Hasselblad 503CW TTL Flash and ISO Dial

[Brian Hirschfeld]

Hello all,

Today I learned that the ISO dial on the side of my 503CW is used for controlling TTL flash, or at least informing the TTL flash what the ISO setting of the camera is. I assume that this means that somehow the shutterspeed and aperture are being communicated no? I truly don't know how TTL flash works but I was wondering if you guys could help explain it to me on an electronic level since obviously the body isn't powered, so the power is coming from the flash unit (again I assume) and I don't understand where this communication is occurring, I don't know if it matters if I am shooting my 120 CFi, 50mm CFi, or 80mm CF, thanks.

Best,
BH

[Chris Livsey]

http://www.hasselbladhistorical.eu/pdf/hasmanuals/503cw.pdf

Page 17

[Mike Guilbault]

You set the ISO dial to your film, but you can over or underexposed the flash by using the ISO dial. Your ttl flash reads the ISO you set and compensates the output of the flash according to the value you select. Hope that makes sense. I used this method on my 503cx ans 503cw with a Quantum Q-Flash.

[fdisilvestro]

The system does not need aperture or shutter speed information, just the ISO. There is a cell inside the body that measures the light reflected from the film during exposure. That information is sent through the SCA module to the flash so it knows when to stop.

It is like the old auto flashes but with the measuring cell inside the camera, this makes it unnecessary to know the aperture, filters, lens transmission, etc.

[Chris Livsey]

Please read the manual, as linked. No power from the flash or communication from the lens is required.
The system relies on reflection off the film surface. The characteristics of film vary so different emulsions will give different results, you will need to test before relying on the system, as described in the manual.
I have no experience with a digital back on this model with flash but the reflection from a digital sensor is going to be much higher than from film but more consistent perhaps, but easier to test 

[fdisilvestro]

From the manual you linked:

"The flash unit powers the camera electronic's and also the flash adaptor, when that is used"

The flash adaptor is the SCA module and nobody mentioned communication from the lens.

[Chris Livsey]

The flash adaptor is the SCA module and nobody mentioned communication from the lens.

Well actually the OP did  

I assume that this means that somehow the shutterspeed and aperture are being communicated no?

and

 I don't understand where this communication is occurring,