Digital Camera Specifications Simplified
We present here a variety of topics that may answer questions about the features of digital cameras, the terminology used in digital photography, and part of the technical side of picture taking.
Last change: 8/15/11.
Click on the desired topic.
What is a Stop?
Optical vs. Digital Zoom
ISO
What Shutter Speed?
F/Stop, Shutter Speed, ISO, Together
3x, 2x, etc. Zoom
6x, 3x, etc. Binoculars Magnification
Zoom in Millimeters
Fields of View vs. Millimeters
Why Millimeters and Focal Length?
Why 35mm Equivalents?
Zoom F/Stops
Exposure Value
Exposure Compensation
Depth of Field
Spot Metering, Weighted Metering
Histograms
Crop Factor
Viewfinder Accuracy
Flash Guide Number
Image Stabilization F/Stops
How Many More Megapixels?
Sensor Size: What is 1/2.5?
A quickie: An SLR (single lens reflex) camera gives you the view through the main lens via the optical (peephole) viewfinder. Actually, all digital cameras' LCD panel viewfinders also give the view through the main lens.
Another quickie: A "prime" lens is a non-zoom lens, namely a lens with just one focal length or, when used with a particular film frame size, giving just one angle of view.
What Is One Stop?
The measurement unit or step or notch or increment most often talked about in photography is a "stop". One stop stands for a doubling or halving of the amount of light admitted to the camera for example changing the shutter speed from 1/50'th of a second to 1/100'th of a second stands for one stop less light.
The term "stop" comes from the fact that the iris or aperture plate in the lens assembly "stops" light from going through to the film or sensor except through the opening or hole or aperture provided. One stop represents the doubling or halving the area of the aperture. Increasing the diameter about 41% doubles the area; doubling the area quadruples the area for a two stop increase.
Exposure Basics in a Nutshell
Exposure, including working with ISO, works the same way for digital cameras as for film cameras.
You need enough light to take a picture.
We all know that a sunny day is brighter than a cloudy day.
The larger (wider) the lens opening (aperture) the more light gets into the camera.
But, the larger the lens opening, the more accurate focusing needs to be and the range in front of and behind the subject in which other objects will also be in reasonable focus (depth of field) will be smaller.
In general, the most limiting aspect of a camera is its maximum lens opening.
The slower the shutter speed, the more light gets into the camera.
But the slower the shutter speed, the more blur you get from moving objects and possible shaking of the camera in your hands.
The higher the ISO, the less light the camera needs to take the picture in the first place.
But the higher the ISO, the greater the graininess or speckled appearance of the picture.
Shutter speeds 1/100'th second, 1/50'th second, etc. are sometimes but not always marked as one stop differences (doublings or halvings of one another). Automatic cameras may use intermediate values
ISO is usually marked as doublings: 100, 200, 400, etc. and is usually chosen manually
If you double one thing and halve another you end up with the same exposure. Or if you double one thing and leave other things unchanged, you double the exposure, etc.
Guideline: Hazy sun gives half the light (requires twice the exposure) as bright sun. Cloudy bright is half the light of hazy sun. Heavy overcast is half the light of cloudy bright.
F/Stops, Lens Speed
The aperture settings themselves are referred to as "f/stops". The standard aperture settings f/1.4, f/2.0, f /2.8, f /4.0, f/5.6, f/8, f/11,etc. are such that each setting represents a one stop change, or a doubling or halving of the aperture area or amount of light admitted. Doubling or halving the f/stop "number", for example f/4 versus f/8, represents a fourfold increase or decrease in the area of the aperture and therefore the light intake. Don't forget that the larger the "number" (8 versus 4) the smaller the aperture. F/1.8 is about halfway between f/1.4 and f/2.0. F/3.5 is about halfway between f/2.8 and f/4.
The main problem we all run into is when the lens opening is as large as it can go and still not letting in enough light (for example indoors or at night). Then we have to make adjustments to other things like the shutter speed and deal with possible adverse consequences there.. A "faster" lens has a larger maximum aperture. A lens may be called "faster" than another because, all other things being equal, it permits using a faster shutter speed.
