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09-06-2007, 03:12 AM #1
Long-focus lens and telephoto lens
Do you know that there is a difference between the two? AOTBE, the ungainly long-focus lens is better but may not be very practical.
09-12-2007, 01:38 PM #2
that's the opposite of retro-focus, right? long-focus lens is where the effective focal point is in front of the front element, while the retro-focus lens is where the effective focal point is behind the rear element.
09-12-2007, 03:29 PM #3
All Other Things Being Equal. AOTBE.
09-12-2007, 09:17 PM #4
However, you gain a great deal in the modern telephoto and almost nothing in the modern retrofocus (the latter also known as an inverted telephoto) except that it is the only type of design that can be used on a slr or dslr camera.
The telephoto design has shrunk in physical dimensions and is far easier to design to the same standards as the long focus design. Not so the retrofocus wide-angle lens. That is why slr and dslr wide-angle lenses are still a poor cousin to their true wide-angle design. It is also bulky, the very opposite of the telephoto. You save bulk in one and gain bulk in another.
You can find out if your "long teles" are telephoto or long focus simply from their physical dimensions. A long focus lens is at least as long as its focal length minus your camera's lens register. Roughly, if a lens of 300mm is at least 256mm long plus your camera's register of 44mm (Canon EOS body) then it is a long focus lens. Otherwise it is a telephoto. Another giveaway is the diameter of the lens. A 300mm f/2.0 long focus lens will have a front element that is at least 150mm in diameter-a giant of a lens. At even longer focal length at fast lens speed you will need a truck to carry your long focus lenses. That is the reason why the modern telephoto is almost used exclusively today.
09-13-2007, 12:01 PM #5
Ng 6 :-) It will be nice if you post example photos of "telephoto" and "long focus" lens for illustration.
Last edited by Marky; 09-13-2007 at 12:06 PM.
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