Over exposure

[Henik]

  I wanted to photograph my new grandaughter. I  used a pocket wizard TT1 to fire  my 580EX II which was mounted on a Pocket wizard TT5.  Firing into an umbrela, the 580 speedlite was set to manual full power. I used a light  meter to measure the output and then set my Canon 5D MK3. Setting were F5.6 at 60, ISO 200.   Checking the image, I found the exposure  to be over exposed by one F stop.  I checked all my setting and everything was correct.  I checked my meter against another meter both in the ambient and flash modes and found them to be the same within 0.2 of a stop. 

  Can anyone suggest  why this would happen to give me a 1 stop over exposure.

[TCampbell]

What light meter are you using and how are you metering the flash?

I have a few Sekonic meters that will meter flash... the meter must be placed on the subject... distance is IMPORTANT because light falls off based on the "inverse square law" (each time the distance changes by a factor of about 1.4 (which is the rounded value of the square root of 2) then the amount of light will either halve (if moving farther) or double (if moving closer). This is because as the distance from the light source increases... the light is spreading out ... so the number of photons that land in a given area will be fewer as you are farther away.

The meter must be at the identical distance from the flash as your intended subject or the metering will not be accurate.

To meter flash, the light meter must be in the correct mode to meter flash (otherwise it will report the available or "incident" light rather than the amount of light in the tiny fraction in which the flash is illuminated.)

[Henik]

I'm using a Minolta V meter. and metering right in front of the face.   Flash is firing into a 45" umbrella that is about 5-6' in front of subject.  At that distance the light should be pretty consistant  top to bottom and side to side.  I certainly understand the concept of flash meters.  I'm metering the same way that I  used to meter when I used to shoot film.  Thats why I'm having a hard time understanding why I'm getting over exposure.  If I meter the light at  F5.6, at 1/60 and ISO 200, the same setting on my camera  (manual mode) should produce proper exposure. I shouldn't have to stop down to F8. My granddaughter is 1 month old, placed on a small chair on the table.  I can understand light drop off on a big group or other situations, but not this.

[Skirball]

I can't help with the lightmeter, just don't see the point in the digital realm.

But full power out of a 580 at f/5.6 and ISO 200 is way too much.  I'm surprised it's only a stop, you must have the brella pulled back aways.  I'd start at 1/4 or so if you insist on using the meter.

I know the traditional folks hate the chimp method, but I'm going to recommend it anyway.  Set you camera to expose the ambient how you want and then I'd start my 580 at 1/4 for ISO 100 and pull the umbrella in close to really highlight just the subject  and adjust as necessary.  Unless you're trying to light the whole scene with the umbrella, but I wouldn't bother with a 5d3.

You can also just use TTL.  I don't use it for portraiture, but if I'm mixing ambient and a single flash I find it quite useful if trying to move quick.  With newborns I haven't had much of a problem with them blinking (common with eTTL), but after they get a few weeks old I'd just use manual.  I usually just stick the flash in a home-made beauty dish and hold it with my other hand, adjusting distance to fine tune.

[Henik]

To not see the point in a digital situation  raises this question.   If you're  not shooting TTL, how do you know where to set your camera.  Yes your camera meter will give you a good reading in ambient light, but it can't measure what external lights will put out.  That's where a light meter comes in.

[Skirball]

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@Henik wrote:

To not see the point in a digital situation  raises this question.   If you're  not shooting TTL, how do you know where to set your camera.  Yes your camera meter will give you a good reading in ambient light, but it can't measure what external lights will put out.  That's where a light meter comes in.

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The short answer: I chimp and use my histogram. I also shoot RAW and post process all my images, which gives me additional flexibility over exposure values.  Coupled with experience I think it’s just as quick and effective as a meter for the majority of situations.

This is a very common discussion on these forums, and I see both sides of the argument.  I’m not saying using a light meter is pointless, I’m simply saying that it has become significantly less of an advantage with digital.   I can get in the ballpark with a couple of quick shots and checking my preview/histogram.  The whole process doesn’t take more than a minute unless I’m doing some really complicated lighting.  Most of my time is spent fine tuning my lighting: adjusting fall-off, feathering, rim light, spectral highlights, etc.  A light meter can’t help me with these things.  Not much anyway.

Again, I’m not saying a light meter doesn’t have its uses, I’m just contesting the idea that it’s necessary for flash photography.  Many people have been using them for years, decades, and I wouldn’t expect them to change if it works for them.  But it seems the majority of the time a discussion on light meters comes up, it’s because it’s not working for someone.  If it’s not working, why not try another method and see if that works better for you.

[ScottyP]

I'm a chimper, and I am not ashamed to admit it. 😉