One other note about lens aperture is that, in general, the wider the aperture, the more subject material closer to and further away from the camera's focused distance will be out of focus. This is referred to less "depth of field" for a wider aperture. Automatic cameras usually focus on something near the center of the picture.
Outdoors on a sunny or lightly clouded day, f/8 is a good all around choice for aperture, if you can make the choice. Small point and shoot cameras may have f/8 or f/5.6 as the smallest aperture since one idiosyncrasy of light and optics is that a very small opening tends to lead to blurriness.
The term "f/stop" is more "proper" than of just "stop". The aperture setting number itself (such as 5.6) is usually preceded by a slash because the number itself is the ratio between the focal length of the lens (numerator just called "f") and the diameter of the aperture (denominator).
What Shutter Speed?
Making the shutter speed twice as fast means the film or sensor gets one stop less light. Having the shutter open for a quarter of the time, for example 1/200'th second instead of 1/50'th of a second is a two stop decrease in light intake.
Generally the faster the shutter speed, the better. The faster the shutter speed, the less likely unsteady hands holding the camera will result in a blurry picture. The faster the shutter speed, the more sharp a moving subject will be. The problem we all run into is that at the desired shutter speed not enough light gets into the camera (for example indoors or at night). Most people do not think about "shutter speed" per se (and should not have to) but when the picture comes out blurry, the corrective action is usually centered around choosing a faster shutter speed or using a tripod or other steady camera support.
Most point and shoot cameras and most automatic cameras don't tell you what the shutter speed will be for a given shot. You just have to use past experience for what lighting conditions are likely to give you a faster shutter speed.
The faster the shutter speed, the bigger the aperture (lens opening) you need, all other things being equal. Once the camera reaches its maximum aperture, you can speed up the shutter in the following ways if the camera allows you to:
* Select a higher ISO (at the risk of getting a more grainy picture),* Use less (optical) zoom, which usually results in a larger effective aperture (adding back digital zoom will not help),
* Deliberately underexpose the picture. This may be accomplished using exposure compensation.
If you are using flash bulbs, you generally have to set the shutter no faster than 1/30'th second otherwise you will not get the full benefit of the flash which takes that long to deliver all of the light output.
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The higher the ISO, the less light (per square millimeter of film or sensor area) is needed for the picture. This lets you use a faster shutter speed and/or a smaller lens opening or a lens that doesn't have such a large opening. ISO for a digital camera's works the same way as the film speed (also described using ISO) for film cameras.
If the ISO is doubled, then the camera needs one stop less light to take the picture with. If the ISO is quadrupled, then the camera needs two stops less light.
For most automatic cameras, selecting a different ISO generally does not brighten or darken the picture in typical sunlit or cloudy-bright conditions. Actually changing the ISO will not brighten or darken the picture under any non-flash conditions except when the camera reaches its limitations for f/stop and/or shutter speed. ISO, shutter speed, and f/stop all interact. For manual settings, if the ISO is doubled, the shutter speed should be twice as fast or the aperture should be set one stop smaller to get an equivalent picture.
For both film and digital cameras, the higher the ISO, the more likely or more obvious a speckled appearance in some or all parts of the picture will be seen. This is referred to as graininess in film or added noise in digital pictures. Higher ISO may be necessary for low light or flash or fast motion situations. ISO 100 or less is suggested for outdoor shots in sunlight while ISO 400 or more is suggested for nighttime or indoor shots. If you don't want to keep changing the ISO, ISO 200 is probably the best all around choice. At least with digital cameras you can change the ISO for each shot whereas with film cameras you have to wait until the roll of film is finished.Some digital cameras are better than others in this regard and you would want to read magazine or on line reviews.
"ISO" stands for International Standards Organization which has defined standards for many different products besides film and cameras.
