better chance with Eastman-Kodak film using a facility that does mostly
Eastman-Kodak film and Fuji in a Fuji facility, etc.

8. You can push / pull E6 and C41 films to get a higher / lower speed.

Fact: Yes and No. Pushing film raises fog. In negative films, the EI is therefore
higher. Contrast goes up, raising EI. Toe contrast goes up so apparent ASA or ISO goes up.
In reversal film, fog goes up lowering Dmax and thereby making mid tones lighter giving
the appearance of higher speed. In my experience with negative films, about 15 seconds
equals about 0.1 log E and about 5 – 10% in contrast. Professional films are more
pushable. Pulling films lowers fog and decreases contrast somewhat. Threshold speed (ASA
or ISO) go down.

C41 films still have a ways to go when pushed. Threshold speed appears
to go up due to increased toe contrast, and mid scale contrast and therefore EI goes up as
well. As you push harder and harder, you truncate the long straight portion of the curve
and accentuate or lengthen the shoulder, but that is about 2 stops push or probably
higher. I have not done that high a push for a few years.

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With the appropriate exposure and push, I have gotten over 1200 out of a 400 film with
good results. Grainy, high contrast, but good image. One image set was done at 2400. Very
short latitude, and very grainy, but the image was usable.

AFAIK, E6 is a process to completion after the MQ. The fog in the MQ step controls
push. RA paper is a process to completion. It is very hard to overdevelop Endura. Supra II
was easy to overdo, but Supra III solved that problem pretty much.

9. Stabilizers stabilize film

Fact: Yes they do. They react with couplers just as a developer does chemically,
preventing excess coupler from turning brownish, preventing excess coupler from reacting
with dye and forming leuco dye, etc. In papers, stabilizers at one time provided proper pH
buffering and an oxygen barrier layer for long term keeping. Film stabilizers should not
be used with paper, and paper stabilizers should NOT be used with film. The newest paper
stabilizers are only recommended for use if wash water is limited. The bulk of the paper
stabilizers are in the paper itself.

10. Color fixers are different / the same as B&W fixers.

Fact: I see people state this both ways. Some people say they are the same, some
different. Some say color is more complex, some say simpler, some more concentrated,
others more dilute. This is a big field. Color fixers are usually pH 6 – 7 solutions of
Ammonium Hypo with ammonium sulfite added for stability and sometimes they contain
accelerators to assist in silver removal. Remember, in color, one roll of film is about
equal to 3 rolls of B&W because of 3 layers, plus you are removing every bit of silver
(you hope). Also, that silver is restrained by heavy doses of DIR coupler residues and
other image enhancing chemicals. So.. you take a guess. Which is more complex? Color
fixers are a bit more complex. A simple fix will work, but you have to leave the film in
the fix about 2x longer to remove the silver halide. AND.. all color fixers are
unhardened. So never use a hardened fixer or a strongly acid or basic fixer on color films
unless you like to ruin your images or at least seriously disturb them.

11. Kodak had a C21, C42, E5, E7 etc, process.

Fact: E5 is the only real process above. It was used for Aerial Ektachrome in a
motorized reel to reel processor used in the field and in a roller transport processor. It
was virtually identical to E4. E5 is actually similar to E3, in that it has no
prehardener. E4 had a prehardener and ran at 85? F, E3 ran at 75? F, and E5 ran at 70?
F. The others never existed. Only two other processes were seriously considered during my
knowledge of processes at Eastman-Kodak, and they never saw the light of day much less got
a process number. Their consideration lasted for a short time and they were abandoned.
There were many valid film and paper processes not mentioned above such as E1, E2, E3, E4,
P122, K14 and etc. These are well known in the literature.

Process EA-5 has been
replaced by Process AR-5. The aero films now include hardener. Process AR-5 uses EA-5
chemicals except for the prehardener and neutralizer.

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12. You cannot cross process C41 films in E6 processes.

Fact: Yes you can. You get a low contrast masked color transparency that can be used for
duplication purposes in certain cases. The result is similar to a masked version of ECO
film.

13. E6 films cross processed in C41 require heavy filtration for
printing.

Fact: Since any daylight film has a certain speed relationship, the E6 film will print
close to a C41 film in filter pack. The mask in negative films is just a mask for color
correction, not a filter. I know what you are thinking, but it doesn’t quite work out the
way logic would tell you, as the speeds of the negative film have been adjusted for the
mask in the first place. It all works out in the end being pretty close. However, see also
myth 17.

