Question about exposure while shooting in Manual

birdfish

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Okay let's say I want a shall DOF, so I set a low f#. I look through the viewfinder, compose my shot, and then adjust my dial to 0. Does that guarantee my image is going to be exposed correctly every single time if I follow this logic? There is no way it can be that easy.
 

KmH

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Your camera has at least 3 light metering modes you have to choose from: Evaluative/Matrix, Center-weighted, Partial,Spot - but you also have to consider the light meter can be fooled.

The light meter in the camera is calibrated such that it assumes the overall average brightness of most scenes is going to be right about 18% gray.

Consequently, the photographer has to sometimes add or subtract a bit of exposure. This time of year a lot of winter scenes get under exposed because all the white snow fools the light meter. Wedding photographers have to account for the white dress most brides wear.
 

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Not even close.
The meter will usually be a bit off depending on the scene.
Experts can evaluate the compensation adjusts needed at a glance....the inexperienced will be constantly scratching their heads.

This is the beauty of Evaluative or Matrix....the camera will to some extent make the corrections for you. You paid a lot of money for an expensive camera....let it earn it's money.

Experienced pros who shoot in Manual mode do so because they have good reasons for doing so and they have the skills to make it work well for them.

Inexperienced shooters should be using Evaluative or Matrix......at least until they understand the reasons why you may not want to use it in some specific situations.
 

MLeeK

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Adding to keith's note... You have to understand what your camera is metering the scene as. The newer cameras do have a color metering system, however... this explanation still applies for the most part:

In camera meters don't measure the light in your scene. It's not like a scale or a tape measure that measures the ACTUAL LIGHT in any quantitative measurement. It measures what the reflected light from your subject looks like. A hand held light meter actually measures the LIGHT of your scene and tells you what proper exposure settings should be. It's a ruler for light.

Now you are saying... um... ok.... what is the difference? Let's use snow as an example: A foot of light fluffy snow could weigh 1 ounce. A foot of heavy wet snow would weigh more like 1 pound. They both APPEAR the same-it's a foot of snow!!! But in reality one is heavier. It's the same with light. Things can look the same, but they aren't.

Back to the real subject of metering...
Your camera's meter takes that reflection off of whatever you are metering-could be snow, could be a black backdrop. No matter what it is, your camera tries to make that reading equal middle of the road or middle gray on the light to dark scale. The camera doesn't know if you are metering a black scene or a white scene. It only knows that average exposure should be middle gray or about as bright as this:
gray-18.jpg

Now that you know that much, you also have to consider what the metering modes are using your scene and trying to average to middle gray.
Evaluative metering is measuring the whole scene. Sky, water, child playing in the sand... EVERYTHING and it's trying to make it average middle gray. Just like a grade in school it adds all of those pixels up and tries to equal middle gray when it divides them out. On the beach with the sky and water? Probably not going to be extremely accurate. For example this photo of Haley on the beach.
5629395008_bed501f63b.jpg

Convert it to grayscale and look at the bright and dark of it:
5557193130_1aed6a6f8a.jpg


If I average the pixels out this is the gray they come out.

5556608597_a74cebc8f7.jpg


Compare that to middle gray and it's a lot brighter tone-and there was a lot of dark stone in that one.
If you're on a white sandy beach on a bright day your gorgeous child playing in the sand is probably going to be drastically underexposed. You have lots of bright sky pixels, lots of bright sand pixels and a few dark ocean and child pixels... The bright ones win and hold the average up. In high contrast situations like my beach example evaluative doesn't really work well.
Consider an average setting like maybe your living room (assuming your walls are fairly light) with your kids playing. It might work really well!

Center Weighted average metering takes all of the pixels into consideration, but like a mid term and final test is worth more points than any other test, so are the pixels in the center of your scene. It averages all of them together and counts the center ones multiple times to make them more important than the outer pixels. It would sure help with that beach scene to make the pixels that were of your child more important. Closer at least!!!

Then there is Spot Metering. Your meter only evaluates the pixels you put your SPOT on. This works well if you can train yourself to look at the scene in terms of light and dark and decide what you want to be the middle tone. White, non-african/asian/indian etc skin is not usually middle gray It's much lighter. Think of when you convert to black and white. Is skin ever that color ^ up there? Nope. I find that your average grass is a good middle gray outside. My light oak hardwood floors indoors are a good middle of the road. For the image of Haley I would have metered Haley's skin on the back of her arm and then set my exposure to about +1 or JUST before the skin would blow out.


So, now that you understand metering a little better and have a better friendship with your meter it'll be easier to make it do what you want it to do.
 