F/Stop, Shutter Speed, ISO, Together
The f/stop, the shutter speed, and the ISO setting all interact. That is, if one of them is changed, at least one of the others must also change in order for the picture to come out the same way. In other more practical words, if the picture is coming out too dark, you must change at least one of these to brighten up the picture.
For example, if you make the aperture smaller (say, one stop less light) and you also have the shutter open twice as long (slower, one stop more), then things even out; the light admitted is the same; there is a zero stop difference.
Here is the standard series of lens aperture settings going from small (admitting less light) to large (more light):
f/64, f/45, f/32, f/22, f/16, f/11, f/8.0, f/5.6, f/4.0, f/2.8, f/2.0, f/1.4, f/1.0.
Here is a typical list of shutter speeds in one stop increments going from fast (admitting less light) to slow (more light):
1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1 second.
Here are some lists of ISO (same as ASA) settings or film speeds in one stop increments going from slow (needing more light for example needing a slower shutter speed) to fast (needing less light).
25, 50, 100, 200, 400, 800, 1600, 3200, 6400
16, 32, 64, 125, 250, 500, 1000, 2000, 4000
Suppose you choose one value from the f/stop list (as shown above), one value from the shutter speed list, and one value from an ISO list. If the picture is too dark then you must choose a setting further to the right on at least one of the lists. If the picture is too bright, choose values further to the left.
Settings can balance each other out; for example if you move two steps to the left on one list, one step to the right on a second list and one step to the right on the third list then you get a picture of the same brightness..
With most automatic cameras, you can adjust the ISO but you cannot specifically adjust the f/stop or shutter speed. In fact the camera usually does not tell you what the f/stop and shutter speed are at the moment the picture is taken.
When you zoom in (with optical zoom), the maximum available f/stop usually becomes smaller (the number is larger).
You will usually not notice any "problem" until the shutter speed ends up being so low that a red indicator appears suggesting that you might not be able to hold the camera steady for the shot or you see that the entire picture is blurred due to camera shake.
Most of the time, set this to zero.
This is more or less the same as the lighten-darken control on Polaroid instant cameras. This causes the camera to deliberately use a greater or lesser exposure than it would otherwise determine automatically. Its purpose is to bring out shadow detail in dark areas of the scene or prevent washed out highlights in bright areas but either at the expense of the other. Plus one means increase by one stop or double the amount of exposure to lighten the picture while minus one means halve the amount of exposure to darken the picture. Usually the range provided is from minus 2 (darken; one fourth the originally computed exposure) to plus 2 (lighten; four times the exposure).
If you think (or you observed on your LCD viewfinder) that you cannot hold the camera steady enough for a sharp dim light shot, try "minusing" the exposure compensation which will speed up the shutter although make the picture darker overall.
When you take two pictures of the same subject to try different amounts of exposure compensation, be sure to frame the shot (aim the camera) exactly the same way for both shots. Otherwise the camera will compute a different automatic exposure depending on light/dark scene content to begin with, then apply the exposure compensation you chose, and give unpredictable results.
You do not have to know anything about exposure value (EV) or what the EV number is when using exposure compensation. Also "exposure value" and "exposure compensation" work in opposite directions. You add value to brighten the picture using exposure compensation but you subtract from the EV number to brighten the picture if you use EV.
Optical Versus Digital Zoom
We suggest that you ignore digital zoom ratings when shopping for a camera and, if your camera has digital zoom, you adjust things so it never kicks in.
With any decent lens, optical zoom always captures more detail in the resulting scene as you zoom in.
Digital zoom never captures more detail in the resulting scene as you zoom in.
Digital zoom does no more, no less, than what you can accomplish by cropping or zooming in on the picture at the store photofinishing kiosk or at your home computer after downloading.
This is relative to that camera's widest angle view with a given lens, not to any particular absolute view angle.
Set the camera to its widest angle. If you stood at half the distance to the subject, that is the view you would get from the original distance and using 2x zoom. If you stood at one third the distance, that is the view you would get from the original distance at 3x zoom.
