[Cosmo]

Can someone please explain how the baseline lengths and viewfinder magnification effects the camera, all I know is that the longer the effective baseline, the easier it is to focus close up with faster lenses.

[Mike Cash]

Since a rangefinder doesn't look through the lens, how could it possibly matter how fast the lens is? You can focus a rangefinder with the lens cap on. Can't imagine a much slower lens than that.

[Cosmo]

DOF is shallower with a faster lens, so it's easier to get focus right. I think there's just some fundamental problems with close focusing on a rangefinder or something, and baselength has something to do with it, I think.

[noblepa]

Mike is right. The aperture of the lens has absolutely nothing to do with focusing a rangefinder, since you are not focusing through the lens. What you are saying about it being easier to focus with a fast lens is true of an slr, either film or digital, since they DO focus through the lens.

A rangefinder need not even be attached to the camera. It works by using mirrors and lenses to triangulate on the subject. In a rangefinder camera, you look through a viewfinder (not the lens). Inside the viewfinder, there are mirrors that split the image, usually top to bottom, in two pieces. Through the mirrors, you are looking at the top of the image via the mirror on the left, while the bottom of the image is shown through the mirror on the right. This is just like your eyes. As you focus, the mirrors turn slightly, so that they are forming a shallow angle. Basic trigonometry tells you the distance to the subject, based on that angle.

In the thirties, forties and fifties, when many cameras were neither slrs or rangefinder cameras, they had distances marked on the lens barrel. You would simply guess at the distance and set it accordingly. If you wanted to be a little more accurate, you could buy an auxilliary rangefinder that would clip onto the accessory clip on top of the camera. You would focus with the rangefinder, read the distance off the scale and transfer that to the lens. These still appear on ebay with some frequency.

I think that the baseline you are referring to is the distance between the two mirrors. In a 35mm rangefinder camera, this is limited to only a few inches. On WW II battleships, before radar became widely available, they used rangefinders that were about six feet long to calculate the distance to the big guns' target.

Rangefinder cameras were never known for their ability to accurately focus very close. For extreme closeups, photographers often resorted to using a tape measure. Look at the top of many old rangefinder cameras (or even many film SLR's) and you will see a small circle with a line through it. This indicates the exact location of the film plane. It is to this mark that you would measure and then manually adjust the focus on the lens. Unfortunately, you never knew whether you were successful or not until you developed the film.

[Marc Sabatella]

Actually seems to me it would be the other way around - shallow DOF on a rangefinder would mean there is less tolerance for error.

[jake.astig]

hello,
as mentioned, rangefinders work using the concept of triangulation. the wider the baselength, the higher the accuracy. the finder magnification just makes it easier to line up the two images when you focus.

[Talisker]

A longer baseline or greater viewfinder magnification both give more accurate focusing - the longer baseline gives a more accurate triangulation; the magnified viewfinders give a more accurate view of the rangefinder patch. Thus longer baseline/magnified rangefinders are able to adequately focus longer lenses or shorter lenses at wider apertures where there is a shallower depth of field.
The longest lens most 35mm rangefinder cameras were normally judged able to focus was around 90mm; those with greater magnification viewfinders (such as my Voightlander Bessa T) can happily focus 135mm lenses. Leica did make 200mm lenses for their rangefinders, but you had to add magnifying 'spectacles' over the rangefinder window and viewfinder.
The other issue with close focusing is parallax error as the viewfinder is some distance from the lens so does not give exactly the same view - the closer you get, the more apparent this is. In modern rangefinders the brightline in the viewfinder moves to compensate for this, but brightlines aren't that precise, and you may not have the right brightline available for the lens you are using.