So Im getting a monolight kit do I need a light meter

[tirediron]

The power of the flash shouldnt change that much if you change the angle, isnt that correct?

I did a materinity set recently; six basic poses, each one with a completely different lighting arrangement. I could have 'shot and chimped' but having a flash meter (Minolta Flash V) that will trigger my lights made it VERY easy to get within about a half-stop on the first shot. It also makes it a LOT easier to determine your lighting ratio.

Remember that even if you don't change the output of the light, a change in the distance or angle between the subject and the light will affect the final image.

 

[Mike_E]

The only reason to get a flash meter is if you want to control your ratios.

Say if your subject is just about right then a butterfly light might be in order but if they're 30 pounds overweight then you would want to short light them at maybe a 3:1 but if they are only 17 or 20 pounds then you might want a 2:1 or even a 1.75:1.

Unless you buy very expensive lights that are super consistent you won't be able to do this even with a tape measure and calculator. You do know how to set the ratios with a tape and calculator, right?

get the meter.

 

[shmne]

Meters make life faster and simpler, unless you don't understand lighting then it will make it a bit more confusing at first.

This is what a meter does exactly:
You set your camera to 1/200 shutter speed (assuming this is the safest sync speed for your flash and camera) then you set your iso to 100. You then set your meter iso to 100.
Stand where your subject will be, then fire the flash. This will give you a reading like f16. That means if you set your aperture to f16, your subject will be properly exposed. Now instead of guessing how to expose your subject, you know exactly where to start.

Some uses for meters to give you an idea (starting out simple and getting a bit more complex)

-You have your subject sitting on a chair. Your flash about 5 feet away (distance is noramlly relevant, however I'm just trying to draw you a mental picture- the light or subject won't be moving so the distance isn't actually relevant in this example). You meter where the subject is after popping the flash, and it says f8. You dial your aperture to f8, have the subject sit, take the picture and walk away knowing it is perfectly exposed without double guessing.

-You are outside, and want to drop the background 1 stop while using the flash to keep your subject at a properly exposed level. Meter the sun (iso on meter set to 100), it says f16. Now you know what the natural ambient is, you can increase your aperture 1 stop (Thus underexposing the entire scene by 1 stop), and bring in 1 stop of light from your flash as the fill. Now your background is 1 stop darker while your subject should remain lit the same.

-You have a white background you want to blow to pure white. Your subject is about 6 feet from the back. You have two lights pointing at the backdrop, one on each side (remember the Inverse Square Law of light) Now your main and fill lights are set to expose your subject at f8, that means to overexpose your backdrop to pure white you would need about 8 stops of extra light on that background. So your background lights need to be putting out f16 worth of light. The background will be overexposed to the camera by 8 stops, why? Because your lights would be properly exposed at f16 (assuming 100 iso and 200 shutter speed), however your camera is set to f8 in order to properly expose the subject. This means the background is now 8 stops brighter than the subject, this blown to white. These numbers probably aren't perfect as it has been a long time since I've used a meter, but I think you get the idea.

All of this would be set with your light meter so that by the first shot you are already 80% of the way there. That last 20% is just tuning it in perfectly. However after using your lights many times and getting used to certain set ups you just start tossing the meter aside and getting an 80% accurate shot right off the bat. Although there are always situations that things will not work out, low ceilings, no ceilings, water, mirrors, white walls, there are so many things that can reflect light and increase exposure that you will eventually need to meter in situations.

One last thing, if you don't know what the inverse square law is I suggest you looking it up. It is actually extremely important to photography.

Edit: Please if I made an error anywhere let me know, I was never formally trained in photography. I learned most of this on my own, with help from things like strobist, and blogs to fill in the blanks.

 

[ghache]

Even with no flash i use my meeter.

I get my reading arounds the models face so i get well exposed face or body.

 

[AgentDrex]

Like I said, I just go around without my camera. I use my light meter to meter the light output and attempt to memorize what shutter speed for which aperture for which lighting conditions and subject. Its fun but my friends think I'm just a little odd to do so...

 

[Mike_E]

I'm not going to reinvent the wheel here so follow the link.. Lighting Ratios and Incident Metering Demystified

 

[kundalini]

.....This means the background is now 8 stops brighter than the subject, this blown to white. .....

Not to be argumentative, only clarifying in my mind, but at 8 stops over, wouldn't you also want a fire extinguisher handy? Seriously, I was lead to believe that 1-1/2 to 2 stops would be sufficient to overexpose the background without getting blowback on your subject.

