Way to Read Light for Fast reliable purpose...

[mad1]

In Slide film I read the light 'ambient' (with the white bubble on) but It

doesn't work for B+W... i.e. I I use a 100iso film and use the 'ambient light'

for my reading, what should be the real iso it has been exposed? (for the

developpement) Or how many stops should I pull or push to reach a well

developped sheet film?

 

Thx,

 

Marc-Andre Dumas (M.A.D.)

[profhlynnjones]

Hi

 

If the meter is reasonably accurate, you should aim the dome of the meter so that it is illuminated in exactly the same way as the subject. Theoretically, this will compensate for any significant angle of light. If you have one of those tiny little domes, aim it slightly toward the light source.

 

If you wish to test your meter, camera, or lab, photograph a "neutral grey card", filling the card and fully illuminataing it, and when you take your film to the lab, ask the lab to read the grey card density. If they ask what colors or some other dumb question, say, Neutral, as well as R, G, B.

 

They may bill you for a few bucks (probably $10).

 

The appropriate readings for all of the above should be .70 +/- .05 If all the readings are off in the same direction by more than .10 (1/3rd of a stop up or down, re-set your film speed and re-test. 1/3rd f stop is one number up or down on the film speed setting (100 ISO speed at +.10 {.80} reading, change the film speed to ISO 80).

 

If the three color readings are off differently and your lighting is mid day sun or with the use of a good quality flash unit, then you must suspect the lab and try a different lab to test.

 

Lynn

[profhlynnjones]

By the way, this is just the beginning of acquiring good exposure readings. If this works, but other peculiarities persist, then try to figure out what you are doing, regarding your shooting technique that needs to be addressed.

 

Lynn (again)

[mad1]

Sekonik L-508 zoom master is my metering tool

[wigwam jones]

When you take an incident light meter reading, you are measuring the light that falls on the sensor, so as stated above, you should ideally have the meter positioned where the subject is, and the white dome pointed back towards your light source. This is different from reflected light meter readings, where you stand where the camera is and point the meter towards your subject, or spot-meter readings, where you point your meter specifically towards the area in in your subject that you think represents medium gray.

 

If using the meter in that way does not work, you'll have to give us some understanding of what is happening. Are you consistantly underexposing or overexposing? Presuming you are developing your film normally (neither pushing nor pulling it), then the reading you get from an incident light meter reading, used properly, should be accurate enough to use in most situations.

 

Another possibility has to do with your scene. Light meters do not know what you are taking a picture of. They only translate the light that hits them into a correct exposure for medium gray. If your scene is exceptionally dark, light, or even very contrasty, your incident light meter reading might not be the reading you want to use.

[stan_belyaev]

I feel that there is nothing wrong with the lightmeter.

There are many variables that affect the results of b&w photography.

1. Film and developer combination (some developert increase or decrease film speed)

2. Agitation and temperature during the film development.

3. Subject brightness range (difference between the brightest and the lightest ares)

4. I guess many others....

 

I had a similar problem a while ago with Minolta VI. (i thought I had a problem)

 

These lightmeters average the falling light, but they dont know who bright the subject is under this light. The brightness range of the subject may easily exceed the capability of emulsion to record it or our capability to print very contrasty negatives.

 

To overcome this problems use a spotmeter (sekonic 508 has it).

Just place a shadow that you want to look very dark, but not completely black ON THE PRINT to zone 3 (spotmeter it, read the meter, set the camera according to the results, then set the exposure compensation dial of the camera to -2).

 

Avoid using the box speed of the film. Set the meter/camera to 50% of what the box says. Decrease the development time by 20-25% form the manufacturer's data.

Try 1 or 2 rolls, then find a book Edge of Darkness by Barry Thornton and read it.

[helenbach]

Lynn,

 

Are you referring to colour or B&W film with your description of the aim density method?

 

MAD,

 

For really simple incident readings with B&W neg film you can set the meter to the box speed and read in the shadows - open shade, not deep shade. This goes along with the general idea that it's usually better to base the exposure for negative film on the shadows. That's not the only way and it isn't always the best way, but it's a common way.