Ysarex

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Okay let's say I want a shall DOF, so I set a low f#. I look through the viewfinder, compose my shot, and then adjust my dial to 0. Does that guarantee my image is going to be exposed correctly every single time if I follow this logic? There is no way it can be that easy.

Back up. Let's say you want shallow DOF so you set a low f#. You don't need the camera in M to do that. Put the camera in A (Av) mode and set the low f#. Now the camera will take care of setting the matching shutter speed so the meter is zeroed. Setting the shutter speed yourself in M mode takes more time and is less efficient.

Next step: Keith, MReid, and MLeek all pointed out that internal camera light meters don't always get you the best exposure because they have to meter the light reflecting off the subject, not all subjects are average, and the meters don't know what you consider important. There's no setting for that problem. However there is a tool on the camera: EC (exposure compensation). If you know the camera meter reading will be correct then you only need to put the camera into A (Av) mode, set the f/stop and shoot. If you know the camera meter reading will be incorrect then you only need to put the camera into A (Av) mode, set the f/stop, set the EC factor and shoot.

Joe

P.S. Flash changes everything.
 

KmH

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Manual mode is used when you have both DoF and motion stopping considerations to take into account and control.

Using Av or Tv modes still requires keeping close track of the what settings the camera is choosing.

For some of us, using Manual mode takes little if any concious thought for adjusting the settings to produce the DoF and motion stopping we want in an image.

There are airline pilots today that don't know how to fly an airpalne manually. So, when the auto functions on the airplane fail, they crash.

Many can't even tell that their auto systems are malfunctioning.
 

greybeard

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They use to make a white domed cap that would be placed over your camera lens for incidental metering. Hand held meters had a little dome that you placed over the sensor. You would go to the subject, old the meter in front of the subject with the dome part facing up and read the light falling on the subject. This domed cap over the camera lens would let the camera meter work the same way. You would just take the camera to the subject, sample the light fall on it, match needle and then take off the cap, compose the shot, leave the exposure set to the earlier reading and shoot. This was the most fool proof metering I ever used.
 

KenC

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Another issue is that, depending on your ISO setting, you may not be able to shoot at a low f number if you are in bright light. For example, at ISO 200, a typical sunny day exposure would be about f16 and 1/250, so if you set your lens to f2.8 (5 stops more exposure than f16), the correct shutter speed would be 1/8000 (5 stops less exposure than 1/250). Some cameras have shutter speeds this high, but if yours doesn't you will not get the right exposure.
 

greybeard

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Another issue is that, depending on your ISO setting, you may not be able to shoot at a low f number if you are in bright light. For example, at ISO 200, a typical sunny day exposure would be about f16 and 1/250, so if you set your lens to f2.8 (5 stops more exposure than f16), the correct shutter speed would be 1/8000 (5 stops less exposure than 1/250). Some cameras have shutter speeds this high, but if yours doesn't you will not get the right exposure.

ND filter
 

KenC

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Another issue is that, depending on your ISO setting, you may not be able to shoot at a low f number if you are in bright light. For example, at ISO 200, a typical sunny day exposure would be about f16 and 1/250, so if you set your lens to f2.8 (5 stops more exposure than f16), the correct shutter speed would be 1/8000 (5 stops less exposure than 1/250). Some cameras have shutter speeds this high, but if yours doesn't you will not get the right exposure.

ND filter

Sure, but just trying to make the point to the OP that the camera doesn't necessarily take care of everything.
 
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birdfish

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Adding to keith's note... You have to understand what your camera is metering the scene as. The newer cameras do have a color metering system, however... this explanation still applies for the most part:

In camera meters don't measure the light in your scene. It's not like a scale or a tape measure that measures the ACTUAL LIGHT in any quantitative measurement. It measures what the reflected light from your subject looks like. A hand held light meter actually measures the LIGHT of your scene and tells you what proper exposure settings should be. It's a ruler for light.

Now you are saying... um... ok.... what is the difference? Let's use snow as an example: A foot of light fluffy snow could weigh 1 ounce. A foot of heavy wet snow would weigh more like 1 pound. They both APPEAR the same-it's a foot of snow!!! But in reality one is heavier. It's the same with light. Things can look the same, but they aren't.

