View Full Version : Running Film Speed Tests on Color Neg Film

brian steinberger
1-Oct-2005, 21:19
I just received some prints back from the lab on Kodak Portra400VC and the blacks were very black, basically underexposed. I know how to run tests to find the appropriate ISO for transparencies and of course black and white, but how do I determine an ISO for color negative film when a pro lab is doing the processing and making adjustments during printing? Does anyone else shoot 400VC and rate it at a lower ISO, such as 250 or 200? Thanks

ronald moravec
2-Oct-2005, 06:36
Look at the shadow areas and there should be detail there just like black and white.

Have someone with a color densitometer check the negs. The red channel needs to be a certain density.

Run a bracket of four exposures, +1 stop, +1/2 stop, rated speed, -1 stop. send them in at the same time and have them printed. Include a sign in each neg so you know how it was exposed.
This sign will display in the print.

Any metering technique used with color tranparencies, will work with color neg. An incident meter reading is close to impossible to screw up as it frees up the necesity of picking a mid tone.
That`s the reason movies are done with one as they can`t reshoot and can`t bracket.

Lastly, whatever works for black and white will transfer to color neg without a problem. Prints from under exposed negs will look grainy and lack color saturation. Blacks will look "light black" to dark grey if they tried to underexpose the print to compensate for a thin negative.

phil sweeney
2-Oct-2005, 06:55
You have to have a color contact print made, because of all the lab automation used when analyzing the negative for the print. Its is probably best to include a gray card in one exposure and ask them to cal to that exposure and use that for all contact prints. If you are using 4 x 5 ask them to contact print 4 negs on one 8 x 10.

Ralph Barker
2-Oct-2005, 07:59
A small suggestion - tell the lab that you're testing, and ask them not to make adjustments beyond their calibrated filtration. Otherwise, as you've noted, they'll try to "correct" what they think are exposure errors.

ronald moravec
2-Oct-2005, 09:41
I would have suggested the above, but I have found most consumer labs unwilling to turn off the autmation. That is why you get green people with red sweaters and other such nonsense.

You will need a pro lab or just print them yourself as black and white.

Kirk Gittings
2-Oct-2005, 12:39
I don't shoot VC 400, but I have never seen a color neg film that didn't have an exaggerated asa, pro or amatuer. For 30 years I have shot pro 4x5 asa "160" films and had to rate them at 100. Do the old proper proof as I do, minimum exposure necessary to render the film edge as black and you will find the right asa.

neil poulsen
2-Oct-2005, 12:48
Film manufacturers a publish a range of color densitometer readings for middle gray for each film they produce, assuming the film has been properly exposed. Take photos of a gray card at different ASA's (I use 3rd stop increments) and have the lab read the gray card in each sheet with their resident densitometer. I like to select the lowest ASA that stays within that range.

Mark Woods
2-Oct-2005, 13:03
Hello all. Being in the Film Industry, I've had to learn how to work with automated processors. There is no other way. That said, I've written extensively about it for the International Cinematographers Guild Magazine, and posted articles on my website: www.markwoods.com. The article that relates to testing color negative is: LAD Article For Film Evaluation. The short version of the article describes how to use the same technique the labs use for quality control, to determine your film speed and if there is any color shift inherent in the film emulsion. This approach, with the use of a densitometer, takes all the technicians and their opinions out of the loop. It also gives you an idea of how the lab is printing your work. There also is a test to determine the correct printer lights to make a correct density print from a correct density negative. Enough here. If you're interested, take a look.

Kind Regards,