Help with Shutter, aperture, and iso?

[dyckpwn]

Can somebody explain how shutter, aperture and iso affect image quality? Thank you.

 

[snowbear]

Understanding Exposure

 

[photo1x1.com]

May I humbly suggest to watch my youtube video series? While ISO really affects the image quality, the others usually don't really. They determine the look of your image.

 

[480sparky]

Understanding Exposure

We need a "Best Answer" option down with the Winner, Like etc buttons.

 

[KmH]

Understanding Camera Metering and Exposure
Understanding Depth of Field in Photography
Understanding Dynamic Range in Digital Photography
Digital Camera Image Noise: Concept and Types
Understanding White Balance
Bit Depth
Diffraction Limited Photography: Pixel Size, Aperture and Airy Disks

Nine combinations of shutter speed, lens aperture, and ISO will all deliver the same exposure. Only 1 of those combinations will be the correct 'artistic' exposure settings based on your artistic intend for the photograph.

A Stop
A stop of exposure is a fundamental photograph exposure concept.

A full 'stop' is a doubling (2x) or a halving (0.5x) of the amount of light that reaches the recording media, be it film or an electronic sensor.

Since exposure is a triad of adjustments (shutter speed, ISO, lens aperture) you can change 1, 2 or all 3 of the triad settings.

If you want 1 more stop of exposure (brighter) you can adjust just one of the 3 by 1 more stop.
Or, you can change 2 of the 3 by 1/2 more stop each for a net gain of 1 stop of exposure.
Or, you can adjust all 3 by 1/3 more stop for a net gain of 1 stop of exposure.

You can also change the triad of settings and have no change in the exposure.
If you change 1 of the 3 settings by 1 stop more exposure and change a 2nd setting by 1 stop less exposure the net change is zero.

Suppose you subtracted a stop of shutter speed to help stop subject motion, you could add a stop of lens aperture to keep the exposure the same. However, adding a stop of aperture will also affect the total DoF (depth of field) by a small amount. So, if you don't want the DoF to change you would add a stop of ISO instead, however, adding a stop of ISO will increase by some amount the image noise in the photo.

Note: DSLR cameras are set by default to adjust the exposure settings in 1/3 stop increments.
Most DSLR cameras let you change that to 1/2 stop or 1 (full) stop increments.
However, the advantage of 1/3 stop step increments is more precise control of exposure.

 

[Ysarex]

Can somebody explain how shutter, aperture and iso affect image quality? Thank you.

That's a very broad question and merits at least a short booklet. Above you have links to a book on the topic, a bunch of videos, and tutorials from a website. All contain pretty fundamental inaccuracies. Photography is like that because it's a popular avocation.

I'm not writing you a booklet but here's some basics. First you need a proper definition of exposure because the three things you asked about all share exposure in common. I assume you're using a digital camera and what you need to expose is a digital camera's sensor. Wiki's definition is a good one: "In photography, exposure is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance." Exposure (photography) - Wikipedia

Note very carefully in that definition what determines exposure: shutter speed, lens aperture and scene luminance. Scene luminance is the brightness of what you're photographing, for example a sunlit scene or a rainy day scene or an indoor scene. Scene luminance is variable (brighter in the sun, darker indoors) and also something that you often can't change. Given that "given" nature of scene luminance it's not uncommon to find abbreviated definitions of exposure as just determined by shutter speed and aperture.

So, very simple: you're going to expose the camera sensor to a quantity of light over time and you have a means to attenuate the light as it passes through the lens (aperture). Time is easy -- the shutter opens and closes and the rate is variable -- shutter speed. Open for a longer time increases exposure; open for a shorter time decreases exposure.

Likewise simple: the aperture in the lens attenuates the light passing through the lens. A larger aperture increases exposure; a smaller aperture decreases exposure. Both aperture and shutter speed can be used together to increase or decrease exposure.

