How do YOU use exposure index?

[patrick_gainer]

I read many posts here and other places where the writer says "I rate

xxx film at yyy". I am curious to know what that means to those of you

who use other than the manufacturer's ISO. How do you set your meter

and how do you make the readings? I have a feeling that the answers

will not all be the same.

 

I am not looking to criticize. Obviously, whatever technique you use

must be satisfactory for your purposes. It may be that all the

different techniques will give the same result, but I doubt it. I

think many of us can profit from expert viewpoints on this subject.

[sm. alec]

I tested my film speed and development time with the use of grey card, densitomer, etc etc. Granted, this is for 35 mm roll film so I'm just shooting for "good" neg's under optimum lighting. When I do shoot entire rolls under one lighting condition I'll adjust my developement accordingly. Metering depends on subject, for most "wide angle" and quick kid shots i use the multi-segment meter. In closer or slowing down I'll use partial (6 degree), and for "artistic" shots I'll spot meter and compare it against the partial, adjusting for light/dark tones. Currenly I'm using HP5, rated at 200. D76 1:1 for 9 minutes. Condenser enlrgr. Typically print (not as often as I'd like!)at grade 2 1/2

[andrew_hull]

I over-expose from the rated speed by 1/3 to 1/2 a stop. I then pull development by 15-25% because of using a Jobo with constant agitation. I also bear in mind on what I am metering (white, I overexpose, darks and I underexpose) from what the meter tells me. If I am shooting in a general area, I will AE lock on something close to middle grey and shoot for a while at that setting.

[skygzr]

I have tested a number of B&W films with a densitometer, enough to know that a good working EI is usually one stop slower than what is says on the box. The exceptions I�ve found are medium and slow films in a speed-boosting developer (like Beutler�s). I can shoot these at rated speed. That and poor old HP5, which gives me an EI of 160 every time I test it (haven�t tried it lately).

 

To expose, I use a spot meter. I find the darkest thing I care about and put it on Zone III. If the dark stuff takes up a significant portion of the image, I put it on Zone IV. I sometimes expand, and seldom contract. Clearly, I don�t worry about overexposure! I can�t recall ever running out of headroom. Most films are quite forgiving.

[jay_de_fehr]

Hi Patrick. It could mean that I've gone to the trouble of testing the film to determine how much exposure is necessary to get the densities I want in the low values, or it could just be an educated guess and insurance against underexposure, or it could mean that given the present lighting, I need yyy speed, and will give the film as much exposure as is possible in the situation, and try to give it enough development to push the film up to yyy, or it could mean that the last time I guessed I wasn't 100% accurate (no way!) and I want to make a small adjustment to the minimum exposure one way or the other. For me, exposure index is a value assigned to a film when used in a particular set of circumstances, to acheive the desired densities in the low values of the negative, and is very fluid. It changes with subject, lighting, equipment, developer, printing paper and mood. Exposure index is the tip of the sensitometric iceberg, about which there is much to learn from many of the excellent contributors to this forum, and there are of course, many good books on the subject, a popular introduction being Phil Davis' Beyond The Zone System. Oh, I didn't answer the last part of your question; I use a Luna Pro F meter in incident mode 90% of the time, so I just set the dial to my e.i. and meter from my subject's position, making small adjustments to the angle of the meter depending on the lighting.

[m0002a]

Patrick, I have raised that exact question previously on this forum. It is particularly applicable to people make claims of 2-3 stop pushes above the ISO speed.

 

I am not questioning the veracity of those claims, but most of those claims are made by people using 35mm auto-exposure cameras (with multiple different metering modes available with their cameras), which not only depend on the metering mode (average, spot, matrix, etc) but also usually depends on the what the center of the frame happens to be aimed at.

 

If the center of the frame happens to contain some shadow areas, more exposure will be given by the camera and the effective EI is less than claimed. IMO, this make such claims difficult to be applied by other photographers who have different metering systems or happen to be aiming at a scene with less shadow area in the metered area of the frame.

[mike_scarpitti]

Two points:

 

1. The ISO speed is based upon a fixed development time, which is somewhat higher than what's best for highest quality images, and measures shadow detail as the criterion of speed. This results in an inflated value (film speed number) for most films.

 

2. Most photographers customize their film speeds based upon a more realistic development than given by ISO requirements (meaning LESS development). This also means somewhat more exposure than the ISO speed calls for, usually about 2/3 of a stop. Doing this also raises the shadow detail a bit higher on the film curve to a straighter region, giving a bit better tonality to the shadow areas.

[barry_kenstler]

Patrick,

 

I'm sure your question will bring many varied responses.

 

I will preface my response by stating that I do not use a densitometer.

