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Old February 20th, 2004, 01:48 PM   #1
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Camera help, please!

How can I learn the various mathematical relationships of camera equipment and operation, such as lens descriptions (16-35mm f/2.8), f-stops and focal ranges?

Dorothy
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Old February 20th, 2004, 02:26 PM   #2
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There are several posts around here that I've made on the subject, so you could search the archives if you want more details. The focal length of the lens is expressed in mm. The 16-35mm indicates the lens is a variable focal length lens (zoom lens) and the focal length changes from 16mm to 35mm. The F/2.8 designation indicates the maximum aperture (widest setting, lets in the most light) is F/2.8 and is constant through the zoom range.
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Old February 20th, 2004, 03:09 PM   #3
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"The focal length of the lens is expressed in mm. The 16-35mm indicates the lens is a variable focal length lens (zoom lens) and the focal length changes from 16mm to 35mm. The F/2.8 designation indicates the maximum aperture (widest setting, lets in the most light) is F/2.8 and is constant through the zoom range."

Jeff, thank you, but I cannot grasp the relationships you describe. What I really need are visual aides to explain your explanation!

I shall be most grateful for recommendations for such a reference.

Dorothy
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Old February 20th, 2004, 03:38 PM   #4
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The lens you describing is the Canon 16-35mm F/2.8 L series zoom lens. You can find info about it here. The lens is an EOS EF lens, meaning it fits all EOS cameras (film and digital) and of course is Auto Focus.

As you look at the picture of the lens on Canon's site the ring to the right, is the zoom ring. The ring will rotate and as you rotate the ring the focal length of the lens will change from 16mm to 35mm. This control works similar to the zoom ring on a video camera, if it has one. Some video cameras only have electronic control of the zoom. Electronic controls are usually in the form of a rocker switch, push in one direction to make the picture smaller, push in the other to make the picture bigger.

The ring to the left is the focus ring. While the lens is AF, it does have a manual focus control, should you want to manually focus the lens.

The aperture is electronically controlled and you use the controls on the camera body to change the aperture.
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Old February 20th, 2004, 08:26 PM   #5
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"The lens you describing is the Canon 16-35mm F/2.8 L series zoom lens

As you look at the picture of the lens on Canon's site the ring to the right, is the zoom ring. The ring will rotate and as you rotate the ring the focal length of the lens will change from 16mm to 35mm."

I'm grateful for your explanation, Jeff, and the helpful Canon site - which provokes further questions!

Is the focal length of a lens defined as the distance from its widest point to its longest telephoto point?

Does F/2.8 refer to the lens aperture or the aperture the lens creates on the camera?

I'd like to study and learn more about stops, apertures, focal range/distance, shutter speed, etc. Any suggested texts would be appreciated!

Dorothy
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Old February 20th, 2004, 08:50 PM   #6
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The focal length is derived by determining the distance in mm from the rear nodal point to the chip (film plane). The rear nodal point is determined mathematically and is near the rear most glass element in the lens. When you rotate the zoom ring and change the focal length (zoom the lens) the rear nodal point changes.

The F number (F/2.0, F/2.8 etc.) is derived by dividing the focal length of the lens by the physical diameter of the aperture. If you have a 50mm lens and the diameter of the opening is 25mm, you have an F/2.0 aperture. That is why as the opening gets smaller the F number gets larger.
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Old February 20th, 2004, 11:36 PM   #7
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Appreciate your help, Jeff!

Now can someone recommend a good basic photography book, PLEASE!!!

Dorothy
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Old February 21st, 2004, 08:25 AM   #8
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Dorothy, this was my photography textbook when I was in film school at UT-Austin.
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Old February 21st, 2004, 01:25 PM   #9
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Chris, your recommendation of "Photography" by Barbara London is most appreciated! Dorothy
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Old February 21st, 2004, 01:52 PM   #10
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Dorothy, there's lots of good, to-the-point "free" photography information found here:

http://www.kenrockwell.com

Here's another good link:

http://www.ferrario.com/ruether/articles.html
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Old February 21st, 2004, 04:45 PM   #11
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Thanks for the links, Frank! Here's one I found last night:

http://webs.kodak.com/US/en/digital/dlc/index.jhtml

Dorothy
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Old February 21st, 2004, 05:56 PM   #12
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Good link. ;-))
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Old February 22nd, 2004, 12:36 AM   #13
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The "Dummies Guide To..." series of books are excellent beginners books. I'm sure they have one on photography. If I need an instructional book on something, they are the first place I look.


ALthough not a beginners book, I'd toss in Matters Of Light And Depth as a personal favorite. I lost my copy of it when we moved a year ago, and I'm still mad.
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