Next step: Let's say during the life of your camera you take 50,000 photos. For each of those 50,000 photos, no matter how bright or dark the scene luminance, the sensor in your camera requires the exact same exposure to produce a best result, best quality photograph. Let's go ahead and quantify that. Every day the sun shines with the same brightness. (When that stops we're dead.) So with afternoon sunshine as a constant for scene luminance we can say that the sensor in your camera will get the exposure it requires with a shutter speed of 1/500th sec. and the aperture set to f/11. What we're doing quantifying this specific exposure amount is determining your camera sensor's exposure requirement. We're going to assign an indexing value to that and let the International Organization for Standardization help us. ISO is an indexing value that we use to establish the exposure requirement for our camera sensors. The exposure quantity noted above: afternoon sunshine + 1/500th sec. + f/11 is a pretty good match to ISO 200. Let's phrase that differently: An ISO 200 sensor will be well exposed on a sunny afternoon with a shutter speed of 1/500th sec. and aperture (f/stop) of f/11.

Nothing more critically determines overall photographic quality than a proper exposure.

You now have all the pieces you need to understand the graphic above. Ambient light is the scene luminance. ISO informs us of the sensor's exposure requirement and we use that information to select our two exposure determinants, shutter speed and f/stop (aperture).

Note in the above graphic that shutter speed and f/stop both determine exposure but are also independently related to other aspects of the photo. This gets directly to your question. The shutter speed is related to motion and the f/stop to focus depth or what we call depth of field. Again the shutter and motion are easy: A too slow shutter speed (below 1/100th sec. shall we say) will not freeze motion and you'll get a blurry photo because you can't hold the camera still (your motion) or your subject isn't still. You need to learn what shutter speed(s) you need for what conditions and subjects.

Depth of Field (DOF) refers to what's in focus in your photograph. For your lens to progressively render 3D depth in sharp focus you need to adjust the aperture to progressively smaller openings. An f/stop value of 2 will pass more light through the lens and reduce the DOF relative to an f/stop value of 8 which will pass less light through the lens and increase the DOF. In a landscape you may prefer more of the scene foreground and background in focus while in a portrait the opposite. You'll need to get a better understanding of the parameters that effect DOF.

Inside your camera is a light meter. It measures the scene luminance. Remember what determines exposure: scene luminance + shutter speed + aperture. The meter is a measuring tool that helps you achieve proper exposure for you camera's sensor. If you select too fast a shutter speed and to small an aperture the meter will indicate a measurement that shows underexposure -- not enough exposure, and of course the opposite should you select too slow a shutter speed or too large an aperture, overexposure -- too much exposure. Both are bad and both degrade your photo. Modern cameras set to auto/semi-auto modes use the meter measurement to automatically set the shutter and aperture. Regardless of whether the camera is setting shutter speed and aperture automatically or you're setting them directly you need the meter's measurement to determine a shutter speed and aperture combination that will properly expose the sensor. The meter, set with the sensor's ISO value, measures the scene luminance and allows you to determine an exposure appropriate for the sensor.

NOTE: that while you're making changes to the shutter speed and aperture to adjust the rendition of motion and DOF both will also effect exposure. You may have to compromise and this requires you to make choices. For example you have an ISO 200 sensor and on a sunny day your meter informs you that 1/500th sec. and f/11 will properly expose your sensor. Take a nice picture. But then clouds roll in and soon storm clouds. You like the drama in what you're seeing but your camera meter is measuring a substantial drop in scene luminance and now it's 5 stops darker (a stop is twice as much or half as much luminance). To maintain a proper exposure you must compensate for the drop in scene luminance and slow the shutter speed 5 stops to 1/15th sec. Oops! You can't hold the camera still. Then slow the shutter speed to 1/125th sec. and open the f/stop to f/4. Oops, you'd really like a little more DOF than what you get from f/4. OK, back to 1/15th sec. and set up your tripod. What do you mean no tripod? Where's your tripod?!!

