Westinghouse Photoflash Bulb no. 11
No. 11 Class “M” 20 milliseconds to peak.
Set Shutter to “M” or “X” for zero delay but to be used at 1/25 sec. shutter speed only.
Exposure guide numbers
Shutter
Speed ASA 80-125 ASA 160-250
|
1/25 |
330 |
460 |
|
1/50 |
280 |
400 |
|
1/125 |
260 |
360 |
|
1/250 |
200 |
280 |
|
1/500 |
150 |
220 |
Select guide number for the film and shutter speed that you intend to use.
Divide the guide number by the distance in feet from bulb to subject. The result is the proper lens opening (F-Stop) for correct exposure.
Example:
Film rating is 100 ASA
Shutter Speed is 1/250
Guide number is 200
Divide 200 by distance 5 (feet) = lensopening F stop = 4