ISO vs aperture vs sharpness/detail

[Terry Rogers]

Given a lighting, to get the most detail of say a head shot, would it be tween to shoot wide open at f2.8 on a 17-55 2.8 and say ISO 800, or stop down to f4 and ISO 1600? I know that lenses don't generally perform at their best wide open, but is the increased noise of ISO 1600 worse than the loss of sharpness when shooting wide open? This is shooting on a T4i

 

[Marsu42]

Given a lighting, to get the most detail of say a head shot, would it be tween to shoot wide open at f2.8 on a 17-55 2.8 and say ISO 800, or stop down to f4 and ISO 1600? I know that lenses don't generally perform at their best wide open, but is the increased noise of ISO 1600 worse than the loss of sharpness when shooting wide open? This is shooting on a T4i

It depends on the type of detail and how the post-processing noise reduction responds. In the unlikely event that you've got very fine detail that gets "buried" by the noise, high iso hurts. Other than that, iso1600 on crop is still ok-ish *if* you expose properly, i.e. to the right. And if you've got uniform areas you can denoise/sharpen to hell as there's no detail anyway.

... but really, usually you decide on the depth of field you want and worry about tech details unless you really need to. It's not like you're reaching top level iq with your gear anyway. And are you really going to print/view these head shots so large that you'll see the difference on pixel level? Better get some more flashes, softboxes and busy yourself with making a good impression on the client/model, *that* does make a visible difference.

As for the lens: the difference is noticeable, but not very large: http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=398&Camera=736&Sample=0&FLI=4&API=0&LensComp=398&CameraComp=736&SampleComp=0&FLIComp=4&APIComp=2