questions on using a light meter

[raytoei@gmail.com]

hi,

i use a sekonic l-408 and i am happy with it, recently i have been having questions which i thought it'd be good to post here, hopefully some of the more experienced members can help me:

a. my sekonic consistently underexpose in the studio, compared to the Minolta flash meter that the studio lends out. I read somewhere that sekonic tends to underexpose by half a stop ?

b. i use to take outside incident metering, until i found out that since a portrait face is probably the focal point, i have started using spot metering on the face. Any advice ?

c. lastly, if i shoot at night, say a street scene (eg. 9pm )where there are strong shadows and street lamp. If i use a reflected reading off a light meter, i should get an average grey (12 or 18%). Now since this is night, i don't need average grey luminance, does this mean I should perhaps underexpose by a couple of stops to have an real night scene ?

raytoei

[135format]

each manuafcturer uses their own standards for determining the output reading so its not surprising sekonic and minolta differ. But the usual film speed tests you do for any film/meter combination should iron that out.

Spot metering is always fine if you know what your film and dev will do with with the setting you use from the reading. Just hope your subject doesn't move/turn between metering and tripping the shutter.

for night shots I would use your spot meter and meter for a highlight around zone 7 or 8 and open up accordingly, something nearish to those street lights. The shadows will go where they go and it'll look like night.

[mdarnton]

As 135format says, what any meter tells you is just a start; if it's consistently telling you the wrong thing, you need to consistently correct that, perhaps by setting the meter to an EI where your exposures are correct.

The problem with metering a face is that a face isn't neutral grey, but metering it will give the right exposure to make it 18% (that is, it will underexpose one stop). If you start by opening up a stop from the reflected meter reading, that's a good start. Probably, unless you want to develop a full understanding of what is going on, it's better to use an incident reading at the face position.

If you want to really understand, you really should work your way through the Zone System so that you understand it. You won't be obligated by the Photographers' Union to follow it to the letter from the time when you understand it, but the principles involved will help you make intelligent decisions about exposure. All of the questions you have asked are within the principles of the Zone System, and it's the most complete explanation you will ever get about the principles of exposure.

About night: this is more obvious with digital cameras, which immediately tell you that everything is coming out looking like daylight. You need some strategy to avoid that. Usually I just set my camera to underexpose 1 or 1.5 stops, which will darken things without making shadows totally disappear, but that's my taste. I would rather push things back to night time in the printing rather than exposure--that way you get fatter, more complete shadows, more appropriate to what you actually can see at night.

[sevo]

Originally Posted by raytoei@gmail.com

a. my sekonic consistently underexpose in the studio, compared to the Minolta flash meter that the studio lends out. I read somewhere that sekonic tends to underexpose by half a stop ?

Sort of, but far from that much. There is no such thing as a average grey - how much of what should by definition belong into that average is a perceptive (human) factor. This is expressed as the K factor in ISO calculations. Sekonic use a quite mainstream K factor, while Minolta are at the high end of the common range. That is, Minolta tends to overexpose (compared to Sekonic and the majority of meter and SLR makers - the statistics behind their factor calculation are as valid as any other) by about one sixth stop.

[135format]

I think minolta assume use of positive film. Sekonic may assume negative film. There is a difference.

And 18% is close to only 2 1/2 stops less than 100%, regardless of your subject brightness range, which is worth thinking about.

18%
36% 1 stop more
72% 2 stops more
100% = approx 2 1/2 stops brighter than 18%
144% 3 stops more = not possible (if in same light)


p.s. Minolta use K factor of 14 in my spot meter F but the difference between that and 18 or 12 is almost neglible.

[Chriscrawfordphoto]

Incident meters don't have a K factor, they use a different calibration constant. I've got a couple of Minoltas and used to have a Sekonic and they matched each other. I suspect that Ray's meter just needs recalibrated.

[sevo]

Originally Posted by Chriscrawfordphoto

Incident meters don't have a K factor, they use a different calibration constant.

Right. For incident it would be C - where Sekonic should overexpose by a mere 1/12 stop relative to Minolta. Even less of a explanation for the behaviour. I suspect that the L-408 (assuming it has been bought new) will still be quite close to Sekonic specs, while the rental Minoltas (not that fresh any more, Minolta having handed over meter production to Kenko some seven years ago) have by now and across a few dozen adjustments drifted to the house standard (probably the in-house average across meters to compare to) of the rental place.

[Steve M.]

You'll drive yourself nuts using multiple meters. Best to find one, work w/ it all the time, and get to know how it relates to your exposures. It really doesn't matter whether the meter is under or over a little, it's getting to know how it relates to your shots. Make some test shots (especially w/ the portraits) and see what works best.

That said, if I'm using B&W film I just make sure things are in the ball park. Wonderful exposure latitude takes care of the rest.

[Chriscrawfordphoto]

Originally Posted by Steve M.

You'll drive yourself nuts using multiple meters. Best to find one, work w/ it all the time, and get to know how it relates to your exposures. It really doesn't matter whether the meter is under or over a little, it's getting to know how it relates to your shots. Make some test shots (especially w/ the portraits) and see what works best.

That said, if I'm using B&W film I just make sure things are in the ball park. Wonderful exposure latitude takes care of the rest.

Ain't that the truth! I have two Olympus OM-4T bodies. One of them overexposes a mere 1/3 stop over the other (the 'good' one matches both of my handheld meters perfectly). 1/3 stop is nothing, barely noticeable with negative film, but it f--king drives me nuts to the point that I set the camera's film speed dial to underexpose 1/3 stop to compensate when I use it.

[raytoei@gmail.com]

thanks again for all the replies. let me slowly internalize this.

[charjohncarter]

For spot metering a face, if it is a white face, you will have to open your f-stop one stop. This will give you a gray card equivalent.

[Joakim Målare]

Originally Posted by charjohncarter

... if it is a white face ...

Now that's a note you rarely see in exposure theory. In most Zone sheets it just says "skin". Hah! I shake my head / roll my eyes everytime. (getting dizzy by now)

I wonder how many stops "skin" would cover if you started measuring... For us northfolks it's more like Zone 7, at least at this time of the year

[charjohncarter]

Originally Posted by Joakim Målare

Now that's a note you rarely see in exposure theory. In most Zone sheets it just says "skin". Hah! I shake my head / roll my eyes everytime. (getting dizzy by now)

I wonder how many stops "skin" would cover if you started measuring... For us northfolks it's more like Zone 7, at least at this time of the year

Could be, and I spent time living in South America and the white face theory goes out the window there. Still, I would hold my palm (I'm, the politically correct term, a Norwegian-America with just enough Hawaiian, to bring to Zone 6) up to the light the face was in and use that as Zone 6.