flash range 420ex

[G3Hawaii]

What's the range for the 420EX? How far can I be from the subject and still get decent light from the flash?

[BruceW]

The manual indicates the following Guide Numbers for Normal Sync at 100 ISO, in meters;

Flash Coverage (mm)........Guide Number
24......................................23
28......................................25
35......................................31
50......................................34
70......................................37
105....................................42


I think you divide the figure on the left by 5 to get the equivalent value for digital cameras. Also don't forget that the G3 will default to 50 ISO when it can using auto selection.

Bruce

[BruceW]

G3Hawaii,

Sorry, I probably assumed more than I should with the above info.

In case you don't know, Guide Number, usually abbrviated to GN, is an indication of the power of a flash. To determine the maximum distance it can work over you need to know the ISO setting, the aperture of the lens and the flash coverage required.

Flash coverage is basically related to the zoom setting on the lens. If you choose a wide angle lens setting, then an adjustable mechanism inside the flash will spread the light in a wider arc, which reduces the reach.

GN divided by aperture gives distance. So as an example, for 100 ISO, F2.0 and lens at mid range (10mm digital or 50mm film) the calculation would be:

- GN is 34, from table above.
- Distance = 34/2 = 17 meters.

If you wanted to calculate for a different ISO you need to use the following formulae:
GN2 = GN1 (Square Root (ISO2/ISO1))

eg. if GN is 34 at ISO 100,
then at ISO 400 the GN will be 68 (ie. 34 x 2).

Often you will see GN expressed in both meters and feet, allowing you to choose the one with which you are most comfortable. The 420EX manual only gives the meter values.

Bruce

[Peter Aczel]

Simply: GN/Ap=distance

for example: GN=40, aperture=4, distance=10m

Manufacturer gives GN for wide, normal and tele - if the flash can zoom.