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Most basic Terms of Digital Photography such as...


17 Apr 2004 12:15AM
Hello everyone. Although its been a month I am attached with a camera. And I have no experience of taking snaps from before this month. Now there are a few things confusing me a lot. Terms .. Any help would be great.. Little over view here in forum or the link of any other site who provide the basic guide.

ISO, I need to know what actually it does.. some time it work sometimes not. so I want to understand it..

DOF...

Exposure, although I kinda get a figure what it do, but still need some thing to know it better.

and stuffs like that.. will be waiting to read
Anthony 20 5.7k 17 United Kingdom
17 Apr 2004 12:43AM
Hi, welcome to the site. There will be others with further information, but heres what I know, I hope it helps.

ISO - this is the sensitivity of the film/digital sensor. For example, 50 ISO (or ASA) is a very fine grain/noise. I would say its ideal for very bright conditions. A higher number ISO, would give a greater sensitivity, but with an increase in grain/noise, better for lower light situations. In essence you are increasing the film/digital sensor's sensitivity to light.

DOF - is Depth of Field. The area of sharpness in front of and behind the focus point. The effect is like having a greater DOF for a landscape, to give sharp images front to back. A shallower DOF would give a blurred foreground and background. The f-stop settings are used to vary this effect depending on what you are trying to achieve. f1.4 or so, gives a very shallow DOF, f5.6 gives an approximate setting for a portrait, and f11 or greater would be used for maximum DOF, like a landscape.

Exposure - I would say its the length of time that the film/sensor is exposed to your subject. A short exposure may give a darker than you'd expect image, with probably a very fast shutter speed or high numbered f-stop, too much DOF. A short or under exposed image, has not had enough light hit the film/sensor. A long exposure may give burnt out highlights, or weak looking images. A long shutter speed for example, allows too much light into the film/sensor, and you over do the image. The correct exposure, gives good tones. Black looking blacks, and white looking whites. The correct amount of light has passed through the lens, onto the film/sensor.

If I'm wrong, anyone can feel free to correct me, I wont be offended.

Hope this helps in some way. Keep the questions coming.

Regards

Anthony


tim franklin 17 2.7k
17 Apr 2004 7:53AM
ISO stands for International Standards Organisation. The ISO rating does what Anthony says, but is originally a measure of the speed (ie sensitivity to light) of film. If you want details of how such things are measured, the info can doubtless be found somewhere on the web! The ISO system replaced earlier measurements such as the ASA (American Standards Organisation) - though ASA and ISO numbers are usually the same - and the German DIN rating (if you look at a film box the speed is usually rated in both ISO and DIN (eg Fuji Velvia is ISO 50 / 18 DIN). On a digital camera chip, raising the ISO level means thaat the signal is amplified. The effect is to raise noise levels.

DoF is indeed depth of field. It has to be said that there is an enormous amount of misinformation spread about this, mainly due to over-generalisation in books aimed at beginners (see Anthony's comments about stopping down to f/11 or below for landscapes). In reality much depends on the focal length in use. As an example, if I stop my Voigtlander 21mm down to f/5.6, I can get everything sharp from 1.5 metres to infinity. At f/11 (which is as far down as I would choose to use 35mm) the closest "in focus" point comes down to just under 0.8 metres. Using a 50mm lens at f/11 gives from just under 4.5 metres to infinity. The glib response; to suggest stopping down to f/16 or even f/22 with the 50mm is missing the point. For a landscape you would be unlikely to use a 50mm if it was desired to have something so close in focus right through to infinity. The angle-of-view of the lens just isn't suited. The normal landscape lens would be between 24mm to 35mm (or their equivalents in larger formats) depending on taste. In 35mm it just is not necessary to stop down beyond f/5.6 to f/11 to maximise depth of field. Longer lenses are normally used for picking out details in the landscape, and because the point focused on is either going to be further from the photographer, or a specific detail to be isolated in the photograph, stopping right down is again unnecessary.

It is one of the curses of the autofocus age that the immensely useful depth of field scales have disappeared (or been so compromised as to be useless) from most lenses, especially zooms. Canon EOS users are slightly better served, as they have access to the DEP mode. However, there are DoF calculators such as Focus+ and f/calc available for Palm type devices, or it should be possible to find and print out tables. If your lens has decent distance markings then finding the right point to manually focus the lens should be within reach of most.

Exposure is a combination of shutter speed and lens aperture to obtain the desired effect in the photograph you are making. That may be a slow speed to induce motion blur in a moving subject, or a fast one to freeze motion, narrow DoF to isolate your subject (or just part of it) or more DoF for a landscape as described above.

Either way, you should always bear in mind that the meter (whether in-camera TTL or a separate hand held type) sees everything as 18% grey (actually more like 12%, but 18% has become such a convention), so if your composition includes large areas of higlights the picture may come out underexposed, or if there are large shadow areas it may be overexposed. The trick is to learn how your meter reacts under given conditions. Even for a pro user it is not vital that the meter is accurate under all conditions (though that would be nice!), but that where it might fail is predictable, so appropriate compensation can be applied to the exposure before taking the shot. If a meter behaves in an unpredictable manner; say veering between getting it right and underexposure under certain lighting, then its not a valid professional tool.
17 Apr 2004 10:57AM
hmm briefly brief.. Thanks alott fellows.. Thanks alot.. Still more help welcomes always for me and obviously for others like me.
Carabosse 18 41.7k 270 England
17 Apr 2004 12:19PM
Kodak have a glossary of photographic terms HERE

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