Set the camera to its widest angle. From the same vantage point, imagine a cross dividing the viewfinder into four equal parts. One of these quarters corresponds to the view you get with 2x zoom. Imagine lines dividing the viewfinder into thirds both vertically and horizontally, giving nine equal parts. One of these parts corresponds to the view you get with 3x zoom.
Set the camera to its widest angle and take a picture. From the same vantage point set the camera to 2x zoom and take a picture in the same direction. Repeat for 3x zoom, etc. An object still in the view at 2x zoom will be twice as wide in that picture compared with in the picture without zoom. An object still in the view at 3x zoom will be three times as wide in that picture compared with in the picture without any zoom, etc.
Using the focal length in millimeters, double the widest angle focal length to get the 2x zoom focal length, etc. For example if the widest angle is 35mm, a 3x zoom would correspond to 105mm.
When comparing two cameras, if their widest angle in 35mm equivalent focal length is different, then 2x zoom on one will be different from 2x zoom on the other. The camera with the wider widest angle will seemingly have less zoom at the equivalent 2x, 3x, etc. setting.
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Magnification in Binoculars
This works the same way as telephoto lenses or zoom lenses on cameras except that 1x corresponds to 50 mm (in 35mm film camera equivalents) rather than the 35 to 38 mm widest angle of the typical point and shoot camera. (Then 2x magnification would correspond to 100 mm and 6x would correspond to 300mm.) The field of view of the human eye corresponds to about 50mm and also the standard angle for professional cameras and SLR cameras is 50 mm.
Unfortunately most point and shoot zoom cameras do not have an indicator that tells you when they are set to exactly 50mm focal length.
It is sometimes difficult to quantify 3x, 4x, etc. in binoculars. If you look through the binoculars with just one eye, if the binoculars are 4x (or zoomed to 4x) then the bird or other object should look four times as wide through the binoculars compared with as seen by your other eye.
We have found that a digital camera with its LCD viewfinder is not a good direct viewing substitute for binoculars. The picture is too grainy given the resolution of the LCD panel. The best telescopic view obtainable using a camera is obtained, admittedly in a cumbersome way, by peering through the optical viewfinder backwards with the camera set to its widest angle. But if you forgot to bring the binoculars, we think that taking a number of pictures with a 5 megapixel camera set to 3x zoom will give you pleasing memories.
The standard jargon for referring to the field of view is in terms of what field of view a 35mm film camera gets with a lens of a given focal length in millimeters.
Unless you are or want to be a camera expert, ignore the absolute millimeter ratings for focal length such as 5-23mm marked on the digital camera's lens. Instead, compare cameras using the "35mm film camera equivalent focal length" which should be stated in the instruction manual. The "standard angle" lens for a typical point-and-shoot camera is around 35 to 38mm in focal length, and 28mm is a typical wide angle. The standard angle lens for most SLR and professional 35m film cameras is 50mm, and 38mm is considered wide angle. The most common zoom range on point and shoot cameras is 3x, typically 35 to 105mm or 38 to 115mm in 35mm film camera equivalents.
To put a given wide angle or normal angle or telephoto view on a given size film frame or sensor, the lens must be a given distance in front of the film frame or sensor (and of course must focus at that distance, hence focal length). For lens systems with several lens elements, the focal length is usually measured from somewhere between the elements; we don't have exact formulas. The smaller the film frame or sensor, the smaller the focal length for an equivalent field of view. In order to compare cameras with the same field of view and different frame/sensor sizes, the lens focal length is usually translated for discussion purposes using a "common denominator" consisting of the equivalent focal length of a lens designed for a 35mm film camera.
In the early days of photography, most precision lenses were made in Germany where millimeters and centimeters were used for measurement instead of inches.
Why 35mm Equivalents?
Just about any professional or expert photographer can relate lens focal length to field of view in 35mm film cameras.
