a57 v d5100 for first DSLR

Started Apr 6, 2013 | Questions thread
peevee1
Senior MemberPosts: 5,123Gear list
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Re: Neither
In reply to Fat Dragon, Apr 12, 2013

Fat Dragon wrote:

peevee1 wrote:

Fat Dragon wrote:

Leonard Migliore wrote:

It's not a free lunch. Shots taken with exposures consistent with high ISO's will be noiser than ones with more exposure. It's just that the ISO dial doesn't do much besides change the exposure.

Let's say you're shooting indoors and need 1/2 second at f/2.8 at ISO 100. You know that's no good for motion blur. You want to shoot at 1/125. The standard way to do this is to bump the ISO to 6400. And this is going to be noisy. But with the Sony, you would get the same noise and better highlights if you kept the ISO at 100 and set your exposure manually to 1/125. Your JPG would be just about black but if you bump up the RAW file, you'll get the same result as increasing the ISO because that's all the camera does.

You'll get more noise with low exposure regardless of the ISO setting. So bumping up brightness 6 stops in an ISO 100 shot will show the same noise as if you took it at ISO 6400.

So it's just a software function within the camera. Gotcha. Is that true for all digital cameras or just some?

Now, it is BS. Typically, it is a combination of software and hardware, for example, up to ISO 6400 it is real hardware signal amplification, and after that a software multiplier. The difference is that, say, you have a typical level of noise equal to 0 or 1 at ISO 100. Then if you multiply by 16 digitally (ISO1600), all your noise will be 0 or 16, and if you amplify, it will be in the range 0-16, much smoother, with fewer spikes to 16. And part of the noise will not be even multiplied, leading to even lower noise in practice.

That clarifies a lot about how ISO works and affects IQ, but I'm trying to figure out exactly what you're calling BS. Do you mean that it's BS (as in disappointing) that Sony uses a system that starts the software multiplier at anything above 100, or that it's BS (as in not true) that Sony's cameras have no hardware ISO amplification?

That. Specifically these: "Your JPG would be just about black but if you bump up the RAW file, you'll get the same result as increasing the ISO because that's all the camera does."

and

" So bumping up brightness 6 stops in an ISO 100 shot will show the same noise as if you took it at ISO 6400."

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