How to get to know your lenses

When using SLR or ILC cameras you have a choice to make about which lens to use for each picture you take.

But how well do you know your lenses?

It is clear that some are better than others at specific jobs, some have a wider capability than others. So the key question is - how well do you know yours?

Read this article by Australian phographer Peter Eastway as he tell you how to experiment and find out what your lenses really are doing to your pictures.

When Does Your Camera Have Enough Pixels?

Cameras have a history of increasing the number of pixels with each new product release. We have seen digital cameras starting off around 1.5 to 2.5 million pixels (MPx) and now you can get up to 20 MPx readily and even more for big, and expensive, pro cameras.

Your Smartphone probably has something between 4 and 8 MPx even though the actual camera occupies a small corner of a hand sized technology packed package.
So what is a pixel and when does the number of MPx matter?

What is a pixel?

Digital pictures are made of small squares of photo information and each individual square is called a 'pixel'; it's a name derived from the concept of a 'picture cell'. These are the individual elements of the digital picture that are connected back to the separate parts of your camera's sensor that respond to the light falling on it.

Before we go on to the examples it is important to view this web page on a computer monitor as the size effects will not show on many smart phone screens, the size and resolution is too small.

Computer displays and resolution

Gears-200x150-2This picture shows an image at a resolution of 200 x 150 px, that's 30,000px or 0.03 Mpx. You can clearly see the jaggedness imposed by the large blocks cause by the individual pixels that comprise the image.

Gears-20x15This is the same image but now at an even lower resolution of 20x15 pixels, 300Px. It is now impossible to tell what the object is.

Gears-1000x750This picture has bee recorded at a resolution of 1,000 x 750 pixels, 0.75 Mpx; it is shown here as only 300 pixels wide. Click on the picture to see it at full size (use our browser's Back button to return here). On any monitor or projector (other than the highest professional equipment) it is practically impossible to discern the blocks.

For on-screen display the largest resolution that can be displayed is that of the display itself. In recent years that has come to mean 1,600 x 1,280, i.e. a fraction over 2MPx. In practice, on a website, the picture only occupies a proportion of this space and our example of 1,000 x 750 will normally display well.

Photo Printing and resolution

However, the picture changes when we look at photo printing. Prining is inherently a higher resolution process as the final printed image is an analogue object and the resolution is not limited by pixel size. The limitation is now the acuity of your eyes.

Many experiments have been undertaken and it is established that the resolution necessary for a good quality printed image is 300 dpi (that's dots per inch, or pixel). Really top quality prints will go further, but you stray into Pro territory here.

Given the 300 dpi and the standard sizes of photo printing, what resolution do you need from your images to get good quality prints through the process?

Width (ins) Height (ins) MPixel Image PX width
6 ins 4 ins 2.2 1800
8 5 3.6 2400
10 8 7.2 3000
12 10 10.8 3600
Width (mm) Height (mm) MPixel Image PX width
297 (A4) 210 8.7 3507
210 (A5) 149 4.3 2480
420 (A3) 297 17.4 4960

So, from this it is clear that if your camera has 10MPx then you can print up to 12 x 10 or A4 with good results.

Smartphone cameras are now 4 to 5 Mpx so should print up to 8 with excellent quality and be quite acceptable up to 10 x 8, quite remarkable for such a tiny device. But there's a lot more to know about Smartphone cameras; but that's for another time.

The effect of cropping on picture quality

Another factor to take into account is cropping. When you crop a picture you reduce the number of pixels that make up the image. To see the size of the effect, let’s do a simple calculation.

Let’s use some small numbers so the math is clear, say we start with an image that’s 400 by 300 and crop 10% from each edge. Our original image has 120,000 pixels.

Now let’s do that cropping. The width is reduced by two lots of 40 (10% each side) and, similarly the height is reduced by two lots of 30. Thus we have an image that has shrunk to 320 x 240 pixels, that’s 76,800 pixels.

The new image has only 64% of the pixels of the original image. Ouch!

So it really is important to fill your camera’s frame with your picture to get the best printed quality!