14. Tungsten films are daylight films with a filter layer (or vice
versa).

Fact: Nope, daylight and tungsten films are different. They have completely different
speed relationships by means of using different emulsions.

15. Freezing will preserve film almost indefinitely.

Fact: Freezing or refrigeration slows down all chemical changes in unexposed or exposed
film. This means that curve shape and speeds among other properties remain close to when
you bought the film. Fog continues to rise due to cosmic or ambient radiation. Heat
induced fog is slowed down or virtually stopped depending on temperature. This varies from
manufacturer to manufacturer and from film to film. Negative films seem to survive better,
because the fog can be ‘printed through’. In practice, though, no film keeps forever.

My
oldest films are from the 80s, and most are still good. My biggest surprises were PPF2
just slightly out of date but frozen, being very foggy but good in contrast and speed and
Agfa XRS 1000 frozen, changing in color balance by about 30 red. Developing a set is so
severe in some old films that I have trouble getting them onto the reel for processing; I
spent 45 minutes with one old roll recently.

16. Fuji and Kodak negative films don’t print on each others papers.

Fact: Kodak does not appear to print well on Fuji papers. Fuji appears to be acceptable
on Eastman-Kodak papers. I know that Eastman-Kodak tries to maintain compatibility with
Fuji and Agfa films, but it is sometimes difficult (see 10 above), as there are other
factors involved in getting good prints across manufacturers products. Kodak has published
and uses the silver criterion for balancing color paper to film, and by publishing this
method, has tried to induce others to follow the same methodology to achieve
intercompatiblity. This methodology does not limit the quality of color reproduction or
tone scale as some would think.

17. Contrast has no effect on printing color slides / negatives

Fact: Yes it does. Color negative papers, with an average contrast of 2.5, matched with
a negative film of 0.6 average contrast moves at 2x the apparent rate of color shift than
a color reversal paper with a contrast of 1.0 and a film of 1.7. You need a bigger filter
change to see the same visual effect when printing slides than when printing negatives.
Back in the days when slide printing from Ektachrome paper was very popular, Eastman-Kodak
published a special note on this effect and cautioned photographers about it.

If you
have cross processed Ektachrome as a negative, a very tiny filter change may make a huge
shift in balance. In addition, any crossover further confuses the issue. However, the
starting filter pack of Ektachrome cross processed should be close to if not the same as
your starting pack for average negative films.

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18. Prints from slides are equal to or better than prints from
negatives.

Fact: They appear very sharp due to high contrast, and the color saturation is high, but
color accuracy cannot equal a negative unless you use a color mask, and contrast will
always be too high unless you use a contrast mask. Color negative film is designed for
making prints and only making prints, either on reflection or transmission support. The
curve of the original is multiplied by the curve of the print material during the printing
process, and due to the toe in a transparency and the toe of the print paper, you compress
highlight and shadow detail. A negative film with a long straight line curve only has the
toe and shoulder of the print material to contend with and therefore will always have 1/2
of the tone compression or detail loss of a print from a transparency. I am grossly
simplifying the calculus involved in this transaction.

19. Film has no speed limit / has a speed limit. Digital has no speed
limit / has a speed limit etc. ad nauseum.

Fact: There is a theoretical speed limit to film due to radiation and heat effects. A
film of about 20,000 would be possible, but would fog very rapidly due to the above
effects. It wouldn’t go through airport security stations worth a darn. Digital images
suffer from thermal ‘dark noise’ effects unless cooled in the camera. Until the heat
generated by digital sensors is decreased, they may suffer speed limitations due to the
heat that they generate themselves. Pushing film or digital increases noise (grain) and
compresses tone scale.

20. Professional vs Consumer films, wow what a mess. People say they
are the same others say they are different, others say they are selected etc.