35mm equivalent focal length is just one standard to go by when discussing and comparing how wide an angle of view one camera will take compared with another camera. (A 35mm film frame is 43-1/2 mm corner to corner and 36x24mm in size.) If the digital sensor is half the size from corner to corner, the actual focal length of a lens needed to capture the same view must be half that of the lens on the camera with the larger sensor. The 35mm equivalent focal length is defined as the focal length of a lens that would give the same field of view on a 35mm film frame.
If an interchangeable lens is taken off of one camera and installed on a camera with a different film frame or sensor size, its actual (absolute) focal length (must) stay(s) the same but its 35mm equivalent focal length is different. The lens is still projecting the same image into the camera body but the new sensor is spanning (and picking up) a different portion of the image yielding a different field of view. To obtain the new 35mm equivalent focal length, take the old 35mm equivalent, multiply by the diagonal of the old sensor and divide by the diagonal of the new sensor.
It is certainly possible to talk in terms of specific cameras, for example Canon SD700 equivalent focal length or Pentax Optio SV equivalent focal length and so on. But there are so many different cameras and sensor sizes and so many permutations of focal lengths that things would quickly become too confusing. Therefore there is just one standard, 35mm film camera equivalent focal length. If you are baking a cake with someone and all the measurements are in tablespoons, there is nothing wrong with discussing all of the the measurements in milliliters so long as the other person realizes it and understands it.
For casual shooting, it is of course much easier to use the viewfinder rather than compute degrees.
Field widths to nearest 1/4 degree
Simplified field widths to nearest 5 degrees
Lens Field Width Simplified Field Width
25mm 71.5 70
28mm 65.5 65
35mm 54.5 55
38mm 50.5 50
50mm 39.5 40
70mm 28.7 30
75mm 27 25
100mm 20.5 20
105mm 19.5 20
111mm 18.5 20-
140mm 14.5 15
150mm 13.7 15-
200mm 10.2 10
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When a zoom lens is marked f/2.8-5.6 or something like that, it specifies two numbers:
1. The maximum f/stop at widest angle,
2. The maximum f/stop at maximum zoom.
These numbers are important because they indicate how well the camera can take pictures in low light situations. Almost always the maximum available aperture is smaller at maximum zoom.
There are two other related numbers, usually not publicized:
3. The minimum f/stop at widest angle,
4. The minimum f/stop at maximum zoom.
These last two numbers only suggest limitations on the camera in extremely bright situations such as on the beach or snow scenes, and are usually not discussed much. Some point and shoot cameras do not have irises (for adjustable apertures) and these numbers will then be the same as #1 and #2 preceding, respectively.
For any zoom lens, if the aperture remains the same diameter in millimeters when the zoom is increased meaning the focal length is increased, the f/stop gets smaller. On some cameras the aperture will change automatically and the f/stop will stay the same as the zoom is varied so long as the range implied by all four numbers above is not violated.
Exposure value is a single number that stands for the amount of light (per square millimeter of film area) admitted to the camera. The whole number values: (more light) 11, 12, 13, 14, etc, (less light) stand for one stop differences i.e. doublings/halvings of the amount of light. "Exposure value one" stands for one second at f/1.0. For most daylight shooting with today's cameras, exposure value is around 14.
An automatic camera may or may not tell you what the exposure value is prior to taking the shot.
Exposure value is changed manually by adjusting lens aperture and/or shutter speed. Different exposure values go with different picture taking conditions such as sunny, cloudy, etc. For example EV 15 goes with ISO 100 and bright sun.
ISO is not used to compute the exposure value; rather, if you use a different ISO then you need to use a different exposure value to get an equivalent picture in terms of brightness.
At twice the ISO you need the next higher exposure value number given the same scene lighting conditions. At half the ISO you need the next lower exposure value number.
(Getting a bit more techical) For example EV14 corresponds to (approximately) f/16 at 1/50'th second or f/11 at 1/100'th second or f/22 at 1/25'th second. EV15 is f/22 at 1/50'th second or f/16 at 1/100'th second. EV14 is the correct exposure for a subject in bright sun using ISO 50 film.
