RE: Fast Lenses: Why so expensive?

[enitka <enitka@twcny.rr.com>]

Kevin - it has nothing really to do with the diaphragm - it has all 
to do with the physics of correcting light to produce an acceptable 
image.  It is the engineering and in many instances the use of 
special glass such as aspherical lens surfaces.  Your previous 
impression about the speed of opening up the diaphragm doesn't add to 
the expense of the lens and in the case of rangefinder lenses there 
is no opening or closing of the aperture once it is set on the lens.

ernie


> I previously was under the impresson the the diaphragm opened when 
> the picture is taken. I theorised that a fast lens was fast because 
> a diapragm opening to f/1.4 @ 1/1000 would be faster than a lens 
> that opened to
> f/5.6 @ 1/1000. Obviously that isn't the case.
> There is much that I do not understand regarding the physics of 
> light. It just seems from a non-engineering point of view that 
> building a lens with a large aperture shouldn't be any more 
> expensive than a lens with a small aperture.
>
>
> Kevin
>
> 	-----Original Message-----
> 	From: Ernest Nitka [mailto:enitka@twcny.rr.com]
> 	Sent: Tue 12/24/2002 12:17 PM
> 	To: List for Photo/Imaging Educators - Professionals - Students
> 	Cc:
> 	Subject: Re: Fast Lenses: Why so expensive?
>
>
>
> 	Kevin - simply put the faster the lens the more correction has to be
> 	designed into the lens so the distortions don't get the best of the
> 	image.  The opposite of this design requirement is the pin 
> hole camera - a
> 	hole without a lens at say f/256 will give you an image 
> albeit not terribly
> 	sharp.  The more technical on the list can give you all the 
> technical reasons.
>
> 	ernie