[rollei_list] Re: Rolleiflash Disaster
- From: CarlosMFreaza <cmfreaza@xxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Wed, 9 Dec 2009 15:35:39 -0300
Perhaps this is is a well known fact for the members, perhaps not, but
most standard flashes are designed to cover a basic area of 60º
horizontal and 45º vertical and the basic flash calculations for the
automatic modes are thought on this size, since this area is similar
regarding the area covered by a 35mm lens for 35mm format (and it's
enough for MF too), any longer focal length has a smaller area to
cover and then if you adjust the flash automatic mode for the right
distances range, the exposure will be right using a 35mm lens or a
135mm lens, you don't need a flash with zoom to do it.
The only advantage for a flash with zoom is that for longer FL lenses
than 35mm, the flash reduces the illuminated area according the lens
angle of view area concentrating the light proportionally; the flash
guide number is increased this way and you can reach more meters or
feet with the flash light if you are using a tele lens, but if you
already have a flash with a good basic GN, the advantage could be very
relative or no existant directly (if your flash has a higher GN than
the zoomed one for the longest focal length). For wider angles than
the flash standard, most flashes, zoom or no zoom, need difusser
screens.
In fact and f.e., the Metz MZ 54 manual says that using a zoom lens
it's better to keep the flash zoom fixed at the widest zoom lens focal
length, f.e. at 35mm for a 35-90 zoom, to assure a right exposure for
any zoom lens focal length, except if you, for some special reason,
needs to use the highest GN for a specific focal length, f.e. for 90
mm to gain a few meters of light, but for this case you need to recall
to re-adjust the flash zoom again because if you use it for a 35mm or
50mm FL, the light will be poor around the image center.
In other words, the flash zoom function is not so impressive and
useful as it looks initially.-
Carlos
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