Flash GNC mode???

[rafikiphoto]

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I was reading through the section of David Taylor's book about using flash with the M 240. In the paragraphs about setting 'automatic flash' one of the steps he lists to achieve this is setting the flash to GNC (Guide Number Control) mode. I looked at the mode options but didn't see GNC mode. Looking at the menu on my SF 58 flash unit I see an A mode and a TTL mode in addition to M. Which of those first two is GNC mode?

[FlashGordonPhotography]

GNC= Guide Number Control. It's an early attempt at digital TTL versus the system built into the modern flash units. TTL flashes built for the film era couldn't do the required preflash measurements for accurate exposure with digital sensors. So GNC was added in firmware to allow some older flashes to work with digital, although in a limited way. The only flashes that needed to be put into GNC are the older Metz units that used the SCA3012 (version 4 or 5) adaptors.

 

I'm guessing that part of the book hasn't been updated since the M8 version.

 

The modern relative of GNC on your SF 58 is TTL.

 

Gordon

[rafikiphoto]

Thanks for that explanation Gordon.

 

I often leave my M240 in auto ISO with a max setting of 3200. Is auto ISO compatible with TTL flash on a SF 58? If so how/when does the ISO setting become selected? I can see no reference to this in either the M240 manual nor the SF 58.

[FlashGordonPhotography]

In both TTL and auto modes the ISO value is transferred to the flash from the camera. This includes auto ISO. The exposure is locked on a half press of the shutter.  That's when the ISO settings are read by the flash. 

 

Gordon