Optimum ISO for my camera

[mandab99]

Hiya
I have found out that there is a optimum ISO for each camera out there. Now being a newbie to photography I would have thought that iso 100 would be the optimum for all cameras but apparently not. From what very little I know each make and model has a optimum iso that is not necessarily iso 100, its called a "native" iso. Can anyone explain this and how would I know what mine would be for a canon 550d??? Thanks!!!!

[ricktas]

native ISO and optimum ISO are different.

Lowest Native ISO is usually the lowest ISO your camera has that is a number. So you have 100, but you also might have Low 1/Low 2 or similar, and siimilarly you might have a highest ISO of 6400 and then a Hi 1 / Hi 2. These Low and Hi ISO's are not native, in that they use a processing algorithm in the camera to achieve them, rather than being a standard electrical ISO level. ISO on digital camera's is about electrical current that is sent to the sensor, but that can get rather technical, but it is good to know how it is done.

Optimum ISO is really the ISO you need to use to get the shot. For landscapes and portraiture, yes your lowest native ISO is worth using, but if you are shooting sport on a dull day and want to freeze the action, you might need something like ISO 800. So for fast moving sport, your optimum ISO may be 800.

There are arguments for not using the lowest ISO but the one above that, as the image degradation from going one ISO stop above the lowest is extremely minimal and it allows for faster shutter speeds. Ultimately, you have to choose the optimum ISO depending on what you are shooting and what you want to achieve from each shoot.

[mandab99]

So interesting and sheds some light on the matter for me, thanks Rick!

[Kym]

Generally, I would suggest enough ISO to ensure a fast enough shutter speed to get a sharp image.
ISO 400 or 800 are not that noisy and are fine for normal good light conditions.

Obviously you need to factor in the aperture.

See: http://www.ausphotography.net.au/forum/showlibrary.php?title=New_To_Photography:Appendix_E_-_How_to_obtain_tack_sharp_images

[kiwi]

I'd suggest that unless you are an intermediate to advanced photographer that you never go below iso400 regardless, in fact make that the default

[mandab99]

Thanks Kym, will check that link out!
Kiwi really? why?......