 

[Derrel]

Kundalini is absolutely correct--eight stops' more worth of light aimed at a white background would be dramatic overkill. In the case of metering the background light, the white background case is one where you need to measure the light coming from the background by pointing a reflected light meter at the background, and comparing the reading of the reflected light coming from the background back to the subject, and comparing that reading against an incident light reading taken at the subject position. In that way, you can determine if any different neutral background paper or wall will be rendered as "white". Due to the huge number of variable involved, such as different background colors and reflectance values, different distances from lights to the backdrop, different types of modifiers fitted to the background lights, etc,etc, it's impossible to state with any degree of accuracy "how much" light needs to be sent to the background to make it come out white. If it is ALREADY white paper or white-painted wall, it will not take much light to make it render as pure white; if it is gray paper, it will take more light than white paper would require. With white paper, 1.5 f/stops MORE light than the subject's light level will ensure a totally, 100% white background, with the light measured at the back of the subject's head.

Anyway...a flash meter can tell you a lot of information...

 

[gsgary]

Kundalini is absolutely correct--eight stops' more worth of light aimed at a white background would be dramatic overkill. In the case of metering the background light, the white background case is one where you need to measure the light coming from the background by pointing a reflected light meter at the background, and comparing the reading of the reflected light coming from the background back to the subject, and comparing that reading against an incident light reading taken at the subject position. In that way, you can determine if any different neutral background paper or wall will be rendered as "white". Due to the huge number of variable involved, such as different background colors and reflectance values, different distances from lights to the backdrop, different types of modifiers fitted to the background lights, etc,etc, it's impossible to state with any degree of accuracy "how much" light needs to be sent to the background to make it come out white. If it is ALREADY white paper or white-painted wall, it will not take much light to make it render as pure white; if it is gray paper, it will take more light than white paper would require. With white paper, 1.5 f/stops MORE light than the subject's light level will ensure a totally, 100% white background, with the light measured at the back of the subject's head.

Anyway...a flash meter can tell you a lot of information...

Can it tell me what the lottery numbers will be for this weekend ?

 

[Mike_E]

The numbers 28, 4, 8, 56, 11 and 22. take your pick

LOL

 

[shmne]

I was just pulling numbers from almost a year ago now Although we used to shoot with a total distance of 12 feet to the background, not sure what distance you're considering. I feel like we exposed 8 stops over.

 

[jands]

Well I don't know about you KBarredo, but after reading this post, I'm definitely buying a light meter!

 

[Derrel]

I was just pulling numbers from almost a year ago now Although we used to shoot with a total distance of 12 feet to the background, not sure what distance you're considering. I feel like we exposed 8 stops over.

I'd say it's unlikely that you were eight stops over the mainlight exposure if you were using a white background only 12 feet behind the subject...that is simply a HUGE differential in power levels. Not trying to start an argument or anything with you, but, did you use a light meter? This is a good example of how "feel" can be easily quite incorrect or easily distorted by the passage of time...yet is quite easily remembered for years if the actual light meter readings are jotted down even once or twice.

Now...lt's say your backdrop was actually a tightly stretched black photographic velvet background...and you needed it to be recorded as pure white...A) while it depends on the light modifiers used to send the light to the background (umbrellas? soft boxes? parabolic reflectors with 50 to 65 degree beam spreads? bare-tube heads blocked by gobos?---the absolute number of watt-seconds/distance/beam spread all "depends" on multiple factors) to get a pure white backdrop rendering B) the light meter will tell you when the backdrop will be white as soon as the reflected light reading at the subject's back-of-head reaches about 1.5 stops OVER the INCIDENT LIGHT reading falling on the subject's face. Eight stops over would be pretty outrageous on a white or gray background of paper or muslin.

Speedotron Brown Line packs that have a two f/stop Asymmetrical power difference between the A and B channels are pretty useful for getting a white background when using gray seamless, by using the LOWER-powered lights in the B-channel outlets 3 and 4 for the main and fill lights, and then using the higher-powered A-channel outlets 1 and 2 shined onto the background paper from roughly the subject's distance on a typical 9 foot wide roll of seamless with about an eight to 10 foot background-to-subject distance, using 65 degree reflectors. With a 600 watt-second pack, that would be 180 watt seconds, each, from heads 1 and 2 on a gray background, and 45 watt-seconds, (45 watt-seconds from each light unit) from heads 3 and 4 to use as main and fill lights.

Anyway--Kbarredo, if you do NOT have a light meter, here is a short tutorial describing how to use the camera's LCD and the over-exposure "blinkies" to get a pure, white backdrop. Metering A White Background

 

[ulrichsd]

So now that everyone's getting a light meter, now the question is analog or digital? I have an analog sekonic L-398 that I still have from when I did more film (movie). Its nice because it never needs batteries, but I'm sure it is a little less accurate. But for me it works fine.

 

[tirediron]

I have both (Luna Pro F and Minolta Flash V). The only thing that I really like more about the Minolta is that it has a PC port so that I can trip my strobes with the meter from wherever I want to be. I actually prefer the analogue display because you get an immediate appreciating of how close you are to where you want to be and/or how much or little adjustment is needed.