Judging Exposure Confusion

weepete

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Hi all,

I've heard said a few times now that you should never judge the exposure by using the LCD screen on the back of the camera, but this has got me a bit confused. Given that a histogram is just the graphical representation of the value of the pixels for that image really the only thing it can tell me is whither I've clipped the shadows or highlights. I could in theory take a picture with a normal looking histogram, no clipping, in which the subject could be exposed incorrectly. Add to this the fact that the in camera meter not allways right and can also produce a picture in which the subject is not properly exposed.

So if I can't trust the camera meter, can't tell from the histogram and not supposed to use the LCD how on earth am I meant to judge the correct exposure in camera?
 

cgipson1

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Hi all,

I've heard said a few times now that you should never judge the exposure by using the LCD screen on the back of the camera, but this has got me a bit confused. Given that a histogram is just the graphical representation of the value of the pixels for that image really the only thing it can tell me is whither I've clipped the shadows or highlights. I could in theory take a picture with a normal looking histogram, no clipping, in which the subject could be exposed incorrectly. Add to this the fact that the in camera meter not allways right and can also produce a picture in which the subject is not properly exposed.

So if I can't trust the camera meter, can't tell from the histogram and not supposed to use the LCD how on earth am I meant to judge the correct exposure in camera?

The meter is OK... and will always give a reading! With experience, you will know how to integrate the meter reading with the subject /foreground / background to get the exposure you want. A lot depends on how you meter (single point, wide matrix, etc...).

If you have a white subject (SNOW?), the meter will try to make it gray (12% or 18%)... and it is up to you to know that you need to overexpose that subject 1.5 to 2 stops. The meter read it correctly... the meter just doesn't read white... it reads gray.

If you have a very contrasty subject... you may need to pick where and what you want to meter (at 12% or 18% gray) to properly expose what you want exposed... not what the camera GUESSES you want exposed.

In my opinion, if properly used... you can almost always trust the camera meter. And the histogram is what will confirm that. (but don't trust the LCD)

Some useful reading on Histgrams:

http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml

http://digital-photography-school.com/how-to-read-and-use-histograms
 
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amolitor

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The LCD screen is very hard to read properly. Mine, for instance, happens to render pictures as if they have rather more exposure than they do. If I am eyeballing by LCD, I need it to look substantially OVER exposed on the back of the camera, for the shot to be exposed right. At least some of this depends on how you have set your camera up (you can probably adjust the degree of LCD backlight) and what the ambient lighting conditions are. I have not investigated because I don't much care, but I suspect that I have the backlight turned up quite high, which makes the LCD rendering appear much brighter than the actual picture is.

The histogram gives additional information, as you stated it tells you about clipping, but it also gives you a rough idea of how the tones look overall.

The histogram needs to be looked at in the context of what you're shooting, though. If you're shooting a dark mass with a few bright things in it, you might get two lumps on the histogram, a big one for "most of the frame" down toward the bottom, and a smaller one up toward the top for the "little bright things".

A more normal scene will be one big wide lump which should be centered, or if you prefer, placed as far to the right as possible without clipping.

The meter provides yet more different information, depending on how you use it. You can spot meter bits and pieces of your scene, and set exposure accordingly.

There's a lot of stuff in play. It's really almost surprising how often just doing what the meter tells you will produce pretty much what you want.
 

KmH

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To consistently make high quality digital images requires obtaining a good fundamental understanding of how digital images are made so you can control the process.
In the days of film, the lab that developed the film handled most of that for the photographer. Today's digital photographer has to have that knowledge, because so much of the image development process is now done in the camera.

a picture with a normal looking histogram
There is no normal looking histogram. Scene content determines what should be 'normal'.
A accurate exposure of a white dog on a snow covered field will produce a very different histogram than the histogram of an accurate exposure of a black dog on an asphalt parking lot.

The rear LCD view of a photo can't be used to accurately judge exposure because:
1. It isn't a calibrated display, and can't be calibrated.
2. It can only show a JPEG thumbnail.
3. The ambient light falling on it is inconsistent, which impacts how it displays an image.

Understanding Digital Camera Histograms: Tones and Contrast
Understanding Digital Camera Histograms: Luminosity and Color
Optimizing Exposure
ETTR
http://wwwimages.adobe.com/www.adob...e/en/products/photoshop/pdfs/linear_gamma.pdf
 

KenC

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With experience the histogram will tell you what you need to know. Until then, you do the best you can with it and whatever info you can get from the displayed jpg.
 

