Tuesday, August 21, 2012

Speed up your shutter : Shutter Speed

In our last post we learnt about Aperture, I guess now our readers would be enjoying blur background and a sharp foreground.

Today we would be moving forward to our second pillar of photograpy, Shutter Speed!!

Shutter priority refers to a shooting that allows the photographer to choose a shutter speed setting and allow the camera to decide the correct aperture. This is sometimes referred to as Shutter Speed Priority Auto Exposure, or TV (time value) mode.

Below will show you Nikon and Canon screen,

Shutter speed is the fraction of time for which the shutter stays open; it’s the time to which your camera sensor is exposed to your picture or if you are the ones who had hands on film cameras, it would be the time that the film was exposed to the scene.

Very short shutter speeds can be used to freeze fast-moving subjects, for example speed like 1/1000sec at sports events. Very long shutter speeds are used to intentionally blur a moving subject for artistic effect like 1/30sec. Short exposure times are sometimes called "fast", and long exposure times "slow".

Shutter speed is measured in fraction of seconds, like 1/1000 is said to be faster speed than 1/10 where in 1/1000 mean to be 1000th fraction of 1 sec.

It is said that 1/60sec is a man hand hold speed, anything slower than this would create a shakiness which could blur the picture, and however for slow shutter speed we can use tripods, or some concrete plane surface to support camera. Through practice and special techniques such as bracing the camera, arms, or body to minimize camera movement longer shutter speeds can be used without blur

To avoid camera shake it is suggested to have Shutter speed equal to 1/[focal length of the lens]

The shutter speed can be as fast as 1/4000sec to as slow as 30secs. Increasing shutter speed by one stop and decreasing the aperture one should give you similar exposure level.

Shutter speed is always used when we have to show movement or things are moving like a racing event. You can freeze the moment by choosing the high speed like 1/2000sec or you can have a blurry look by choosing 1/20sec.

Example, you are driving an open jeep, and you friend tried to click you at say 1/70sec speed. You will find your image is sharp however everything passing you buy is blurred




 









 Always remember it’s not only shutter speed which makes magic it’s the three Aperture, ISO added creates the magic. As you change speed you might need to change Aperture [or ISO] to compensate.

The below picture can give an idea how does the Aperture added with Speed creates more realtistic picture.

This is because if you increase your shutter speed by one stop [1/60  1/125] this will let half as much light into your camera, to compensate you might require to increase your aperture that means less the number [f11f8]. Or you can choose the faster ISO [100400] we will talk about ISO in our next post.


Zoom Burst [Wiki] :

Zoom burst is a photographic technique, attainable with zoom lenses with a manual zoom ring.

Using the technique involves zooming while the shutter is open with a relatively slow shutter speed, generally below 1/60th of a second. For this reason low light or small apertures are required. It is also possible to achieve a similar effect with either computer software like Adobe Photoshop (after the photo has been shot) or a photographic filter. In these cases the shutter speed can be as fast as necessary.

Photographs taken with this technique are characterized by blurred streaks emanating from the center of the photograph. The effect is nearly identical to a motion blur image in which the camera is traveling towards the subject. For this reason the zoom burst is typically used to create an impression of motion towards the subject.
 


We will discuss about ISO in out next post ..

Keep clicking ....

Friday, August 10, 2012

Aperture and You

Couple of days ago we were talking about the modes that would have been used while we are clicking some of our best moments. We discussed about 3 important modes – Aperture Priority, Shutter Priority / Time Value and Manual

Let’s start with understanding what does Aperture mean in Aperture Priority mode A or Av (for Aperture value)

Under the aperture-priority mode, you select an aperture and the camera chooses an appropriate shutter speed. The main purpose of using aperture-priority mode is to control the Depth of Field.

Remember that window and rising sun example, the portion of opening is called Aperture.

When talking about camera Aperture is simply the size of the opening in the lens when a picture is taken
Above picture can give you a small idea how does light enter from lens. When we hit the click button of our camera a hole opens up that will allows light to enter the camera and an image sensor at the back will get an image of what you are trying to capture.

The Aperture is that opening that would decide the hole to be bigger or smaller in regards to amount of light that should enter and should be enough for image sensor to create a good picture.

Above image is a snapshot of lens aperture ring, here you can see some number written over. Aperture is actually measured in ‘f-stops’– for example f/2.8, f/4, f/5.6,f/8,f/22 etc.

