Camera Basics

A Look at Focal Length

Focal length is the length of the lens. Common focal length ranges go from 16mm-200mm. There are lenses that go up to 800mm and beyond but for primary usage something in the 16-200mm range is usually sufficient. The top of the line Canon Zoom lenses cover this range. In the Canon line up 3 lenses are needed to cover the range: 16-35mm, 24-70mm and 70-200mm. There are multiple versions of each but all of them are excellent high performing lenses.

The lenses are engineered so that the maximum amount of glass in the lens is being used when it is being used on a full frame camera. When these lenses are used on a cropped sensor camera not as much of the lens is used due to the smaller sensor size. This creates the same effect as cropping the image which is why camera manufacturers talk about the cropped field of view. On Canon cameras it is typically a factor of 1.6x which means that if you have a 16mm lens on a cropped sensor camera you would need a 25.6mm lens on a full frame camera to duplicate the field of view. Clear as mud?

There are lenses that are made specifically for cropped sensor cameras and while those lenses aren’t compatible with full frame cameras they are typically made to have focal lengths that are equivalent to similar full frame lenses. For example Canon has a 10-22mm lens that can only be used on cropped sensor cameras. The crop factor for Canon’s sensors is 1.6x. So 10-22 on a cropped sensor will produce the exact same image as a 16-35mm on a Full Frame camera. This can be useful when it comes to needing more reach. For example, a 200mm lens on a cropped camera will give you the equivalent of 320mm. Below are examples of various focal lengths throughout the 16-200mm range using a full frame camera. For these photos the camera was fixed to a tripod, all camera settings were kept the same, the only thing that changed was the focal length and the lens.

As you can see there is an enormous difference between 16mm and 200mm. A slight amount of distortion is also evident in the 16mm shot. These shots are intended to give you an idea of what field of view to expect with each focal length. It is typically said that 50mm on a full frame camera gives close to what you see with your eyes. To achieve this same field of view on a cropped sensor a 35mm lens would be sufficient. Both of these lenses are extremely popular choices!

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Understanding Sensor Sizes

In the last article I discussed megapixels. Your camera operates by using a digital sensor to capture light. Each pixel senses light and sends the information that it senses to the camera for it to be processed into an image. Essentially each pixel captures 3 black and white channels, one red, one green, one blue and the brightness of each. This information is relayed to the processor of the camera as a digital string of numbers. The processor then deciphers the data and produces a color image. This is the basic premise of an extremely complicated process but I think that it’s enough information to understand the topic of the day: sensors.

 

As you can see in the photo there are many different sensor sizes used in the digital camera world. The smallest box is close to the size of an iPhone sensor while the “Full Frame” box is most closely related to traditional 35mm film. This is where understanding megapixels and how pixels work comes into play. Regardless of how large or small your sensor is X megapixels is X megapixels.

Since the iPhone is 12 megapixels and also the smallest sensor on our list we will use 12 megapixels as the reference point. 12 megapixels on the smallest sensor will give you very small pixels. In order to fit 12 million pixels on a chip that tiny, the pixels have to be small. As you go up in size and get a larger sensor the pixels can be larger on the sensor. What’s the benefit of larger pixels? Light sensitivity. A larger pixel will be able to detect light more accurately than a smaller pixel thus giving better image quality all around and especially in low light. Since capturing light is what photography is all about I’d say that larger pixels should be a priority.

This is also why I mentioned megapixels not being everything in the article about megapixels. 12 megapixels on a small sensor are not equivalent to 12 megapixels on a large sensor. It may seem like the same thing, and you’re effectively getting the same number of pixels but the quality and the performance of those pixels will be very different. This is also one reason why large prints made from photos that were taken with cell phones often look atrocious. Optics also plays a major role in this but that is a topic for another day.

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The Megapixel Myth

It seems that every time someone asks me about which camera to buy the word “megapixel” comes flying out of their mouth. It’s as if this mysterious megapixel is some sort of end all be all in camera conversations. If the camera has more megapixels it’s obviously better, right? Camera companies and their marketing departments have tried exceptionally hard to get people to believe this, and it has apparently worked. The fact is most people aren’t really even sure what a megapixel is, or how it relates to image quality.

First we need to understand a few things. In the print industry a professional quality print is typically 300dpi which is the resolution and means that there are 300 dots printed per inch. This is the standard for something viewed up close, meaning anything viewed from 2 feet or less. As you get farther away from the image less dpi are required for the image to appear clear to our eyes. However if you print something at a lower resolution it will look fuzzy up close, so keep that in mind when you’re ordering prints. This was a very brief crash course on DPI and printing resolution and should give you enough understanding for us to continue talking about the main subject here, megapixels.

A megapixel is defined as a graphic unit of resolution equivalent to one million pixels or exactly 1,048,576 pixels. This means that the width of the image multiplied by the height of the image equals one million pixels. The iPhone 7 has 12 megapixels while most current point and shoot cameras are in the 18 – 20 megapixel range while current DSLR cameras start at around 18 megapixels and go up from there. This means that the lowest camera resolution currently readily available for purchase (late 2017) is 12 megapixels. But do we really even need 12 megapixels?

To properly answer this question let’s take a look at how many pixels are needed to make a 300 dpi print in common sizes. But first what is a “common size?” In my years of taking photos I have covered many events where I offered prints for sale, including; weddings, engagements, newborn photos, a school semi formal and senior portraits. In all of the sessions I completed not one person, ever, ordered a print larger than 11×14. This also rings true of what I see in peoples homes. Most people have framed photos throughout their home with the most common size being 4×6 or smaller with the occasional 8×10 or 11×14. That’s not to say that people don’t order larger photos but in my experience 11×14 is the absolute maximum that people are going to order.

An 11×14 photo at 300 dpi is 3,300 x 4,200 pixels, or 13.8 megapixels. Drop that 11×14 down to 275 pixels per inch and you have your 12 megapixels. The drop in DPI will likely be noticeable to a keen observer but the average passerby will never notice the difference. Also worth noting here is that you aren’t likely to be staring at an 11×14 from 2 inches away, more likely is you’ll be viewing it from a couple of feet, or more, away which will make the drop in DPI even less apparent.

Does this mean that you should go out and print a bunch of 11×14 images from your iPhone? Or that a standard point and shoot is going to give you the same results as a DSLR? The answer to both questions is “not necessarily.” There are other factors at play that are far more important than resolution, such as sensor size and lens quality that are beyond the scope of this discussion.

In conclusion, megapixels aren’t important for the casual user. If you never intend to print something larger than 11×14 10-12 megapixels should suit your needs just fine. For years I shot with a Canon 40D which has 10 megapixels. All of my paid gigs were shot with that camera and I never had an unhappy customer. I have even printed 20×30 posters for my own personal use with images from that camera and they look great. If I were to make a billboard or some enormous prints for a gallery show I may be more worried about it but for standard sizes 10 megapixels is more than enough to get you by. My advice is to worry less about megapixels and more about the sensor and lens quality.