less
on
each side than the
24
x
36
mm
frame. This matches the w
indo
w
of
slide
mounts, so
that
there is no
cut-off
in
pro-
jectio
n. The image on the scr
ee
n
of
the
ALPA
half frame cameras measures
exactly
18
x
24
mm or 17x22.5 mm.
The
sc
r
ee
n image is m
ag.
nified, to give
life-size
with
the standard
50
'mm
lens, and even
with
small diaphragm
openings the entire image is
bright
into
the corners - most useful
for
comp
osition,
focus, de
pth-
of-f
ield.
An
optio
n
al
0.7 xeyepiece r
ed
uces
magnifi-
ca
tion, so
th
at persons
with
deep-set eyes
or wearers
of
glasses
ca
n
see
the entire
field.
Ev
en w
ith
small
flstops,
telephoto
lenses and
bellows
or
tubes, etc.
The
viewf
inder has a rotatable
bayonet
-
mounted
rubber eyeshield cu p
wh
ich
exclud
es
extraneous l
ight,
and
whic
h can
be replaced
by
a magnifier
or
a
right
-a
ngl
e
viewf
ind
er.
People with eyesight needing correction
can
fit
special lenses
into
a
mount
fixed in
the eyepiece. The
powers
available are:
- 4, - 3, - 2, - 1, +1, +2,
+3,
and +4
diopters.
2)
Focusing
on
the
screen
The
ALPA
11
el h
as
a screen which
combines a
split-image
rangefinder
with
a circular
zo
ne
of
microprisms. The lens is
focused
by
means
of
the ring
which
turns
the lens in its helical
mount.
Sharpness is
co
ntroll
ed
over all the
sc
r
ee
n
by
means
of
one
of
the systems mentioned
below.
a)
by
rangefinder
The groundglass screen has a
built-in
rangefind
er
formed
by
a pair
of
prisms
w
hi
ch appear
as
a pa
ir
of
semi-circles in
the middle
of
the screen. Choose a definite
detail in the subject and focus the lens
until
the image
of
the line across the range-
finder is in perfect a
li
gnment:
the subject
is
no
w sharply focused
(f
igs. 3 and
4).
The clear ring helps you
to
identify the
object
you
are
focusing
o
n.
In
photo-
micrography the
ae
rial image is focused
and it
is
necessary
to
see
it clearly at the
same time
as
one
of
the lines -
that
i
s,
without parallax (fig. 4).
Both
sem
i-cir
cular prisms w
ill
appear
unif
ormly
bright
under normal
conditions
.
Under certain circumstances (smaller lens
apertur
es,
close-up
photography)
one
of
the semi-circular prisms may appear
to
be
shaded. In this case
you
can align
yo
ur
image between the other, bright prism
of
the sp
lit-
image and the clear glass ring.
The scales indicated
by
the cross are useful
for
compa
ri
son (figs. 3 and
4)
, especially
in
photomacro-
and micrography.
b)
by
microprism
Mi
cr
op
risms
ar
e
actually
a large
number
of
small rangefinders which
show
clearly the
smallest mistake in
focusing
;
as
long
as
the foc
us
is wrong the image is very
blurred, As
soon
as
the
focus
is correct
the image snaps
into
clarity.
.3)
Focusing
by
distanc
e scale
All
ALPA
lens
es
are calibrated
for
distance.
It
is thus possible to
se
lect a certain
distan
ce
by using the scale
(for
example
whe
n using flash). Es
timating
the distance
of
the subject, it is set on the scale, taking
into
account
the
depth
of
field. This
method is useful
when
it is impossible
to
focus, either
when
there is
no
time (as at
a sporting event)
or
if it
is
too
dark
(when
u
si
ng
flash etc.).
5
