Low ISO - Why the need for a big stopper?

[Guesty]

Hi folks,

Been wondering this for a while. Some of the pro DSLRs offer an Iso 50. Why don't we see ISO 10 etc?

This would allow long exposure in camera without the need for a filter.

Just a thought.

Mark

[collywobbles]

Re: Low ISO - Why the need for a big stopper?

They used to go lower; I often used to use 25 ISO Fujichrome slide film for really good quality slides. - No P.S. here! You HAD to get it right in camera.
But I agree with you, why can't we have lower ISO s?

[SamFisher]

Re: Low ISO - Why the need for a big stopper?

Can't remember ever seeing ISO 25 Fujichrome but I often used ISO 25 Kodachrome and ISO 50 Fujichrome Velvia
Those were the days but would I go back to shooting film? - I don't think so

Mike

[S_J_P]

Re: Low ISO - Why the need for a big stopper?

It's a good point Mark!

Camera sensors are optimised for a particular ISO, the point at which there's the best signal/noise ratio, and that's usually around ISO 200-400, when you depart from this optimum noise will increase, whichever direction you go (up or down). I understand that turning up the gain to obtain higher ISO will also amplify the noise causing noisier images, and I assume that when attenuating the signal to get low ISO the noise will increase in proportion to the attenuated signal, so quality will deteriorate whichever way you move from the optimum.

I think we'll have to carry on carrying ND filter sets around with us!

[Guesty]

Re: Low ISO - Why the need for a big stopper?

Cheers guys. I thought it'd be down to noise. If cameras can now produce usable images at ISO6400, surely they could go as low as ISO25?

[ColytonJohn]

Re: Low ISO - Why the need for a big stopper?

I was surprised when I got my 7D to see that the lowest ISO was 100 while my G10 is 80. I know high ISOs are subject to noise but hadn't realised low ISOs may be too.

Cheers,
John

[jimsphotography]

Re: Low ISO - Why the need for a big stopper?

I suspect it also has a detrimental on the dynamic range of the image
James

[Riggers]

Re: Low ISO - Why the need for a big stopper?

Maybe the future is a lens with built in NDs and ND Grads :)