Using the Aperture

 

If you’ve been following this blog recently, I explained what the whole deal was about the quintessential term APERTURE. If you need a refresher or want a hopefully simpler explanation than you’ve heard so far, do head back to the post: Technical Terms in Photography – Aperture.

Now that we know what Aperture is, its time to see what Aperture used for. As we saw, the Aperture is the opening in the lens which controls the amount of light coming onto the image sensor. The larger the aperture, the greater the amount of light falling on the image sensor and hence, the “brighter” the picture.

Let’s see the difference visually. The three photographs are from my window and shot in sequence at the same time of day. I varied the aperture setting on my camera and the setting is shown on each photo.

The photo in the middle is typically as close as possible to a correct exposure. Most of the detail is visible and the colours are well balanced out. This was on a bright day at a medium size aperture, f5.6.

The photo on the top is an overexposure. This means that there is more light in the photograph than is necessary. The result is a washed out image as if the whole scene was enveloped in a mist. As can be seen, the details are suppressed and the colours are very light. This is at a very large aperture size, f 3.7.

The photo at the bottom is an underexposure. As you might have guessed, this is due to inadequate light falling on the image sensor. The camera sensor is unable to capture the details and hence the image looks like it was captured at dusk under fading light. Again, the details are lost in the dark tones and colours are very dull. This is at a very small aperture size, f 8.

Exposure is a term that comes from the days of film photography. The amount of light to which the film is exposed to would determine how good the photograph is. This amount of light is controlled by the size of the aperture and how long the film is exposed [shutter speed]. Getting a correct exposure manually is the holy grail of photography.

So in conclusion, the ability to get good detail and correct colours depends on the aperture being open at the right size for the existing light available. While it is also important to consider for how long the image sensor is exposed [The shutter speed], the aperture size will determine the correct amount of light needed for the scene to be captured well.

What aperture settings to use when?

The main determinant of aperture size, just like the human eye’s iris, is incoming light. Depending upon the amount of light in the scene, either the camera or you will have to adjust the aperture size. If the lighting is bright, the aperture should be small. If the lighting is low, use a bigger aperture.

A list of typical subjects being captured and the typical aperture size is given below:

f-stop	Used in situation when
f 1.4	Dark night landscape
f 2	Moon lit night landscape, stars
f 2.8	Night photos
f 4	For most situations in artificial light, like a bulb lit room
f 5.6	For most situations
f 8	For most situations with bright light, like a spot-lit performer or an outdoor shot on a bright sunny day
f 11	Sun lit objects other than snow like light coloured walls
f 16	Snow landscape on a bright sunny day, well lit white objects
f 22	Bright light, Sun lit snow

If your camera allows you to adjust aperture settings, it is important you learn to do this manually. This would not only give you more control on the photograph, but will also allow you to get more creative with the photographs.

A note to point and shoot camera owners: If your camera does not allow you to change aperture settings, do not feel bad. This essentially allows you to concentrate on composing good pictures, while ‘outsourcing’ the technical work to the camera. Your camera will have a number of SCENE modes which essentially are presets of aperture and shutter speed. So in a way, when you use each scene mode in the appropriate situation, you are effectively adjusting your aperture and shutter speed, with a little help from the camera :)

Another very important aspect of photography that is dependent on the aperture is Depth of Field [DoF], but that is the subject of another post.

Until then, do leave your comments and suggestions. I’ll also be happy to answer any questions that you might have.

Photo Tip – The half press

 

This is a new category of posts that I’m starting post Valentine’s day to let the love for photography spread. Every once in a while, I intend to post a photo tip that will help you improve your photography. I’ll post them as I learn them or when I have that “Oh yeah” moment, so watch out for these ones.

So here goes. The photo tip for today is: The half press button technique

How many times have you clicked a photograph and found it out of focus, blurred or hazy? You did everything right, positioned everything, held the camera steady, pressed the button in one smooth action…. yet, blurry picture!!

I clicked the below photo with my phone camera, which is a 3.2 megapixel autofocus camera using exactly everything that was mentioned above, positioned the subject, held the camera steady and pressed the button quickly in one go.

The result, as you can see, was good, but not very impressive. The photo is definitely not sharp and not worthy of the 3.2 megapixel camera that clicked it.

So what did I do wrong??

Well, its not exactly something I did wrong, but something I did not do.

And that something is the half press action.

The shutter release button is the button you press to capture the photograph. All autofocus cameras have the shutter release button which has two levels of press, the soft press and the full press.

 

Now lets do this practically. Turn on your camera and put your finger on the camera button. With a light pressure, press on the button and feel it go halfway down till you meet with some resistance. The camera should not yet have clicked the photograph. If your camera display is on, you’ll see a green square or a filled green circle at this point on your screen.

Now hold the button in this position. Congratulations….. you’ve just soft pressed.

By pressing the button halfway, you allow the camera to adjust its focus and settings for the best possible exposure. This is where the camera decides on the aperture size and the shutter speed. When you see the green framing square or the green circle, the camera is indicating that it has read the view and is ready to click the photograph.

Now you can press the button till you see the flash or hear that familiar click that tells you that you’ve just clicked the photo.

So what did I get when I followed the half press trick??

Voila, as tack sharp and as clear a photograph as is possible. Once the camera has focussed and set itself up, the resultant photograph is much better. Definitely worthy of the 3.2 megapixel rating.

