Glossary
1. Aperture
In photography, the camera lens opening and its relative diameter. Measured in f-stops, such as f/8, f/ I 1, etc. As the number increases, the size of the aperture decreases, thereby reducing the amount of light passing through the lens and striking the sensor/film. The aperture setting has a two fold impact:
1. The higher the value, the smaller the amount of available light.
2. The higher the value, the wider the depth of field. The lower - the shallower.
2. Bokeh
Another stumbling block in Photography terminology. Bokeh basically describes how a lens handles parts of images, that are not in focus - the blur.
A good Bokeh usually is defined as being smooth, with out hard lines in it.
A "bad" one however is not able to smooth out the entire blurred area, and leaves contrast lines in areas where you have differences between light and dark. Since that id somewhat distracting, it is considered to be a bad Bokeh.
Practically speaking however - both ends of the spectrum are more or less rare.
In general the Bokeh improves with the optical quality of the lens.
3. Chromatic Aberration
Chromatic Aberration (CA)
Huh? Circumventing scientific explanations I will try an example. We all know that our white light contains all colors in the spectrum. We have all seen, what happens when light is led through a prism. We see the whole rainbow spectrum.
Now - in a lens light is led through optical elements and usually several of them.When we see chromatic abberations in our images, it means that the optical elements display this prism effect to a certain degree, because they haven't been produced thoroughly enough to counter these effects.
And we end up - usually in areas with high contrast differences (e.g. dark and light) - with red, blue or purple fringes in between dark and light areas.
CA Effect left. Treated by desaturation - right
In general - this annoying effect does appear more frequently in cheap optics and more likely in a zoom lens than it does in a prime lens.
While there is nothing that can be done about it while shooting - some software like Adobe's Lightroom and others can reduce it in postwork. From my experience so far I was not impressed however.
My method to get rid of it, is hands on and utilizes the fact that this effect appears in areas of hightened contrast - and use the sponge tool (desaturation) tool of my software - most better software products have it.
I set a brush size of about the size of the CA's width and set the desaturation value to maximum. Then I zoom in as far as it makes sense and brush over the color abberations, until the color is entirely gone.
And - as you see in the above example - it works quite well.
4. DOF
DOF=Depth of Field
DOF describes the area in the picture your camera can deliver in sharp focus. It depends on focal length, the lens itself and the aperture, you or your cameras automatic settings have chosen.
Main factor however is the aperture. As a rule of thumb you can bank on the following fact.
Low aperture value = shallow DOF
High aperture value = wider DOF
5. EXIF
Besides information about the pixels of the image, most cameras store additional information such as the date and time the image was taken, aperture, shutterspeed, ISO, and most other camera settings.
These data, also known as "metadata" are stored in a "header". A common type of header is the EXIF (Exchangeable Image File) header. EXIF is a standard for storing information created by JEIDA (Japan Electronic Industry Development Association) to encourage interoperability between imaging devices. EXIF data are very useful because you do not need to worry about remembering the settings you used when taking the image. Later you can then analyze on your computer which camera settings created the best results, so you can learn from your experience.
6. Exposure Compensation
Sooner or later you will encounter situations, where the metering of your camera is messing up. Most often those situations occur in light, that has a wide dynamic range.
(See Glossary for more). Basically you have hard sunlight and deep shadows and everything in between in the scene before you.
And that will lead to having objects you actually target over or underexposed.
Most Prosumer and professional cameras offer a way to compensate - and that is changing the Exposure Value - commonly abbreviated EV.
Setting the EV to +1 will double the light value your image is being exposed with.
My most commonly used value is -0.7 EV, since I shoot mostly not only on the pretty strong Florida sun - my favorite subject are white Birds. And they reflect light like crazy and if there is no compensation for this issue - whites are blown (that means instead of seeing feather details, there is just one big and pure white spot with little or no detail).
So if you run into frequent over - or under exposure - check your camera and adjust the EV's!
7. F-Stop
Simply the aperture value. When photographers talk of having to stop down, loosing a stop, they usually talking of loosing light, having to lower the aperture value.
8. Focal Length
Focal Length:
While most everybody knows what's behind that term - many however have problems put it in relation to real life. So here we go - I try to put focal length into perspective.
Before the time of Zoom lenses 50mm was the Alpha & Omega of all Lenses. Why? Because it is the closest resemblance to our human field of view. Not so much what the angle is concerned, but in terms of magnification. - It's pretty much what we see. And ever since it has become a standard reference point.
With the advent of APS size sensors we have to add 35mm focal length as the equivalent to the 50mm lens in full frame cameras.
And from there we have a better way of determining, what a lens actually can do for us.
Important to keep in mind, what Camera sensor you use. Unless it's a full frame camera, which currently are the exception, calculate with the 1.5X factor that has to be applied to the conventional focal length nfo.
A 10 -20 mm lens turns into a 15-30mm, 70-200mm into 105-300mm and so on.
9. Image Stabilization
IS | OS | VS | VR | Shake reduction ( internal and External)
Abbreviations. Don't you hate them? The more since all of them mean the same. But - coming
from different companies, they sure have to have their own name.
For the sake of argument I will use IS (Image stabilization) in this post as the term.
Internal? External?
Well - there are basically two methods - one is providing the stabilization within the camera, the other
is to have the technology integrated in the lens. In most cases it is achieved by a floating lens that correct the image that falls on to the sensor by compensating for pitch (up/down) and yaw axis(vertical) movements, arriving at a better image result.
In camera stabilization works similar - but instead of a floating lens - it is the processor itself that is being moved.
While results are overall similar - the in the lens stabilization has a slight advantage, since the technology is adapted specifically for the lens.
While all of that sounds good and all - but does it help? Yes - it does! Always? Nope!
Here's where IS helps. Handheld shots in low light. Everyone knows that shooting with shutterspeeds beyond 1/125sec is, depending on the shooter, a risky business. IS can improve your odds in the range of 2 - 4 stops. (Come again?) Well - think of it that way. It's dawing - and the available light fades away. You tricked out ISO to the max - opened aperture to the max - and still - your camera wants more light - the best you can get is let's say 1/50sec shutter speed. The odds are - it'll be shaky. Two stops will catapult it in practical terms to soemwhere of 1/100 sec, 4 to 1/200/sec, both actually managable - and hence you get a picture in good quality, where you couldn't get one before.
Where it fails: Strong shake, fast movements, way to little light and believe it or not - on tripods. (at least it's not recommended, it might produce odds results).
In general - compare it to cars ABS (Anti Brake lock systems). It'll help in "normal" situations, but if you're too fast - you will crash. In general it's a support tool - not a miracle. Used accordingly it'll help you considerably.
10. ISO
ISO is a measurement of a digital camera’s imaging sensor’s light sensitivity or in film terms, the sensitivity of the film material. A high value allows shooting in lower light. But there is a price to be paid.
The higher the ISO value, the more grain (film) or noise (digital) appears in the image. ISO sensitivity currently is the center of research and improvements. The latest top camera’s have extended the range significantly. As an example - the Nikon D3 works up to 25600 ISO with noise values, that some years ago were equal to ISO 1600. And at even ISO 3200 this camera is basically noise free.
How ISO is being handled is also a significant difference between Point and shoot cameras and SLR’s.
DSLR’s do handle low light as a rule of thumb significantly better that P&S cameras are able to.
