Archived posting to the Leica Users Group, 2002/03/30
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]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 > > __________________________________________________ Do You Yahoo!? Yahoo! Greetings - send holiday greetings for Easter, Passover http://greetings.yahoo.com/ - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html