Using Light Meters - Incident and Flash Metering

04/17/2007 10:07:38 AM · #1

I mentioned in another thread that I stopped using RAW files once I learned to properly use my light meter. A couple of people PM'd to ask me to tell more about using a light meter; I will answer their questions here in hopes that it can benefit others as well.

I use this meter: Polaris Light Meter - $159.95 at B&H

I'll begin with some borrowed text from ephotozine.com by Peter Bargh because its well written and I have no desire to reinvent the wheel here:

Guide to using a hand-held light meter·

Your camera may be the latest all-singing, all-dancing model with multi-whatsit metering and flashy exposure modes, but the fact is nothing beats the use of a hand held meter if you know how to use one.

The main issue with metering, no matter how sophisticated it is, is that it's computed to ensure the subject comes out as an average of the scene it's measuring. In simplified terms, the scene's tones are scrambled up inside the camera's metering cell to calculate a single brightness value, which is then used as the basis for the shutter speed and aperture selected. The camera will ensure this single brightness level is equivalent to a mid grey, which is fine when the subject has a wide variety of tones, or is predominately of a brightness similar to mid grey. But things go wrong if the subject is all white, such as snow or a white car, or all dark, such as a black suited person or black car. In these situations the camera will adjust the exposure to compensate and ensure the snow comes out grey and the black suit comes out grey. If you use a hand held exposure meter and point its meter sensor at the subject the same thing happens. This type of meter reading is known as a reflected reading, as it measures the light reflected from the subject, but a hand held meter can be used differently and that's why they are still very popular, despite the availability of advanced camera metering systems.
By turning the meter around you can use the sensor to measure the light falling onto the subject, so it doesn't become fooled by the subject's reflective qualities. This type of metering is called an incident reading and can produce very accurate exposures.

Many meter's have a dome that slides over the sensor to provide incident reading. To use it you have to slide a dome over the metering cell, which is usually a 180 degree translucent plastic diffuser. The meter then reads the light falling on the subject from all angles. It still scrambles the reading and adjusts the exposure to produce a mid grey, but this reading hasn't been affected by reflective or absorbent subject matter and will ensure that the dark subject stays dark and a light one stays light. If you've ever seen wedding photographers walking up to the bride and holding a gadget up to her face, now you know what they were doing.

Using a meter in ambient light
The first thing to do is set the film speed on the meter. On basic models this is a dial that you rotate, placing the film speed you are using against a marker. On the more expensive LED and LCD models you key in the number using up and down buttons, like you would on an electronic camera.
You then press a button on the meter to activate it. Holding the button in on some locks the exposure on others it allows a continuous reading so you can move around checking the exposure levels around the subject. More advanced models allow multiple selection, where you can take a reading from, say, the highlight and one from the shadow and the meter then computes the average.

Taking advanced reflected readings
As reflected readings are more prone to errors one way to help you meter correctly is if you start to visualise pictures in black & white. By splitting the subject into grades from 0 (black) to 10 (white), with mid grey at 5, it's easier to evaluate the exposure required to ensure the subject appears the correct tone. This method of metering was developed by legendary landscape photographer Ansel Adams and is known as the Zone System where each brightness value is given a zone rating. If you struggle to see colours as greyscale, a filter called the Mono View is available to help you see in black & white.
You would then take a reading knowing that it would create a mid grey, whatever your subject matter, then you would adjust the reading to over or under expose, making the subject go whiter or blacker.

The easier approach
An incident reading saves you trying to understand how the Zone System works and is the quick and accurate approach to photograph difficult lighting situations.
When using a meter in incident mode on subjects that are front lit, just point the meter, with the diffuser cone in place over the sensor, towards the camera, making sure that the meter is positioned in the same light as that falling onto the subject. The reading will not be correct if you hold the meter in an area of shade, while the subject is basking in sunlight.

A white subject with strong directional sunlight from above causes a very contrasty result, especially as it's offset from the dark background. This is an easy job for an incident meter.

If you are photographing a distant subject using a telephoto lens and can't get the meter near, the reading will be the same, providing the same light is falling on the subject as the metering cell. For instance, you may be in an office that's illuminated with fluorescent lighting and want a long shot of an employee. A person sat at their desk nearby can be used as the metering reference point. Similarly, a clear-skied landscape will have the same reading at the taking position as the distant tree that you're framing up.

Spot metering
Several SLR cameras and a few exposure meters have a spot meter that narrows the angle of the metering cell so you can point it at specific areas of a scene. As this is a reflected reading you must, once again, use the reading only as a guide, being aware that its value will produce a mid grey. This type of meter is often used to take several readings from a scene and then using your head as a calculator work out what the best exposure should be to ensure everything comes out as expected. Spot meters should really only be used by those who have grasped exposure and are able to apply compensation to ensure the results are correct. Just pointing and relying on the indicated exposure is a recipe for disaster.

