1)what does 'full-time manual focus mean'?What's the use? 2)how does teleconverter affect image quality? 3)what is a life size converter? 4)will a petal-type hood usually found fisheye lens be useful for other lenses?

-- tokamak (sir-tokamak@hongkong.com), April 18, 2001

Answers

1. FTM means what it says, i.e. you can twist the foucussing ring while AF is switched on and it will change the focus (and it will not reduce the focussing motor & gear to ground-down parts).

2. Not very much at best, negatively in most cases, especially if you use 3rd party ones.

3. It allows 1:1 image scale with the 50m/f:2.5, which goes just to 1:2 without it. (Note that that's still pretty good, many macro lenses don't go further either without accessories.)

4. Not if that hood is dedicated for the fisheye lens, but generally the idea is OK.

-- Oliver Schrinner (piraya@hispavista.com), April 18, 2001.

1b)"What's the use?" - With most Canon bodies can move the autofocus start to a button on the back of the camera with custom function #4. (The cheap ones wont do this.) When you do this you can press the back button for AF and/or turn the focus ring for MF with out switching anything. More convenient/faster. Even without CF#4 you still have some advantage with FTM after you press & hold the shutter button half way.

4) Petal-type hoods provide the best coverage of the rectangular image with a given size of hood. You can often improve the hood by simply making it longer & wider, but if you want a usable size hood with a wide lens the petal shape usually works best.

-- Jim Strutz (jimstrutz@juno.com), April 18, 2001.

Regarding number 4: you're usually better off using a dedicated lens hood for a particular lens. The longer the lens, the smaller the angle of view, so the bigger the hood can be (thus blocking more stray light). Since fisheyes are the widest lenses, their lens hoods block the smallest amount of stray light. For the $20-30 that a dedicated lens hood costs, it's well worth the investment for every lens in your bag.

-- Todd Garlow (toddgarlow@hotmail.com), April 19, 2001.