Funny, I was wondering about that too, and had come to the conclusion that it was a compromise to help in reaching circular polarizers. (is that why there's a cutout in the bottom of the 18-55 kit lens' hood?)
And.. if there's anyone else out there with a 31 ltd (or even a fast 28 or 35) that they're thinking of parting with, I've been looking for some enablement myself. :) j >-----Original Message----- >From: Tom C [mailto:[EMAIL PROTECTED] >Sent: Tuesday, March 15, 2005 1:18 PM >To: [email protected] >Subject: Re: FA 31/1.8 Limited Enabled > >Clear answer... Thanks. I figured it must have to due with >possible vignetting, as many wide angle hoods are rectangular. > I didn't put two and two together and realize that the petal >shape was a deliberate compromise for size. > >Tom C. > > > >>From: David Oswald <[EMAIL PROTECTED]> >>Reply-To: [email protected] >>To: [email protected] >>Subject: Re: FA 31/1.8 Limited Enabled >>Date: Tue, 15 Mar 2005 10:07:03 -0800 >> >> >> >>Tom C wrote: >>>Yesterday I received my FA 31/1.8 Limited. Purchased from another >>>list member who heard my pleas for help in finding one at a decent >>>price. He had one in brand spanking new condition, which I was able >>>to purchase at a reasonable price. >>> >>>A beautiful lens. >>> >>>I'm curious why it has a flower-shaped lens hood with only hooded >>>sections at the top and bottoms, and is not a complete circle. >>>Probably a foolish question to which the answer is obvious. >> >>Flower-petal lens hoods are a "best comprimise" solution. As >you know, >>the image captured by a camera is not circular, it's some sort of >>rectangle, wider than it is high. By extending the portion >at the top >>and bottom of the hood longer, you get more coverage where possible, >>without growing the hood to some unacceptably inconvenient size. And >>of course at the sides, where the film plane is literally capturing a >>wider portion of the lens's image, the hood, at its specific >diameter, >>must be shorter to prevent vingetting. >> >>A round hood of constant "length" would either have to be of larger >>diameter, or shorter overall length to avoid causing >vingetting in the >>corners and sides of an image. If it's larger diameter, it becomes >>both less convenient, and less effective. If it's shorter, >it becomes >>much less effective. By using the petal design you get a >narrow enough >>diameter to be effective at blocking a lot of ambient light, while at >>the same time remaining conveniently sized, and while avoiding >>contributing to vingetting. >> > > >
