ISO rating for Fuji NPH

Hello all,

 

I've looked through the archives for the answer to this and have come

across some opinions. However, I would like to better understand the

following:

 

1) It would appear that NPH is better rated below ISO400, but it is

not clear whether the rating would vary under different lighting

conditions, or whether a constant rating of, say ISO250 is preferred.

 

2) I suspect if I ask 'what ISO rating?' I'll get lots of different

opinions backed up by sound experience, but I'd like to ask anyway -

reduce NPH ISO by 1/3, 1/2, or 1 stop?

 

3) To clarify, if I derate NPH, do I get the film processed at its

normal ISO400 rating - and is there any other advice I need to give

the (pro) lab?

 

4) By derating NPH I take it I need to be careful about applying any

extra exposure compensation? For example, with available light

portraits I would either use an incident meter, or spot meter off the

(caucasian)skin tone rather than meter off any shaddowed areas to try

and bring those out (since the derating should take care of this)?

 

Many thanks for your consideration in this matter.

 

Richard de Garis

ISO ratings generally represent the very minimum exposure to get a decent result with negative films. With color print films a little extra exposure (1/3 to 1/2 stop) results in more shadow detail and smoother grain. Since negative films, color and B&W tolerate overexposure much better than underexposure a little extra exposure also serves as a safety factor. You dont need to inform the lab that you're using a lower EI (exposure index). Before about 1960 the ASA method of rating film included a safety factor of 2.5. When this was dropped all the films magically doubled in speed (eg. Tri-X went from 200 to 400)

Pushing or pulling a negative film (different lab processing) is done to get different film characteristics. Doesn't sound like this is what you are asking about - therefore 3) no!

 

Rating a negative film differently in a camera body for normal processing is done to account for metering and personal exposure preferences. You decide what you like and how you like to work under different conditions. Underrating (setting ISO for metering to a lower value) is biasing the metered exposure toward over exposure and thicker negatives.

 

You have to actually evaluate your negatives for consistency and density. If they aren't consistent, you are worrying about a fine detail when other things will do more to improve your work. If they are consistent, then you need to figure out if they had more density and run a bracket experiment to figure out by how much.

Craig makes a good point about meter differences that isn't stressed enough when someone says how to rate a film. Technically, you should calibrate your meter (there's a few posts here on how to) and then decide what you need to set your ISO for a particular film. Experimentation is the key for each body and knowing how a given film reacts. Just as important as understanding lighting IMHO.

 

There are many here who will say tho, that NPH looks good at +1/3 to +1/2 over it's nominal rating. In other words, it's not really a true 400 film. Yes, you can expose it 400 (let's assume your meter is perfect) and, in most cases, you'll get good results. However, let's say you need extra shadow detail in a groom's tux when you try to expose for the beadwork detail in a bride's white gown; then the extra exposure will many times makes a difference.

My answer is rather simplified. I've been shooting NPH for both portrait and wedding work. If I need to set it at one ISO rating when shooting fast, I simply set it at 250 and go to work. The only time I shoot NPH rated @ 325 is if I'm outdoors and I have quite a bit of natural reflected/ambient light to work with. Even then, if I'm unsure, I still overexpose a bit more (same thing as setting the ISO at 250).

I've found this to be true of Fuji pro films - overexposing is the best approach. I shoot NPS 160 rated @100, and I prefer to rate NPZ800 at 625. Run your own tests - especially using flash or strobe scenarios. That's where you'll start to see the differences stand out and you can make your own choices.

 

The bottom line on why I do this is I get brighter, snappier colors, better shadow detail, an appearance of tighter grain, with an added bonus of still retaining excellent, smooth flesh tones. These are relatively low contrast films that just don't seem to respond well to shooting at their intended speeds.