Jargon for the photographer

Well, as the psycho sits in-front of his computer monitor, thinking about the many many things that can be put down in today's post, photography once again draws his attention.

So here's today's post, filled to the brim with all sorts of terms about photography.

1. Shutter-Speed:
Well, shutter speed is not a technically correct term, as every speed is usually measured in "per unit time" terms, but, shutter-speed is measured in "time" terms.

It is the duration for which the shutter of the camera remains open to allow the light to fall on the film/sensor to create an exposure.

Some of the typical shutter speeds are 1 sec, 1/2 sec, 1/4 sec, 1/8 sec, 1/15 sec, 1/30 sec, 1/60 sec, 1/125 sec, 1/250 sec, 1/500 and 1/1000 sec. On modern cameras, this scale is extended on either side for more control on the photographic technique.

The shutter speeds are also sometimes mentioned as the reciprocals of the time in seconds for which the shutter is open. This way, a bigger number does indicate a faster shutter speed, e.g., 1000 (1/1000 of a second) is a much faster shutter speed than 60 (1/60 sec). (This shutter speed is also related to how some lenses are called "fast" - but we'll get to that when discussing Aperture and F-Number).

There are various photographic technique terms related with shutter speed, such as stopping motion, motion blur (& panning), long exposures, blurring etc. Another related topic is Image Stabilization, especially for hand held exposures in low light conditions where the shutter speeds are slow.

Another Jargon term related to shutter speed is X-Sync, but we'll discuss it later.

2. Focal Length, Field of View & Crop Factor:
In a photography system, the focal length is usually referred for the focal length of the "Lens" that isn't just a piece of glass but is actually an optical instrument made of multiple glass pieces.

The Focal Length (in photography) is the distance from the rear nodal point (virtual point at which all light rays from outside seem to converge before emanating towards the sensor/film) to the image plane, where the film/sensor itself is placed, when a subject at infinity is in sharp focus.

The term focal length does not have to do much with the focusing of the image, but actually is closely related to the field of view. The field of view is the angle measured horizontally, vertically or diagonally that is seen by the film/sensor of the outside world being photographed.

A shorter focal length lens has a FOV, and is thus called a wide lens. This is because the image plane being very close to the rear nodal point, the film/sensor subtends a very large angle at the nodal point and thus can also see this same large angle of the outside world.

Conversely, a longer focal length lens has a very narrow FOV. Such lenses are called tele lenses or long lenses.

If you hear someone speaking the words "normal lens", it is a lens that has a 35 mm equivalent focal length of 50 mm. It is called such because this focal length produces images of same magnification and perspective as the human eye.

The "35 mm equivalent focal length" thingy might be slightly confusing - as the FOV depends both on the sensor size and the focal length of the lens, and because the 35 mm film system has been really popular for a long long time, most of the manufacturers of digital cameras (whose sensors are usually much smaller than the 35 mm film frame size of 36 mm x 24 mm) give the equivalent focal length so that photographers can easily estimate the approximate FOV. A small sensor needs a smaller focal length to give the same FOV. Thus, if a sensor is 18 mm x 12 mm in size, a lens of focal length 25mm will give the same FOV as a 50 mm lens on a 35 mm system film frame. This particular camera manufacturer will state that its 25 mm lens has a 35 mm equivalent focal length of 50 mm. A multiplication factor of 2 is used here, and this is also called the "crop factor" of this particular camera system. (My Panasonic DMC-FZ50 camera uses quite a small sensor, and thus its zoom lens of 7.4 mm to 88.8 mm focal length has a 35 mm equivalent focal length of 35 mm to 420 mm, the crop factor being about 4.729).

For larger formats (film size larger than a 36 mm x 24 mm frame), the crop factor/focal length multiplication factor is a number smaller than 1. A normal lens for such systems has a focal length larger than 50 mm.

3. Aperture & F-Number:
The aperture is the size of the opening that determines the amount of light going through the lens to fall onto the film/sensor. One more thing to be kept in mind is that the amount of light does not only depend on the size of opening, but also the Focal Length of the lens being used. For example, a 25 mm aperture on a 10 mm focal length lens will admit the same amount of light as a 50mm aperture on a 200 mm focal length lens. Thus, the more popular term used in the realm of photography is relative aperture - and this is quantified by the F-Number, which is the ratio of the focal length to the aperture diameter. A 50 mm focal length lens with a maximum relative aperture of 1.4 can be designated as 50 f/1.4.

One thing to remember very clearly here is that the smaller the F-Number, the larger the aperture.

Successive sizes of relative apertures are called aperture stops - or F-stops. Now, as we have already seen that the shutter speeds are in multiples of two. thus to maintain a parity in the system, the total light falling onto the system at two successive aperture stops must have a ratio of two - and thus the F-Number must have a ratio of the square root of 2. This is simplified to 1.4 in photography systems, and thus you can see F-Number stops of 1.4, 2, 2.8, 4, 5.6, 8 and so on. Each successive F-Number stop halves or doubles the amount of light it allows to pass, and thus to maintain the same exposure, the shutter speed is also to be adjusted by one stop.

Now, a F-Number of 1.4 allows a LOT of light into the camera, and thus, in bright light conditions, one can use a very fast shutter speed to get a good exposure. Thus, a f/1.4 lens is called a fast lens. A lens with smaller F-Number is always a faster lens than one with a larger F-Number.

There is another property of lenses called "depth of field", which is directly related with aperture, but it being a slightly advanced topic, we'll discuss it some other day.

4. Prime Lens & Zoom Lens
A lens with a fixed focal length (fixed FOV) is called a prime lens in camera terminology. For long, the only lenses that were available on the market for cameras were prime lenses, and even today, the best pieces of glass are primes.

A lens that can vary its focal length is called a Zoom Lens. These are becoming more and more popular these days, and with advances in technology are now beginning to tread on encroach on prime territory.

While not better in versatility than zoom lenses, they are clearly superior in terms of optical quality - exceptional sharpness and non existent distortions; they are often much faster than zoom lenses; they also are available for focal lengths the zooms dare not touch. With a faster prime, you can stop motion, or get good snaps in low light. Other than that, because of the sharpness and distortion advantages, the resultant image quality is also better.

Zoom lenses on the other hand are so much more versatile. You need not move to frame your shot perfectly just twist the zoom ring, and in some cases, perfect framing absolutely cannot be achieved by moving if there are some obstacles or unreachable places. Though traditionally slower and optically inferior to Primes, Zoom lenses are popular just because of the versatility they offer. Lens makers are proud to office the best zoom ratio - the ratio of the wide end to the tele end of focal lengths - these days the number often being greater than 10 in the do-it-all.

One specific trait of zoom lenses is that their maximum relative aperture (F-Number) varies with the focal length. A typical Zoom Lens might be designated 18 - 50 mm f/3.5-5.6. This means that the F-Number of the lens is 3.5 at its 18 mm wide end, but goes to 5.6 at its 55 mm tele end, thus being over a stop slower.

With advances in technology, the zoom lenses have over the years advanced in optical quality, and the best ones are now reasonably fast too (f/2.8 throughout the focal length range - though the zoom ratio is usually limited to 3 on such lenses) but you still cannot get a f/1.4 or a f/1.2 zoom, and perhaps never will.

There is a lot more to write about photography and photographic equipment, but for the day this should suffice.