Off-camera flash issues

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Raid

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Darren
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Hey Guys,

This evening I plan to photograph a Jag with my 580EX II on a brolly using a Yongnuo RF-603C trigger. I have been practicing on some hazlenuts but have come across a problem I can't get my head around...

I metered at 1/30s at F/5.6, I wanted a wider depth of field so went to 1/15s at F/8 and then 1/8s at F/11 which theoretically should produce the same exposure. Everything is set manually both camera and flash, however each time I change the settings equally the image gets darker and darker.

Any ideas?
 
Nope
If your flash is Manual, the variables are distance and power, so a smaller aperture requires more flash power or a closer flash.

Your shutter speed only affects the contribution from your ambient light.
 
Raid said:
Hey Guys,

I metered at 1/30s at F/5.6, I wanted a wider depth of field so went to 1/15s at F/8 and then 1/8s at F/11 which theoretically should produce the same exposure. Everything is set manually both camera and flash, however each time I change the settings equally the image gets darker and darker.

Any ideas?
Click to expand...

It will do, as phil says if the flash and subject are in the same postition, adjusting exposure has no effect on the final image other than let in more or less ambient light, ie everything that isn't illuminated by the flash.

If you are closing down your aperture by a stop, you will either need to up your flash output by a stop or raise your ISO setting by the same. Personally, i'd up the ISO first as it will save your flash batteries.

eg, if your exposure is fine at f8, ISO 200 and flash at 1/8 power, at f11 you would either have to set your flash to 1/4 or your ISO to 400
 
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As Paul says above, increasing the ISO to cater for the change in f-stop can help you retain some recycling speed/battery charge, although in this situation I'm not sure how much a static hazelnut demands maximum frame rate :lol:

Anyway, flash to subject distance can also be altered but this in turn creates the problem of apparent light source size, depending on the type of light you're after and how big the adjustment in distances actually are....

When it comes to photographing your are then you will probably need all the power you can get so think about the type of diffuser used and how much light it actually sucks up.

Looking forward to seeing some images :)
 
As others have said, your theory is correct for a continuous light source but not flash , flash is controlled by apperture so if you stop down the apperture you need to increase flash power to maintain exposure
 
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