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Thread: Determining which ISO to use with fill-flash

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    Default Determining which ISO to use with fill-flash

    This is something I've always wondered.. how to you determine which ISO value to use when using fill flash? As the shutterspeed is usually dictated by the flash, does it not really matter what ISO you use (thus should choose a lower value)?

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    If you're using the flash as fill-flash, the flash unit needs to be in high-speed sync mode or it will be permanently locked at 1/250s which can obviously lead to over exposure in bright conditions. You are then free to use whatever ISO you choose and the shutter speeds will be free from the 1/250s limit.

    Of course along with higher shutter speeds, this can mean that your shutter speed can now dip low just as if the flash wasn't there. Sometimes it can be good to force the flash back to 1/250s in low-light areas as you will then be effectively using the flash as the primary light source.

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    Fill flash is not actually determined by the use of the flash Adam. You are supposed to use the normal exposure you would without the flash attached. All the flash is doing is "filling" in the shadows. You should be able to use whatever ISO you were going to anyway. All you do is adjust the FEC or "flash exposure compensation" to adjust the flash output. Make sense?

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    Quote Originally Posted by Paul Randall View Post
    All you do is adjust the FEC or "flash exposure compensation" to adjust the flash output.
    You will probably find that since you seem to favour the smaller, bush-birds at close quarters you will have to dial back the amount of FEC as Paul's mentioned by maybe as much as - 1 2/3 to 2 full stops or your subjects may look 'over-flashed'. I find - 1 2/3 FEC a good starting point for small birds up close.

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    Quote Originally Posted by Paul Randall View Post
    Fill flash is not actually determined by the use of the flash Adam. You are supposed to use the normal exposure you would without the flash attached. All the flash is doing is "filling" in the shadows. You should be able to use whatever ISO you were going to anyway. All you do is adjust the FEC or "flash exposure compensation" to adjust the flash output. Make sense?
    Got ya, that makes perfect sense. Thank you gents!

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    Quote Originally Posted by Richard Hall View Post
    You will probably find that since you seem to favour the smaller, bush-birds at close quarters you will have to dial back the amount of FEC as Paul's mentioned by maybe as much as - 1 2/3 to 2 full stops or your subjects may look 'over-flashed'. I find - 1 2/3 FEC a good starting point for small birds up close.
    Indeed. I've been shooting quite a few parrots at close quarters recently (as they are close to home and haven't had much time with the new gear), and have been using between -2 and -3 FEC in most instances.

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    Some situations will dictate that you use flash as "main light" rather than "fill flash". For instance, take a Yellow Robin in deep shade. You might only be able to pull off a SS of 1/50th or something similar. Fill flash and that exposure is probably going to give you a motioned blurred image (unless the bird is super still). In this situation I would use a faster shutter speed than what the camera came up with (this is "flash as main light"). You will get a few flash shadows and possibly a black BG but this can sometimes work visually and is probably preferable to a blurred image.

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    I feel I'd rather use flash as main light using the camera's manual mode than not get an image at all. It makes a big difference. I tend to do that once there is no sun, especially, that is, when it's dusk or dawn. And also when it's slightly overcast, or if I use stacked TCs. You still have some light, so you may not get a totally black BG (especially if it's close to the subject) and depending on your aperture and ISO used, you may get a semi-natural looking shot. I have taken this image with stacked TCs in the late afternoon sun, but in manual mode, with flash as main light.

    http://www.feathersandphotos.com.au/...-bird-portrait

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