Why don't most cameras allow control of metering?

[Graystar]

Very good and detailed answers. I was unaware the exposure compensation button could also be used as an exposure lock, that helps a little.

On DSLRs, EC and AE Lock are separate buttons. Every single Nikon has the EC button behind and to the right of the shutter button, and they all have an AE-L button on the rear of the camera that can be reached by the right thumb.

I also do have a canon P&S that allows a tiny bit of control over the flash, but only 3 stages, and its the only camera I've ever seen to have it, from what I hear, most dslr's don't even have this ability besides a couple nikons. I think every camera should all have it standard.

Every single Nikon from the entry level D3000 on up allows manual control of the built-in flash. For Canon the 60D and better allow manual control of the built-in flash.

I'm not sure why you want manual control of the built-in, as intelligent TTL modes set the flash perfectly based on distance and all cameras have Flash Exposure Compensation.

I am a bit confused why some people seem to be relating the metering to shutter speed and aperture though. To my knowledge they are completely seperate things. For example I can go in manual mode, set aperture to 2.8, shutter speed to 1/500, and iso to 100. Those are set, and not changing, yet depending on what I point the camera at, whether its bright, or dark, the metering still changes the overall exposure.

Well...a better way to put it is that the meter reading changes. Exposure is set by the aperture and shutter, and in manual mode that's not changed by the meter.

I couldn't find the article again, but I believe the explanation was something like a full complete histogram has more than 5 brackets, something like around 10, but the camera can only capture 5 brackets. It cannot capture both very bright, and very dark at the same time, so it basically slides up or down the scale accordingly. So Its a bit confusing why people are saying metering has anything to do with shutter speed/aperture.

The term Exposure Value means two things. First, it refers to a level of luminance from the scene. Second, it refers to a combination of aperture and shutter. When the EV of the scene equals the EV of the aperture/shutter combo, you have correct exposure. This is what the camera's auto modes are doing...adjusting the aperture or shutter to achieve an EV that matches the EV of the meter. So while neither aperture nor shutter has anything to do with the metering process, there is a direct relationship between the meter's indicated EV and the aperture/shutter.

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[Graystar]

What I had read was that digital cameras cannot capture the entire tonal range, only a small portion of it, (the 5 stops shown on a histogram). But that the whole tonal range is actually larger than that, lets say 10 stops for the sake of example since I can't remember the actual number. So out of those 10 stops, the camera basically would slide its 5 stop histogram bracket up and down this scale. A darker image would perhaps use brackets 2-6, and a lighter image would perhaps use brackets 4-9. Effectively changing the range that the camera picks up, and altering the final picture.

It’s true that the Dynamic Range of a scene will frequently exceed the DR of the camera. In such a case, you do have to make some decisions about how you’re going to control exposure. You can expose your subject correctly and allow the bright areas to be overexposed. You can underexpose the entire scene, and then correct the brightness in software using special functions such as highlight compression to control areas from becoming too bright. You can use filters on the lens to balance the lighting. You can also change the composition of your image to make the lighting more even (reduce the DR of the scene.)

As for the histogram...they usually have 5 divisions but there's no relationship between the divisions and stops of DR. The divisions are just divisions. If a camera can capture 8 stops of DR, then that's what the histogram represents.

Perhaps this was wrong info? Or perhaps it doesn't apply to manual mode?

90% of my picture taking is always in manual mode, and I had assumed this still applied because the picture preview on the lcd would still change dramatically depending on the brightness of the object you were pointing at, however I just did a test photographing a light bulb directly, and also indirectly, and although the preview did change drastically, the final picture was the same brightness. That's what I had always believed would be the case, until whenever I read that article that said elsewise. I think it may be a situation where I used to understand fully, until a misunderstood article may have changed my perception.

You’re talking about a LiveView preview, and that has nothing to do with exposure. Some LiveView previews do provide exposure simulation, while others simply brighten or darken as necessary to allow you to view the scene (which is why you’re in LiveView in the first place.) Most DSLR users don’t use the rear LCD in LiveView to judge exposure because they’re looking through the viewfinder. If you understand exposure then you don’t need to look at the rear LCD to see what you’re going to get. You know what you’re going to get based on the lighting of the scene, your selected metering point, and the metering bias you apply (which is based on the tone of the area metered.)

