Ext.A vs Ext.B

[tecboy]

I recently bought 600EX-RT. There are two interesting features. One is Ext.A, and another is Ext.M. I assume these work like TTL but the sensor is reading from the speedlite and not through the lens. Can someone explains these features? I don't quite understand.

 

[table1349]

Have you read page 36 & 37 in the manual?

 

[tecboy]

I still don't understand. At Ext.M, what ISO and aperture have to do with flash? What does it mean by "stops the flash when the standard exposure is reached?"

 

[table1349]

Ok, in Ext. A. takes the ISO and aperture readings from the camera and uses the built in metering sensor rather that TTL to determine the flash power needed.

Ext. M you inter the ISO and aperture in to the flash unit and it does the same thing.

 

[tecboy]

So Ext.M, I adjust the ISO and aperture in the flash unit. Do I need to do the something on my DSLR?

 

[tecboy]

Oh, now I get. Didn't read the whole thing. I have to set the same ISO and aperture on both flash unit and my DSLR.

 

[table1349]

Oh, now I get. Didn't read the whole thing. I have to set the same ISO and aperture on both flash unit and my DSLR.

 

[tecboy]

I read somewhere in the internet about the Ext. A and Ext. B are older technology, TTL is much better.