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RE: [OM] Lens Hood question

Subject: RE: [OM] Lens Hood question
From: "skipwilliams@xxxxxxxxxxxxxxxx" <skipwilliams@xxxxxxxxxxxxxxxxxxxxxxxxx>
Date: Thu, 31 May 2001 17:11:37 -0400
Logic would suggest that using a wider-than-necessary hood would only result in 
possible flare from light outside the FOV cone hitting the front objective.

In the cases you describe, I wouldn't worry.  It's not going to vignette, 
you're just not the proper, narrow-er hood for the 35 or 50's.  Personally, I'd 
use the 40/85/100 rubber hood on a 50mm lens, as it is very forgiving re: 
dents.  And that hood is easy to find.

A potential overlooked issue is that some hoods are designed with a specific 
angle of view + front objective set-back (from the hood mounting point) to 
maximize the hood's functionality.  But I don't think any of the OM lenses or 
hoods are built with such deep-set objectives where that would cause a problem.

Some musing on the OM hoods:

The hood for the 28-48/4 seems particularly wide, but you have to remember that 
it spans a significant focal length and it also rides on the outer 55mm filter 
ring.

The aformentioned rubber 40/84/100 hood seems counterintuitive that it should 
work on these three lenses; with their widely differing focal lengths.  But you 
have to remember that the 40mm lens had a front objective element that is VERY 
close to the filter ring, so the incoming FOV light cone diverges very quickly 
away from the lens.  The same hood on the 100/28 sits much further away from 
the objective.

The 90/2, 135/4.5 hood is another compromize example, fitting both lenses and 
probably optimized for neither.

And don't forget the 21/3.5, 35/2.8-Shift hood.  It's very wide, accomodating 
the 21mm FOV of the 35-shift lens.  If you used a 35 hood on the 35-Shift, you 
could be OK; as long as you didn't shift the lens.

As an aside, I have several wide angle lenses (i.e., 35/2.8 CZ Biogon Pre-War) 
whose add-on hood is very small and seems too small to help.  But when you 
couple it with the extremely deep-set front objective, it works.

Geez.  I didn't know I was so long-winded on hoods.  Maybe it's time to go home?

Skip


Original Message:
-----------------
From: Bill Stanke bstanke@xxxxxxxxxxxx
Date: Thu, 31 May 2001 13:01:29 -0700
To: olympus@xxxxxxxxxxxxxxx
Subject: [OM] Lens Hood question


Hi Zuiks:

What happens if you use the wrong shade on a lens - vignetting?
Specifically, if I use the hood for a 28 mm /F2.8, 28 mm /F3.5
(#108-221) on a 35 mm /F2.8 or  50 mm /F1.8.  I notice that the 35 mm
and 50 mm have a different part number (108-230), but is there a
function difference?

Thanks!

Bill Stanke

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