ECX flash

[steve_d6]

<p>Does anyone have a flash range for this flash using ISO 25? The manual only provides ISO 100 = 2 meters.</p>

<p>Steve</p>

[steve_d6]

<p>I'm really confused as to how to calculate the distance when the film ISO, flash Guide Number and f/ is known? Is the formula GN ÷ f/ = distance in meters? That would be 12 ÷ 3.5 = 3.5m or 11.5 feet.<br>

Is the GN halved when the ISO is reduced one stop (GN of 12 @ ISO 100 reduced to 6 @ 50 and 3 @ 25?<br>

I can calculate the distance for the Minox 8x11 flash (GN 12) and the ECX flash (GN 12), but what about the cube flash? I read the box and the GN depends on the shutter speed selected. With an X synch (1/30 sec) the GN indicated is 100 for ISO 100 film. ISO 25 film results in a GN of 55.<br>

Is this somewhat on track? Sorry for such fundamental questions, but I'm dealing with "non auto" flashes!<br>

Steve</p>

[steve_d6]

<p>I think some reading straightened me out. I forgot GN ratings for a flash are specified in meters or feet for standard 100 ISO film. It is best to convert the GN to feet if that is your desired goal and there are calculators for this purpose. A GN of 12 (at 100 ISO) for the 8x11 flash or the ECX flash is in meters. A conversion to a GN in feet works out to 39.4. For a film having an ISO of 25, the GN in feet is 19.7.<br>

The formula then works for determining the distance using the ISO 25 at full power (no choice for the Minox flash). Distance = GN ÷ f/. For the f/3.5 Minox sub mini cameras that works out to 5.63' = 19.7 ÷ 3.5. Now I can sleep tonight. Of course, the film will have latitude and it'll allow for fixing later.</p>

[Jochen_S]

<p>Sleep well. GN math: Half ISO means GN : 1.4, Quarter ISO = half GN</p>