Archived posting to the Leica Users Group, 2002/03/30

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Subject: [Leica] Re: [MUGers] Magnifier issues
From: Henry Ting <henryting10@yahoo.com>
Date: Sat, 30 Mar 2002 09:25:08 -0800 (PST)

Thanks Erwin. The best posting on the question of the
Leica VF. 

- --- Erwin Puts <imxputs@ision.nl> wrote:
> There has been some discussion about the loss of
> viewfinder transmission
> when using the magnifier.
> Generally there is always a loss in light
> transmission when there is a
> magnification without compensation for the Entrance
> Pupil Diameter. Look
> through a 8x42 binocular and a 10x42 and you may be
> able to notice a loss in
> light transmission.
> This also works for the several viewfinder
> magnifications in the M bodies.
> The 0.58 has the finder with the highest clarity and
> the lowest flare
> factor. The 0.85 has a finder that is a bit dimmer
> and a somewhat highr
> propensity to rf-patch flare. With a higher
> magnification the Exit Pupil
> Diameter becomes smaller. The Exit Pupil of the RF
> patch has a diameter that
> is close to the average diameter of the eye. But
> when you focus in the dark,
> the Pupil of the eye is enlarged and becomes wider
> than the RF Exit Pupil,
> which causes a slight loss of the transmission
> values. So in general when
> you focus in dim (non)-available light with the
> Leica RF, you will
> experience a loss of brightness, as outlined above.
> This loss is most likely
> compensated for by the eye's sensitivity as no one
> ever complained about
> this. The loss is greater with the 0.85 than with
> the 0.58.
> Now the magnifier. As is the case with every
> magnifier (remember the
> Apo-Extenders?) there will be a loss of brightness
> with the magnification.
> With the 1.25 magnifier it is 1.25^2 (1.25 squared),
> that is 1.5625
> (calculated with the HP 41 (the Leica of the
> calculators). This is a half
> stop and not the full stop as mentioned in recent
> discussions.
> Adding A plus B, we may note that the 0.58 finder
> with a 1.25 magnifier has
> equal brightness as the unaided 0.72 finder. And the
> 0.72 with magnifier is
> equal to the unaided 0.85 finder.
> 
> I hope this clarifies the issues involved. A half
> stop by the way is not
> noticed at all when we study and analyse the natural
> vignetting of a lens.
> 
> Erwin
> 
> 


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