Sunsets are fairly easy to shoot, but getting the right balance is the trick. If you want a rich orange sky point at the sky and if you want detail in the landscape point downwards first and lock the exposure. If you prefer a mid point, take a reading from both places and average the two - a spot or partial meter helps here.

Using filters
Whenever you attach a filter in front of the lens the amount of light reaching the film is reduced and the exposure needs to be increased to compensate. It's easy to use filters on an SLR when you're using the camera's built-in meter because the through the lens (TTL) meter sees what's in front of the lens and adjusts accordingly. This obviously can't happen when you use a separate meter, but to help filter manufacturers print the filter's exposure details on the box, around the filter's rim or in the instructions. You simply take a reading and then knock off the number of stops suggested for the filter manufacturer. A red filter, for example, reduces the exposure by three stops. So if the hand held meter suggested 1/250sec at f/8 you could open up the aperture to f/2.8 or increase the shutter speed to 1/30sec.
The problem comes when a filter increases the exposure by a third of a stop, and that's when the more advanced meter, with it's 1/10th stop accuracy is again worth its weight in gold.

What about EV numbers?
EV is an abbreviation of exposure value and is something that's used mostly by professional photographers. It's a combination of the shutter speed and aperture and some meters give the reading as an EV number which is then set on a dial to give the shutter speed and aperture combinations. If you know the EV number you can select any aperture and the shutter speed is adjusted accordingly. It's almost like having program exposure on a meter.

Using a flash meter
A flash meter measure light in much the same way as an ambient meter so can often be used as incident or reflected with the same issues being raised. Most basic flash-only meters will only work in incident light mode because the dome is fixed in place. More expensive combination meters offer both options.
Taking a reading depends on the flash meter you use. More advanced ones allow the flash sync cable to be plugged in and you press a button on the meter to trigger the flash. This gives you the benefit of being able to move close to the subject. With a basic meter you don't have this option and would need someone at the flashgun to trigger it while you hold the meter in front of the subject. This could be the model you are photographing, but on still life sets you may have a problem.

Using a Grey Card
If you can't justify the cost of a meter and want better pictures using your camera's exposure meter, buy a grey card. This is an 18% grey card, which is the same as the tone that the camera's meter scrambles to. Taking a meter reading from a grey card placed in front of the subject will give a similar exposure to an incident meter reading.

Position the card in the same light as the subject and take a reading, set this and the exposures will 99 times out of a 100 be spot on.

Getting to know your meter is vital for better pictures the more you understand it the more success you will have.

Now with that basic info in mind, I would be happy to answer any questions regarding the use of light meters as best I can. If I don't know the answer I will research it for you and post my findings in this thread.

04/17/2007 10:34:00 AM · #2

Good morning miss cindi, and thanks again for being so darned HELPFUL! ;)

I know that using a meter can help greatly, and it HAS helped me lately to set up shots where I'm using more than one light (comparing the relative brightness)...

Can you give us some tips on selecting shutter speed in studio? For example, should we always set it to the fastest available sync speed, or can it be useful to try slower settings?

Thx!

Spork99

Canon EOS M6 Mk II

Canon EF-M 22mm STM Lens

04/17/2007 10:37:57 AM · #3

Originally posted by idnic:

I'll begin with some borrowed text from ephotozine.com by Peter Bargh because its well written and I have no desire to reinvent the wheel here:

That's good advice.

I have a question, but it's not related to the content of the article, but to the article itself: Did you get permission to reproduce the author's text here? If not, a link might be a better approach. Even though you've cited the source, you should still get permission. Posting an article you didn't write without permission is no different than posting a photo you didn't take without permission.

Message edited by author 2007-04-17 10:44:28.

04/17/2007 10:41:51 AM · #4

Originally posted by rossbilly:

Good question, Billy. In the studio you typically want to use the fastest shutter speed possible for your strobes (typically 1/125th) when you are shooting fast moving objects like children or animals. However, when you are shooting adults who can be more still, or unmoving objects its sometimes a good idea to use a longer shutter speed to get greater effect from ambient light or to give reflective objects a more glowy look.
Try this experiment: Put an unmoving object in front of your camera, set the strobes where you want them, and leave the modeling lights on. Now shoot the object with shutter speed at 1/125, 1/60, 1/30, and 1. See the significant differences? Try the same test on a string of christmas lights..... :D

This shot was done at about 1 second to give the christmas lights in the background and the candles that lovely glowy look. A faster shutter speed would record the candles & lights much the way the eye sees them, but slower speeds here gave a more desirable effect.