 

I judge my negatives by the way they print. I adjust my development to give negatives that will generally print to my liking with a 2.5 grade filter on my cold-light enlarger. That is 2.5 with MY paper of choice, MY light source, and MY particular paper developer, but God knows what it would be on another worker's setup.

 

I use three incident meters and one spot meter which agree within 1/3 of one stop.

 

I shoot mostly portraiture and an occasional product. As a result I rely heavily on incident readings.

 

When I use a new material, I shoot sample portrait scenes at different exposure indexes surrounding that recommended by the manufacturer and then develop the rolls or clips of rolls at different times. I also include scenes, usually non-portrait, that show how the film performs at alternate speeds with light that is more and less contrasty than I typically select. I then select the best looking negatives and see how they print. I select an average development time and exposure index based on those prints.

 

In the studio, I take incident flash readings to determine my lighting ratios and expose accordingly. I often use a spot meter to adjust background lighting to produce the desired gradation of gray tones. I know it is terribly unscientific, but from experience I know where the grays tones will fall in the print based on their spot meter value relative to an 18% card reading.

 

I also mix spot and incident values outside, especially when balancing flash with the ambient light. Using an all-out zone approach is impractical for me, since I often mix color and b&w roll film in a shoot and must move quickly.

 

Patrick, I just want say how much I enjoyed the article you had published in Photo Techniques some years ago describing your experience with Salt, Sodium Sulfite, and ascorbates in grain control. The photos in that article were very helpful in understanding the contributions of the additives. Please continue to explore and publish. I always enjoy reading your stuff.

[conrad_hoffman]

I rate my FP4+ a little more than half, about 80. For me, that just means setting the meter dial on my F3 at what looks like 80, setting the thing to automatic, and blasting away. There is, however, a short software loop that runs in my brain saying "is what's in the center weighted area normal?" If so, shoot. If not, meter around a bit more, check for backlighting, and make a good guess as to how much to compensate. I don't use the Zone System per se, but do think in terms of place and fall. I rarely change my development for 35mm work, having found what I consider an optimum value for my typical roll and my condenser enlarger.

[robert_davis2]

My EI is a result of testing the film with my camera,shutter,meter,developer and processing. In other words it's accurate for me. Basically the goal is to cancel out all the mistakes-)

[al_kaplan1]

Incident readings, manufactrer's ISO, and then usually open up 1/2 to a full stop just based on experience. It's something you learn over time. My cameras don't have meters for the most part. Those that do lack batteries.

[tim_curry]

Regardless of manufacturer's ratings, I base my film speed on a negative which prints a correct zone I. When the negative edge prints pure black (like the paper without any film over it) and the zone I is a true zone I in the test print, I have a correct film speed. This should also give a good zone III as well. This exposure of the film on a contact print is "film base plus fog" and gives the maximum information with the minimum density.

 

Once this baseline has been established, I do development tests to establish zone VIII. After this, I forget about film testing and just shoot. Fine tuning is available from zone VIII tests which did not work, this is N+ and N- information.

[lex_jenkins]

I play fast and loose with my exposure indices. The EI is whatever I say it is for a given situation.

 

I use the number as a gauge for processing, not as an indicator of a film's true speed. I already know the difference between true speed and "effective speed," the latter of which I define as how midtones are rendered through a certain combination of film and developer.

 

If I say it's 1600 for TMY to be souped in Microphen, or 1200 for Tri-X destined for Diafine, well, that's what it is. That's "effective speed."

 

Likewise if I say it's 200 for HP5+ or 64 for FP4+ to be developed in ID-11 at 1:1 dilution, well, those numbers are just as valid. Those numbers are closer to the true speed for each film.

 

Again, the EI - which I write on the completed film cassette - is strictly a gauge for the most appropriate development.

 

Works for me.

 

The advantage is that I can write a single number - my EI - on the cassette and know several weeks or months later how to process a roll. That's important because I'm just now getting caught up on film development left over from the summer. Our A/C didn't work correctly most of the summer so I delayed processing film 'til cooler weather prevailed. Now I can pull those rolls from the fridge, read the cassette and know immediately how to process them.

[patrick_gainer]

Thank you, gentle people. It is pretty much as I expected. Each one of us has a different technique that is found by experience to suit the situations we run into and the kind of negative we like to print from.

 

I had a lot of experience taking pictures of the Norfolk Symphony Orchestra from my chair as first oboist, (during rehearsals, of course). I could only shoot when I had a few bars of rest, and did not have time to make exposure adjustments. This is a difficult situation, not well suited to any kind of built-in meter. The directional lighting, the dark shadows, the white music in the foreground, etc. made presetting necessary. I would set my built-in or manual meter to 1600 for Tri-X and take a shadow reading. I would set this reading (nowadays I would use manual mode on my Canon) and leave it. I suspect this is equivalent to setting Zone III for 400 ISO. It was ASA then.

