Let's talk exposure

[mabas9395]

It may have been mentioned (but I'm too lazy to read that whole post again) that what the camera "thinks" is the correct exposure can be different depending on which metering mode you are in.

The camera can consider the average brightness of the entire frame (evaluative metering), the brightness of just a portion of the middle of the frame (partial metering), a very small spot in the middle of the frame (spot metering), or an average of the total brightness with extra emphasis on the center (center-weighted average metering).

So if your frame has some bright spots and/or dark spots, you will get a different "correct exposure" depending on where you tell your camera to look.

A question on a seperate topic though, when in P-mode for exposure, out of all of the technically correct exposures, how does it come up with the one it has chosen? There has to be some logic built in to it, it can't be random.

 

[jann1033]

It may have been mentioned (but I'm too lazy to read that whole post again) that what the camera "thinks" is the correct exposure can be different depending on which metering mode you are in.

The camera can consider the average brightness of the entire frame (evaluative metering), the brightness of just a portion of the middle of the frame (partial metering), a very small spot in the middle of the frame (spot metering), or an average of the total brightness with extra emphasis on the center (center-weighted average metering).

So if your frame has some bright spots and/or dark spots, you will get a different "correct exposure" depending on where you tell your camera to look.

A question on a seperate topic though, when in P-mode for exposure, out of all of the technically correct exposures, how does it come up with the one it has chosen? There has to be some logic built in to it, it can't be random.

you still set the metering mode in Canon p mode at least

 

[Groucho]

A question on a seperate topic though, when in P-mode for exposure, out of all of the technically correct exposures, how does it come up with the one it has chosen? There has to be some logic built in to it, it can't be random.

I believe that it's probably slightly different for each manufacturer, but what I think the camera does is first figure the exposure needed via the metering mode chosen. Its first priority is to shutter speed - probably close to the rule of thumb that 100mm requires 1/100th of a second, etc. Next up are ISO and aperture, and it will raise those until it can't go any higher.

I think that the shutter speed will only drop below a certain point once the aperture is wide open and the ISO is maxed out.

My camera allows me to choose the priority in Program mode - MTF (the lens' sharpest aperture), high speed, depth of field, or normal. I originally put it in MTF but found that I was getting some blurry photos, as the shutter speed was being lowered in order to keep the aperture at its sharpest. I now keep it on high speed and am pretty happy with that. When I want DoF, I go to Av (or spin one of the dials, which drops it into Av instantly without changing the mode dial from Program.)

 

[Geoff_M]

I believe that it's probably slightly different for each manufacturer, but what I think the camera does is first figure the exposure needed via the metering mode chosen. Its first priority is to shutter speed - probably close to the rule of thumb that 100mm requires 1/100th of a second, etc. Next up are ISO and aperture, and it will raise those until it can't go any higher.

I'll second that explanation. "P" could also stand for "point-n-shoot" because that's the metering technique most point-n-shoot cameras use.

 

[cmwade77]

Wow, awesome information, I now want to break out my old camera that can control each of these individually and start playing again, my newest camera has other great features and the one between the two has yet other great features, so now I get to play with which camera is best for what again, I do this a fair amount, but now that I understand it a little better, I can have some more fun

 

[My2Girls66]

Thanks for the great explanation! I have a question, tho. Say I change the ISO on my camera to a higher # while in 'A', 'S' or 'M', if I go back to 'Auto' or 'P' mode does the camera still use the higher ISO or does it go back to the lower ISO?(if that makes sense). The reason I ask is I tend to forget to go back and lower my ISO after playing with it. Would I notice it in my pictures if say I did go back to 'P' mode using ISO 800 on a sunny day? Maybe the camera would just adjust the shutter and aperature to adjust to my screw up? I use a Nikon D50.
Thanks

 

[pixie dust 112]

Mark~

Thank You! Thank You! Thank You! At last an understandable explanation for thick people, like me, who are trying so hard to understand this! I've printed out your poat and will be sticking it in my camera bag!