Fact: Professional and consumer films from Eastman-Kodak are different products, not
selected cuts from a master roll, and not specially aged versions of consumer product.
First, as Eastman-Kodak states on their web site, professional films are more pushable,
especially the press variety. This is due to the fact that pros generally expect to run
into situations where they need to have this capability. Second, the pro is expected to
want fresh film, but may keep it outdoors on a Safari in Africa, so it is expected to be
refrigerated until use, but then used under adverse conditions. Latent image keeping is
not expected to be a problem. No pro would let the film sit for 10 years in a dresser
drawer. And lastly, pros expect their film to be the most stable in color balance from
batch to batch. Therefore, the pro film is, to my mind, a more robust, stable film up
until use, with more processing latitude. After use, it should be re-cooled as needed and
then processed promptly. This means that professional and press (I put them in the same
category), and consumer are two families of film products with different properties
tailored to the intended market. They may and probably do contain many of the same
chemicals, and emulsions, but their proportions in the films are adjusted to achieve the
desired properties. This does not appear to be so for Fuji films. According to their web
site, professional films are a special cut of film from a master roll to insure
uniformity. Now, you can interpret this following comment any way you want, but I believe
that if Eastman-Kodak had that kind of uniformity problem with coating, the master roll
would be scrap. Eastman-Kodak expects uniformity from side to side and end to end in a
master roll. There may be enough variation in a master roll to give parts of it a
different emulsion number due to a slight color balance shift for example, but if it was a
professional coating all of it would be good enough for professional use.

21. Color processing at home is hard / expensive.

Fact: Color processing at home is easy. You have one time and temperature you can stick
with for all films, unlike B&W, and you can be assured of hitting things right on if
you do things the same way every time. Color is more expensive, but rather economical if
you do enough to keep the solutions from going to waste. If you let them sit too long, and
they spoil, then it gets expensive. So, keep your temperature, times and agitation
constant and you can’t go wrong.

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22. Color chemicals spoil fast.

Fact: They keep at least as long as B&W. Bleaches, fixes and stabilizers actually
keep longer; I have had C41 bleach and stabilizer keep for over 2 years in closed
containers with occasional use. The only ones to worry about are the developers and the
blixes. Blixes sulfurize rapidly even in closed containers. My record for keeping
developers is about 6 months for RA. IMHO, the best plastic containers (most oxygen
impermeable) are JOBO 1, 2 and 5 L bottles. They are superb but expensive. I have 4
different kinds of bottles, and the JOBO always performs best for keeping developers. I
have a nitrogen tank to use if necessary, but even without nitrogen, I got that 6 month or
so keeping with the RA developer in a 2/3 full container. I got that good keeping before I
installed the nitrogen tank, so I figure I can get a 1 year keeping on developers now. I
mix my blix just before use and expect about 1 – 2 weeks keeping. Blix unmixed keeps for
up to several years as a two part concentrate. Developer concentrates probably keep about
two years. I have had developer go bad if the developing agent concentrate is in plastic
containers – sometimes within a year. If in glass, I have kept the concentrate for about 5
years and it still is good.

If you wonder how or why I have kept some of these so long,
well, I usually buy 2 – 4 1 gal or 10 L kits at a time and put them aside to use as
needed. Depending on darkroom activity, I may use them up in a year, or it may take me 2 –
3 years for some kits. I go through an E6 kit less rapidly than C41 and go through C41
less rapidly than RA.

23. Color paper spoils if you keep it at room temperature

Fact: My darkroom varies from 18? C in winter to about 30? C in summer. If I have an
open box of paper, I leave it out. I find no significant problems over a period of about 1
year keeping with the following caveats: a) Supra I lost red speed and became reddish over
1 year. Correction with color filters (about 20R in one year) fixed the problem. There was
no significant fog or curve shape change. b) Supra II was foggy if overdeveloped and was
slightly more sensitive to that problem (I think, I don’t have enough data) if kept at
room temperature. c) Endura is too new for me to evaluate, but at 6 months looks good. d)
the Supra III I have has been on the shelf at room temperature for nearly 1.5 years now
and is just showing a bit of red shift, about 0.10 if any. No fog increase yet and no
apparent curve shape change. So, it changes, but slowly and the changes can be compensated
for over one year with CC filter changes. It does not spoil, per se. Of them all, Supra I
and Supra II were the most sensitive and they were still usable even so. Take this one for
what it is worth. Just personal darkroom practice and experience. As a side note Ektacolor
70 kept rather poorly at room temperature. Ektacolor 20 was even worse. They lost speed,
gained in Dmin and got softer in the toe over about 1 year.

