Positive film or negative

[Guest Daniel J. Ashley-Smith]

I have just started work in a camera shop. I was told about this transparent film, being extremely good quality. I think it was 50 ISO. What?s the difference between positive and negative film?? Negatives need to be inverted to get the colour correct, and positive just stays as it is.

Maybe they said it being good quality as in, being 50 ISO. But is there any difference in quality between negs and positives?

 

Now, 50 ISO is very good quality besides that, it can be stretched further than most other film. Although there is a great deal of light compensation needed.

 

When making a film, would you use positive, negative or is it a choice?

 

And, I heard when using film in film production, they use testers. Like the Polaroid that goes in the back of a medium format camera, i.e. hassleblad. Are these testers just a single neg (or positive) ? Or do you actually get a strip of it?

[David Mullen ASC]

Negative is designed for being printed. Print stock is also a form of negative, but essentially you are making a negative of a negative so thus end up with a positive image. The contrast of negative is very low so that once added to the contrast of the print stock, the final contrast and black levels look correct when projected.

 

Reversal film is designed for direct projection of the original so it has the contrast of a print made off of a negative. Therefore most methods of duplicating that reversal positive original so that prints can be made creates more contrast than looks normal.

 

Hence why motion pictures are overwhelmingly shot on negative film.

 

Even if the goal is to digitize the image, starting out with the negative stock gives you so much more exposure information than if you used reversal, making it easier to work with in electronic transfer systems like telecines. Plus you have more latitude to make exposure errors -- reversal requires rather perfect exposing.

 

Reversing a negative image in a telecine or scanner is pretty basic.

 

Until the 1960's, the 16mm format was mostly reversal, especially color, for a number of reasons. (1) 16mm was originally an amateur format and consumers wanted to project their original, not make prints; (2) early color processes like Kodachrome were reversal; color negative was not invented in the late 1940's; (3) it's harder to get hide of dirt and dust with smaller formats because of the degree of enlargement, and with reversal, dust shows up as black specks, not white specks as with negative; black is considered less distracting.

 

But generally the negative stocks got faster and faster, to the point where documentarians and whatnot working in 16mm in the 1970's wanted to use the 100 ASA color negative sold rather than the 25 ASA low-contrast reversal stock developed for people who needed to make prints. Labs started getting better at keeping dust off of the film; eventually by the end of the 1970's, 16mm had switched over to being mostly shot in negative, not reversal.

 

Using polaroids to preview the image has nothing to do with the actual film in the movie camera; the polaroid is a single sheet image. Some people are using digital still cameras to preview the lighting, etc. as a rough guide. It's not the same thing as developing test strips as used to be done in the days of b&w, especially for people shooting special effects. Back then, they would shoot and quickly develop on the spot a strip of b&w movie film to make a quick judgement.

[Guest Daniel J. Ashley-Smith]

Ok I see. When you say print stock, do you mean the paper that the picture is being printed on?

 

Anyway thanks for your help in this.

[David Mullen ASC]

No, a motion picture print is not on paper but on a transparent base. But the principle works either way: the final contrast that looks natural on the print (paper or projection print) is designed with the whole neg-to-pos system in mind, working under the principle that contrast is increased with duplication, so the negative is a very low contrast element.

 

Plus a print has to be very high in contrast so that the blacks look black, particularly when talking about projecting very bright light through the movie print and shining it onto a white screen and yet still having decent blacks.

[John Sprung]

early color processes like Kodachrome were reversal;

Whether you get a positive or a negative image depends on how the film is processed. Develop and fix the exposed grains and wash out the unexposed grains, and you get a negative image. Develop and wash out the exposed, then expose the remaining and develop and fix. and you get a positive image. Raw stock intended for one process or the other will have different distributions of grain sizes to get the contrast you want, and in color you have that orange stuff that compensates for the poor cutoff of blue and green dyes -- also used in IP stock.