Spot Metering, Weighted Metering
All automatic cameras use the brightness of the scene you are photographing to determine the exposure. Spot metering means that only a small part of the scene at the center is used. This generally makes the subject look good all of the time but a lighter background may be really washed out or a darker background may be really shadowy. There is also an overall scene metering that can do the opposite, make the most of the picture look reasonable but a small subject in the middle that is much brighter or much darker does not come out well. Weighted metering is a compromise, more emphasis is given to the middle of the picture but the edges are also taken into account a little. You will have to experiment with your camera to see what works best for you. With some cameras you can aim at a subject slightly to one side and push the shutter release button halfway. The camera sets its focus and exposure for that subject and holds it while you choose a different shooting angle.
Depth of Field (semi-advanced topic)
This refers to how sharp subject matter a little closer and a little further from the camera is after focusing on the desired subject. It is subjective although it is expressed in terms of calculations. In reality only material at a specific distance is truly in focus. Depth of field describes how much closer and how further away additional subject matter can be and not be obtrusively out of focus.
The larger the aperture, the smaller the depth of field. Among other things this means that focusing has to be more accurate.
A lens may have a depth of field guide next to the focusing ring that looks somewhat like this:
16 11 8 5.6 4 2.8 4 5.6 8 11 16
With the lens set to f/2.8 you would set the focus so the distance for the most important subject is at the "2.8" marking. With the lens set at f/16 the range of distances between the two "16" markings will be in reasonable focus although you should still set the distance of the most important subject material as close to the middle (the "2.8" here) as you can.
When zoom or telephoto lenses are used, the same aperture but a different 35mm equivalent focal length will result in a different depth of field.
Sometimes it is desired to have the background out of focus to make the subject stand out more. With most point and shoot cameras you do not have enough control over the aperture to make this possible. But you can sometimes focus on something in front of the intended subject, making the subject a little out of focus but not obtrusively so, and making the background more out of focus as desired.
A spot focused "perfectly" on the film or sensor will have a diameter of so many microns. Technically, depth of field is measured in terms of what percentage larger the spot is (or would be) due to being out of focus because the camera to subject distance was changed without refocusing the camera.
One interesting fact that is supported by the usual depth of field calculations: Consider any two cameras (sensor size may be different, lens quality may be different, etc.). If the aperture is the same and the lens focal length or degree of zoom is the same in 35mm film camera equivalents, then once the same scene is photographed and finished prints of the same size (for example 8x10 inches) are made, the two prints will show the same depth of field.
Dynamic Range, Histograms, Very Light and Very Dark Material (semi-advanced topic)
If the scene contains both very light and very dark material, it may be impossible to capture the detail in both of these areas in the same shot. The technical way of saying this is that the dynamic range of the camera is not great enough.
With both very light and very dark material in the scene, your best bet is to take two or even three shots and decide later which you like best. One shot would be deliberately "overexposed" to reduce burying of the shadow detail and one shot would be deliberately "underexposed" to reduce washing out of the highlights. Use the exposure compensation to accomplish this. This procedure is called "bracketing the exposure." You can lighten or darken the picture a little using the photofinishing kiosk in a store or using your computer but we still suggest you take multiple pictures with different exposure settings and choose the one that looks best.
Many cameras have a histogram feature. If the histogram shows a lot of material (tall black area; a "mountain") up against the right only (lots of bright content), that suggests that the picture might be overexposed to begin with and highlights may be washed out. If there is a "mountain" against the left side only for a lot of dark material, that suggests that the picture might be underexposed and shadow detail may be buried. If there is a lot of material both at the extreme left and at the extreme right, this suggests that you might have insufficient dynamic range for that scene and you may want to take two more shots, one with more exposure and one with less exposure, as mentioned above.
Only you can be the judge. Having the histogram mountain in the middle is usually best for starters, but for some shots the desired subject might not look good until you take another shot, brightening or darkening the picture making the mountain move off to the side.