 

It's better to take two incident readings (one in the shade and one in full illumination) to estimate the likely brightness range of the scene. This was described by Minor White in his Zone System Manual - it is the simple version of Zone System metering. The Zone System then goes off and matches the amount of development to the brightness range. If you want to get into that there are a few books, each with their own flavour. The well-worn, simple description of the Zone System is 'Expose for the shadows, develop for the highlights'.

 

Your L-508 can also be used as a spot meter, as already mentioned by Stan. In theory, with the L-508, the spot meter reading from a 12.5% grey card will be the same as the incident reading - or the spot reading from an 18% grey card should be half a stop different (indicating less exposure) from the incident reading. But that's only in theory. My L-508 reads almost the same between an 18% grey card and incident.

 

You might find that you prefer to use the spot method for some situations and the incident method for others. I do.

 

Best, Helen

[pete_andrews10]

I don't know what the fuss is about here. An incident light reading works just as well for B&W as it does for colour. In fact, the incident light method of exposure metering was in use long before colour film became commonplace, and before the current ASA/ISO speed rating system was finalised too. So if anything, it's colour film that's out of step with B&W ratings, not the other way round.

 

In most cases, an incident reading will indicate the same exposure as a reflected light reading from a 13% grey card. So what's the diff? It's what you do with a light-reading that counts, and not the method used to get it.

[mad1]

I think it's 18% of reflected light...

[helenbach]

"I think it's 18% of reflected light..."

 

It's debatable.

 

For a meter that has both incident and reflective reading capabilities, you can use the two calibration constants to calculate what reflectance corresponds to an incident reading. You have to decide whether to use the calibration constant for a flat disk (having a cosine response, most like a grey card) or a dome (with a cardioid response).

 

For the flat disk a Sekonic meter should read the same in incident mode as the reflective reading from a 16% card. If you use the dome, and have unidirectional light, the equivalent would be 12.5%.

[helenbach]

An incident dome reading can't really be compared to a grey card reading in multi-directional light because the dome has a different angular response. When I wrote 'flat disk' I also meant the lowered position of the dome for Sekonics like the L-508.

 

But it rarely matters - metering isn't that exact a science.

[profhlynnjones]

Hi Helen,

 

For someone getting started, the answere to your question is yes for both.

 

Regarding multidirectional light sources, Don Norwood created the first incident meter by placing a dome on the original Weston meter and recalibrating it to exactly mimic the reflected light reading on a grey card. This was in the 1930's, after WWII He created his own small Norwood director (now identical with the the Seconic) and the Spectra and Spectra 500 Combi meters similar in look to the original modified Weston.

 

Don created these meters in the motion picture industry because multliple light sources were very difficult to control using reflected light meters. The incident meter would allow the lighting tecnician to control each light individually and then with all the lights, establish an average exposure. Frequently, after that a trim test would be done, but when I was in the commercial/industrial/scientific motion picture business, we just exposed film and processed it in our own lab (we had a Kodak licensed Professional Motion Picture Lab of which I was general manager).

 

I learned from my Cine teacher, Rex Fleming (nearly 50 years ago), at Brooks to always keep an extra Spectra meter and every few months, send one in to manfuacturer to test and calibrate them because we worked to very precise exposures.

 

Don died a few years ago but he was a genius in light measurement.

 

Lynn

[helenbach]

Lynn,

 

I use aim density as the basis for film speed test for MP colour film, and I have a couple of comments on your suggestion of 0.7 for all three channels:

 

Different films have different aim densities, particularly with still film. EK's current MP films have consistent aim densities, however. Examples, for Status M red channel for an 18% grey card correctly exposed, range from 1.0 for 100UC down to 0.7 for some Fuji films.

 

The red, green and blue densities should be different from one another for colour negative - the density should increase from red to green to blue. It's because of the two masks and the associated impurities in the image dyes. For example the Status M aim densities for EK MP camera film are 0.8 red, 1.2 green and 1.6 blue. For interneg and interpos films they are higher. There's even a slight variation in the aim densities for print film (this time Status A): 1.10 red, 1.06 green and 1.03 blue.

 

If you have different densities in the three channels when reading a B&W film it is nothing to do with the colour balance of the light used to expose the film, of course.

 

Best,

Helen