 

The first single strip color film was invented by Mannes and Godowsky at Eastman Kodak, but Leonard T. Troland at Technicolor got a very broad patent on single strip color about the same time in the mid 1930's. So the first use of single strip color was a low contrast reversal stock called "Monopack", which was intended as a source for making separation internegs that you could cut into a conventional three strip Technicolor show. That made it possible to use an Eyemo now and then. I've heard that the stuff in the rapids in "African Queen" was done that way. Monopack was a sort of ancestor to the ECO of the 1950's and 60's.

 

Agfa in Germany had a single strip color neg process just a little later, and it was used during WWII, when they weren't particularly concerned about infringing American patents. They did a "Baron Munchhausen" feature, escapist fantasy, from which I've seen a few stills.

 

Perhaps John Pytlak can give us exact dates on this, and corrections if I'm remembering any of this wrong.

 

 

 

-- J.S.

[Filip Plesha]

Depending on the scanner and it's calibration and settings, reversal films

can be scanned without any problems. I suspect that today's motion pictures

scanners are optimized for negative films. Reversal film would probably not be scanned in its full glory, as negatives are. (even If they recalibrate it)

This is my guess of course. But it is not impossible to get a good scan out of reversal film with the latest CCD sensor technology. It is just a matter of manufacturers choice, will he or will he not optimize its scanner for reversal film.

[John Pytlak RIP]

The Kodak website has an excellent Chronology of Kodak Motion Picture Films:

 

http://www.kodak.com/country/US/en/motion/...t/chrono4.shtml

 

And a history of Kodak:

 

http://www.kodak.com/US/en/corp/kodakHistory/index.shtml

 

Marty Hart's "American Widescreen Museum" also has some good history on the development of color motion pictures:

 

http://www.widescreenmuseum.com/oldcolor/oldcolor.htm

 

Cinetech has a chronology:

 

http://www.cinetech.com/html/stocktimeline.html

[David Mullen ASC]

Yes, you can perfectly scan a reversal original but that doesn't get around the fact that it has the contrast (gamma) of a positive print, not a negative. Therefore you can't simply digitally turn it into a negative version of itself for output to an internegative and expect the same exposure range of something shot on negative to begin with.

 

You can use digital technology to stop any INCREASE in contrast fron duplication so that the digitally output internegative retains the contrast of the reversal original, but any attempts to lower the gamma to the level of color negative creates some compromise because a reversal does not record the same level of exposure information that a negative does.

 

I've shot some color reversal for normal E6 processing and transferred it to video and found that exposure latitude was much more limited than color negative and contrast less natural. If that was the look you wanted AND you had nailed your exposure, it looked great, but you had no flexibility in color-correcting compared to a negative.

[John Sprung]

David has it exactly right. It's the gamma of the film stock that limits the dynamic range of reversal. Low gamma yields large dynamic range and vice versa. Telecine scanners have nothing to do with the problem. The range of densities you get on the film isn't that much different between the two. All this is so much easier to explain if you can sit down with pencil and paper and draw H&D curves.

 

 

 

 

-- J.S.

[Filip Plesha]

Yes, of course.

Converting the reversal image to low contrast of negative film

for recording onto negative stock would show that the bright areas have less

latitude and that there is not much more aditional information beyond the

white point like there is in the negative.

Once you have converted the image to negative film contrast and recorded

it to film, the densities on the negative would go up to a certain point and

there would be no higher densities (other than noise), because of smaller latitude. And this maximum density should be aimed in the printer when making the print. If this "maximum" density was set as the white point in the print, the look would be pretty much the same as in the original reversal.

In other words (and in the case of cineon format) the entire range of tones

from the reversal scan should be put between 95 and 685 in the file. After 685,

there would be no higher densities when printed onto the negative, whereas

if the scan was made from the neagtive, there would be more values, all the way

up to 1024. The trick is to set the printer to make the print whose highest density

would match this lowest density on the negative (which was 95 in the cineon file),

and the lowest density in the print should match the highest density in the recorded negative (which was 685 in the file). If the light was stronger or weaker

in the printer than this, then the image would show either fogy balcks or yelowish/greyish whites.

 

All in all, It is possible to pass the reversal film through DI and make a print

without showing its smaller latitude. But as you said, any correction of exposure,

contrast corrections (other than the cineon contrast correction) would be very hard to do without showing the results of small latitude.