But if that's the case, then why is metering type even an option in manual mode if it doesn't change anything? Is the sole reason of choosing a type of metering in manual mode simply to determine what area of the image effects the readings of the little on screen light meter, but doesn't change photo composition at all?

Yes. The metering mode affects the meter indicator only.

You need to take some time to understand how the meter works and what it's actually indicating, and how that indication actually relates to the scene. A person will select different metering modes based on his ability to use the scene to correctly set exposure. An example I've already given is blue sky and the sunny side of green grass. Spot metering either will set your exposure to the midpoint of the DR of the scene. That means that objects with a tone similar to middle gray will come out correctly exposed (such as blue sky and grass,) and objects that are very bright or objects that are very dark risk falling outside of the available DR of the camera. If that happens then you simply have to make a decision on the DR of the scene, and adjust accordingly.

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[gisle]

What I had read was that digital cameras cannot capture the entire tonal range, only a small portion of it,

A small nitpick You're mixing dynamic range (DR) and total range . Maximum tonal range in digital photography is determined by the number of bits used to represent digital data. Maximum dynamic range by the difference in stops (or EV) between the sensor's noise floor and full well capacity. You are obviously talking about dynamic range here, not tonal range, so I'll just assume that this is what you said.

(For a lot more details, see this article for details: http://dpanswers.com/content/tech_zonesystem.php )

(the 5 stops shown on a histogram).

But that the whole tonal range is actually larger than that, lets say 10 stops for the sake of example since I can't remember the actual number.

Another nitpick: The maximum dynamic range is now about 13.9 stops for the best sensors available http://www.dxomark.com/index.php/Cameras/Camera-Sensor-Database/Nikon/D7000 - I've never heard of a digital sensor as bad as 5 stops.

But your point is clear: You want to discuss what happens when DR of a scene is bigger than the maximum DR that can be recorded by the camera. Say the scene spans 20 stops, and the maximum DR of the camera is 13 stops.

So out of those 10 stops, the camera basically would slide its 5 stop histogram bracket up and down this scale. A darker image would perhaps use brackets 2-6, and a lighter image would perhaps use brackets 4-9. Effectively changing the range that the camera picks up, and altering the final picture.

Yup, but only in one of the automatic modes (Program, Aperture priority, or Shutter priority). In these modes, the computer inside the camera changes the aperture and/or shutter speed automatically, in effect moving the histogram up and down the scale. If it is a Nikon camera using matrix metering and ADL, the computer will try very hard not to burn out any highlights (i.e. keeping the entire histogram left of the right "wall", (and, as a result, let the shadows become black). If you're using spot metering, the computer will position whatever you are metering right in the middle of the histogram. If that results in the shadows becoming completely black and/or the highlights becoming completely white, that is the way it is.

Perhaps this was wrong info? Or perhaps it doesn't apply to manual mode?

No, it doesn't apply to manual mode. In manual mode, the computer doesn't change anything for you. Instead, it will use the little on-screen light meter readout to tell you how much the current settings for aperture and shutter speed will be "off" from what the computer thinks is the "best" exposure. ANd what the computer thinks is "best" is influenced by the mode you've set - spot, matrix, or centre weighted will meter different areas of the scene. But this meter readout is just data that you can choose to ignore if you want to.

90% of my picture taking is always in manual mode, and I had assumed this still applied because the picture preview on the lcd would still change dramatically depending on the brightness of the object you were pointing at, however I just did a test photographing a light bulb directly, and also indirectly, and although the preview did change drastically, the final picture was the same brightness.

Yes, this is how the camera is supposed to behave.

But if that's the case, then why is metering type even an option in manual mode if it doesn't change anything?

Because it is nice to see what the camera's computer "think" is the right exposure for whatever mode is set. At least, I think it is sometimes helpful to see this. If you're not interested in this information, just ignore it.

Is the sole reason of choosing a type of metering in manual mode simply to determine what area of the image effects the readings of the little on screen light meter,

Yes.

but doesn't change photo composition at all?

Yes again. In manual mode, you're in control - the computer does not interfere with the settings.
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– gisle [ See profile/plan for equipment list ]

 

[Red13]

It is possible I may have gotten confused over some possibly bad info in the past. I tried to find this info again, but could not find it anywhere.

If this thread represents your experieince; I would say it is possible for you to be confused.