Don't get caught like that, but when you do, you have one more option: you can deliberately underexpose the sensor. Your camera will allow you to set an ISO value that's higher than the true ISO rating of your camera's sensor. This will cause the meter when measuring the scene luminance to recommend a reduction in exposure that is less than the sensor's requirement -- you're going to underexpose the sensor. You can get away with that and still get a reasonable photo if you don't underexpose too much. Underexpose as little as possible but do it -- the photo is worth having. Two things happen when you raise the ISO value on the camera. As we just noted the meter recommends an exposure reduction and it's assumed you'll do that. That reduced exposure reduces the dynamic range of your sensor (you record less data) and the data you do record is noisy. The more you underexpose the nosier it gets. Underexposure produces noise. More underexposure produces more noise. ISO then tells the camera electronics to boost or brighten the recorded data in compensation by an appropriate amount that gives you an image that appears normally exposed, but is degraded by noise and by a loss of color and dynamic range.

1. Typically you don't want a blurry photo -- think shutter speed. 2. Typically you want your subject in focus and want to control how much of the foreground and background likewise appear in focus (both more or less can be good) -- think aperture. Regardless of 1. and 2. above you have to get a proper exposure for the sensor. Overexposure is just a crash and burn. But ISO allows you to adjust the meter to determine a specific amount of underexposure (introduces noise and reduces DR) and then through the camera electronics boost the brightness of your underexposed data.

Joe

 

[KmH]

Two points to consider relative to Joe's in depth post.

1. The light meter in a DSLR camera only measures reflected light (scene luminance).
The in the camera light meter is calibrated for an average scene luminance. Particularly bright, dark, or high contrast scenes are outside that average calibration and the meter in the camera is not capable of accurately metering the light. In those situations you will have to decide how much to adjust the exposure settings values to get a good exposure.

For very fine control of exposure photographers use a separate from the camera, hand held light meter that can not only measure reflected light but that can also, in turn, measure incident light, and strobe (flash) light.
Guide To Using A Hand-Held Light Meter

DSLR cameras have different light metering modes, usually 3 or 4 modes - Spot, Partial, Center-weighted, Matrix/Evaluative.
Each metering mode has a different purpose and at times you'll need to change the metering mode to suit the subject matter you're wanting to shoot.
You may want/need to meter a scene with 2 or more metering modes to sample the scene more accurately as you decide what exposure settings values to use.

2. For many photographs you will need/want to add supplemental light, either reflected ambient light, constant light from an electric light, or light from a strobe (flash). When using flash we can control the exposure of ambient light separately from light from a flash unit(s) all with a single exposure.

 

[photo1x1.com]

Hi guys,
you two are definitely right on the information you give. May I just throw in the experience I have with many people new to DSLR, or photography in general. People that do not know anything about aperture, shutter speed and iso usually are overwhelmed by too much in depth knowledge. I am a techy myself and love all the scientific background. But I have seen beginners that even gave up due to everything being way too complicated, while in fact it is not complicated at all, if you start out the easy way.
For most people that is all information they may ever need, because the percentage of people that go professional is pretty small, and those can learn the science part of it later in their career.
Hand held light meters are awesome, but people who hesitate to buy a 50mm 1.8 for $125 will hardly be interested in the cheapest Sekonic for $126, especially since that would totally swamp them, if they don´t even know hot to set manual exposure, or even use aperture priority.

I´m pretty new here in the forum, and you two are honourable long term members. While I don´t really feel entitled to raise my concern, I still think I need to humbly throw that into the discussion. What do you think?

 

[robbins.photo]

Can somebody explain how shutter, aperture and iso affect image quality? Thank you.

Ok, so extremly basic overview

Shutter speed. The higher your shutter speed the less time the shutter is open, so the less time the sensor has to accumulate light. Faster shutter speeds will require higher ISO's or lower apertures or a combination of both to achieve "correct" exposure. Higher shutter speeds are nice to have when possible, higher shutter speeds will cancel out blur caused by you moving the camera "camera shake" and will also help avoid motion blur, blur caused by the subject moving. So in general if you can achieve a higher shutter speed, it's a good thing.

Aperture: Is a measure of how wide the lens is open - the wider it is, the more light it lets in and therefore the more light you have to work with. So wider apertures mean you can lower your ISO, or increase your shutter speed, or a combination of both while maintaining correct exposure. That's the upside.

