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Re: [Rollei] Fundamental WL Finder and magnifier question
- Subject: Re: [Rollei] Fundamental WL Finder and magnifier question
- From: Randy Holst <mistervolvo >
- Date: Thu, 29 Jun 2000 01:35:24 -0700
- References: <20000628212224.89214.qmail >
Javier Perez wrote:
> I've noticed that on just about every medium format camera
> the focusing screen does not have a magnifier. Magnification
> is carried out by the eye loupe alone and the results are more than adequate.
> On 35 cameras however, the the screen has a magnifier on top of it and the
> eyepiece provides additional magnification. I like the medium fornat solution
> better since it's simpler but I'm not sure if it's actually superior.
I think you are confusing the condenser lens, attached to the focusing
screen on some cameras, with a magnifier. The purpose of the condenser
lens is to increase image brightness in the corners of the viewing
screen by directing the light rays toward your eye. In some cases a
fresnel lens is used for this purpose and in others both a condenser and
a fresnel lens. There is only one magnifying eyepiece in either a 35mm
SLR or a medium format TLR.
> My question is simply how did this develop this way? Wouldn't one
> optical element provide better brightness than 2. Is the premagnifier
> there on 35s in case a pentaprism is used?
Again, it's not a "premagnifier", it's a condenser lens. I imagine the
condenser lenses came first, then later the fresnel lens, which performs
the same function but is thinner and lighter. With either method, the
purpose is to make the viewfinder image easier to see, not bigger.