24. Color chemicals are more toxic than B&W chemicals, and are
vastly more toxic than digital imaging.
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Fact: Yes and No. Color developers are inherently B&W developers with a different
developing agent. These color developing agents are selected for low toxicity and are
about on the same level of hazard as HQ or Metol. Blixes are Ferric EDTA, Ammonia and
hypo. This is not bad, in dilute form (about 1:10 parts water) for putting on your oak
trees and rhododendron plants – about like MIRACID or MiracleGro without the acid. The E6
reversal bath contains Stannous Chloride, and the tin in it is not very good. The
stabilizers for film contain formalin which is toxic and nasty. So, the real bad actors
are the stabilizer and the reversal bath. Now, lets compare that to a B&W selenium
toner. Nasty stuff. The toxicity level of the toner and the stabilizer can’t be compared.
The selenium is probably an order of magnitude more toxic than the formalin. IDK for sure.
I wouldn’t drink either one or put either on my flower bed. The color paper process is
rather benign by comparison. Color developer and blix. About the same for a B&W film
or paper. If you run any of this down the drain, what can you expect. Well, basically the
BOD and COD are high for color solutions (Biological Oxygen Demand and Chemical Oxygen
Demand). This means that color solutions deplete oxygen in the water and suffocate
organisms. But, the COD is lower if you mix the blix or bleach with the developer. So,
color processing solutions have a BOD like B&W and a lower COD than B&W if the
developer and blix are mixed and dumped.

Where does all of this get us? Conventional
Color processing solutions are about as toxic as B&W solutions. The stabilizer in
color processes, and the reversal bath are similar to working with the more toxic of the
toners such as selenium, but not quite on that level. The COD is lower, and the BOD is
about the same as B&W.

Lets go to Ilfochrome. It is basically a B&W process with a VERY acid bleach. If
you neutralize it, then all you have left is a solution of organic chemicals similar to a
B&W process with two additions. These are the fragments of the dyes bleached in the
process, and the catalytic bleach agent. These are anilines and a phenazine derivative.
They are carcinogens, but in very low concentration and probably selected to be of the
lowest possible toxicity.

Now digital. First, the manufacture of sensors requires doping with arsenic and
selenium among other chemicals. The manufacture of computer chips and memory chips are the
same and the video monitors use lead. The phosphors on the screens are toxic heavy metal
compounds in some cases. The inks used in color printing are azo dyes and are somewhat
toxic.

Now film making – color and B&W. These are mature industries that have worked for
40 years to eliminate all heavy metals and toxic effluent. There is no longer cadmium and
mercury used in making film, nor is formaldehyde used. Methylene chloride is used in
making the support, and a lot of the coupler synthesis is about as toxic as making the
Ilfochrome azo dyes or the digital azo dyes, so film making is not an extreme
environmental hazard.

In the end, to summarize, photography overall offers a reasonably safe working
environment if precautions are taken such as ventilation and rubber gloves. Dumping into
the sewer system is probably ok for the home hobbyist because the levels of chemicals is
so low. The film stabilizers, E6 reversal bath, and selenium and other toners are to be
watched out for and handled with caution, but except for the selenium are not severely
toxic and don’t present any special hazard other than as noted. It is probably more toxic
to dump a computer in a landfill than to dump a years worth of your photographic solutions
into the sewer system IMHO.

One last note. I have read recently that pyrogallol is very toxic. I want to warn you
of that. Another warning is that you should avoid putting too much acid in fix baths as it
can generate two toxic gases, SO2 (sulfur dioxide) and H2S (hydrogen
sulfide). See the recent post about this latter hazard using a citric acid fix from
Anchell.

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25. Color films of different speeds have those speeds by virtue of
having different emulsions with different speeds in them.

Fact: Yes and No. Color negative films have different speeds from differing emulsion
speeds. This is true for ASA, ISO, and EI measurements. A slight tweak in speed may be had
by adjusting contrast upward, but this is often so detrimental to the final tone scale
that it is used with great caution and does not result in much speed. It looks like a push
process right out of the box.

Color transparency films are slippery things when it
comes to speed.

Go here: http://www.photo.net/making-photographs/film
and scroll down to the Agfa 100 and 200 reversal film examples. Please note that the DMax’
of these two films differ by a considerable amount. This DMax difference is actually
similar to what happens in a push process of reversal films. Densities above 3.0 are hard
to detect visually, so if one designs two identical films, but with different fog levels,
or coupler levels, the D-max difference can result in a different EI, with the same ISO
speed. If you look closely, the actual threshold inflections of these two films are hard
to determine, but if you imagine the film with the lower D-Max, having it raised, you will
see that the EI goes down nearly matching the slower speed film.

