Re: Kodak HIE/HSI and flash bulbs

[Clive Warren <Clive.Warren@xxxxxxxxxxxxx>]

At 2:08 pm -0400 9/8/99, Gary Beasley wrote:

>At 08:32 PM 08/09/1999 +0200, you wrote:
>>Gary,
>>
>>Thank you for the suggestion - unfortunately it is the flash bulb output in
>>terms of Joules/Lumens/GN etc that is of interest.  I have a variety of
>>bulbs ranging from the sublime to the ridiculous.
>>
>>Have alwaus harboured a desire for one of those bomb flashes that used to
>>be used for night aerial photography :-)
>>
>>We have a new tethered helium balloon in the city centre here in Bristol
>>that has unfortunately rekindled my interest in infrared night photography.
>>Luckily I am too busy to investigate it further at the moment ;-)
>>
>Tell me, would a flash meter get a reading from a flash bulb? My Minolta
>III flash meter will read through an 87C filter, maybe something like that
>would allow testing a few bulbs for relative output and derive a useful
>guide number from that.
>Gary Beasley
>http://beasleyglb.home.mindspring.com/


Gary,

A good idea and one which I tried out using a Gossen flash meter a while
ago.  The problem with flash bulbs is that the light intensity increases
over time and then decreases at approximately the same rate. Shutter speed
(leaf shutter) is an important variable for shorter exposures in
calculating GNs for bulb flash.

Most older shutters have a switchable delay for bulb flash, usually in the
order of 30mS, to allow the flash bulb to hit peak output before allowing
the shutter to open.

Flash meters are designed to record an almost instantaneous light from a
strobe head.

The result is that you get a low reading on a flash meter as it is not
designed to measure the cumulative output of a flash bulb.


All the best,

             Clive   http://www.cocam.co.uk
                     Photographic Services, Filters and Equipment
                            http://clive.bel-epa.com
                            Adventures in Cyberspace - Digital Art and Photos


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