Leica M9 - Bright-line Viewfinder and Rangefinder

Bright-line view- and rangefinder / 131
Bright-line view- and rangefinder
The LEICA M9’s bright-line view and range finder is
not only a very high-quality, large, brilliant and bright
viewfinder, it is also a highly accurate range finder
coupled to the lens. It has an enlargement factor of
0.68x.
The size of the bright-line frame is optimized for the
full format of the LEICA M9 and thus corresponds ap -
proximately to the sensor size of 24x36mm
1
with a
distance setting of 1m. The bright-line frames are
linked to the distance setting in such a way that paral-
lax error - the misalignment between the lens and the
viewfinder axis - is automatically compensated. The
bright-line image and the picture are practically identi-
cal over the entire distance setting range of 0.7m to
∞. Practically identical means that at distances of less
than 1m the sensor records slightly less than is dis-
played by the inner edges of the bright-line frames
and records slightly more at longer distances (see
adjacent graphs). These slight variations, which are
rarely significant in practice, are due to the operating
principle:
Bright-line frames on a viewfinder camera must be
adjusted to the angle of view of the relevant lens focal
lengths. However, the nominal angles of view change
slightly when focusing – due to the changing exten-
sion, i.e. the distance between the optical system and
the sensor plane. If the set distance is less than infini-
ty (and the extension is correspondingly larger), the
actual image angle is also lower and the lens records
less of the subject. In addition, the image angle differ-
ences are greater at longer focal lengths as a result of
the greater extension.
All pictures and bright-line frame positions relate to 50mm focal
length
A Bright-line frame
B Actual image field
Set to 0.7m: The sensor records approx. one frame width less.
Set to 1m: The sensor records exactly the image field dis-
played by the inner edges of the bright-line frame.
Set to infinity:
The sensor records approx. 1 (vertically) / 4 (hori-
zontally) frame width(s) more.
1
The exact format is 23.9 x 35.8mm, corresponding to the usable
format of analog Leica M models.
A
B