>Ken,
>
>Yes the compendium hoods that cinematographers use are ideal for
>coverage and protection, but not ideal, from cost, complexity and ease
>of use. These are mostly used in studio conditions even by still
>photographers (most large-format cameras have compendium hoods available
>as did Hasselblad). There are a few 3rd party compendium hoods for
>35mm. The only one I've used is the Ambico, but I'm not very happy with
>it (it's pretty flimsy).
>
>The round funnel or round tube designs are the easiest to design and are
>very compact (rubber round funnel collapses, round tube can either
>retract or be reversed on the lens).
>
>For wide angle lenses the round hood must be made very short to avoid
>vignetting the corners of the frame.
>
>One way to get a more effective hood for a wide-angle lens is to use the
>round funnel or tube design and cut back the corners making the petal
>design.
>
>Someone said that a lens was round so the hood must be round as well,
>that's not really correct.
I said that, as the lens is round, the optimal hood cannot be rectangular.
The rectangular hood is optimal only for pinholes.
>Lenses are round as is the image they
>produce (and the section of the world that they see. But, and it is a
>big but, our cameras crop a 2:3 rectangular piece out of that round
>image. So the hoods are best rectangular.
Hoods are usually best rectangular, but they are not optimal.
Think of a 200mm f/2.8 focused at infinite. The ligth that will form the
image in one of the corners of the negative will come from a 71mm diameter
light cylinder at 6 degrees in the diagonal direction.
It's easy to see that it doesn't match the corner of the hood unless it's
rounded.
The bigger the aperture, the more rounded it will need to be.
>The best hood, sort of a compendium would be a rectangular pyramid with
>the lens stuck through the small end. There's a cute one up on eBay:
>
>http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=1236279414
>
>It's not really easy to see the picture, but the hood is pretty
>effective for the lenses covered. It works for both 50mm and 35mm,
>because the Retina's 35mm lens' front element is closer to the edge of
>this particular hood (the 50mm front element is recessed into the hood).
>
>I do agree, that a rectangular hood would take up a lot of space in a bag.
That's one important point of petal hoods. If it's easier to pack, it can
be made bigger, so it can protect more than a rectangular one.
For every rectangular hood, a petal shaped hood that gives more protection
can be made. It only need to be big enough (diameter greater that the
rectangular hood diagonal).
>Also, hood don't do anything but act as bumpers if the light source is
>not beside or in front of you. If the light is behind you, the hood is
>not doing anything optically.
>
>As far as I'm concerned the Canon FD hoods were about as good as you can
>get. The EF hoods are a pale imitation for durability, coverage, ease
>of use and storage. It's almost as if Canon said, we must obsolete
>EVERYTHING with this new line of cameras. Our customers must not be
>able to make use of ANYTHING they already own.
Don't think so.
>Mr. Bill
Best regards
Vicente
*
****
*******
***********************************************************
* For list instructions, including unsubscribe, see:
* http://www.a1.nl/phomepag/markerink/eos_list.htm
***********************************************************