Remember, the half press works with every single autofocus camera, be it a humble mobile camera to a high end dSLR. The shutter release button on all cameras today have this type of two way construction. And it is always mentioned in the manual under the “Taking Photos” section. But then you never did read your manual, right??

What should I be careful about when using this tip?

Remember, when you half press the camera button, the camera takes a reading of what it is pointed at. but that is only till the time you keep the button depressed. If you release the button without clicking the photograph, the camera loses the reading. So while taking the picture, half press the button to take the reading till the green indication is seen on the LCD screen and then press further down to take the picture.

Also, if you take a half press reading while pointing at one scene and then point the camera at something else and click the picture, chances are that the resulting photograph would not be all that great. That is because the reading taken was for that scene only. To click another scene, take a half press reading for that scene, wait for the indication and then press the button fully to capture the photograph.

My camera does not have a button. I have a touchscreen. How do I do it?

This is a question I’ve got especially from mobile camera users. I have a mobile phone of this type. For some sad reason, mobile phone manufacturers decided to do away with the button in some phone models [See what happens when the designer is not a photography enthusiast?]

However, you can still use the half press trick provided your mobile phone has an autofocus camera. Point your camera at the scene you want to capture, press your finger on the designated area on the screen and keep it pressed there till you see the green indication on the screen.

Now take your finger off the screen to capture the photograph. You’ve got a focussed image. This screen pressing technique actually introduces some shaking when you release the screen, so you’ll have to practice to take steady shots.

So go on and try the half press technique. And do let me know if this helped your photography. As usual, queries and suggestions are welcome.

Technical Terms in Photography - Aperture

 

One of the most important terms you will hear on any photography related website or blog is camera aperture. Whenever you encounter a good photograph exhibited by a photographer, either in a gallery or in a magazine, chances are you will see a series of numbers alongside, describing the camera settings while taking that particular shot. One of those numbers, usually prefixed with the letter ‘ f ’ is the aperture setting.

So what does the term ‘Aperture’ mean anyway?

In the strictest sense, Aperture means a hole or opening through which light is allowed to pass. So a camera aperture is the hole in the front of the camera through which light is focussed onto the image sensor. Simple?

The best way to understand this is to compare a camera with the camera inside the human body, the eye.

The circled area termed aperture is the hole through which light gathered by the lens is focussed onto the image sensor.

Now, comparing the cross section of the human eye with the simple cross section of the camera, it is easy to see how closely the camera is designed like the human eye. In the human eye, the iris (pictured below) is a muscular ring like structure which opens and closes depending on the amount of light the eye senses. This opening, called the pupil (the dark hole in the centre of the iris), controls the amount of light entering the eye and falling on the back of the eye, the retina.

 (Image courtesy: Petr Novák, Wikipedia)

Similarly, in the camera, a diaphragm controls the size of the aperture, the hole through which light passes and falls onto the image sensor on the back.

 

What does the aperture do?

Just like the pupil in the eye, the aperture controls the amount of light falling on the image sensor. The larger the aperture, a higher amount of light is allowed to fall on the image sensor.

Adjusting the aperture allows the image sensor to record the right quantity of light to capture the subject perfectly. Too large an aperture would cause too much light to fall on the image sensor, causing the image to become very bright and white, a condition photographers refer to as a washout.

On the other hand, too small an aperture causes the captured image to be under lit, in other words, much darker and low detail than the scene really is.

 

Making sense of aperture numbers

On a camera, the aperture settings are defined as f-numbers or f-stops. this is usually denoted as the letter ‘f’ followed by a number, e.g. f4.4, f22

Typically the f-number can be varied to any number, but practically this type of continuous adjustment is difficult to achieve given the mechanics of the lens. Hence, certain preset ratios have been identified and universally adopted in most lenses. These presets are known as f-stops.

The main f-stop numbers which are universally available in all lenses are a range between these numbers:

f-stop	Relative Size	Used in situation to capture…
f 1.4	Very large	Dark night landscape
f 2	Large	Moon lit night landscape, stars
f 2.8	Large	Night photos
f 4	Medium	For most situations
f 5.6	Medium	For most situations
f 8	Medium	For most situations
f 11	Small	Sun lit objects other than snow
f 16	Very Small	Snow landscape, well lit white objects
f 22	Very Small	Bright light, Sun lit snow

These particular f-numbers are chosen as presets for a very interesting reason. When you switch from a f-number to the next f-number in this series, the effective amount of light falling on the image sensor is reduced by exactly half. So the aperture size at f5.6 allows half the amount of light to fall on the image sensor as compared to the amount of light the aperture size at f4 would allow.

Fixed lens cameras and point and shoot cameras would have a small range of f-stop settings, typically f-4 to f-8. The dSLR Cameras with interchangeable lenses do not have a aperture range of its own, it is the lenses that each have their own range.

 

How do you adjust aperture? 

Almost all cameras today allow the aperture size to be handled by the camera. This way, a light sensor on the camera reads the light level in the scene, the camera figures out the appropriate size of the aperture required to let in the right amount of light. So you just set up your shot, the camera figures out the settings and depressing the button, you have a pretty picture.

Some cameras allow you to select the aperture size. This is done either digitally using a joystick or buttons on the back of the camera, or manually by rotating a ring on the lens. This gives a photographer better control on the amount of light falling on the image sensor and if necessary, allows him to be creative by deliberately underlighting a scene or slightly washing out the scene.

We will look at how the aperture actually affects the photo and how to use aperture in a future post. Until then, do send in your comments and suggestions.