# Photography Basics - Exposure



## Sylvanite

Some time ago, I was in the hospital for tests and had to wear a gown that fastened in the back - with nothing on underneath.  Walking down the halls, I definitely felt "over-exposed".  That is not, however, what I plan to discuss today.

No, by "exposure", I mean controlling how bright one's photograph turns out.  An overexposed photo is too light.  An underexposed photo is too dark.  A correctly exposed photograph looks exactly as bright the photographer intended it too look.

Signs of overexposure include: 
Loss of detail in the highlights - which we call "blown out".  
A general pale appearance.
Colors that lose their vibrancy - that is they appear pastel or "washed out".
Signs of underexposure include:
Loss of shadow detail.
An overall dark appearance.
Low contrast, which produces a dull, or "muddy" tone.
A correctly exposed pen photograph will show good detail in both the shadows and the highlights, and have rich, vibrant colors.

There are three things that control exposure in todays digital cameras:
Aperture.
Shutter speed.
Sensitivity (a.k.a. "ISO setting").
Just like the iris of the human eye, which opens and closes in response to brightness, the camera lens contains an adjustable "aperture" that controls how much light passes through.  A wide aperture setting admits more light; a narrow aperture transmits less.  Aperture setting is measured by "f-stop".  A lower f-stop means a wider aperture.  A higher f-stop means a narrower aperture.  Many people find this counter-intuitive, as higher values admit less light.  They are also numbered in a way that makes sense mathematically, but not to most users.  Aperture affects depth-of-field, which is the topic of a another discussion.

The camera body has a "shutter", which opens to expose the image sensor to light, and shuts again when done.  The duration that the shutter is open is the shutter speed.  It is typically measured in fractions of a second.  The longer the shutter is open (the slower the shutter speed), the brighter the exposure.  Very slow shutter speeds can lead to blur if the camera or the subject move at all.

For film cameras, different photographic films are available that have different sensitivities to light.  "Faster" films, that have higher "ASA" or "ISO" ratings, react more quickly to light.  Digital cameras typically have an adjustable sensitivity usually called the "ISO setting".  Just like with film, a higher value means the sensor is more sensitive to light and will produce brighter images.  The downside to higher sensitivity is increased noise.  On film, that noise is referred to as "grain".  In digital cameras it typically shows up as "pixelization".

In automatic modes, a digital camera will adjust aperture, shutter speed, and ISO setting to control the exposure.  The results are generally acceptable for most snapshots, but often disappointing for staged pen pictures.  For the best quality photographs, one needs to take control of these settings.

Some controls to set exposure:
*Macro*.  Many cameras have a close-up or "macro" mode.  It's typically indicated by a flower icon.  What exactly this mode does varies by manufacturer.  Generally, it will favor moderate to small aperture and balance the other two settings accordingly.
*Landscape*.  Again, the exact details are brand/camera specific, but "landscape" mode favors small apertures.  The camera sets shutter speed and (possibly) sensitivity as well.
*Aperture priority*.  In this mode, you pick the specific aperture you want, and the camera sets the shutter speed accordingly.  It may also set the sensitivity, or you may specify the ISO setting.  Check your camera manual for details.
*Aperture priority with exposure compensation*.  Sometimes, the built-in light meter simply doesn't do what you want (often when using a white or black background) and over or underexposes a picture.  To handle such situations, many cameras have an "exposure compensation" setting.  It allows you to increase or decrease the exposure - usually by some number of "EV units".  Each EV unit will halve or double the shutter speed.
*Manual*.  Most digital cameras have a manual mode, which allows you to pick the aperture, shutter speed, and ISO setting you want.  This gives you complete control of the exposure.
Some additional helpful camera features:
*Exposure bracketing*.  Some cameras can take multiple pictures, varying the exposure.  Then you can pick which one looks best later.
*Histogram*.  A histogram is a graph that shows how much of a picture is how bright.  Many cameras have a built-in histogram display.  If the histogram shows a peak at the very left, the photo is probably underexposed.  A peak on the right inidcates overexposure.  You can adjust exposure accordingly.
*Blowout indicator*.  When previewing a photo, some camera viewscreens blink in areas that are overexposed.  That might indicate a need to change exposure.
About "f-stop":

  Remember I said that f-stop numbering makes sense mathematically, but not intuitively?  Well, that's because f-stop is a measure of diameter, and the amount of light the aperture lets through is proportional to the square root of 2.  F-stops are conventionally numbered: 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc.  Many camera lenses permit adjustments between these values, but each full f-stop increase lets in half as much light (remembering that higher f-stop value means smaller aperture).  So (keeping ISO constant), if you want to maintain a given exposure, for each single increase in f-stop, you'd need to halve the shutter speed (double the exposure time).

Whew, that's a lot of information.  Does it help you take pen photos?  Probably not, but it's necessary groundwork to understand for later discussions.  I plan to present some of those topics in future threads.

I hope that was interesting,
Eric


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## Brian G

Thank you for posting this.  I look forward to the next topics.


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## lorbay

All thought very confusing I understand this completely . I just have to wrap my mind around it. I love your picture taking abilities.
Lin


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## Boz

A well done and concise tutorial on the basics of exposure.  I work as a curator for a photography museum and work with a lot of educators who bemoan the fact that in the digital world the students don't think they need to know the basics like this.  They just think you set the camera to A mode and shoot.  Most of the good teachers make the students memorize the f-stop string then the shutter speed string.  If you don't have a firm grasp of the basic variables you are dealing with then how can you hope to do advanced work?


