What Are Focus Points In Digital Photography

You pick up your camera with a primary objective of taking a picture of your subject. First of all, you’ll want to ensure that your subject is in focus before you take a picture. Conventionally, DSLR cameras a configured in such a way that when you press the shutter button halfway down, the camera locks focus on the subject and when you press the shutter button way down, the image is captured. This method of acquiring focus is a pretty standard method except the camera is otherwise configured.

acquiring_focus
Acquiring Focus

What Are Focus Points?

Let’s assume we’re using the conventional method I mentioned earlier whereby you pick up your camera and press the shutter button half-way down to acquire focus; the moment you look into the viewfinder you’ll see some black dots which become red when the focus is locked (depending on the camera model). These dots are called Focus Points. As photographers, we make use of focus points to draw the attention of the viewer to a part of the scene which we want them to look at. A typical example is the image of my Graphic Tablet sitting next to my laptop on my office desk. The focus was on the pen which threw every other aspect of the scene out of focus.

graphic_tablet
Graphic Tablet

Selecting Focus Points.

When it comes to selecting focus points, we could either let the camera do this for us automatically or we take control of what should be in focus and do it ourselves. Having a camera in Autofocus mode has an obvious disadvantage, which is; the camera may decide to lock focus on a different point within the scene which could be totally different from what we want… Here’s an example.

phone_display
Phone Display

 

I had the camera set on autofocus and wanted the Vimeo thumbnail to be in focus but the camera selected the facebook thumbnail.

So this is a summary of what focus points are in Digital Photography. I tried to make it as simple as possible to understand. Let me know in the comments section if I missed out on any point or If you have thoughts to share.

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ISO : Understanding Exposure in Digital Photography

In today’s editorial, we’ll be looking at ISO as the third primary factor which plays a contributory role in capturing a perfectly exposed image. The first we discussed was Aperture, next we looked at Shutter Speed, and now we’ll be looking at ISO as it relates to Exposure in Digital Photography.

What is ISO?

DSLR Camera sensors have a way of interpreting/responding to light. Their response to light, however, determines how bright or dark the image captured is. This mode or response can be referred to as ISO. ISO is measured in values such as 100,200,400,800 etc and can be controlled automatically or manually via the camera settings.

ISO VALUES EXPLAINED.

Like we mentioned earlier, ISO can be used to control the brightness of an image. The higher ISO values you apply, the brighter your image is. But it gets to a certain value where you begin to notice grains on the image; otherwise known as noise. This noise is acceptable by some photographers while some don’t like it. Personally, I don’t like noise in my images. I love them clear and crisp.

ISO Understanding Exposure in Digital Photography
ISO Understanding Exposure in Digital Photography Aperture f/9 Exposure time 1/160 sec ISO 100, Focal length 50mm

To achieve the highest image quality from your DSLR camera, it’s advisable to stick to the Base ISO. The base ISO here is the lowest ISO value your DSLR camera has. Unfortunately, we can’t always stick to this value at all times due to the conditions in which we’re shooting especially in low-light conditions.

What ISO value is best for you?

Pick up your camera and start experimenting. Set your Aperture to around F4 and your shutter speed to about 1/160th sec and ISO set to your base ISO. Start taking pictures with varying ISO values until you get to a point where the noise/grains are unacceptable. That would then give you an idea of the best acceptable ISO value for you to shoot at using your DSLR camera.

Conclusion

This is just a basic knowledge of ISO as related to Exposure in Digital Photography. We’ll go deeper into how it can be controlled when we discuss the Exposure Triangle.

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SHUTTER SPEED : Understanding Exposure in Digital Photography

The next important factor to be considered while trying to achieve a perfect exposure in digital photography is shutter speed. Like I mentioned earlier, the other two are Aperture and ISO. Firstly, we’ll give a brief introduction to what the shutter is in a DSLR camera, what it comprises of, how it works before we finally go into discussing shutter speed and features associated with it.

What is a shutter in a DSLR camera?

In photography, a shutter is a device that allows light to pass for a pre-determined period, exposing photographic film or a light-sensitive electronic sensor to light in order to capture a permanent image of a scene. The shutter is constructed such that it automatically closes after a certain required time interval. Operation of the shutter is triggered by a button called the shutter button or shutter-release button.

What is a shutter button?

