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[OM] Re: E-1 craving

Subject: [OM] Re: E-1 craving
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Thu, 10 Aug 2006 22:43:14 -0400
I think you're confused.  The size of the viewfinder isn't the size of 
the viewfinder lens you're looking into.  The size of the viewfinder is 
the size of the screen which is close to the size of the film.  The 1/2" 
eyepiece you look into is just a magnifying glass that allows you to 
look at the screen.  And the greater the magnifcation it provides you 
the less the intensity of the light to your eye since a given amount of 
light is getting spread over a larger area.

The 35mm and 6x6 100mm f/2 lenses let in exactly the same amount of 
light *to a given area of film*.  That should be clear from the fact 
that the exposure will be the same at f/2 regardless of the format.

My point was that it's hard to find a normal 6x6 lens (90mm) that's 
faster than f/4.  The problem is that the larger format lens has to 
cover a larger area of film.  That makes the optical design more 
difficult although that is ameliorated somewhat by the fact that the 
larger format lens doesn't have to have as much resolution as the 
smaller format lens.

I wouldn't doubt that someone has made a 90mm f/2 lens for a Hasselblad 
but I probably don't have enough money to buy one.

Chuck Norcutt

Dan Mitchell wrote:
> Chuck Norcutt wrote:
>  >> Hmm. If this was the determining factor, you'd think that
>  >> medium-format SLRs should have had really bloody bright
>  >> viewfinders.
>  >> AG
>  >
> 
>>No, regardless of the size of the viewfinder and a whopping big mirror 
>>you can't have a really bloody bright viewfinder with an f/4 lens.
>>
>>Chuck Norcutt
> 
> 
>   But comparing:
> 
>   35mm camera, 100mm/f2 lens, 1/2" square viewfinder to
>   6x6mm camera, 100mm/f2 lens, 1/2" square viewfinder,
> 
>   the latter would have a brighter viewfinder, because a 100mm/f2 lens 
> that covers the image circle of 120 film is letting in more light, so 
> there's more of it to be concentrated onto the viewfinder (if the 
> viewfinder's the same size).
> 
>   Presumably there's some sort of optical reason it's hard to find 120mm 
> 100/2 lenses -- though Hasselblad make a 100/2.2:
> 
> http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=362306&is=REG&addedTroughType=categoryNavigation
> 
>   That takes 77mm filters, whereas a 100/2 in 35mm size takes a 55mm 
> filter. I'm not sure if I understand the optics well enough to know if 
> that makes sense or not, to be honest..
> 
>   -- dan
> 
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