Re: [Frameworks] projector question

From: David Tetzlaff (email suppressed)
Date: Thu Aug 19 2010 - 08:03:32 PDT

On Aug 18, 2010, at 2:25 PM, Carl Lee wrote:

> I'm curious -- why would the 38mm on the Elmo be wider than the ISCO
> 35-65mm if it's zoomed out all the way?
> Carl

Well, of course, it shouldn't be, and I don't think anyone said it
was. Sometimes manufacturers measure focal length differently, and one
brand of (XX)mm does not necessarily have exactly the same coverage as
another. But you may have been confused by Alain's remark:

> The ISCO 35-65 is f1.3 while the Elmo 38mm (I believe) is f1.5. If
> the image is wider on the Elmo and with the slight difference in
> speed, you'll see a difference in brightness.

The key word being the 'if', which would mean the ISCO is not zoomed
out all the way, but zoomed in enough to create a somewhat smaller
image that the Elmo, which given the extra speed of the ISCO, could be
perceievably brighter.

Of course, f-stop ratings aren't consistent either from maker to
maker. And while there shoudn't be much difference between f1.3 and
f1.5 at the same focal length, an ISCO is nice and bright and could
well be passing more light than another lens rated at the same f-stop.

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