AboutScott Valentine Expertise Most anything about digital post processing (Photoshop, etc), effects, and image restoration, some technical information about digital imaging systems, light and electron microscopy, optical physics and image analysis. I can help with shooting basics, lighting setups, and getting the most out of your digital camera. I am also an 'expert' here for Photoshop (Computers/Technology > Software > Graphics Software > Photoshop).
Please - NO operating, trouble-shooting, or purchase questions on point-and-shoot or video cameras.
Experience Author, "Real World Compositing with Photoshop CS4" (available January 2009 from Peachpit.com). I've been an image analyst and advanced amateur photographer for over 6 years. I run an Adobe user group, focusing on digital media, and have lectured on digital image capture systems. Currently, I am an administrator for a rather large instructional Photoshop forum
Organizations Adobe User Groups, National Association of Photoshop Professionals, Advanced Imaging Specialists
Publications CommunityMX.com, Real World Compositing with Photoshop CS4 (Adobe Press)
Education/Credentials Bachelor of Physics, University of California, San Diego
Awards and Honors Winner: Best in Show and several category first place awards - Imaging Professionals of the Southwest Print Competition (multiple years)
I don't know how to word this in a more sophisticated way - but how the heck do you differentiate one zoom lens from another? All the point and shoots just say "5x Optical Zoom" or "10x Optical Zoom." But now I have a DSLR and everything is broken down into MM. Can you explain how this works - and is there any way to convert, say, 50-200mm into "Optical Zoom?"
Thanks!
-Dave
Answer Hi Dave,
The basic answer is that magnification (i.e., 5x zoom) is relative to a given system. While the typical convention is to compare with a 35mm camera, it's not always clear whether the magnification is given in relation to a 50mm lens on a 35mm film camera, or in relation to the lens' widest setting. So, it's a bit of a marketing game. The more 'legal' way of doing things would be to compare with a shot taken at 50mm, which closely approximates the human eye's characteristics for perceptual field of view.
There is no direct way of converting 50-200 into something that relates directly to magnification, except as noted above.
The 'length' of a lens is the distance between the sensor plane and the aperture, and controls the apparent magnification. A 200mm lens sets the aperture 200mm from the focal plane, for example. A zoom lens moves the aperture and lens assembly back and forth. Now, this is a very simplistic view, as what really happens inside a zoom lens is somewhat complicated - elements (or lenses) within the housing move in addition to the aperture, so that the actual range may be less than the actual stated amount.
In this case, the millimeter reading is effectively related to the magnification, but may not be the actual distance from aperture (or nodal point, more correctly) to the film or sensor plane.
Given this information, you may be confused about pocket-size cameras with magnification ratings. Clearly, a small point-and-shoot doesn't have 200mm of play, but may provide similar magnification. In this case, the lens has a very short focal length and a correcting segment that causes the image to be magnified, though again, this is a simplified description.
If you'd like to learn more about optics, check the Wikipedia entry for "Focal Length" and "Lens, Optics". These entries should give you plenty of information!
As always, please let me know if you have further questions!
