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George B · Joined: 05 Jun 2008 Posts: 37 Location: Northern New Jersey

A retired photographer just gave me a dozen GE No. 31 class FP bulbs.
I'd like to use them with a between the lens shutter, X sync, in a 12 inch SV studio reflector.
Since the flash duration is long would a 1 sec. shutter speed be about right for capturing the full output ?
I imagine the GN would be around 450 @ ASA 100.
The camera would be a tripod mounted Fuji GW690II, X sync only.

George B · Joined: 05 Jun 2008 Posts: 37 Location: Northern New Jersey

Ya know, after thinking this over maybe 1/15th of a second would be in order.

45PSS · Posted: Mon May 23, 2011 8:08 pm Post subject:

http://www.donsbulbs.com/bulbs/g632/l/ge1954/09.gif
has a graph of the burn time for this bulb.

http://graflex.org/flash/navy/ has some good information.

Now according to the graph the #31FP bulb reaches 3/4 of peak in approximately 15ms. then burns for approximately 55ms. before the light output is below the 3/4 of peak illumination. To get the full light of this bulb the shutter needs to be full open for 70ms. if shooting at full open aperture, if using smaller apertures then the shutter blades need to be open equal to or greater than the aperture opening. For the shutter to be open for 70ms on the close side your fastest shutter speed for full open is between 1/5 and 1/8 second.

1/15 second shutter speed is 67ms full cycle, the bulb would only be burning above the 3/4 of peak point for 18ms of the closing 33.5ms. if the shutter is working perfectly.

http://www.flutotscamerarepair.com/Shutterspeed.htm
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George B · Joined: 05 Jun 2008 Posts: 37 Location: Northern New Jersey

45PSS... Thanks for the info and the links.
This is exactly what I needed to know.