 

[brack]

Mark~

Thank You! Thank You! Thank You! At last an understandable explanation for thick people, like me, who are trying so hard to understand this! I've printed out your poat and will be sticking it in my camera

I'm considering sticking it to my forehead!

Seriously ..... great thread! Thanks Mark for starting it.

 

[Geoff_M]

Thanks for the great explanation! I have a question, tho. Say I change the ISO on my camera to a higher # while in 'A', 'S' or 'M', if I go back to 'Auto' or 'P' mode does the camera still use the higher ISO or does it go back to the lower ISO?(if that makes sense). The reason I ask is I tend to forget to go back and lower my ISO after playing with it. Would I notice it in my pictures if say I did go back to 'P' mode using ISO 800 on a sunny day? Maybe the camera would just adjust the shutter and aperature to adjust to my screw up? I use a Nikon D50.
Thanks

I looking at the D50 manual, here's what I can say:
1) If you have Custom Setting #9 (ISO Control) set to "On" (the factory default), then the camera will determine what ISO to use in "Auto" and the other "Scenic" modes. For P, S, A, and M you get to pick the ISO yourself. Unless....
2) If you have Customer Setting #10 (Auto ISO) set to On (the factory default is "Off"), then you can set a desired ISO setting to start with and the camera will adjust it automatically in any metering mode as it sees fit. The only exception to this is when you have #9 set to "On" and that takes precedence when you're in "Auto" or the other "scenic" modes.

There's a chart on Page 91 of this manual that shows how these two settings work: Link

So back to your question... If you're using "Auto" mode and haven't changed setting #9, then you don't get to set the ISO, the camera does. So you'd get back control when you switched back to A, S, P, or M. Switching between A, S, P, or M don't alter any ISO setting you've selected. Note that the camera doesn't tell you when it alters the ISO, you can only tell what happened when looking at the EXIF data in playback mode after the fact.

 

[Pea-n-Me]

Mark, do you mind if I link this on the Learning Curve thread?

 

[My2Girls66]

I looking at the D50 manual, here's what I can say:
1) If you have Custom Setting #9 (ISO Control) set to "On" (the factory default), then the camera will determine what ISO to use in "Auto" and the other "Scenic" modes. For P, S, A, and M you get to pick the ISO yourself. Unless....
2) If you have Customer Setting #10 (Auto ISO) set to On (the factory default is "Off"), then you can set a desired ISO setting to start with and the camera will adjust it automatically in any metering mode as it sees fit. The only exception to this is when you have #9 set to "On" and that takes precedence when you're in "Auto" or the other "scenic" modes.

There's a chart on Page 91 of this manual that shows how these two settings work: Link

So back to your question... If you're using "Auto" mode and haven't changed setting #9, then you don't get to set the ISO, the camera does. So you'd get back control when you switched back to A, S, P, or M. Switching between A, S, P, or M don't alter any ISO setting you've selected. Note that the camera doesn't tell you when it alters the ISO, you can only tell what happened when looking at the EXIF data in playback mode after the fact.

Thanks!

 

[EnchantedPrincess]

Thank you so much for writing this!! So much easier to understand than the two books that I have been trying to read. THANK YOU AGAIN!!

 

[JR6ooo4]

I am seeing some focal lengths of 600, 700 and even 900. Is the program taking into account cropping of a file? My biggest lens is a 70-300!

Mikeeee

well hey, reading is beneficial! Hehehehe

from the help file

Unexpected results:
The Path List is there for debug options, if you find some unexpected results, say you're charts show some 1600mm images, but you don't have a lens like that.
Now you can use the Path List to find out where the 1600mm files are located.
Place a check mark at he "Focal length" option (at the bottom of the Path List tab), and start analyzing, the created sorted list shows the lens length followed by path, filename, make and model.
If you crop an image some programs will alter the focal lens tag in the EXIF, a 1600mm could be a cropped image made with a much shorter lens.

