metering question

[dee seegers]

Lets say it's a sunny, clear sky day. Sunny 16 rule kind of day. If I meter in reflecting mode, facing north and get a reading of 1/100 @ f16 with filmspeed of 100; Should I be able to turn around and face south and meter again in incident mode and get the same reading?

I'm using a Sekonic L 508c (it really dosen't have a 1/100 sec speed setting, but 125 is close enough). Would I be more accurate to meter off a grey card instead of north sky? It seems like I should be able to turn around and face south and get the same reading in incident mode.

I've tried this but the sky wasen't exactly clear. (some high thin white clouds were present). I don't remember the results, but I remember they weren't the same.

dee

[george jiri loun]

You would get more or less the same reading only if your measured a surface with the same reflectance as that to which your incident meter is adjusted.

[Ralph Barker]

"Should I be able to turn around and face south and meter again in incident mode and get the same reading?"

Yes. No. Maybe so, depending on how you hold your mouth. ;-)

There are so many variables involved in metering techniques that discussions of them are often more confusing than illuminating. (pun intended, of course)

[Alan Davenport]

Why should a reflected meter reading give the same value as an incident reading? All a reflected-reading light meter knows how to do, is to read a subject that reflects 18% of the light that strikes it. If the subject is lighter or darker than that 18% middle gray, the meter reading will differ accordingly, requiring the photographer to manually adjust the actual exposure from what the meter recommends.

An incident reading assumes the same 18%, since that is what gets through the dome and strikes the metering cell. The difference, of course, is that the incident meter is not affected by the subject reflectance. Of course, if the subject is extremely light or dark, the photographer may still need to adjust...

IF the subject reflects 18% of the light, and IF the meter is used correctly in both reflected and incident modes, THEN the two readings should be the same.

[Peter Hruby]

Hi Dee,

I second to Alan's opinion. Meters are calibrated for certain reflectance, I'd say around 18% (there are few great threads here around how exactly are meters calibrated).

what is important, if the desired scenario overall is lighter than 18% grey you might ended up to uderexpose film if you take reflected reading and that I presume you do not want. On sunny day I would take incident readings on a sunny day to get accurate readings, again unless whole scenario is not in shade or something.

[Richard Schlesinger]

Please post the answer as to how many angels can dance on sphere of a Sekonic meter.

[Will Strain]

42

[d.s.]

""IF the subject reflects 18% of the light, and IF the meter is used correctly in both reflected and incident modes, THEN the two readings should be the same.""

This is what I wanted to know.

And...it's the square of the shutter speed divided by the inverse square of the f/ stop times the log of the E.I. that determins the number of angels that can fit on the incident dome. I think I saw a formula on this at P.net.

[Jim Rice]

Now I have all of those tiny footprints on my sphere. I lost count, too.

[Scott Davis]

I would say that actually, depending on the angle of incidence of the sun, you would get a different reading, because the incident dome would be in the shadow of the meter when you take the reading from the south, assuming you are holding the meter truly perpendicular to the ground. That would explain your variance in readings.

[Dean Tomasula]

Will, that can't be possible. 42 is the answer to the question of the universe. :-)

[Graeme Hird]

Close Dean - 42 is the universal answer ..... ;)

[John Berry ( Roadkill )]

By the time the angels reach our average age here the number drops off to 13

[Will Strain]

well - for all we know, the question is the one asked here. Somebody ask a mouse.

Too many variables on the metering question tho.

[Bill_1856]

It takes a certain amount of experience to use a light meter properly. You're not going to learn by asking hyp0thetical questions involving lots of variables. Doing it yourself, hopefully in the presence of someone else who knows what they are doing, is how you will develop the technique that you need.

[Alan Davenport]

Dean, Graeme's right: 42 is the answer to life, the universe and everything.