fpdave
newbie
Reged: 23/09/2007
Posts: 2
Loc: High Peak, Derbyshire
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This is a canon EOS compatible flashgun from just before the digital era, and is nice and powerful (> £100 for modern equivalent), and I dont really want to have to throw it away, but can someone confirm that it wont work with my newly acquired Canon Powershot S5 IS?
Can anyone point me at an article that explains why not, or give a brief explanation?
I always thought the flashgun fired and the camera told it when to stop.
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Canon Powershot S5 IS
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El Sid
Going potty
Reged: 14/04/2003
Posts: 9277
Loc: Sussex-by-the-Sea
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If it has manual mode or other non-TTL option (eg thyristor control) then you can use it in that. As it's an EOS designated flash the trigger voltage should be OK.
You won't be able to use it in TTL mode as the flash system is different with digital cameras.
TTL flash works by measuring the light reflected from the film surface during the flash and shutting off the flash when sufficient light has been delivered. The problem is that film has a matte surface while sensors - or rather the filters in front of them (low pass, IR cut) - are very shiny. This means that far more light is reflected and as a result flash guns calibrated for film would underexpose horribly.
Flash guns for digital emit a small preflash immediately before the main event and the necessary flash exposure is calculated from this.
FWIW I have the same issue using my Canon EZ540 flash with my EOS digitals...
HTH
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Nigel
Completely BSRIPN 
ElSid Gallery
A camera in the hand is better than one in the cupboard........
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fpdave
newbie
Reged: 23/09/2007
Posts: 2
Loc: High Peak, Derbyshire
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Many thanks for the clear explanation.
the flash has 2 manual modes as well as the TTL mode, but it OVER exposes horribly in all 3 of the settings.
I'm surprised there doesnt seem to be more control over the manual settings. Is there any reason why the manual modes would also massivly over expose?
I'll play around a bit more. I think the S5 has a flash compensation settings of +/- 2 stops so maybe I can use that.
At least you've made me think that I'm not completely wasting my time trying. Maybe I'll have to dig out the manual for the flash and see what controls it has (seems minimal number of buttons tho - just TTL/M-L/M-H)
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Canon Powershot S5 IS
Edited by fpdave (24/09/2007 13:31)
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El Sid
Going potty
Reged: 14/04/2003
Posts: 9277
Loc: Sussex-by-the-Sea
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Quote:
...but it OVER exposes horribly in all 3 of the settings.
Of course I am forgetting that digital cameras of course don't actually have the sensor in the base like what the film ones do...  This means there isn't actually anything to cut off the flash at the right - or indeed any - point. The net result is every time the flash fires it's effectively at the maximum setting hence the gross over exposure.
With the Canon EZ540 I can manually reduce the power of the flash by up to 5 stops to compensate; note this has to be done on the flash as the camera's own compensation controls have no effect on this unit (I'd need an EX unit for than) and I rather suspect the same will apply to your combination too. If the Sigma jobbie doesn't have the manual power option you can possibly fool it into reducing power by setting a higher ISO on the flash (I assume it has ISO settings) than is set on the camera...
I'm quite impressed that the Sigma actually talks to the S5 enough to trigger the flash. I have a Cobra unit that works fine with film EOS but does absolutely zilch when attached to a digital one...
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Nigel
Completely BSRIPN
ElSid Gallery
A camera in the hand is better than one in the cupboard........
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