At 02:20 8/4/02, Chris Barker wrote:
Dear all
With my newly acquired OM4Ti (Mint in box!) I received a flashbulb holder
for the hot shoe. It is called an Olympus Flash CL. However, Shipman
says that only the OM1N can be used with Photo Flash.
Does anyone have any experience of using Flash Bulbs (the ones I have are
Type 1B) and if the GN calcs on the pack are reliable? If I get no
replies I shall have to do some tests...
You made me dredge out the Kodak Master Photoguide, circa 1978!
What is the shape of the reflector? This determines guide number.
AG-1B guide numbers for ISO 100, in feet, and X-sync at 1/30th:
Polished bowl and hi-power flash cube: 130
Shallow dish and standard flash cube: 90
Shallow cylindrical reflector: 65
You likely have a very wide angle shallow dish, or the polished
bowl. Don't forget, with AG-1B's you must X-sync at 1/30th or you will
lose approximately 1 stop of light! Don't set the OM-1n to "FP" as this is
for long duration "FP" type bulbs only (e.g., 6B and 26B).
To convert a guide number from ISO 100 other film speeds, multiply by:
ISO 25: .50
ISO 32: .56
ISO 40: .63
ISO 50: .71
ISO 64: .80
ISO 80: .90
ISO 100: 1.00
ISO 125: 1.12
ISO 160: 1.25
ISO 200: 1.40
ISO 250: 1.60
ISO 320: 1.80
ISO 400: 2.00
ISO 500: 2.25
ISO 640: 2.50
ISO 800: 2.80
ISO 1000: 3.20
ISO 1250: 3.60
ISO 1600: 4.00
ISO 2000: 4.50
ISO 2500: 5.00
ISO 3200: 5.60
Note: these approximate multipliers are sufficiently accurate.
-- John
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