Dao

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I sometimes use spot meter and point it to an area where I think the camera can get me a correct exposure and then press the exposure lock button.

i.e.
Pointing at the human face/skin.
Pointing at the grass.
Pointing at the grey colour object.

And definitely not black or white.
 

cgipson1

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I sometimes use spot meter and point it to an area where I think the camera can get me a correct exposure and then press the exposure lock button.

i.e.
Pointing at the human face/skin.
Pointing at the grass.
Pointing at the grey colour object.

And definitely not black or white.

Black and White is fine... (and sometimes a good point to judge from), as long as you dial in proper EC.
 

480sparky

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..........And definitely not black or white.

Spot metering the brightest and the darkest parts will give you the dynamic range of the scene. This is valuable in comparing to the dynamic range your camera is capable of.
 

hirejn

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You can trust the camera meter 100% -- to expose every subject for 18% gray. Easier said than done, which is why I prefer an incident meter.

The LCD got a bad rap probably from the early days when it might not have been accurate. With new cameras, some of the LCDs are even calibrated for accuracy, and many pros judge lighting by the LCD, so the notion that the LCD is useless is garbage. If the brightness is set to neutral, in many instances a quick look at the LCD gets you in the ballpark. So the answer is you can use the LCD as a confirmation of informed exposure. But if you don't know how to expose and the LCD is max brightness, then you're guessing.

I think not understanding exposure is a big reason people have problems with the LCD and historgram: They use those tools to make an exposure instead of the right tool -- their brains. If you simply let the meter tell you what to do, then you're not really making an informed exposure and therefore you won't be able to predict what the shot should look like. But if you have a system and understand it, you will know before you take the shot what it should look like, and thus the LCD will be a good confirmation. With experience, you can use the review to make a quick adjustment and know you got it. If you don't understand exposure or don't use an incident meter, you can't do this.

The histogram also gets a bad rap. The problem with a histogram is you don't know what a histogram should look like. Every shot is different. A low key shot will have the histogram more to the left and it will look underexposed but will be accurate for the shot. But it's a valuable tool. If you already know how to meter and expose, the histogram is a better blinky. The blinkies tell me only whether highlights are blown out, not by how much, so for me the histogram has an advantage. It tells me how much the highlights are blown out, and I can make a quick adjustment. Even when incident metering, the reading can be off by a third stop, so a quick check of the histogram confirms that I have detail in the highlights.

The other problem with blinkies is if they're not blinking, you can't just assume the exposure is perfect. Again the historgram tells me how much detail is in the highlights, and it might be too much. For example, the histogram might go no further than the center, but I know the scene has highlights so it should be further right. The blinkies can't tell you this. The histo is also an essential for "shooting to the right," or maximizing highlight detail. For anything other than highlights or shadows, the histogram is not practical to decipher accurately. It's one more tool that can help you see how close your exposure is, but it doesn't do everything. Some people hate it but I have a way of using it that helps me.

So, the only way to know is to use an incident meter or have a lot of experience with reflective metering. The LCD, blinkies and historgram are just tools to help you gauge exposure. They are not tools by which to begin an exposure. In reality, with today's RAW files and software, being off by a half stop isn't huge. Being off by a third is nothing because a slight tilt of the incident meter can do that, and the meter could be off by a 10th of a stop from a given reading. If you're off by more than half, then you need to get better at metering and exposure because there's no sense fixing stuff when you can do it right in camera. The closer you are, the more time you save in post.
 
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candidchick

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Sounds like you are little more inexperience when it comes to histograms and metering, and that's why you are here. I understand its frustrating and confusing. I myself have been learning more and more about it too, as I am doing photography classes and have to meter and use histograms to get the exposure. I would suggest in investing in a 18% gray card, and they're really cheap on Amazon. Zooming in onto the gray card and metering off it will help with exposures, and to know weather to overexpose or underexpose but one or two stops, like on snow, or if its just right when you do meter and adjust the settings. Light meters help also but those can be on the pricey side. Bracketing is your friend and that's what people use to do with film cameras. (bracketing is a technique of taking several shots of the same subject using different settings aka exposures)
 

bratkinson

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As I've said in another thread, I tend to be a 'lazy' amateur photographer. I like to let the camera 'tell me' what it wants to do, then take that as a 'starting point' for what =I= want to do. I'm fairly new to using the histogram (about a year or so), so although I don't pretend to really 'know' it, I do use it.