This must be accompanied by two other numbers: an ISO rating (film speed) and measurement units (typically a choice of feet or meters). Divide the guide number by the f/stop number to get the maximum shooting distance for an automatic camera, or divide the guide number by the shooting distance to get the f/stop setting for a manual camera. Example: Guide number 56, maximum lens opening f/2.8 means up to 20 feet for the ISO specified. For a camera with a zoom lens you will have to estimate the f/stop number if the zoom is neither at minimum nor at maximum. If the ISO is doubled, then the guide number is increased by about 40%. If the ISO is quadrupled, then the guide number is doubled.
The instructions for most point and shoot cameras specify the flash shooting distance so you do not have to make calculations using the guide number.
Usually the LCD screen viewfinder on a digital camera shows you the exact picture you will get. Usually the optical (peephole) viewfinder shows a little less than what you will get. You will have to get used to your camera to better guess what you will get when using the optical viewfinder.
There is more unpredictable guesswork because you might compose the picture so the important subject material goes nearly to the edges and then the photofinisher who makes your prints (snapshots) crops a little more off of the sides of the picture. Or you may leave room on all four sides anticipating that the photofinisher may crop the sides but then he does not.
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Crop Factor (advanced subtopic)
Unless you are dealing with SLR cameras or other cameras with interchangeable lenses, you should not have to worry about crop factor.
The published crop factor is defined as 43-1/2 divided by the diagonal of the sensor in the camera that the lens will be used with. The diagonal of a 35mm still picture is 43-1/2 mm.
(A crop factor relative to any two cameras would be the diagonal of the film frame or sensor that the lens is designed for divided by the diagonal of the film frame or sensor the lens will be used with.)
When the lens designed for a larger sensor (or film frame), say 24 x 36mm, is installed on a camera with a smaller sensor, for example 16 x 24 mm, only a (cropped) portion of the projected image is captured or spanned by the smaller sensor. In this example the finished picture has the same view that a 35mm film image would have when taken with a longer (1.5x) telephoto lens compared with a 24 x 36 mm image taken with the lens in question.
So we can no longer use the focal length stamped on the lens as-is when comparing performance with other cameras. Again, 35mm film camera equivalent is the common denominator when comparing cameras and lenses. Multiplying the original focal length by the crop factor gives us the new equivalent focal length relative to that lens and the new camera/sensor.
There are many different sensor sizes for digital SLR cameras that accept standard 35mm film camera lenses. Therefore many different crop factors will be mentioned in discussions involving camera and lens combinations.
If a lens designed for a smaller frame or sensor is installed on a camera with a larger frame or sensor, a crop factor of less than one would apply. This usage is not recommended. There will undoubtedly be lens aberrations and/or fall off in brightness at the sides and corners that degrade the image quality of the finished picture since the film or sensor is spanning an area bigger than the sweet spot of the lens.
... as in "This camera has one stop of image stabilization."
"The lens opening was maxed out so in order to brighten the picture by one stop you have to have the shutter open twice as long instead."
With optical image stabilization turned on, the average person holding the camera not perfectly steady can usually get the same picture sharpness with twice the shutter open time (one stop of I.S.) or four times the shutter open time (two stops of I.S.), etc. compared with no image stabilization. The increased shutter open time together with the lens aperture already maxed out of course can give a better picture in low light conditions. So if you are good at holding the camera steady enough using a 1/30'th second shutter speed, then two stops of image stabilization should generally give you just as sharp pictures with 1/8'th second shutter speed. It is still desirable to take more than one shot just in case your hands shook more on a particular shot.
Image stabilization is not meant to sharpen up moving subjects.
Pixels Wide versus Megapixels
Here we give sample common horizontal by vertical pixel counts for digital cameras with a 4:3 aspect ratio (width to height ratio) which most digital cameras have. The irregular pixel count numbers reflect technical characteristics that are not important to know. For the larger megapixel ratings we also give the percentage increase in the horizontal direction which you can see is quite small for each added megapixel or two. "More width" refers to how much more you can enlarge pictures and still have at least the same sharpness. When you print pictures you can make them almost any width you want.
. Hor x Vert More Width Over...
