[Leica] Hoods???? Who makes square ones???

["BIRKEY, DUANE" <dbirkey@hcjb.org.ec>]

>   The cylindrical hoods can be built-in to the lens.  The light 
entering
>the lens forms the shape of a cone, determined by the angle of view of 
the
>lens.  As long as the edges of the hood lie just outside this incident 
cone
>of light there will be no vignetting and the hood should operate most
>efficiently, no?  The long dimension of rectangular hoods leave gaps
>between this entering cone of light, offering more space for stray 
light,
>and leading to a greater likelihood of flaring the lens. This is the 
way I
>understand it, anyway. Off-axis light rays that can get into the lens 
can
>contribute to a loss of contrast.  So what's this business about the 
ideal
>shape of a lens hood being the same as the format of the film?  The 
only
>case where I can see that this might apply is for panoramic cameras. 
Can
>anyone fill in the gaps here for me?

>- -GH

The most efficient hoods are the ones that block the most amount of 
light of light from hitting the front element.   Canons round hoods 
with cut-outs are as efficient as plain rectangles.  They certainly are 
more convenient because you can reverse them on the lens.  Unlike the 
hood for the 35 Summicron ASPH...... groan!

If you are shooting into the sun and the sun hits hits the front 
element  (whether it is in the picture or not)  you will get some flare 
or internal reflections with many lenses.  I have a zoom lens that is 
very difficult to use if you include the sun.  

Leicas control of internal reflections is one of the reasons I am now 
using M  EQ for much of my location work.

Besides that, if round hoods were more efficient, don't you think that 
Leica would make all of theirs round???????  Instead, all of their 
(most at least?) wide angle hoods are square.

Reminds me of a Huey Lewis song...  I think I'll sing it as I return to 
the dark room......

It's hip to be square  (doot, doot do woo oh woot.)  

It's hip to be square.......... here, there and everywhere......  hip, 
hip, so hip to be square........

Must be the fumes...

Duane Birkey
HCJB World Radio
Quito Ecuador