Elinchrom D-Lite RX4 and Guide Numbers

<p>New to studio flash photography and just purchased an Elinchrom RX4 lighting kit. I have a question regarding the guide number as found in the manual which is stated as 64.3 (f/stop at 1m: f/64.3, ISO100).<br>

My question is does the guide number change with the power settings? I understand that the GN = (distance from flash X f/stop) but do the unit power settings change the GN? If so, shouldn't there be a chart? Also, I have found the power settings (2-6) referred to as 5 f/stops. How do the number 2.0 - 6.0 correspond to f/stops? <br>

Thank you!</p>

<p> </p>

<p>The guide number will decrease with the decrease in power setting. I would suggest getting a flash meter (a Sekonic L 308S would be a good economical choice) if you want to be able to easily set power levels that will allow you to set the f/stop that you want to use.</p>

Hi, like Andrew said.

 

I looked at the manual, it appears that full power is at the setting of '6.' Each time you reduce power by one number, from 6

to 5, and then from 5 to 4, etc., the power is cut in half, which is the same thing as one f-stop of light. If you want to figure

a new guide number for each reduced power setting, you can divide previous guide number by 1.4 (the square root of 2).

 

For studio work, though, it's better to work with a flash meter because every attachment, umbrella, soft box, etc., will

change the amount of light. And the light from these won't follow the inverse-square law exactly at close distances. Trial

and error works too, then sticking with predetermined distances and power settings, but the meters are just so

convenient.

Ignore Guide Numbers for studio work. They're exactly what they

say; a "guide" only, and a very approximate guide at

that. Guide numbers vary with any modifier used and the angle of lighting. You're better off chimping with a digital

camera, or using a flashmeter. No need to spend

big on a fancy Sekonic though. There are Shepherd

meters to be picked up used for peanuts. IME

they're more than accurate enough. I can vouch that their FM1000 model is flexible and accurate, with a good range of exposure readings.