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Digital Angle

Digital Camera Lens - A question of duration

Perhaps one of the most confusing in the world of digital cameras is the length of objective. Heard expressions like "TV", "Angle", "field of vision", "5 times" and a host of others describe our objectives. Then once all the business we have determined that the crank other mysterious phrases like "crop factor" and "equivalent in 35 mm ". No wonder it's hard to decide on a target?

While it is easy to understand that a longer length of the lens offers more increases and a short length lens provides a wider view, it helps to understand what a standard lens is long before you start making comparisons.

There is a way to use math to determine what constitutes a standard length for any camera lens and I'll add that touch of fun math at the end of this discussion. That kind of mental gymnastics is something interesting for us geeks, but the photo other 98% of the world I would not root canal.

That said let's make an assumption: The average digital camera with an image sensor APS-firms have a length standard lens (sometimes called normal) 28 mm.

Well, big deal, what does? What this bit of information tells us is that if you mount a lens in a digital SLR and put it in a length 28 mm of sight through the camera shows the world the same perspective that we could see through one eye open. In other words, it is a "normal" or "standard" length lens. We have the reference length that can be used to compare lenses.

Let's do some mental cleansing, first place. I would encourage you to ignore some terms. We can forget "crop factor" and "35 mm equivalent" for now. Since most new DSLR camera buyers did not own a film camera with interchangeable lenses, these terms simply add unnecessary layers of numbers and confuses the issue.

Another term to set aside for the moment is the "X Factor." compact camera lens is described with phrases like "5X zoom ", which frankly is a kind of sense." Expressing the length of the lens in this way is useful, but ineffective, and here's why. A goal that is of 20-100mm is a goal of 5 times, but so is a 50-250mm lens. "Factor X" ad-speak and only superficially useful in the world of compact cameras.

So we are left with telephoto and wide angle and field of vision. These are three good relations that can sink our teeth and do it: As just discussed, a digital SLR with a 28 mm lens has a field of view similar to that of an eye. The entire length of the lens shorter than 28 mm will wider field of view (wide angle), a lens from a narrower field of view (telephoto).

There are some easy, do it in-your-head math now we can use to compare lenses. If 28mm is normal to see then a 14mm lens to take a broader view twice. A 50 mm lens provided a view almost twice. Does it really matter what the equivalent on a 35mm film camera or crop factor is? Nope.

So in the world real, now we can make some well-informed judgments when comparing digital camera lenses. If we are given a lens that is 18-55mm, now we know we have a lens wide angle and telephoto length light that will make the world look twice. Another kit offers a 28-80mm lens and understand that we're getting a lens with zero capacity wide-angle to telephoto about three times closer than our eye.

We've added some new knowledge and our confidence in making a decision between the lenses of digital cameras has increased.

In conclusion, I would like to offer some advice. With all the manufacturers in the world hawking its lens telephoto surge is easy to overlook the sharp part of the equation. If you ever take pictures in your own living room you will be better served if the digital camera lens offers a wide-angle coverage of 28 mm below.

The difference between 28mm and 17mm we know from this discussion provides an overview wider with the shorter lens, but how much larger? In 28 mm that can capture three people scrunched together on the couch. In 17mm we are now receiving the whole sofa and tables as well.

Photo Geeks Corner: The math behind regular glasses

As we did above, there are some assumptions I'd like to offer as a way of cutting to the chase:

1) We are talking about collectively DSLRs APS-sized image sensors.

2) There is a difference between the leading manufacturers of image sensors in the actual size of their sensors. However, the real impact of these differences in size is minimal.

3) The terms "normal" and "Standard" refers to the perspective a lens that does not necessarily his angle of vision.

The rule of the shorter and easier demonstrated over time is that normal lens format chamber is equal in length to the diagonal measurement of the camera frame of the film or sensor. This length lens to capture the world that show the subject in perspective about others as the scene is seen through our eyes.

An average APS-C sensor measures 22.7X15.1mm gives a diagonal of 27.26mm. Nikon uses a sensor that is slightly larger and the performance of a diagonal measurement of 28.4mm. There have been other changes in APS sized digital sensors, but all are about a diagonal of 28 mm. I have therefore chosen to say that a 28 mm in length is considered "normal" in all APS-size digital cameras.

The math looks like this: 22.7mm2 + 15.1mm2 = 743.3mm. Then we find the square root of 743.3mm, 743.3mm √ = 27.26mm

About the Author

Stu Eddins is blogger, instructor, merchandiser, and is generally in charge of a lot of things for Porter's Digital Cameras and Imaging. Years of experience over the counter and in classrooms have turned Stu into an evangelist for image preservation, capturing and sharing memories, and helping people understand digital cameras, digital camera lenses.

Wixey Digital Protractor Electronic Angle Gauge Presented by Woodcraft