Message edited by author 2007-04-17 10:42:06.

04/17/2007 10:45:45 AM · #5

Thank you cindi! That should help alot of people........ and when the heck did you change your name to 'Edith'? ;)

Canon EF 24-70mm f/2.8L USM

04/17/2007 10:50:00 AM · #6

Originally posted by Spazmo99:

I have a question, but it's not related to the content of the article, but to the article itself: Did you get permission to reproduce the author's text here? If not, a link might be a better approach. Even though you've cited the source, you should still get permission. Posting an article you didn't write without permission is no different than posting a photo you didn't take without permission.

I checked first - this is from their site: The material on these pages may be printed out for educational use only. Use as course handouts only with proper acknowledgment of authorship.

To be sure, I've just sent an email describing the article's use here and ensuring they would classify that as "course materials".

Edited to remove unnecessary quoting. Sorry. :)

Message edited by author 2007-04-17 11:21:20.

Spork99

Canon EOS M6 Mk II

Canon EF-M 22mm STM Lens

04/17/2007 10:59:01 AM · #7

Originally posted by idnic:

Originally posted by Spazmo99:

Originally posted by idnic:

I'll begin with some borrowed text from ephotozine.com by Peter Bargh because its well written and I have no desire to reinvent the wheel here:

That's good advice.

I have a question, but it's not related to the content of the article, but to the article itself: Did you get permission to reproduce the author's text here? If not, a link might be a better approach. Even though you've cited the source, you should still get permission. Posting an article you didn't write without permission is no different than posting a photo you didn't take without permission.

I checked first - this is from their site: The material on these pages may be printed out for educational use only. Use as course handouts only with proper acknowledgment of authorship.

To be sure, I've just sent an email describing the article's use here and ensuring they would classify that as "course materials".

Might have been better to ask first and not risk infringing, but at least you're asking.

candlerain

Canon EOS-30D

04/17/2007 11:19:46 AM · #8

Thanks for your help AGAIN, Miss idnic! Always appreciated!

Bernard_Marx

Canon EOS-40D

Tamron SP AF 28-75mm f/2.8 XR Di for Canon

04/17/2007 12:27:55 PM · #9

I simply ~adore~ people that are this candid and helpful. Thanks.

Nikon AF Nikkor 50mm f/1.8D

04/17/2007 01:06:12 PM · #10

Guys - I have a great DVD about using light meters from Sekonic. They were offering it for free to anyone, but I don't see it on their site any more. I'll mail it to the first person who PMs an address if you guys will promise to send it on to someone else when you're finished with it.

_eug

Nikon D50

04/17/2007 01:29:10 PM · #11

I found this very interesting. I especially got curious about EV numbers. I know the relationships between ISO, f/stop, and shutter speed, but come time to put my eye to the viewfinder math goes out the window.

I should practice this a little more.

04/17/2007 02:38:20 PM · #12

PM sent...

04/17/2007 02:53:03 PM · #13

Okay, I'm sending the DVD to Billy. Billy, when you are finished with it please post back here so someone else can request it. Thanks. :)

04/17/2007 03:13:18 PM · #14

I'll do that... but first I'm wiping off all the kisses - might look a little strange comin from a guy! ROFL

<<
Thanks Cindi! Oh, here is a link to Sekonic, where they have some more good information.

04/17/2007 03:23:51 PM · #15

I was just thinking it would be funny to dowse it in purfume before mailing it.... then I thought: I bet Glenda can run pretty fast and you'd have your ass kicked long before you could explain the joke. ;P

04/17/2007 09:46:30 PM · #16

Roll-night bump...

04/22/2007 11:02:10 AM · #17

Just a little BUMP, and a BIG thank you to Cindi! (thx for the love note! ROFL)

I will be back in a couple days to pass it on, and I hope this helps a few more people! (Anyone else who'd like to have the disc next?)

Message edited by author 2007-04-22 11:02:44.

Tamron SP AF 17-50mm f/2.8 Di II LD Aspherical (IF) for Nikon

04/22/2007 11:06:24 AM · #18

Glad it arrived safely, Billy. Its a great DVD. Before I watched it I thought I could do most metering by eye and that buying a meter wasn't necessary. Watching that really changed my mind! It not only tells you how to use a meter, but WHY to use a meter. Hope you get some valuable info from it too. :)

mawear

Nikon D3

04/27/2007 04:28:27 PM · #19

I'm interested in seeing it Billy. You might even save on postage if I can meet you somewhere.

Thanks for the information Cindi!