BetterPhoto Q&A
Category: New Questions

Photography Question 
Robert L. Kern


i was wantintg to know how you can tell a wide angle lense from a normal lens

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10/19/2008 8:50:53 PM

Alan N. Marcus   Hi Robert,

A camera lens acts like a projector. A projector throws (projects) a picture on a screen movie – slide – LCD projector) whereas the camera lens projects a miniature picture of the outside world on a tiny screen inside the camera. The camera makes a recording of this image when you press the go button (shutter).

Now the power of the lens determines if the picture taken is a wide-angle or a normal or a telephoto view. To measure the power of a lens we measure the distance from about the center of lens barrel to the tiny screen inside the camera. We take this measurement only when the camera is looking at a distant subject. This measure usually expressed in millimeters is engraved on the lens barrel or on the camera body. Abbreviated mm, it tells us the lens power.

If the focal length is moderate we call this power normal. A normal lens gives a view that about duplicates the human experience.

If the focal length is short we call this power wide-angle. A wide angle lens projects an image with a wide field of view. Also, the image of objects will be tiny.

If the focal length is long we call this power telephoto. A telephoto projects a magnified view and the angle of view will be narrow.

It’s not the easiest thing to make this classification because the size of the screen inside the camera plays an important part. What I am trying to say is, nobody can tell you if a particular lens is a wide-angle unless we know two facts. 1. Size of the screen in your camera (the film size or the size of the surface of the imaging chip) inside your camera. 2. The focal length of the lens you are asking about.

Now a normal lens for any camera is one with a focal length that approximately matches the diagonal measure of the film or chip your camera uses. Once you tell us the camera model we can look up the diagonal measure. If we know the diagonal, a lens with a focal length that’s about 70% of this value will fall in the realm of wide-angle. If the lens is about 200% longer (2 times normal) it will fall in the realm of telephoto.

I wish I could supply a simpler explanation. Email your camera model and lens and I will give you a more direct answer.

Your friend,

Alan Marcus

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10/19/2008 10:25:27 PM

John P. Sandstedt
BetterPhoto Member Since: 8/8/2001
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  Alan - we need to keep it short and sweet.

Robert - look at the front of the lens, and sometimes on the barrel. Etched on the lens are numbers like f/3.6 and 18-55 mm [for digital]

If you have a Nikon or Canon dSLR, multiply the mm number by 1.5 [Nikon] or 1.6 [Canon.] The result is the effective focal length [comparaed to film.]

A Normal Lens has a focal length of 45-55 mm [film equivalent.] A Wide Angle Lens has a focal length 35 mm and smaller.

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11/4/2008 12:39:25 PM

Christopher A. Walrath
BetterPhoto Member Since: 4/25/2006
  Good answer, Alan. And since asked in the film forum, prob not a dSLR.


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11/4/2008 9:47:39 PM

Alan N. Marcus   Different size image sensors are currently in use. High-end D-SLR’s sport a sensor based on their 35mm film camera forerunner with its 35mm wide film and edge sprocket holes that were needed to transport the film. Sprocket holes consumed lots of film area. The final frame measures 24mm by 36mm the diagonal measure is 43.3mm. These dimensions stem from the Leica camera circa 1924.

Technical and price considerations spawned a smaller sensor now in use in many D-SLR’s. This size is called APS-C. These sensors measure 16mm by 24mm diagonal is 30mm. This size stem from a consortium of camera makers, who in 1996, marketed the Advanced Photo System (APS). These cameras utilized a subset of color movie film with built-in transparent magnetic sound track tape layer. The idea was a hybrid film camera that could chemically and digitally image. It was to transition the public into digital. Additionally the camera manually switched between three formats H to fit HD TV screens (16:9), C (classic 3:2) to make 4 x 6 ratio prints and P to make panoramic prints 4 x 12 inch. The idea failed and the line was scrapped but the C format size prevailed as the ancestor of this sensor size chip.

Now sensor size matters. Pixel count is actually unrelated to sensor size. Higher pixel count delivers greater the resolution. Picture quality is also based on sensor site size. Larger sensors support larger sensor sites. Larger sites are capable of higher ISO and reduced noise (digital equivalent of grain). Thus the large 35mm size senor delivers higher picture quality than the APS-C size.

Now us grayhairs and the used camera market have cabinets full of good but used 35mm film lenses. Some could be fitted to the new-fangled D-SLR’s. Likely some will work but often lenses are electrically and mechanically coupled to the body. Issues of compatibility are to be solved on a case-by-case basis.

Now I can tell you with 100% conviction that future sensors will shrink and so will the camera bodies. Fixed focus “prime lenses” are now exception and kit lenses perform like “Swiss Army Knives”. As time goes by, most old 35mm lens will become museum pieces. The real responses to this question, it seems to me, must be, how do you determine “normal” “wide-angle” “telephoto” as it relates to my camera.

I rest my case! Too long? Erase before reading!

Alan Marcus (marginal technical gobbledygook)

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11/5/2008 8:48:13 AM

Christopher A. Walrath
BetterPhoto Member Since: 4/25/2006
  (no, mommy, I don't like pop tarts) gggggggggg, hnnnnnnnn. whuuu? Have I been here the whole time;P

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11/5/2008 6:29:29 PM

Gregory LaGrange
BetterPhoto Member Since: 11/11/2003
  And it could still be shorter and to the point.
You can tell by the perspective, and focal length if you're more familiar with a particular format.
If you get a perspective similar to the human eye sight, you've got a regular lens. A wider perspective, wide angle lens.
So regular 35mm format, 50mm lens is regular. Smaller than that (35mm on down) wide angle.
Medium format, regular lens is about 85mm. Smaller than that, (like a 50mm for a medium format camera) wide angle.
And I agree, sensors and cameras will get smaller. I've got a camera that's a key chain, and I'm sure it's got a rather small sensor. But that doesn't mean that's what's going to be all there is to use.

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11/5/2008 8:00:32 PM

John G. Clifford Jr
BetterPhoto Member Since: 8/18/2005
  By definition, a wide-angle lens is a lens that has a focal length that is less than the diagonal of the film sheet/image sensor.

A 35mm camera has a 24mm x 35mm image size, and the diagonal (from corner to corner) is around 43mm. Therefore any lens with a focal length shorter than 43mm, e.g., 35mm, 24mm, is a wide angle lens. Any lens with a focal length longer than 43mm is a telephoto. A 43mm lens would be considered 'normal', or giving the same field of view as normal human vision. (Camera manufacturers standardized on 50mm lenses as 'normal' because the slight telephoto effect was pleasing to the eye.)

The quick-and-dirty way to determine whether your lens is wide-angle on a dSLR with a smaller-than-full-frame sensor is to use the 'crop factor'. For example, most Nikon dSLRs have APS-C sensors with a 1.6x crop factor, meaning a 35mm full-frame is 1.6 times larger, in all dimensions, than the digital sensor used in those dSLRs. Divide 43mm by the crop factor (1.6, in this example) to get the 'dividing line' between wide-angle and telephoto lenses. On APS-C sensor-equipped dSLRs (the overwhelming majority of dSLRs), a 30mm lens is 'normal'... that's why Sigma introduced a 30/1.4 lens last year.

In short, on a 35mm or full-frame dSLR camera, anything shorter than 50mm is wide-angle. On an APS-C dSLR, shorter than 30mm. On a 4/3rds dSLR (Olympus, Panasonic), shorter than 25mm. On my Fuji F30 digicam with a 1/1.8" sensor, shorter than 10mm. Etc.

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11/26/2008 10:23:14 PM

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