However when you open a lens wider it affects your DOF - depth of field. When your camera focuses on a certain point that point will be in focus - so it will be sharp in the resultant photo. As you move further away from that point, either closer to the camera lens or further away from it, that sharpness begins to fall off - things become less sharp the further you are away from that point of focus. The DOF determines how far you can get away from that focal point and still have things remain sharp - so a small DOF means that only those things that are at the same distance from the lens as your focal point will be sharp. Smaller DOF means that things that are not on that same plane will get blurrier quicker. Larger DOF means that more elements of the picture will be sharp even though they are further away from that plane.

So if you need more DOF, you have to "stop down the lens" - or close the aperture more. This will give you more DOF, but it also gives you less light. So again, it becomes a trade off - you can get more DOF, but you'll have to possibly reduce your shutter speed or ISO or a combination of both to maintain correct exposure.

Last but not least, ISO - as you increase ISO also start to introduce noise. Cameras will vary based on the size/quality of their sensors as to how high you can turn up the ISO before it starts becoming pretty noticeable. You'll have to figure out for yourself what ISO settings you consider to be workable, and which ones introduce to much noise. You can reduce noise using various editing programs, but again, it's a tradeoff. Reducing noise this way also reduces image sharpness.

So, basically it's a balancing act based on how much light you have to work with - if you have plenty of light it makes things easier, you can usually get higher shutter speeds and stop down the lens for better sharpness without having to push the ISO very high.

However when you start losing light, well then you have to balance the equation a bit. You need to determine based on the situation which combination of the three will give you the best results

 

[astroNikon]

All the above answers are great.

I learned in a particular way which may help you.

I first learned about Aperture / Depth of Field. Not by reading but I bought a 50mm/1.8 lens. This allowed me to see the DOF difference that wasn't obvious to me with my Kit lenses.

Then I learned more about shutter speed but taking a pic of anything that moved. squirrels, cars, airplanes, birds, etc.

Then the glue to the entire thing was the ISO and then it all fell into place.

The important aspect about if though was that I tested each aspect of the camera. I tested and tested and compared until I understood it really well. Just reading about it I wasn't able to take that theory and use it. Continuous testing of the concepts.

Knowing your camera inside out and all the functions is really important too. I bought a book specifically for that.

It is a bit overwhelming, well, totally overwhelming. But tackle one concept at a time. And don't be in a hurry to go out and do a paid photoshoot. A DSLR is not a cell phone camera, you can control a lot and if you don't get it right, it shows.

 

[Advanced Photo]

Ignore everything here. Play with the settings and figure it out first hand. It's faster and will make more sense that way when you see it for yourself.

 

[Ysarex]

Hi guys,
you two are definitely right on the information you give. May I just throw in the experience I have with many people new to DSLR, or photography in general. People that do not know anything about aperture, shutter speed and iso usually are overwhelmed by too much in depth knowledge. I am a techy myself and love all the scientific background. But I have seen beginners that even gave up due to everything being way too complicated, while in fact it is not complicated at all, if you start out the easy way.
For most people that is all information they may ever need, because the percentage of people that go professional is pretty small, and those can learn the science part of it later in their career.
Hand held light meters are awesome, but people who hesitate to buy a 50mm 1.8 for $125 will hardly be interested in the cheapest Sekonic for $126, especially since that would totally swamp them, if they don´t even know hot to set manual exposure, or even use aperture priority.

I´m pretty new here in the forum, and you two are honourable long term members. While I don´t really feel entitled to raise my concern, I still think I need to humbly throw that into the discussion. What do you think?

I think it's a legitimate question/point and a tricky problem. Basically it boils down to where to draw the line between giving a beginner useful info and encouragement and not giving them too much or any false info because it's too complicated to explain how it really works. A simpler photo example: We can count on the fact that some budding enthusiast will be along here soon enough wanting to know why they saw someone using a 35mm lens on an m4/3 camera to shoot a portrait when they had learned that a 35mm lens distorts too much to use for portraits. Originally they were probably given the easy explanation and wound up linking focal length and perspective such that they now believe perspective (and distortion) is a function of the focal length/lens and goes wherever the lens goes. Now they're confused and have to re-learn. In the meantime they've spread the fallacy to a dozen of their friends who proceeded to do the same. (So I already know I'm not going to win this one).