In photography, the shutter button or shutter-release button is a button located mostly on the right-hand side of the DSLR camera body. When the button is pushed, the shutter opens for a pre-defined length of time; allowing light into the image sensor. During this process, an image is captured and the shutter closes afterward.

How does the shutter work in a DSLR camera?

Looking at a typical DSLR camera, the shutter comprises of 3 primary mechanisms; namely the mirror box, the bottom door and the top door. When the shutter button is pressed, the reflex mirror is tilted backward allowing light further into the camera. When the mirror flips upwards/tilts backward, a small door slides open from top to bottom, exposing the image sensor beneath. After that, another door slides down, covering the entire sensor. This process usually varies in time depending on the length of your exposure (shutter speed). After the second door closes, your reflex mirror falls back into place. The doors would then assume their default positions and technically, this process is known as Actuation. A typical DSLR camera can withstand close to 100,000 actuations in its lifetime.

shutter speed-How the shutter operates
How the shutter operates courtesy premiumbeat.com

What is shutter speed?

In Photography, shutter speed or exposure time is defined as the length of time the shutter remains open allowing light to get to the image sensor; also allowing the camera to take a photograph.

Features associated with shutter speed.

  • Shutter speed controls exposure – It is used to control the brightness of an image. The longer the shutter speed, the brighter the image. This is possible because the shutter is open for a considerable length of time to allow the image sensor to gather more light.
  • Shutter speed is measured in seconds – This could be full seconds (i.e 1 second, 5 seconds, 10 seconds etc) or fractions of a second (i.e 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8 etc). The larger the denominator, the faster the shutter speed; the lower the denominator the slower the shutter speed. for example; 1/500 is faster than 1/30.
  • Shutter speed is used to freeze movement in an image – By using a very fast shutter speed, motion is frozen. For example, using the featured image above, the image taken at 1/1000 sec freezes motion.
  • Shutter speed is used to capture motion in an image – By using a very slow shutter speed, motion is captured. For example, using the featured image above, the image taken at 1/80 sec captures motion.
  • Shutter speed and focal length – As a rule of thumb, always use shutter speeds with a denominator greater than the focal length. This helps to prevent camera shake especially in situations where image stabilization is absent

Conclusion

So while making things as simple as possible, we’ve been able to analyze the shutter speed as regards to digital photography and how it plays a significant role to achieve a perfect exposure while capturing an image. We have looked at Aperture, Shutter speed, next would be ISO.

Kindly share your thoughts in the comment section below.

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The DSLR Camera

The term DSLR is an acronym which stands for Digital Single-Lens Reflex. So a DSLR Camera is a digital camera that combines the mechanics of a single-lens reflex camera with a Digital Imaging sensor; as opposed to a photographic film.

The primary difference between the DSLR and the non-reflex single-lens digital camera is that the viewfinder of a DSLR presents an image that is almost equal to what’s captured by the camera’s sensor and not being captured by the camera’s image sensor and displayed on a digital screen.

  1. Lens
  2. Reflex Mirror
  3. Shutter
  4. Image Sensor
  5. Focusing Screen
  6. Condenser Lens
  7. Pentaprism
  8. Eyepiece/Viewfinder

OPERATIONAL DYNAMICS OF DSLR CAMERA’S

The Eyepiece/Viewfinder <8> is situated at the back of the camera. When you look through it, what you see is a reflection of information that has passed through the lens <1>; which means there’s a 100% chance of capturing what you see.

Information in form of light passes through the lens <1> and hits the Reflex Mirror <2> which is positioned at a 45 degrees angle inside the camera structure. This light is then directed vertically to a chamber called the Pentaprism <7>. This light is again re-directed by two mirrors into the viewfinder <8>.

When you take a picture by pressing the shutter button, the Reflex Mirror <2> bends backward, allowing light into the camera. The Shutter <3> remains open for as long as it’s been programmed to. This enables information to get to the Image Sensor <4> which then records the image and then the Shutter <3> closes and reflex Mirror <2> returns to its original position of 45 degrees thereby re-directing light back to the viewfinder <8>.

Once the process ends, the camera then processes information from the Image Sensor (4) and converts it into a pre-defined image format and writes it onto the memory card. This process takes less than a second and in most cases, some DSLR Camera’s can replicate this process of writing images more than 10 times within a second.

This is at best a summary of how your DSLR Camera works.

For an expanded view of how it works, you could follow this link and read more on Wikipedia

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