rating slide film

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some photographers i know rate their slide film at a slightly higher EI rating to underexpose slightly and increase color saturation. is this a general rule of thumb for slide film? is this what everybody does? i simply cant see the difference but im maybe im missing something. i usually use provia or e100sw. any eccentricities or characteristics i should know about? thanks!

-- (mnn@skyinet.net), May 11, 1999


A film's ISO is defined by the amount of exposure needed to produce a minimum amount of density and contrast with a given developer. You can deviate or rate your film differently from the manufacturer's ISO but it's only you who can decide how or whether or not to do it.

See, a "correct" ISO or a generally applicable Exposure Index (EI) is a misleading concept, since there are so many variables (usually different for every photographer) that would determine how to adequately expose a scene. One of these is, as Carlo suggested, personal preference or how you want to interpret the scene, and even what the subject matter is. Another reason people rate their films differently from a recommended ISO is because they are matching their film to their equipment and their development conditions. One of the bigger factors here is the type of metering used (average, center-weigted, matrix, incident, reflected etc.) , the accuracy of the meter, and what part of the subject is being metered. If an idividual photographer's meter tends to over/under expose by 1/3 or 1/2 stop then it would make sense for him to rate his film differently by 1/3 or 1/2 stop and get better results, but this isn't exactly a "discovery of global proportions" as some people would lead you to believe.

Also, there is the matter of light transmission characteristics of the lens. Slow, cheap zoom lenses for example tend to give arouns 1/3 to 1/2 less light than compared to a fixed focal length lens, and if an incident meter is being used, then it would make sense to rate the film a bit slower to make up for this. Others are development conditions...etc....well you get the point. :)

"some photographers i know rate their slide film at a slightly higher EI rating to underexpose slightly and increase color saturation. is this a general rule of thumb for slide film?"

MY method is to rate as is and take an incident reading or (if I absolutely want to be precise) to spot meter the most important parts of the scene,take the subject brightness ratio (lightest and darkest), make sure the areas i want texture in are 6 stops apart, spot meter the important highlights (where I want texture) and put it on zone 7 (open up 2 stops) or 8 (3 stops). This might result in a different reading than what a center-weighted or averaging meter (without taking into account their accuracy) would read if the film was rated 'as is'. Why? take into account the if you over-expose slide film, you lose the detail in the highlights so the 'rule of thumb' here is "meter for the highlights"--> which would result in a slight "underexposure" of what a c.w. are ave. meter would read...which i think is the origin of that such urban legends as "rating slide films at a different EI for slight underexposure to get more saturated colors". I guess my best advise is to get a meter you can trust and one that gives precise and consistent results and not to take 'rules of thumbs' to seriously...since getting precise EIs for the films, equipment, and subjects you use are the anti-thesis of 'rules of thumbs', which are really just low level rules people follow (ex. the 1/focal length hand-held rule).

As an aside, I know people who use Canon EOS Elan IIs who rate Velvia at 40 because the meter in the camera tends to underexpose a bit.

-- Tommy Zablan (lensman49@hotmail.com), May 16, 1999.

For whom are you shooting? Whose taste are you trying to satisfy?

Some people brag about their exposing their film at a different EI, but having it processed normally. Does this make a person a professional? or correct?

Try it out yourself. If it is in you to have bright happy pictures or dark gloomy ones, then go out and try out several rolls and find out what you prefer.

Remember, one scene can be interpreted in several ways. You might want to expose it dead on, I might want it 2 stops under. That doesn't make either of us wrong, as long as that is how we want it.

What is true is that some photographers deliberately under-expose or over-expose to achieve results which they feel are correct. Don't follow this blindly. Experiment first.

I rate my film as is. But, I expose with deliberate plus or minus compensation to achieve what I want.

But on another note, If you are shooting two different film types or brands, you might want to fine tune their EI to match exposures. These do happen, having two different brands or film types which are rated at the same ISO but produce slightly different results. But these usually hover around 1/3 stop difference only.

Happy shooting.

-- Carlo Ma. Guerrero (guerrero@netgazer.com.ph), May 13, 1999.

ASA rating written on the box of a film, transparency or print, is the optimum exposure rated by their respective manufacturer deemed fit in their calculations, resulted from a barage of testing they performed. Therefore, deviating from their recomendation would mean you'll expect a "different" result. And different doesn't necessarily means erroneous. Some say Velvia exposed at its rated speed of 50 will result to a rich saturated color that others find very unrealistic so they do rate it at 40. Others shoot at its rated speed para daw mas acceptable kapag nai-print sa magazine. IT is actually, in my opinion depends on your own preference, but try not to go beyond too far from the manufacturer's recommendations.

-- Alvin S. Granada (binogranada@hotmail.com), June 13, 1999.

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