Even Nikon in their camera manuals describes ISO as determining the sensitivity of the camera and that raising ISO increases sensitivity. (I'm really not going to win this one). But of course that's not true. It's also not true that raising the ISO value on a digital camera makes the photo noisy or noisier. In fact it does the opposite and typically reduces the noise that is caused by underexposure. Neither is ISO a direct determinant of exposure. A correct definition of photographic exposure does not include ISO. So when we "exposure triangle" a bunch of new photographers we plant misleading ideas in their heads.

In argument for: the exposure triangle model is pretty simple and can get them up and functioning quickly with a minimum of pain. But shouldn't we at least assume and respect their intelligence and tell them, "look this model will help you quick start, but it's actually a bad fit to what's really going on." Bet you most of them would immediately ask you to tell them what's really going on.

A story: I'm a retired college prof who still does some part-time teaching. Right now I have a student in my class who is younger than me and also teaching photography. She was encouraged to sit-in my class because I was recommended as a source to help understand color management. A couple weeks ago when ISO came up in class I took the time to explain it. I noticed a look of astonishment on her face (she shoots Nikon -- note comment above). Then she says to me, "so changing ISO on a digital camera isn't the same as changing film. It's really more like pushing film isn't it?" And I said, "Exactly right. You can't change the sensitivity of the sensor but you can 'underexpose it and then overdevelop.' And what always happened to the shadow detail when you pushed film?" And she excitedly says, "OMG! it all finally makes sense. Why didn't they just tell me in the first place?" Now what was the point of keeping her in a fog? She's passing this nonsense on to her students and you can't blame her it's right there in her Nikon camera manual and probably in the textbook she uses.

There's a problem if the explanation you provide for something doesn't make logical sense when you try and think about it carefully. People end up confused. If they are interested in learning more their further learning is retard by the fog they've been placed in and the misdirection they been given. Most photographers out there in fact believe they can increase the light sensitivity of digital cameras by raising the ISO value. Should we really continue to perpetuate that and so many other fallacies?

Joe

P.S. I watched your youtube videos and applaud you for resisting the standard "ISO increases sensitivity" rubbish. Your megaphone and amplifier sliders did a good job of getting across how it really works and you used the term "increase brightness" which is a whole lot more accurate than saying exposure. ISO in a digital camera really is a post processing step that occurs after exposure. Your videos are much better than the average fare in that regard, so you're smart enough to make an adjustment that also gives them an accurate understanding of exposure: luminance + shutter speed + aperture.

 

[vintagesnaps]

The shutter opens and closes and lets in light to record an image. Shutter speed can be faster or slower. The speed is in fractions of a second. My starting point is usually 1/125 and I adjust from there; faster lets in light for less time so I go with a faster speed if it's sunny/brighter light (or if shooting sports/action). If a shutter speed is slow it can cause shutter blur unless a tripod is used. You'll need to figure out what slow speed you can use and still prevent blur (varies handheld, if you brace yourself, at what speed anyone can be still enough so images aren't blurry, etc.).

Aperture is the size of the lens opening. If larger it lets in more light; if smaller, less light. The f stop settings are a fraction of the focal length, so f8 means the lens opening is the same as 1/8 the focal length of that lens. (f8 is my usual starting point because it's midrange and I can turn and adjust it a stop or two either way).

Aperture also affects the depth of field. That's how much of the area between you/your camera and the area in front of you is in focus. A larger aperture means less area will be in focus and more of the background will be out of focus. A smaller aperture means that a larger area between your camera and what's in the distance will all be in focus.