Back to the real subject of metering...
Your camera's meter takes that reflection off of whatever you are metering-could be snow, could be a black backdrop. No matter what it is, your camera tries to make that reading equal middle of the road or middle gray on the light to dark scale. The camera doesn't know if you are metering a black scene or a white scene. It only knows that average exposure should be middle gray or about as bright as this:
gray-18.jpg

Now that you know that much, you also have to consider what the metering modes are using your scene and trying to average to middle gray.
Evaluative metering is measuring the whole scene. Sky, water, child playing in the sand... EVERYTHING and it's trying to make it average middle gray. Just like a grade in school it adds all of those pixels up and tries to equal middle gray when it divides them out. On the beach with the sky and water? Probably not going to be extremely accurate. For example this photo of Haley on the beach.
5629395008_bed501f63b.jpg

Convert it to grayscale and look at the bright and dark of it:
5557193130_1aed6a6f8a.jpg


If I average the pixels out this is the gray they come out.

5556608597_a74cebc8f7.jpg


Compare that to middle gray and it's a lot brighter tone-and there was a lot of dark stone in that one.
If you're on a white sandy beach on a bright day your gorgeous child playing in the sand is probably going to be drastically underexposed. You have lots of bright sky pixels, lots of bright sand pixels and a few dark ocean and child pixels... The bright ones win and hold the average up. In high contrast situations like my beach example evaluative doesn't really work well.
Consider an average setting like maybe your living room (assuming your walls are fairly light) with your kids playing. It might work really well!

Center Weighted average metering takes all of the pixels into consideration, but like a mid term and final test is worth more points than any other test, so are the pixels in the center of your scene. It averages all of them together and counts the center ones multiple times to make them more important than the outer pixels. It would sure help with that beach scene to make the pixels that were of your child more important. Closer at least!!!

Then there is Spot Metering. Your meter only evaluates the pixels you put your SPOT on. This works well if you can train yourself to look at the scene in terms of light and dark and decide what you want to be the middle tone. White, non-african/asian/indian etc skin is not usually middle gray It's much lighter. Think of when you convert to black and white. Is skin ever that color ^ up there? Nope. I find that your average grass is a good middle gray outside. My light oak hardwood floors indoors are a good middle of the road. For the image of Haley I would have metered Haley's skin on the back of her arm and then set my exposure to about +1 or JUST before the skin would blow out.


So, now that you understand metering a little better and have a better friendship with your meter it'll be easier to make it do what you want it to do.

Thanks MLeeK! That's a lot of info but you put it in a way that makes sense to me. Gonna take some practice but at least I have a little better understanding. Thanks again!
 
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birdfish

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Okay let's say I want a shall DOF, so I set a low f#. I look through the viewfinder, compose my shot, and then adjust my dial to 0. Does that guarantee my image is going to be exposed correctly every single time if I follow this logic? There is no way it can be that easy.

Back up. Let's say you want shallow DOF so you set a low f#. You don't need the camera in M to do that. Put the camera in A (Av) mode and set the low f#. Now the camera will take care of setting the matching shutter speed so the meter is zeroed. Setting the shutter speed yourself in M mode takes more time and is less efficient.

Next step: Keith, MReid, and MLeek all pointed out that internal camera light meters don't always get you the best exposure because they have to meter the light reflecting off the subject, not all subjects are average, and the meters don't know what you consider important. There's no setting for that problem. However there is a tool on the camera: EC (exposure compensation). If you know the camera meter reading will be correct then you only need to put the camera into A (Av) mode, set the f/stop and shoot. If you know the camera meter reading will be incorrect then you only need to put the camera into A (Av) mode, set the f/stop, set the EC factor and shoot.

Joe

P.S. Flash changes everything.

I understand what you are saying about it being quicker to just set it to Av and let the camera set the correct ss. I didn't know about EC though. So I was just wondering if, by shooting in manual the way I was thinking if I could come out with a more accurate exposure. Which I now see there is more to it than what I was thinking.
 
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birdfish

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Manual mode is used when you have both DoF and motion stopping considerations to take into account and control.

Using Av or Tv modes still requires keeping close track of the what settings the camera is choosing.

For some of us, using Manual mode takes little if any concious thought for adjusting the settings to produce the DoF and motion stopping we want in an image.

There are airline pilots today that don't know how to fly an airpalne manually. So, when the auto functions on the airplane fail, they crash.

Many can't even tell that their auto systems are malfunctioning.

Well most of the time I am taking photos of my son, so there is definitely motion consideration involved with him. :)
 
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birdfish

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Another issue is that, depending on your ISO setting, you may not be able to shoot at a low f number if you are in bright light. For example, at ISO 200, a typical sunny day exposure would be about f16 and 1/250, so if you set your lens to f2.8 (5 stops more exposure than f16), the correct shutter speed would be 1/8000 (5 stops less exposure than 1/250). Some cameras have shutter speeds this high, but if yours doesn't you will not get the right exposure.

Yeah mine only goes to 1/4000. Thanks!
 

MLeeK

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You are welcome! If you need more help don't hesitate to ask!~
 

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