 

It may be that for the sake of beginners who might read our posts, it would be a good idea to state the technique used to estimate exposure whenever it might be pertinent. I know that if I set my meter at 200 for HP5+ it would be overexposed by my method of estimation. That does not make me right and someone else wrong, but it might help someone who sees,in the same thread, two or three diffferent exposure indices recommended for the same film by experienced and often professional photographers.

 

It's just an idea.

[nicholas_t.]

As I see it there are two philosophies for EI (three if you count push/pull processing).<p>

One is the Zone System (ZS) technique of finding zone 1 and calling it the EI.<p>

The other is "expose for the shadows and develop for the highlights". I suspect many people use this technique. This is because the controls for ZS are precise and require much testing to be accurate. ZS controls really come into their own when individual development of photographs is possible frame by frame. Most people, I suspect, who use the <i>expose shadows, develop highlights</i> technique rate the film at a nominal speed usually between full (ISO) speed and one stop less and develop to whatever time/temp suits the rest of their system, be it printing with a condensor enlarger or scanning negatives or whatever...<p>

My interest in EI is this: how does one abbreviate the process as much as possible and still manage to get across the fact that, the ISO number is not the be-all and end-all, and that developing times should be found according to one's needs by going through the whole process front to finish?

[chris_waller]

Usually I use the Zone System method for determining EI and dev time. But on the basis of experience I will often just make a guess, shoot some film, develop it and see how it turns out, then adjust from there under 'real life' conditions.

[rick_jones5]

I use a spot meter exclusively. Over the years I've found that what I meter in a scene and how I adjust that reading can be a lot more important than the actual E.I. set on the meter although I'm always trying to guard against under exposure by usually rating the film a full stop slower than the manufacturer suggests. If I get a poorly exposed negative it is rarely from using the wrong E.I. Usually it's from poor judgement as to what shadow area in the scene was metered and how I adjusted that reading. Of course some would say an incident meter would solve much of that problem.

[StuartMoxham]

If I shoot FP4+ on my EOS1 I set the iso to 80 and just shoot away using the matrix metering. I do pay attention to what I am photographing and will compensate for an all white or all black scene. If there is no backlighting an no main black or white subject I just shoot away. Sometimes I may bracket the exposure a stop either way just to be sure. I found that EI 80 to produce a higher number of useful negs than the manufactures 125 iso. APX100 I set at 80 and do the same. When take pictures of my daughter (the only person who allows me in my family) I sometimes change to spot metering and place the skin tones on what would be zone 6 (1 stop above the indicated reading) I still use my own EI though. I have been developing to produce negs that print well on grade 2 paper. I feel my EIs are quite good for me because I made some tests through the film bases of these films to find the minimum exposure to produce maximum black on the paper and when I print negatives at this time and apeture the prints come out just fine and don't really need to much work.

[david_goldfarb]

When I've had a densitometer, I've done the formal speed test described in Adams' _The Negative_ to find the EI that puts Zone I at a density of .1 over base+fog, and then I might make small adjustments from there based on printing experience. My densitometer exploded a while back (really!--a capacitor blew and smoke started pouring out of it), and I haven't felt an urgent need to replace it, but when I had it, it did help me to learn what a good negative looks like.

 

Now if I'm testing a new film, I tend to eyeball it and adjust my EI to give good shadow separation without causing problems at the highlight end. Most of the black & white that I shoot is medium or large format, and I tend not to print very large, so I don't feel that I need the absolutely thinnest possible negatives that I would get by keeping Zone I at a density of .1. Tonality takes priority over grain for me usually.

[j.w.]

I didn't know there were YYY ratings for XXX films. Goes to show how much I've missed since I left the Navy.

[roger_hicks1]

EIs vary with subject, metering technique, flare, developer, development technique and personal preference. The correct EI is one that gives you negatives that print well.

 

Anyone who uses a spot meter and meters anything other than the darkest area in which he wants shadow detail doesn't know what he's doing. By all means meter highlights as well to determine optimum development but anyone who meters gray cards is flailing in the dark. This includes the vast majority of Zonies.

 

Other metering techniques may require different EIs but if you use the ISO speed and meter the shadows with a spot meter and don't under-develop (another Zonie speciality) you will normally have adequate ahadow detail. If I'm using an incident or through-lens meter I'll do anything between uprating a stop (foggy days) and downrating a stop (bright sun).

 

You may want to check out PERFECT EXPOSURE, which I co-wrote with my wife Frances Schultz. It was published by Amphoto in the US and David & Charles in the UK. It was also translated into Spanish and French. This is not a subject about which I am completely ignorant.

 

Cheers,

 

Roger