Doubt with 1600 ISO in SD15

Started Apr 30, 2011 | Discussions thread
Bodoh Contributing Member • Posts: 552
Re: Doubt with 1600 ISO in SD15

Ed_S wrote:

Bodoh wrote:

".... In other words, it's better to overexpose a bit at ISOs 800 and 1600 than the > opposite"

OK, this is advice I never really understand. If it's really better to overexpose when using ISO 800, then what is the point of ISO 800? Maybe I should just expose properly at ISO 400. But if the light is low.. then I need 800... oh, but I have to over expose - seems like I can't win. Is it just me, or is something fundamentally wrong about this advice?

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Okay, think of it this way. At least in SD 14 and earlier, the native ISO of the sensor is guessed to be around ISO 75 - 100. At or near that setting, especially in the ISO 50 mode, it behaves a lot like slide film. If you blow the highlights, they're gone. Need to be pretty much spot on with exposure. Because the ISO is, well, virtual as one goes up the scale, especially 800-1600, the sensor effectively behaves more like negative film, in that one needs enough light to fully "expose" the sensor. If it is underexposed, there's not much there to salvage, especially in the shadows.

High ISO settings tend to work better in my limited experience and opinion, in "good" light. Like shooting sports in sunlight or bright artificial light. When shooting in near-darkness or "poor" artificial light, I try to at least shoot at the ISO equivalent, and if I have to err to try to do it toward overexposing a bit. Not saying one has to "give back" each f stop equivalent, but allowing a bit of a margin toward overexposure is "safer" than the opposite.

Hope that makes sense.

Thanks for the responses Ed and Midnighter. Here's what I take away: ISO, other than the base ISO is a crock. Shooting above base ISO just means you're under exposing the sensor since the ISO setting isn't changing the sensor in any way (perhaps AFE excepted), and therefore not using the full range of the sensor. You can sort of make it up later with gain, in the camera or in post, but not using the full range means higher noise. Now the fact that some cameras can perform well at higher ISO's only means they must have a lower noise floor (than Foveon). Maybe I've over simplified it, but for Foveon I think that's what the advice nets out to.

I do note the part about better results with "good light" meaning that the light has a lot of spectrum and not incandescent or fluorescent. And personally I pretty much use only the base ISO too, and just put up with longer exposures and finding a way to steady the camera.

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