What I had read was that digital cameras cannot capture the entire tonal range, only a small portion of it, (the 5 stops shown on a histogram). But that the whole tonal range is actually larger than that, lets say 10 stops for the sake of example since I can't remember the actual number.
Perhaps this was wrong info? Or perhaps it doesn't apply to manual mode?

Cameras, digital or film only capture and process a portion of the available light. The output or image is representational of reality. That is all. Some cameras will capture more dynamic and tonal range but the goal of camera design is to represent what the camera processes as a realistic representation.

Your output device will most likely not output the exact same representation of the camera capture. This is particularly true of printing. Everything is a representation of reality not an exact copy.

But if that's the case, then why is metering type even an option in manual mode if it doesn't change anything?

True but it will give the photographer feedback on his choices which may be helpful.

Mike

 

[John Deerfield]

Disclaimer: I haven't read this whole thread, just bit's and piece's.

Metering is based off of 18% gray (though some will say 12%). A camera meter is a reflective metering. That is to say it read the light being reflected back at it. This simply means that if you spot meter off of something black, the camera will try to turn it gray (over expose). If you spot meter off of something white, the camera will turn it gray (under expose). If you spot meter off something gray, you will get gray! Conversely, an incident light meter will read the light falling on the subject and return the neutral gray value (thus blacks is black, white is white). Once you understand how all of this works, you can begin to control the situation. As example, if you spot metering off of a highlight you wish to protect (with your cameras reflective metering), you will learn that you need to add about 2 and 1/3 stops of EV in order to accomplish this.

Now, I haven't shot with Canon in a few years, but when I did, their histogram was divided into 5-sections. And as a rule of thumb, each section represented about one f/stop of EV. Meaning that if your highlight was at the 4th line, you needed about one stop more EV to brighten it up. This wasn't scientific by any means, just a guideline. Personally, I like the Nikon histogram better. It is divided into four parts, giving you a middle line. The middle line is 18% gray. If you take a picture of a properly exposed 18% gray card, either camera's histogram should be right down the middle, you just have a middle line on the Nikon. Now to interpret the histogram, one must think about how many values there are above and below 18% gray and adjust accordingly.

There is no doubt that camera capture less dynamic range than the human eye/brain can see. I once read that we can "see" about 20-stops. You can be fairly safe in saying that most DSLR's capture 5-6 stops. If you shoot Raw and post-process, you can pick up an additional stop or 2. From what I remember, film had a dynamic range of roughly 7-stops and you can match that now-a-days shooting Raw. And keep in mind that these are all generalities. Different film, different sensors, different lighting, different testing methods, and so on and so forth will all impact these generalities. But for purposes of metering and understanding the histogram, the most accurate advice you can be given is that the middle of the histogram is 18% gray. I have tested my Nikon D300s and know that I need to add 2 2/3 stops if I spot meter off of a white highlight if I want to protect that highlight (which means I have about an 7-stop "everyday" range shooting Raw with a D300s; according to the "testing" it has over 12). I say almost 7 because I need + 2 2/3 for the highlights, and black with detail is four stops under middle gray: 6 2/3rds stops.

In the end, you just need to understand that the camera is a reflective meter: white will be gray. Black will be gray. Gray will be gray. It doesn't matter which mode you use: average, center, spot. The mode just determines how much of the scene is actually metered: all of it, weighted in the center, or just a spot (and some cameras attach the spot metering to the focus point). When reviewing the histogram, just realize that the center of the histogram is 18% gray. Initially, many people might look at a histogram very heavy on the left and conclude the image is under exposed. A better way to look at it is to judge how much of the scene is above or below 18% gray. If the scene is primarily below 18% gray, then having a bunch of pixels on the left would be a "proper" histogram!

 

[dradam]

It is possible I may have gotten confused over some possibly bad info in the past. I tried to find this info again, but could not find it anywhere.

You either had bad information or came away with a poor understanding of good information.

Either way you should get yourself some good information and take the time to understand it. This http://www.cambridgeincolour.com/ is one of the best learning sites I've ever found (DPReview has some good tutorials too). Take the time to read it over and make sure you understand what it is saying. Especially start with exposure, metering, and dynamic range. These are different concepts that you seem to be confusing for eachother.

 

[Dewight McMullen]

But if that's the case, then why is metering type even an option in manual mode if it doesn't change anything? Is the sole reason of choosing a type of metering in manual mode simply to determine what area of the image effects the readings of the little on screen light meter, but doesn't change photo composition at all?

