Once in a year opportunity : ) .... messed up. : (

Started Dec 1, 2013 | Discussions thread
texinwien Veteran Member • Posts: 3,326
Re: Once in a year opportunity : ) .... messed up. : (

GeorgianBay1939 wrote:

clengman wrote:

I don't know if this

read noise decreases as ISO increases.

is so universal as to lead to the tactic of reducing read noise by increasing ISO until the highlights are clipped? In other words set the EV using artistic reasons (DoF, Motion Blur) and increase ISO until the rights side of the histogram clips.

It's not entirely universal. For instance, on an ISO invariant (aka ISOless) camera, read noise won't decrease as ISO increases. For many (most?) ISO variant (aka ISOful) cameras, read noise only decreases up to a certain ISO, after which it neither hurts nor helps you to raise ISO, as long as you don't clip important highlights.

For the E-M5, for instance, read noise has been measured to fall from ISO200 to ISO400, from ISO400 to ISO800 and from ISO800 to ISO1600, after which it seems to stay pretty constant. If I'm at ISO200, have my other settings 'right' and realize that I'm not going to blow any important highlights (live view blinkies for the win here), I can bump the ISO to 400 to get less read noise, as long as I'm still not clipping important highlights. This logic continues for ISOs 800 and 1600, after which increasing the ISO won't hurt or harm the image, as long as important highlights aren't clipped.

How does this relate to Dynamic Range?? Does that determine if I even have the option of the above --- if highlight clipping is critical to me? In other words is the luminance of the highlights so high that my artistic settings (EV) still will cause clipping, even at BASE ISO? In that case I would leave the setting at BASE and either shorten the shutter interval or close the f/ down. If I were on a tripod and WANTED some motion blur in the train lights, I would stop the f/down and set the ss to cause the right amount of blur.

If you are going to blow important highlights at base ISO, you'll have to stop down, choose a faster shutter speed, use an ND filter to cut some of the light or else resign yourself to living with the blown highlights.

This is where the idea of arbitrarily low ISOs (see also here) that Anders W is always talking about becomes very interesting. When this or a similar technology makes it into consumer digital cameras, the base ISO DR advantage of larger-sensor cameras will be a thing of the past.

With this technology, you could just dial ISO down to 25 or 12.5 or however low you wanted to go to make sure you didn't blow any important highlights.

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