[Frameworks] projector question

[Carl Lee]

Hi David --

Thanks for your reply.  Hmm.  I guess I was confused by the original 
post by Christopher Harris. He wrote:

"I very recently bought an Elmo 16 CL DELUXE projector with a 38mm lens 
and I noticed that compared to the Eiki owned by the university where I 
teach the throw is much wider than the Eiki with the ISCO 35-65 16MM 
zoom lens."

I was assuming he had zoomed out all the way on the ISCO to compare the 
throws.  Am I missing something?

Thanks,
Carl



David Tetzlaff wrote:
> 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.
>
>
>
>