As the authors above have clearly noted, there are conditions the histogram is just plain wrong. A white dog in the snow is a good example. The meter gets 'faked out' for whatever reason (choice of metering area, mode, etc) and then the camera takes an incorrect exposure.

So I am always on the lookout for oddball metering situations. I had one recently with a single spotlight on the subject, and comparatively dim lighting for the background, which I wanted to capture as well. Since I am using center-weighted metering, the camera metered the brightly lit subject without regard to the background. My first shot or two had a perfectly exposed subject and mostly black background. It didn't help there was a black curtain behind the group of people behind him, either. The histogram was 'slightly to the right' so I was happy with that.

But in looking at the darker areas on the LCD, I could not make out any faces of the people outside the spotlight. So I opened a little wider and slowed the shutter a tad (who counts stops? I certainly don't!) and then looked at the resultant picture(s) in the LCD. The 5D3 has the ability to 'zoom in' on the picture being viewed and that was worth its weight in gold that night. I could make out the background faces, but the face of the subject was then overexposed.

So I 'backed off' my settings a bit and took a couple of compromise shots. Those are the shots I used in Lightroom. I simply used the exposure sliders to reduce the highlights a bit more and increase the dark areas a tad to get the results I wanted. Problem solved. By the way...that's the primary reason I shoot in raw mode...more latitude in post-processing.
 
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480sparky

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.......A white dog in the snow is a good example. The meter gets 'faked out' for whatever reason (choice of metering area, mode, etc) and then the camera takes an incorrect exposure. ...........


Two prime examples:

Circus2WH.jpg


SlidingSnowOEWH.jpg
 

Ysarex

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So if I can't trust the camera meter, can't tell from the histogram and not supposed to use the LCD how on earth am I meant to judge the correct exposure in camera?

You want to rely on your meter. A hand incident meter as already noted is the most accurate tool but that is often an impractical and/or time-consuming solution. If you decide not to go that route then you fall back on the reflected light meter built into the camera. And I agree with Charlie -- it's OK. You can trust the meter in the camera and learn to use it. You just have to use it intelligently and that takes some practice and experience. Step one in that process: You have to test it.

Using the camera meter then with the controls on manual will allow you to add the necessary "spin" to the exposure based on your evaluation. An alternative that can provide equal results is to learn to use the camera's AEL function and exposure comp. control. Either method will allow you to begin with the metered exposure and then tweak it. How the meter returns a reading is important. You typically have metering modes ranging from evaluative to weighted to spot. I'm going to recommend that a fairly tight center or spot reading is the most useful and makes sense if you plan to evaluate the scene and use the meter as a tool.

Depending on how you're working there's an important qualification about the camera histogram that hasn't been mentioned. The data presented by the camera histogram is derived from the camera's JPEG processor and as such is an interpretation and not a direct reflection of the sensor's exposure. This doesn't matter if the camera JPEG is your goal. In that case the histogram is providing you with good information. However, if your goal is the sensor raw data then the camera histogram is not giving you good information. Are you trying to expose for the best out of camera JPEG or are you trying to expose for the most usable raw file? Those are two very different targets. For example, on my camera when the histogram indicates that I've begun to clip the highlights, I know I need to add a little more exposure for best results and my highlights won't be clipped in the raw file.

Setting a camera exposure has to be one piece of the larger puzzle. For example learning to meter a portrait subject's face for good exposure without evaluating the lighting of the entire scene and assessing the scene contrast is learning to practice fauxtography exposure -- more is required. Getting a good exposure requires that you consciously evaluate the scene lighting and correctly judge the lighting contrast. In theory that's what evaluative metering is supposed to be doing in a modern camera. In practice you can do a better and more precise job with some careful time spent practicing. A note about the hand incident meter relative to this point: An incident meter is very accurate and useful to read the light intensity striking the subject. It's much less useful in measuring the contrast range of the scene.

An assessment of the lighting and scene contrast range can result in the conclusion that no workable exposure for the scene is possible and unless you fix the lighting you should walk away. This is a really critical point to stress. Many photographers erroneously think they got a bad exposure for a shot when it fact there was never a good exposure possible given the lighting condition. It's entirely the photographer's job to make that assessment up front. Neither the camera meter nor a hand meter can do that. And finally this assessment of the scene lighting has to be tailored to the output target. Are you capturing a camera processed JPEG or are you capturing a raw file that you plan to process?

Joe
 

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