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Model
SAL20F28
Pages
47
Size
854.58 KB
Type
PDF
Document
Service Manual
Brand
Device
Digital Camera
File
sal20f28.pdf
Date

Sony SAL20F28 Service Manual ▷ View online

4-8
SAL20F28 (2.8/20) (20mm F2.8)
3)
Move the preset lever to set the preset ring at the open aperture position.
Fig.4-2-11
4)
Turn the aperture unit holding ring to adjust the position that the aperture blades are hidden into the edge completely.
Fig.4-2-12
5)
After the adjustment is completed, apply the adhesive bond (B-10) as shown in the Fig.4-2-13.
Fig.4-2-13
6)
Assemble the lens completely.
7)
Perform “4-2-1. Aperture Diameter Check”, and repeat “4-2-1. Aperture Diameter Check” and “4-2-2. Aperture Diameter Adjust-
ment” until the aperture error is within the specification.
Set the preset ring at the open aperture position.
Preset lever
Aperture Unit Holding RIng
Aperture blades are hidden into 
the edge competely.
Apply adhesive bond(B-10)(3 areas)
Bond
Aperture Unit
Holding Spring
Bond
Aperture Unit
Holding Ring
4-9
SAL20F28 (2.8/20) (20mm F2.8)
4-3.
PROJECTIVE RESOLVING POWER CHECK
Equipment
• Lens Test Projector and Variable Transformer (Output voltage: AC 100 V)
Note:
Connect the variable transformer (Output voltage: AC 100 V) to the lens test projector.
• A-mount Attachment
• Screen (Art paper)
• Tape Measure
• Plane Mirror (For SLRs)
1. Preparations
Note:
Check the projective resolving power of the checking lens at the following focal-length and distance.
Focal-length f (mm)
distance (m)
20
0.7 to 0.87
Table 4-3-1
1)
Perform the following steps (1) to (3), and incorporate the internal lenses of the lens test projector according to the checking focal-
length.
(1) Open the lid of the lens test projector.
(2) Pull up and turn the fixed levers on the right and left sides of the lens test projector.
(3) Remove or insert the lens.
Note:
Be sure to have the right position and direction of the lens.
Fig.4-3-1
Lens test projector
Incorporate of the lenses
according to the checking focal-length (f).
Lens
Fixed lever
Fixed lever
Lid
f=18 to 35 mm
f=35 to 100 mm
f=100 to 200 mm
f=200 to 300 mm
Heat-absorbing filter 
Chart
Chart
Chart
Chart
Filament
Filament
Filament
Filament
4-10
SAL20F28 (2.8/20) (20mm F2.8)
2)
Attach the checking lens to the lens test projector, and set the equipments as shown in Fig.4-3-2.
3)
Turn the fan switch of the lens test projector to ON, then turn the lamp switch to ON.
Fig.4-3-2
4)
Turn the focus ring of the checking lens until the chart image projected on the screen is the sharpest at the center (y’=0).
5)
Set the plane mirror to the center of the projected image (y’= 0), and adjust the projector position so that the mirror reflects the light
to the center of the lens.
Distance
Lens test projector
Chart
Fan switch
Lamp switch
Plane mirror
Screen
A-mount attachment
Checking lens
F
L
4-11
SAL20F28 (2.8/20) (20mm F2.8)
2. Checking Method
1)
Turn the focus ring of the checking lens until the chart image projected on the screen is the sharpest at the center (y’=0).
2)
Read the number of the smallest pitched lines at the center (y’= 0).
Fig.4-3-3
3)
Turn the mount rotation ring of lens test projector until the projected image at a certain peripheral point (y’= 15) on the screen
appears the most unsharp.
Read the number of the smallest pitched lines (both saggital and meridional: 3 lines) at the peripheral point.
Note:
When reading the number of the smallest pitched lines, be careful of the spurious resolution.
Spurious resolution is the reversed image of 2 or 4 lines which appears on screen when focus is beyond maximum revolving
power.
Do not confuse spurious resolution for the smallest pitched lines.
Fig.4-3-4
4)
Check that the all readings (y’= 0, saggital (S) and meridional (M) at y’= 15)  is within the specification of the Table 4-3-2.
When the specification is not satisfied, perform the following procedure.
• Replace the 1 group lens block, 2 group lens block and 3 group lens block.
Specification
Focal-length distance (m)
Number of the smallest pitched lines
f (mm)
Center (y’=0)
y’= 15
(Lines per mm)
S
M
20
0.7 to 0.87
100 or greater
50 or greater
63 or greater
Table 4-3-2
5)
After the checking is completed, turn the lamp switch of the lens test projector to OFF and cool the inside of the lens test projector,
then turn the fan switch to OFF.
The number represents for lines per mm.
Saggital (S)
Meridional (M)
Correct resolution
Spurious resolution
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