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[OM] Re: 58mm lens hood for Vivitar Series 1 90/2.5 macro

Subject: [OM] Re: 58mm lens hood for Vivitar Series 1 90/2.5 macro
From: Moose <olymoose@xxxxxxxxx>
Date: Wed, 18 Oct 2006 22:13:47 -0700
Chuck Norcutt wrote:
> Anybody have or know where to get a 58mm lens hood for a Vivitar Series 
> 1 90/2.5 macro.  Or, if not the real hood, anyone know the specs?  Inner 
> diameter and length of the hood?
>
> <snip>
> Or, all you folks out there with a Zuiko 90mm f/2 or 135 f/4.5 macro and 
> the 108-242 hood.  What's the inner diameter and length of that hood?
>   
I held my pedantic self in check with the little thread about hoods for 
28mm Zuikos, but I don't want to bust a gut...

There is an unwarranted and often incorrect assumption being made here. 
And it is so obvious in this particular example. Has anyone asked 
themself how the same hood can be correct for a 90mm AND a 135mm lens?. 
Using the kind of logic going on here, either the 135 has to vignette or 
the 90 has less than ideal protection, not like Oly at all. :-)

The thing is, the depth and diameter of the hood mean nothing unless you 
know the relationship of the filter thread or slip-on mounting point to 
the front node of the lens. It is obvious that the front node of the 
90/2 is closer to the hood mounting point than that of the 135/4.5, so 
the same hood length and diameter will subtend different angles for the 
two lenses.

So if you get the dimensions of the Viv I 90/2.5 macro hood, you have 
something useful to work from. The dimensions of the Zuiko hood don't 
mean a thing for the Viv.

The only home technique for dealing with this that I know of that 
doesn't involve shooting lots of images* is to project from the film 
plane through the lens. I put the camera with lens and hood attached on 
its back on a light table. Then I lay a translucent screen of some kind 
across the hood. With my light source and a dark room, all I need is a 
piece of white paper.

Then I can zoom, focus and change the aperture while observing the 
projected form of the film opening to see if it hits the hood. It's 
worked for me so far. With a cheap rubber tele hood, if it vignettes, 
you can just cut it down.

Moose

* A viable option with ditgital, where it wasn't for me with film, but 
still more trouble that the projection technique.

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