Therefore, negative films have true EI and ISO speeds, but reversal films can have a
vague definition applied to the speed leading to different speeds based on DMax. This is
clearly seen in the example above.

26. Plotting an H&D curve of a film will give you an idea of its
contrast in-camera compared to another film.

Fact: It will not. It is one method used to test a film for speed and contrast on a
macro scale. Due to edge effects in all films, color and B&W, the micro
contrast is usually different than the macro contrast. In addition, the contrast of a
single color exposure in color films is always different than the neutral exposure
and is a more correct representation of the color saturation of the image.

27. I have a developed film with H&D curve that matches the aim of
the film, so the process was ok.
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Fact: Yes and No. The image in an H&D curve is a macro image not usually seen in a
35mm or similar film image. It represents the general behavior of the film, but not the
behavior when exposed to objects on the order of 1 – 100 microns in size, which is the
case in real images. Therefore: edge effects change the curve shape of a film. Edge
effects are only revealed in micro images or via micro densitometry. Bottom line – you may
be missing a major image fault. It may have the speed and even the grain, but not the
micro sharpness and contrast that meets the manufacturers specifications.

28. My H&D curve shows me that this film is lower / higher in
contrast than that film.

Fact: No. Interimage effects change the contrast of single colors and mixed colors. The
neutral image always meets a certain given aim, but single and double color exposures may
be vastly different in contrast than the 3 color image due to these effects. Therefore,
several films with the same neutral scale may have vastly different interimage, contrast,
and color saturation.

29. Most color films reproduce colors accurately.

Fact: Yes and no. When a survey was run using hundreds of prints, transparencies and
viewers at Eastman-Kodak, it was found that a majority of viewers picked the more
saturated or intense colors unless flesh tones were included for reference. Even then, if
the exaggeration made for tanned or glowing flesh tones, the more intense colors were
picked. When presented with the original subject and color, the response was ‘oh!’. Then
‘but I liked the other print / transparency’ or whatever the photograph was. Inevitiably
the average customer wanted the local garbage dump to look beautiful (approximate quote
from a co-worker who ran the test.)

As a result, most consumer films are gaudier in
color than professional films, a fact often noted on photo.net. More transparency films
appear gaudier, but this is in part from two reversal film properties: 1) the higher
contrast of reversal films, and 2) The method of color ‘corretion’ which requires higher
color saturation to achieve a degree of realism without masking.

30. Magazines prefer transparencies.

Fact: Yes they do, but not for the reasons you think. Editors like to see the image
up-front, not a negative. They want the positive transparency to see how it fits into the
‘gally proofs’ and see what corrections must be made. Then, they alter the transparency
using masks for higlights to adjust contrast, and correct color – in other words they
adjust things to make the slide look more like a reproduction from a negative. In
addition, transparencies fit into their work flow more easily than color negative, but
they will take color negative as well. Most major magazines will take both types of
original. If you give them a dupe positive, they use that for the editing process, and the
negative original for the printing process. (This is not always true, but only a
generalization)

Historically, this has to do with how printing was made. For color
images, color separations needed to be made, which was somewaht easier for slides than for
negatives. Modern digital equipment levels the differences and printing can be done from
negatives just as well.

31. Color transparency film is sharper, finer grained than negative
film.
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Fact: Yes and No. It depends on film. It is much harder to design a color transparency
film than a color negative film wrt to sharpness and grain. Color negative films get edge
effects, interimage effects, and grain improvements during color development from DIR and
DIAR couplers. Transparency films must rely on the MQ for almost all image enhancements,
and they come from edge effects and interimage effects. The color development step
essentially goes to completion although there are tricks applied there as well. (In fact,
this is where most published MQ and CD formulas for E6 films fall down, in the tricks
department, which are proprietary)

The bottom line is that most transparency films
appear sharper due to higher contrast images. This is explained by Mees and James
“The Theory of the Photographic Process”. In addition, the tanning of the
gelatin in some reversal films adds a degree of sharpness.

32. National Geographic photos are made from Kodachrome transparencies
or at least some kind of transparency.

Fact: They use negatives, transparancies, cross processed film and even ECN motion
picture film. They use dupe positives and negatives and all sorts of digital images. They
used Kodachromes way back in the early days because that was the only color film they had
to work with. Then they started using everything they got that was good.

