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16
INTERNATIONAL PROJECTIONIST
October 1931
This distance is the sum of the distances a and b, and their lengths are found through the formula
a M =
b
Insert the length of these distances in the following formula:
f
a b
\
and you will thus be able to find the exact focal length necessary to produce a certain size picture at a certain distance from the object.
This fundamental working knowledge will definitely enable us to cope with optical problems incident to our profession and will lead us to an understanding of the basic nature of the lens. Both will be useful, the first in the practical application, and the second in a heightening of the understanding which leads to a real interest in our profession.
Examples :
No. 1. With a slide which is 3" high,
and at a projection distance of 100 feet, we desire to project a picture 15 feet high. What focal length lens will be necessary?
Given:
Slide height, 3"; picture height, 180";
projection distance, 1,200."
height of slide a M = = or
height of picture
3 a
M = =
1 f
+
180 1,200
3 X 1,200 = 20
1
180 1 1
-\ or
a b f
1,200 + 20
20 1,220
24,000
1,200 24,000
24,000
f = == 19.67", answer
1,220
No. 2. A film is projected through an
aperture 0.6" high at a projection distance of 100 feet, and we desire to project a picture 15 feet high. What focal length lens will be necessary?
Given :
Aperture height, 0.6"; picture height,
180"; projection distance, 1,200".
height of aperture a
M
height of picture
0.6 a
or
M =
180 1,200
0.6 X 1,200^
180 1
= 4 1
f
1
a
+
=
b f
1,200 + 4
1,204 4,800
1,200 4,800
4,800
f = = 3.98", answer
1,204
Characteristics of RCA Photophone Tubes
With explanatory notes covering their use in all types of RCA equipment
Equipment
Amplifier
Radiotrons
Filament Voltage
Grid Voltage
Plate Voltage
Plate
Current
(ma.)
Remarks
PG-3, 4, 6, 7& 8
PA-12A
UX-210
6
— 9
135
3
1. Voltage amplifier using 6 Radiotrons UX-210 connected in 3-stage push-pull circuit. Battery power.
PK-1
UX-250 UX-281
7.5 7.5
—84
450
55 75
2. Power amplifier using 2 Radiotrons UX-250 in single push-pull stage with 2 UX-281 's to furnish plate and grid voltages from A. C. supply.
PG-10
PA-12B
UX-112A
5.
— 9
135
3.1
3. See remarks No. 1 above, except as to type of tube.
PK-1
UX-250 UX-281
7.5 7.5
—84
450
55 75
4. See remarks No. 2 above.
PG-13
PA-41
UX-112A UX-112A UX-112A UX-250
5 5 5 7.5
— 9
— 9 —13.5 —85
115 115 149 425
3.1 3.1
2.7 35
5. Voltage and power amplifier using 3 voltage amplifying stages with single UX-112A in each, followed by a power stage using 4 UX-250's in a push-pull parallel circuit; D. C. power from a 3-unit M. G. set.
PG-28
PA-67
UY-224*
UY-227
UX-245
2.5 2.5 2.5
—1.4
—8
—46
155 140 245
2 4 30
6. Voltage and power amplifier of 3 stages using 2 UX-245's in pushpi 11 in the power stage; completely AC-operated.
UX-280
5
42-50
6a. -42 ma. in PA67A1; -50 ma. in PA67A3.
PG-30
PB-23
UY-224 1 UY-227 ■ UX-245 UX-280
2.5 2.5 2.5 5
—0.6 —6
—44
180 100 220
1 3.5
30
40
7. Voltage amplifier of 3 stages using 2 UX-245's in push-pull in the output stage; completely ACoperated.
PB-24
UX-250 UX-281
7.5 7.5
—75
435
45 67
8. Power amplifier using 2 UX-250's in push-pull; completely AC-operated.
Notes: *Has a screen voltage of 62; t has a screen voltage of SO.
[This table prepared exclusively for Interkationai, Projectionist]