Moving from one f-stop to the next doubles or halves the size of the amount of opening in your [here change in shutter speed from one stop to the next doubles or halves the amount of light that gets in also that will be discussed later how]

Large apertures means more light can enter, have smaller f/stop number and smaller apertures which means less light can enter, have larger f-stop numbers. So here f/1.8 is in fact a much larger aperture than f/22.

When we are talking about Aperture, one the most important factor that comes in picture is Depth of field [DOF]

Depth of field is a term used to describe the 'zone' of sharpness' between nearest and furthest of a subject in focus (to be more exact, distance of sharp focus in front and behind, subject on which the lens is focused), something like in focus / Off focus shot.
Large depth of field means that most of your image will be in focus [image can be close to your camera or far away. An aperture f/22 can give you that kind of image].

Small depth of field means that certain part of the image will be in focus and the rest will be blurred, can be done intentionally also. Try clicking you daughter at an aperture of f/2.8, focusing on her eyes and see the effect yourself
The bigger the apertures used, the zone of sharpness is shallower or vice versa i.e. smaller aperture used will has extended depth of field

Aperture has a big impact upon depth of field. Large aperture (remember it’s a smaller number) will decrease depth of field while small aperture (larger numbers) will give you larger depth of field.

It depends what you are clicking, where and what you want to keep in focus when it’s about DOF
Like clicking landscape would be at smaller aperture to ensure that horizon and foreground are in focus however portrait photography you would like your subject perfectly in focus and to have a blurry background that’s where you choose a large aperture (small number) for small depth of field.

At small aperture say F/22, the light at lens will converge more on image sensor, giving you a tack sharp picture however at large aperture say F/1.8, more opening will let some of the rays enter as usual and some of the rays will converge on image sensor giving you a in focus / off focus image.

Depth of field is governed by three factors: aperture, lens focal length and shooting distance:
  • Smaller aperture  deeper the depth of field. For example, if the lens focal length and the shooting distance stay the same, the depth of field is much deeper at f/22 than at f/1.8
  • Shorter the lens focal length  deeper the depth of field. For example, comparing 11mm lens with a 50mm lens at the same aperture and shooting distance, depth of field is deeper with the 11mm lens.
  • Greater the shooting distance  deeper the depth of field. For example, if the subject is clicked from 3m and then from 8m away, the zone of sharpness in the foreground and background is greater at 8m.
 The following images show another example of the relationship between depth of field and aperture.
 It’s not just the aperture that is required to create an image; it’s the combinations of shutter speed and aperture that will control the light entering through lens, with the ISO readings, these three will create a correct exposure for image sensor to get the best image from available light.
  
The key to an theoretical good EXPOSURE = Aperture + Shutter speed
Aperture value(s): f/64, f/32, f/22, f/16, f/11, f/8.0, f/5.6, f/4.0, f/2.8, f/2.0, f/1.8/f1.4 etc. (WE ARE HERE) Control via the lens section

Shutter speed(s): 1/8000, 1/4000, 1/2000, 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1 sec, etc. Control via the Camera section

For a theoretical "perfect" exposure to be formed i.e. nice color balance, every details shown, take a good combination between using an aperture with the appropriate matching shutter speed for any given film speed (ISO) are required. The faster the film speed that means more the ISO used, you can use to capture lower lighting situation but at the expense of grainer output of prints / slides.
Example in dark or low light situations you would like to use large aperture to make the best use of available light or else your picture will be dark. Similarly on a sunny day, wherein you have enough of sunlight you would choose a small aperture F/22 to get a sharp image giving way to small amount of light to enter or else you will get an over exposed image
Technical stuff on Aperture [Wikipedia]
The amount of light captured by a lens is proportional to the area of the aperture, equal to:
 
Where f is focal length and N is the f-number.

The focal length value is not required when comparing two lenses of the same focal length; a value of 1 can be used instead, and the other factors can be dropped as well, leaving area proportion to the reciprocal square of the f-number N.

If two cameras of different format sizes and focal lengths have the same angle of view, and the same aperture area, they gather the same amount of light from the scene. In that case, the relative focal-plane illuminance, however, would depend only on the f-number N, so it is less in the camera with the larger format, longer focal length, and higher f-number. This assumes both lenses have identical transmissivity.
The above calculation can make you understand why large Aperture means small F number (N) and vice versa.


NOTE: Shutter Speed and ISO will be discussed in our next post.. Keep clicking