33. Only transparency film can give you the vibrant colors you see in a
magazine.

Fact: Any kind of good film, positive or negative, shot well, can be used by a magazine. They
use a lot of image manipulation to get the high quality you see on the printed page. And,
they use CMYK images.

Editor’s note

This article is based on two threads on photo.net and the content has been edited to
include some valuable contributions from those threads. Thanks to those who participated
and thanks to Ron.

Copyright 2004 Rowland Mowrey All Rights Reserved

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    • Edward; Nowhere in here did I say that the C41 process could be run at a lower temperature. I said that the RA paper process could. The C41 process must be run at the specified temperature, but the RA paper process can be run from 68 to 100 deg F (~20 - ~40 deg C) Sorry if there was any misunderstanding on that. Ron Mowrey
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    • Wow, what an excellent collection of knowledge -- thanks for that! Just as a sidenote re lower temperature C-41: About 15 years ago, Tetenal had a 68F (or 75F?) version for C-41 films in one shot vials. The results were horrible though (while I only used it once), really out of color balance. Nevertheless I remeber how appy and pruod I was about my first self developed color film ;-)
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    • The information that c41 can be run at lower temperatures is great news. 90F is easy because you can use a cheap aquarium heater, 100F requires a real temperature controller. How do you figure out the new processing time for a lower temp? If you are scanning and working digitally, I assume the color correction will not be an issue.
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    • Digital images suffer from thermal 'dark noise' effects unless cooled in the camera. Until the heat generated by digital sensors is decreased, they may suffer speed limitations due to the heat that they generate themselves.

      This statement is full of myths of the sort that are supposed to be debunked here:

      1. CCD and CMOS sensors do not themselves generate heat while taking an exposure.
      2. Even cooled sensors will still generate dark current. (Dark current is the cause of dark noise.) With each six to ten degrees C decrease in sensor temperature, dark noise is approximately halved. Only when the sensor temperature becomes roughly as cold as liquid nitrogen (approximately -196° C) does dark noise become so dominated by random noise in the resulting image that it is hard to measure - but even then, dark current is still present in the sensor.
      3. Dark noise accumulates in a sensor photosite at a constant rate at a given temperature. The amount of dark noise is completely unaffected by the camera's ISO setting. (The proportion of dark noise to signal in the resulting image can be affected, of course, but this doesn't fully tell the story.)
      4. Dark noise does not limit the speed of digital cameras; bias noise does.

      In most digital cameras, bias noise is hundreds to thousands of times higher than dark noise under normal picture-taking conditions. Bias noise is contributed mainly by the sensor readout aplifier(s). Increasing aplifier gain (by increasing the ISO setting on the camera) results in both more bias noise (because amplification is higher, the resulting noise is also higher in absolute terms), and in bias noise being a larger proportion of the image's dynamic range.

      Inferring from the way bias noise is known to vary at different amplifications, in current (2004) Canon DSLR cameras, bias noise would be expected to consume 50% of the image bits at approximately ISO 25,600 to 51,200. Of course well before this point was reached the image would be considered completely unacceptable. By contrast, it takes most modern digital cameras several hours of exposure time to become dark-noise limited to the same level. Since bias noise is contributed to an image at the same level regardless of exposure time - it is dependent only upon amplifier gain - it is this which limits digital speeds in almost all picture-taking conditions.

      So I guess I agree with the conclusion that there is a digital speed limit with current technology, but the reasons given for the speed limit's existence needed a little refining.

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    • Ron, in another place (http://www.photo.net/learn/darkroom/color-darkroom.html) you mentioned that color film could be processed at other temperatures. Possibly that comment was a mistake in light of the comment you made above, but assuming that other temperatures are possible for processing color film, what range of temperatures are practical, and what sort of adjustments would one need to make to run at different temperatures? Thanks.
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    • Alan; I have tried to run C41 at other temperatures. The film suffers from severe crossover. There are kits though that purport to be able to do this. I have no doubt that they get some reasonable result, but I myself will not trust them. RA paper is another situation. It works fine at several temperatures. Ron Mowrey
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    • Jeff; You have a point, but let me add this. As you vary temperature at the time of exposure, films vary in fog (noise) less than digital sensors, and as you increase speed, digital sensors suffer more from noise than films. Therefore, you can build an ISO 100, 200 and 800 film with the same foog level (noise), but you see an increase in noise with digital sensors. This is fairly easy to demonstrate by photographing white and dark patches, enlarging them and comparing the film scan with the digital image. Ron Mowrey
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