 

Compact camera scene modes

Most compact cameras, withor without zooms, have a range of pre-set scene modes. These include things like portrait, landscape, sunrise/ sunset, macro (close up) and fireworks modes. What these modes do is to set up the camera to a preset group of settings to maximise your chances of getting a great photo - without you having to learn the best combination of settings.

Some cameras go further and have an Intelligent Auto mode which attemptst o analyse the scene and then select the appropriate scene mode for you.

When do you first go beyond the simple Auto mode and go for a scene selection?

It's when the lighting conditions get out of the ordinary. If you are in a snowstorm the camera wil probably give you a dull grey picture - so select the Snow scene mode. If you are taking a picture close up of a flower, select Macro mode. Photos taken early in the day or towards evening also demand special care.

Here's a quick primer about scene modes.

And here's a detailed guide to many scene modes.

Types of cameras

Today let’s look at the various different types of cameras. There are many different ways of categorizing cameras but let’s start by using some commonly used terms. For simplicity let’s look at them in order of general sophistication, and cost. So here they are...

  • Smartphone cameras
  • Compact cameras
  • Compact zoom camera
  • Bridge camera
  • DSLR/ SLR
  • ILC (Interchangeable Lens Camera)

Smartphone cameras

These cameras are by far the most used for taking pictures. They have grown in performance and capability to the point that the next category of cameras is dropping significantly in sales.

They have increased in pixel count to the point that normal snap size gives decent quality output. They are also improving in apparent low light performance, which has always been their weak point.

Their big advantage is that they are with you almost all the time and are readily connected to the Internet allowing instant sharing. On the other hand their apparent quality is flattered as the majority of photos taken are never used in a way where high quality is needed. Photos uploaded to websites generally do not need to be more than 1Mpixel in size, yet the latest smart phone cameras now exceed 10Mpixels.

Compact cameras

These cameras offer a restricted range of settings and are small and very portable. The sensor is generally larger than that fitted to a smart-phone and, because they are designed as proper cameras are much easier to hold correctly.

However, despite these advantages and their low price, they are rapidly disappearing from most suppliers product lines as purchases fall.

These cameras, like the compact zooms that follow, offer a range of “scene” modes. These allow you to tell the camera about the type of subject so that it can choose the best settings without you needing to know about the technical aspects of photography.

Compact zoom cameracompact-zoom-1

With compact zoom cameras, alongside the settings you have just read about for compacts, the camera has a zoom lens allowing you to take photos that are just not possible with the simpler cameras and smartphones.

Here we see a significant departure from the features offered by the smart-phone as we now have a zoom facility.

The sensor size is still relatively small meaning that low light performance is still not great and there is little control over depth of field.

A few of these cameras allow direct control of aperture, shutter speed and ISO which is important for the serious photographer.

Bridge camerabridge-camera

As you move up the scale so the size of the camera increases as well as the capability.  Now we have reached the cameras that look like one of the big boys.

Yet, whilst the lens poking out of the front is a zoom it cannot be changed. The range of the zoom has steadily increased with each generation of this camera type and now often exceeds 20x.

These cameras also provide “scene” settings for people unsure about detailed camera control as well as providing access to the Aperture, Program and Shutter speed controls for those who do. This concept makes it easier for you to make the change as, if you are not sure about a particular scene, you can go back to the camera’s scene setting.

Sensor size is generally larger again, now getting up towards 15% to 25% of a full frame camera.

DSLR/ SLR Cameradslr-camera

These cameras are characterized by the ability to change lenses, an optical viewfinder and sophisticated, professional type, camera controls. The sensors can be anything from a full frame 35mm sensor at the professional end down to around 30% of that for the consumer types.

The larger sized sensor brings with it a larger (and heavier) body and considerable expense at the top end with cameras and lenses both costing several thousand dollars.

ILC (Interchangeable Lens Camera)

Recent developments have introduced a new breed of camera that is designed to provide the quality of the SLR without some of the size and cost.

These cameras do away with the optical viewfinder and so reduce the size, weight and complexity of that optical system. As a result the systems are considerably smaller and lighter.

 

 

 

DSLR Image courtesy of Nutdanai Apikhomboonwaroot / FreeDigitalPhotos.net