a57 v d5100 for first DSLR

Started Apr 6, 2013 | Questions thread
Leonard Migliore
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Re: Neither
In reply to Fat Dragon, Apr 9, 2013

Fat Dragon wrote:

Leonard Migliore wrote:

Fat Dragon wrote:

To help a layman out, would this test indicate differences in actual ISO levels between various cameras, or simply a different approach to metering in the SLT as compared to an SLR or incident light meter?

Most recent Sony sensors are "ISOless', meaning that their noise levels do not depend on the selected ISO. So all the test indicates is the level of amplification of the sensor signals to produce a specific brightness level on a JPG. Which is something only of significance to the sensor electronics designer and his priest.

I'm probably missing a lot of knowledge here, but it sounds to me like you're saying that I could shoot my girlfriend's A57 at ISO 6400 with the same noise level as ISO 100. Since my girlfriend is slow to pick up the basics of exposure (she insisted on an SLR but in her heart she wanted a point-and-shoot that doubles as a status symbol), I've got a lot of shots on file that she took at higher-than-necessary ISOs, and my untrained eye suggests that they're a lot noisier than the low-ISO shots we've gotten from the camera.

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.

Or maybe you mean that the ISO is essentially a function of the image processor, in which case more processing (i.e. higher ISO) introduces more noise. I don't think the problem is your ability to communicate the idea, but my ability to understand it, since my camera-speke (Photographese?) is pretty basic.

ISO is a standards organization. They developed a photographic exposure standard for film. It's used for digital sensors but it wasn't created for them and it's probably too late to create a new paradigm.

Noise comes from low exposure, image brightness comes from the degree of amplification of the sensor signal. There isn't much noise in the amplifiers anymore; they're just amplifying the noise that's already in the signal.

I think the manufacturers try to set a base ISO that's consistent with the most exposure the sensor can stand without saturating in the highlights but that's sort of a fuzzy concept so there's going to be differences. But whatever they set it at, they can make the JPG's look right with respect to brightness.

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Leonard Migliore

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