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## Sylvanite

*Exposure Compensation*

I wanted to add a bit on the topic of "exposure compensation", as I see people referencing it when describing their pictures.  I'd like to point out that when manually setting the exposure (ISO, Aperture, and shutter speed), "exposure compensation" does not do anything at all.   This is a camera setting that is only active in automatic exposure modes.

So, if you are using an auto-exposure mode (anything from fully automatic to aperture priority), then the camera's built-in light meter will pick one or more settings based on what it thinks will produce an even exposure.  While that generally works well in many situations, it can fall short in product photography - especially if you have a white or a black background.  The camera will try to make the background gray, resulting in a photo that is either overexposed (black background) or underexposed (white background).  The "exposure compensation" feature is a control that lets you tell the camera that you deliberately want to underexpose or overexpose the photo (from what the light meter reads).

That way, if you have a black background, you can set the exposure compensation to underexpose the picture, which cancels the camera's tendency to overexpose.  Likewise, setting exposure compensation to overexpose when using a white background will correct for the camera's innate underexposure.

Of course, if you're using manual settings, you can dial in the exact values you want.  You don't have to trick the camera with exposure compensation.

I hope that helps,
Eric


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## Cwalker935

Ocassionally when shooting in manual mode, my light meter will indicate a setting that results in over exposure. I can see this on the digital screen and typically take additional shots by picking shutter speeds that looks right on the digital screen. What would cause this?

Thanks for your informative posts and I look forward to your depth of field discussion.


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## Sylvanite

Cwalker935 said:


> Ocassionally when shooting in manual mode, my light meter will indicate a setting that results in over exposure. I can see this on the digital screen and typically take additional shots by picking shutter speeds that looks right on the digital screen. What would cause this?
> 
> Thanks for your informative posts and I look forward to your depth of field discussion.


I'm not quite sure what you're asking.  Do you mean that your photos are coming out overexposed, or that the camera has an indicator that shows its light meter thinks your settings will result in an overexposure?  When shooting in manual exposure mode, my Canon 60D displays (in the viewfinder) a scale that tells just how much the camera meter thinks the photo will be over or underexposed.  If I know the reason for that and want to keep my settings, I ignore it.  Otherwise, I might change the exposure.

The Depth-of-Field topic is at http://www.penturners.org/forum/f24/photography-basics-depth-field-116545/.  

I hope that helps,
Eric


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## Cwalker935

Sylvanite said:


> Cwalker935 said:
> 
> 
> 
> Ocassionally when shooting in manual mode, my light meter will indicate a setting that results in over exposure. I can see this on the digital screen and typically take additional shots by picking shutter speeds that looks right on the digital screen. What would cause this?
> 
> Thanks for your informative posts and I look forward to your depth of field discussion.
> 
> 
> 
> I'm not quite sure what you're asking.  Do you mean that your photos are coming out overexposed, or that the camera has an indicator that shows its light meter thinks your settings will result in an overexposure?  When shooting in manual exposure mode, my Canon 60D displays (in the viewfinder) a scale that tells just how much the camera meter thinks the photo will be over or underexposed.  If I know the reason for that and want to keep my settings, I ignore it.  Otherwise, I might change the exposure.
> 
> The Depth-of-Field topic is at http://www.penturners.org/forum/f24/photography-basics-depth-field-116545/.
> 
> I hope that helps,
> Eric
Click to expand...


The photos are sometimes over exposed when the meter on my olympus indicates the exposure compensation value is 0. 

Thanks


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## studioseven

My very first camera was an East German 35mm Pratika, 100% manual.  I had to learn the hard way.  Thanks for the info.

Seven


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## Ted iin Michigan

Duane - me, too!!! I had the LTL. Max shutter was 1/500. But I loved that camera (prob because it was my first).


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## Boz

OK think of it this way.  The camera sees everything as 18% grey. The standard of the photo industry.  If your background is black the meter will see it as grey and give you an exposure that will appear overexposed because it sees the black as grey.  Same with white.  It will underexpose to try and make the white background grey.  If you are in manual mode you have to compensate a couple of stops up or down to achieve correct exposure.


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## Cwalker935

Boz said:


> OK think of it this way.  The camera sees everything as 18% grey. The standard of the photo industry.  If your background is black the meter will see it as grey and give you an exposure that will appear overexposed because it sees the black as grey.  Same with white.  It will underexpose to try and make the white background grey.  If you are in manual mode you have to compensate a couple of stops up or down to achieve correct exposure.



That helps and is consistent with what I just experienced.  

Compensation value 0:

View in Gallery

Compensation value -1.7:

View in Gallery

 Edited photo approximating true color:

View in Gallery


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## Sylvanite

Cwalker935 said:


> That helps and is consistent with what I just experienced.


Mark has it exactly right.  The camera does not know that you have a black background.  It's trying to make the picture average out to medium gray.  Therefore, what it reports as neutral exposure is actually overexposed.  If you want to continue using auto exposure, you can set exposure compensation (-1.75 or -2 stops from your photos).  Or, you could switch to manual exposure (provided your camera supports it) and set the ISO, aperture, and shutter speed yourself.

I hope that helps,
Eric


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## Tage

Eric,
I really appreciate this series of tutorials.  I just got a new dSLR and these will really help.   Hopefully we'll find them assembled together in the in the Library at some point.


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