 

[My2Girls66]

I'm trying to use full manual mode on my camera after years of using program mode. When they talk about 'correct' exposure- they mean when the value on the meter in the viewfinder reads '0', correct? Bryan Peterson says this in his book on many occasions. Adjusting aperature or shutter speed until such a setting indicated correct exposure. Is this what he means? It seems I'm not quick enough to adjust these days! Maybe its just going to take some time to get used to it again. I'm wondering if shooting in 'A' or 'S' would be more practical? Not quite as much to think about.
Thanks!

 

[MICKEY88]

I'm trying to use full manual mode on my camera after years of using program mode. When they talk about 'correct' exposure- they mean when the value on the meter in the viewfinder reads '0', correct? Bryan Peterson says this in his book on many occasions. Adjusting aperature or shutter speed until such a setting indicated correct exposure. Is this what he means? It seems I'm not quick enough to adjust these days! Maybe its just going to take some time to get used to it again. I'm wondering if shooting in 'A' or 'S' would be more practical? Not quite as much to think about.
Thanks!

I've been shooting 32 years and I rarely shoot full manual, I shoot mostly in aperture priority to control my depth of field, but I keep an eye on my shutter speed to make sure I won't get blurred images from too slow a shutter speed,

and correct exposure doesn't neccessarily mean having the meter on zero..there are lighting situations that will fool the meter and then you should know when to use exposure compensation..

 

[InsertWittyNameHere]

If you take a photo of a skier coming down a snow covered hill with the meter set to "0" you will most likely end up with gray looking snow. In a case like this you would need to set the meter to "+1 - +1.5" to get the correct white colored snow.

I agree with Mickey88, I shoot in aperture or shutter priority 95% of the time.

 

[MICKEY88]

to further elaborate on exposure compensation,

2 examples of the need for exposure compensation

the camera tries to expose for 18% gray.

1. so in a situation such as a baby on a white blanket or in a white tub, the camera will underexpose trying to turn the white to grey, so youwould set exposure comp for +1 or 1.5, similar to the snow scene...

2. a woman in a black gown in front of a black backdrop, the camera will overexpose trying to get 18% grey, so in this situation you would set exposure comp for -1 or 1.5

if your camera doesn't have exposure compensation you can accomplish the same thing simply by changing your settings to get your meter to read above or below the zero, this is when you would want to shoot in manual mode

 

[Chikabowa]

Theoretically, yes, metering and then adjusting your shutter and aperture to show a 0 would produce a 'proper' exposure.

But in practicality, there are a lot of variables to watch for so this doesn't work 100% of the time. I shoot 100% manual and learning how to read your histogram will really help out. By doing this, you can adjust your settings in order to get the right exposure.

 

[MICKEY88]

Theoretically, yes, metering and then adjusting your shutter and aperture to show a 0 would produce a 'proper' exposure.

But in practicality, there are a lot of variables to watch for so this doesn't work 100% of the time. I shoot 100% manual and learning how to read your histogram will really help out. By doing this, you can adjust your settings in order to get the right exposure.

I've hear others talk about using histogram, but that confuses me for 2 reasons..

1.

if shooting action events such as sports..once you've taken a shot to check histogram, the action is in the past and you can't get the shot you needed...

2.

the histogram is not accurate in the types of lighting situations I mentioned in my other post..

 

[Chikabowa]

I don't shoot sports... ever... so I cannot comment on that. Although, if I did, I would probably shoot shutter priority. But theoretically, if the lighting situation is constant, you can take one shot, make adjustments, and then sent your exposure without having to worry about it again. This, of course, wouldn't work on something like an outdoor football field where the light is constantly changing.

No, the histogram is NOT perfect, but if you know how to read it properly, you know where you need to make adjustments based on where you want your exposure. When you learn how to read your histogram, you make make compensations with your exposure based on what you already know about the 18% gray, etc.

It's not perfect, nor do I solely rely on that reading - because when I add in my off camera flash my histogram becomes super wonky - but having that as a tool to my disposal is really important.