ISO is a measure of light sensitivity. (edit - ISO stands for International Organization for Standardization; it's a standardized measure used for cameras as well as film.) If you raise it to a higher number the camera can record an image better in lower light. But often with a higher ISO there can be more grain noticeable in film images or more 'noise' in digital images. I usually only use as high an ISO as necessary to have less grain or noise. With film the ISO is determined by the film 'speed'; digitally it can be adjusted.

Use the camera's meter to let you know if you're getting a proper exposure for the light conditions in which you're taking pictures. If the meter is indicating not enough light, then raise the ISO and/or go to a slower shutter speed and/or a larger aperture. If the meter indicates too much light, then go to a lower ISO, smaller aperture, and/or faster shutter speed. It's a matter of which or if all three settings need to be adjusted.

Try practice shots of a subject changing a setting each time, write down what you did, and see what works best. It takes time and practice.

 

[TCampbell]

Here's a very well done tutorial video. It takes 10 minutes to watch the whole thing and it would clear up any confusion.


I do recommend you pick up a good book on the topic such as "Understanding Exposure" by Bryan Peterson. The Scott Kelby "Digital Photography" series is also commonly recommended. Both of these are excellent primers and written for those starting with no knowledge of photography (you don't need to worry that they'll start using terms they assume the reader understands... they'll explain the terms as they get to them.)

One last detail that I personally found helpful to know but is not typically explained in most texts or videos.

While shutter speed values make sense (you know what "1/60th" of a second means)... it's less clear what aperture values actually MEAN... what does it mean to have a lens set to "f/4" and why is the f-stop before it called "f/2.8" instead of f/3 and why is the f-stop after f/4 called f/5.6 instead of f/5 -- in other words why don't f-stops using simple counting numbers?

The answer has to do with what an f-stop is... it's a ratio that you find by dividing the focal length of the lens (in millimeters) by the physical diameter of the clear aperture (the opening in the lens). So if you have a 100mm lens and the clear opening (the area through which the light can pass) is 25mm wide, then 100 ÷ 25 = 4 so that ratio is written as "f/4" (you will sometimes see it written as 1:4, but f/4 is more common.)

By the way, the order of "full" stop values is 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, and 32 -- so what's with the wonky numbering system?

It turns out the "area" of a circle will DOUBLE if you increase the DIAMETER of that circle by the square-root of 2. The square root of 2 is approximately 1.4 (if we round to just 2 digits). So if you have a 10mm diameter circle and area = π*r^2 and r = 10mm then 10^2 = 100 and 100 * π = 314 (square millimeters and yes I rounded that value). If we increase the diameter of our circle by the square root of 2 (we'll just round that to 1.4 to keep the math easy) then our 10mm opening becomes a 14mm opening. The area of a circle 14mm across is about 616 (not precisely double, but very close and we did round off the value... if we hadn't rounded it would have been exactly double.)

So it turns out the square root of 2 (or 1.4 if we use the rounded value) is a very important value.

You'll notice that the order of f-stops multiplies each previous value by 1.4. They are basically the powers of the square root of 2.

The square root of 2 raised the 0 power = 1 (anything raised to the 0 power is 1)
The square root of 2 (or 1.4) raised to the 1 power = 1.4
The square root of 2 SQUARED is 2 again... so that's just 2.
The square root of 2 raised to the 3rd power is 2.8
The square root of 2 raised to the 4th power is 4
and we could keep going. So each "full" f-stop is based on a power of the square root of 2 AND (more importantly) what it REALLY means is that the AREA of the opening in your lens is twice as large as the previous f-stop (or half-as large if you're making the opening smaller).

It makes more sense to use these values (based on the square root of 2) rather than simple counting numbers because each "stop" worth of exposure doubles or halves the amount of light and it's easier to calculate exposures this way.

 

[Ysarex]

Here's a very well done tutorial video. It takes 10 minutes to watch the whole thing and it would clear up any confusion.

It's a nice video but the information is wrong and misleading. At 4:10 in the video they say this: "The higher the ISO the more sensitive the sensor is to light." That's just plain false. The light sensitivity of a digital sensor is fixed in manufacturer and can not be increased or decreased. Digital camera sensors do not get more sensitive to light when you change ISO.

Joe