. ...1 less MP ...2 lessMP
2MP 1600 x 1200
3MP 2048 x 1536
4MP 2272 x 1712
5MP 2592 x 1944
6MP 2816 x 2112 9% 24%
7MP 3072 x 2304 9% 19%
8MP 3264 x 2448 6% 16%
10MP 3648 x 2736 12%
If you have this much more megapixels (column 1) then you can blow up pictures to be this much wider (column 2) and still have at least equal sharpness. Maybe a little more if the finished picture will be hung on a wall (seen from a distance) as opposed to published in a book.
Be aware that the camera's lens may impose limitations more strict than those shown below.
Column 1 Column 2
20% as in 6 versus 5 MP 10% more width(quite negligible)
40% 20% more
66% as in 10 versus 6 MP 30% more
Twice A little under 50% more
Three times 75% more
Four times Twice the original width
Be aware that other camera limitations, notably lens quality, will affect how much more improvement you get with more megapixels.
Sensor Size: What is a 1/2.5 inch sensor? (advanced topic)
First the practical considerations.
The typical sensor (which records the image) in a point and shoot digital camera is about 1/4 to 1/3 inch (6 to 8 mm) wide. Digital SLR cameras have larger sensors but rarely larger than 25 mm wide. (A 35mm film frame is 36 mm wide.)
After you have narrowed down your choice of compact or mid-size point and shoot based on features, price ,and Consumer Reports or other magazine reviews, you probably don't have much choice when it comes to the sensor size.
Sensor size and number of megapixels are quite unrelated.
The larger the sensor for a given number of megapixels, the less noise (graininess) the pictures will have, particularly with a higher ISO selection.
The larger the sensor for a given number of pixels, the more crisp picture detail edges and single pixel wide picture details will be.
Due to the small numbers involved, focal lengths stamped on digital camera lenses may be rounded off and therefore when you try to compute 35mm film camera equivalents yourself, you may get a slight error.
It is true that a more precision lens is needed to get a comparable picture from a smaller sensor. But we can be thankful that lenses have been improved since the days when very small film camera frame sizes (Minox, Pocket Instamatics, Disk cameras) were introduced and people complained about the less sharp pictures.
If a speck of dust gets in the camera and on the sensor, it will appear "humongous" in the pictures you take. Except there is not much difference in sensor sizes among common point and shoot digital cameras so a larger sensor size won't offer much improvement here.
Funny Fractions (like 1/2.5 or 1/1.8) -- (The technical jargon)
First convert them into decimals. The easy way using a calculator, for example, 1 divided by 2.5 equals 0.40 inches.
These numbers. have to do with the diameter of 1950's and 1960's vintage glass vacuum tubes containing similar looking sensors and used in TV cameras. (Many of these tubes were trademarked Vidicon.) The sensor itself is a somewhat smaller rectangle.
Also, look up the sensor size (in millimeters) that goes with the fraction. Here are some web sites that list various sensor sizes:
http://www.bobatkins.com/photography/digital/size_matters.htmlhttp://www.dpreview.com/learn/?/Glossary/Camera_System/sensor_sizes_01.htm
If your sensor size is not listed, estimate it from the others shown. Yes, the larger the number the fraction reduces to, the larger your sensor is. But there is no mathematical formula that relates each fractional tube diameter size in inches to a corresponding actual sensor size in millimeters.
The sensor diagonal is roughly two thirds the tube diameter. For now, just treat the fractions as names.
One story goes that the glass tube size rather than the sensor size was advertised so people would think the sensor is bigger than it really is.
We are not sure whether all of the different tube sizes existed. Expressing sensor sizes using somewhat greater glass tube diameters is confusing enough. Extreme absurdity is the case if some of the tube sizes never existed but were fabricated after the invention of digital cameras only in order to associate each actual sensor size with "a tube size."
Now if only someone could tell me the meaning of shoe sizes (I wear 9-1/2 EE) and children's clothing sizes (4, 6, ..., 18, 20).
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