Some of this is probably not suitable info for the original poster (overly complicated) ... but in terms
of factual quality, there is a huge distinction between dynamic range of a film ("latitude" per scene
contrast), and that point at which the dye curves start to overlap and contaminate each other.
In many landscape or enviro portrait applications, Portra 160 is going to look undersaturated - it is,
after all, mainly a portrait film - once you boost contrast, either PS or via masking, those otherwise
"minor" color repro errors in non-skintones are going to get exaggerated too, mostly irremediably.
Correct exposure with appropriate color balancing for the actual K temp is going to significant improve (or optimize) what these films are actually capable of. Usually with negs, people just expect
a degree of off-tone mud, so when a "better" film like Portra comes along they yell "Yippee", even
though they could do a lot better job with it if they paid attention to certain details. All you've got
to do is study the published dye graphs to see the truth of this statement. Photoshop won't fix
a serious exposure error, even if the general subject is all there. Two differerent problems.
Could you expand on this as from my own admittedly naive reading, a one stop increase in yellow and a one stop decrease in cyan would mean a huge shift in temperature but only one stop doesn't move significantly up/down the dye sensitivity curve?
Originally Posted by DREW WILEY
Also, as far as I know, Porta is actually a combination of three different sensitivity layers for each colour and hence the film almost works as if it' shifting registers. 3 or 4 stops over exposure and you're into the medium speed register, 8 or 9 stops over exposure and you're into the very slow film register. Does that make sense?
Yes, you are absolutely correct in your thinking.
Originally Posted by kbrede
It goes something like this. If you follow F/1.4's suggestion over mine, for the same scene, you will over-expose by one stop. Question is, is that a big deal? It isn't. The negative will be a little denser, but that can be compensated when prints are made. It simply isn't a big deal at all. I bet the images you are taking now are more than one stop off from optimum exposure. It's easy to do that and I do that all the time. I don't always take so much care in everything being optimum.
I said to use the box speed because that's what I do. F/1.4 said half the box speed because for most negative films, error on the side of over-exposure is safer than under. Basically, how big is a "pinch" of salt?
By the way....
I'm thinking OP is in an age group where film is "new". Over the last few decades, there were all sorts of cheap cameras made with inaccurate or no metering what-so-ever. Many point and shoot and ALL of disposable cameras are this way. Yet, they often produce good images. Negative films aren't that sensitive to small errors. It's WAY more forgiving in magnitude of several stops when compared to digital. Don't worry so much.... Enjoy your trip and the company of whomever you'll be traveling with. You'll be fine....
I do enjoy Portra and it's exposure latitude. There are many way to manipulate it's output and good reasons to do so. The thing is, there's not much point in doing things differently unless you have one of those good reasons.
Personally I'm also a little lazy and enjoy easy printing negatives and one of the things that I've learned is that shooting box speed and processing normally is truly reliable and can provide great (not just good, truly great) results.
Kodak (and Fuji and Ilford) actually measures the box speed per an industry standard, if you use your incident meter and your shutter and aperture are accurate you can get very close to shooting at the standard, which means you can print in a nearly standard manner.
Shoot at box speed and have fun. Life will be good.
When bracketing Portra +/- one stop, I noticed that there is a slight color shift even though all settings gave me acceptable exposure results. Since I shoot landscapes mainly, it probably doesn't matter. However, if you're looking to match the actual colors, exact exposure seems to be more important.
That is true - but their testing methodoloy gives you no information about latitude in highlights and shadows. Transparency film typically blows out at +2 stops but can have -6 stops in the shadows (DxO test results) whereas neg has +14 in the highlights and -2 in the shadows.
Originally Posted by markbarendt
Given this information, the 'correct' exposure based on box speed may blow out highlights or block up shadows depending on scene contrast. Without checking, it is therefore better to slightly underexpose transparency film and overexpose neg film. But with checking it's better to place your tones where you want them!
Well first of all we are talking about C41 negative films, specifically Portra, not trannies/slides, and actually the standard does have a very specific relationship to the film curve. That relationship has a "safety factor" built in at the shadow end.
All the manufacturers use the same standard. The beauty of this is that we dont have to test every film to get good results.
The wild card is "us", not the films. Each of us has different expectations and ways of working.
Using negative films, setting exposure with an incident meter at box speed, and developing them by-the-book, IMO provides the most reliable way to get high-quality, easily workable negatives, bar none.
I'm not suggesting that there aren't good reasons to shoot at something other than box speed, or for using spot meters, I'm simply saying that using non-standard settings and reference points should be reserved for "special effects" or "special situations".
If you get the results you want, that's all that matters. But my own objective is to understand color neg films well enough to get them to approximate or even surpass certain expectation I had after years of printing chromes. That takes a lot of testing. And the different Kodak film are really engineered for different markets.
Portra 160 is one thing, 400 another, and Ektar yet a different animal. It's not simply a matter of latitude or contrast. The three color layers in color neg film are not as well differentiated in chromes. Just compare the spectral sensitivity charts of negs vs chromes, or even of the respective color neg products themselves. Films
like Portra 160 are engineered to produce complex warm neutrals, namely, pleasing skintones under a wide variety of lighting circumstances. If you have a similar kind of color in the scene like a warm earthtone or orange,
it is going to fall into the same hue category. Greens still tend to be contaminated with a lot of cyan. Overexposure will overlap the dye curves even more. Not a felony unless you're trying to protect the reproduction of certain fussy non-skin hues too, which if in fact the name of the game in most landscape photography, or possibly in enviro portraiture. A different problem than say, copying a painting under controlled
studio lighting of limited contrast range, then boosting the contrast afterward for reproduction. After a lot of
futzing around (painfully, for sure, given the cost of 8X10 color film and real prints!), I'm beginning to understand
what it take to make these films work as a substitute for chrome. Of course, I'm hedging my bet by stuffing the
freezer with film just in case Kodak tanks. But I made the transition once it was apparent Cibachrome was going
under and RA4 is the future of high-quality color printing. I don't want prints that look like traditional color neg
work! I want clean, crisp differentiated hues across a wide spectrum. But in the process I've learned a few
things that will help just about anyone improve their results, if they're interested.
Unless someone goes to the trouble to test his meter, metering techniques, aperture, and shutter for accuracy, he never really knows for sure his true shooting speed. Therefore, because of the lattitude of color negative films I believe it is best to shoot at some degree of overexposure until such tests are made to prevent underexposure and loss of shadow detail if the shooting errs on that side. Half box speed (one stop over) will probably take care of most errors.