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

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