The thing to keep in mind is that the meter is telling you what it thinks the shutter and aperture needs to be to achieve and "average exposure", where average has been defined by some bit of computer code. As others have pointed out the meter readings you see is just a suggestion which you are free to ignore.

Now, the various meter modes are allowing you to decide how much of the light falling on the scene you want the meter to use when computing its "suggested" settings. If I'm in manual mode and shooting someone on a stage and I want to make sure my subject is well exposed. I might want to know how much my chosen setting deviate from my camera's idea of an average exposure. I could select spot metering and the center focusing point to do this. By watching my meter readings, I can tell when any change in the light falling on my subject will need me to change my shutter or aperture in order to maintain the exposure I want.

In short, the various metering modes are helpful even when in manual mode as it gives you metering reference point based upon your decision regarding the parts of the scene you want to consider when setting your shutter and f-stop. From that reference point, you can then decide how to expose the shot to get the pic you want by under or overexposing the shot as much as you like.

 

[carl1864]

Thanks for all the detailed replies. Picked up a lot of new and useful info.

I actually did have a better understanding for things before I read whatever that one article was that I had read, that actually put me on the wrong track, making me think the metering still changed things even in manual mode. Now I'm back on the right track though, and with a better understanding of the whole metering process.

 

[skyglider]

One function that always seems to be missing is the ability to control the metering, beyond just choosing spot, center weighted, etc. Even when you have your ISO, Aperture, Shutter, flash, etc. locked in, the cameras still want to handle the metering automatically, Often in tough lighting situations leading to highlights being over exposed, or else shadows being underexposed, and you don't seem to have much choice or fine control over it except just aiming the camera around till the auto metering gets it right. Why not allow control over this?

Hi Carl1864,

Having just quick scanned your thread, you received excellent detailed answers and you now have a handle on your question. I just wanted to add this which may be redundant but in simpler terms, if not for you, maybe for other beginners that got lost in the details.

Even compact digital cameras (usually higher end ones) can give you the metering you appear to be seeking. Look for a camera that displays a live histogram and offers quick exposure compensation control. Pressing a navigation button brings up the exposure compensation slider and then pressing the left/right navigation buttons moves the slider to control the exposure compenstion.

While looking at the live histogram, move the slider so the right side of the display is not clipped. This will insure that the highlights are not blown out. You can usually recover the low lighting in post but blown highlights are lost forever.

For beginners who want to check this method before buying, Panasonic compacts like the ZS series can display a live histogram by pressing the display button repeatedly. Then press the "up" navigation button to display the exposure compensation slider. Another compact is the Nikon S8100/S9100. It uses the "right" navigation button to bring up the exposure compensation slider. There are many others but these two may be available on the demo display to check it out.

This method is practical using compacts that can bring up the exposure compensation using a button. If one has to go into a menu to get to the exposure compensation, it becomes a chore.

Sky

 

[Horiz Opposed]

I think many folks have answered this for you very well.

I would just like people to remember that this is a beginner forum. If you can't be patient with a beginner's question, maybe this isn't the forum for you.

Some of the P/S cameras have manual control and you need to look for one that does if you want that control. Or, move to a DSLR. From what I've seen, more P/S do not have manual than those that do.

When the camera is in manual mode, you pick the exposure yourself and the meter will simply be telling you it thinks you are over, under or properly exposed. IOW, the exposure will be what it will be based on your aperture, and shutter speed selection.

The way it reads the scene (spot, center weighted, etc) is simply a way of you selecting how you want the meter to calculate it's reading. On manual it will not affect the exposure.

Apologies for duplicating answers of previous posters who have covered this.
--
Ross Attix

 

[skyglider]

For beginners who want to check this method before buying, Panasonic compacts like the ZS series can display a live histogram by pressing the display button repeatedly. Then press the "up" navigation button to display the exposure compensation slider. Another compact is the Nikon S8100/S9100. It uses the "right" navigation button to bring up the exposure compensation slider. There are many others but these two may be available on the demo display to check it out.

Realized that I should have mentioned that viewing the live histogram and adjusting exposure compensation doesn't work in full auto mode.

For example, the Panasonic ZS series cameras have the PASM modes. P=Program, A=Auto, S=Scene, M=Manual. Set the camera to "P" mode first before trying the method described above.

needs to be set to "Program" mode