sharpness and iso

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Feb 20, 2021
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I know this is hair-splitting, but anyway:
I know sharpness is best about f:8 for most of my lenses.
I know sharpness (details, contrast, low noise etc) is best at low iso instead of high iso.
I didn't know that sharpness is decreasing at less iso than 100: 64, Lo 0.5, Lo 1.
I have just read this in "Scott Kelby's Digital Photography part 4".
I haven't made any tests yet, but my inner pixel peeping dog is awake.
Any thoughts or experience?
Best regards
Jesper

 
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NC, USA
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Aaron
I think Kelby is wrong to state that sharpness decreases below ISO 100. There are plenty of things that can cause you to fail to capture the highest acutance possible, but deviating from an arbitrary ISO number isn’t one of them all by itself.

Going below base ISO (which is not always ISO 100) just means that the camera over exposes and then decreases the exposure in the image data to compensate. It is a built-in ETTR mode. There’s nothing about the ETTR method that would affect sharpness. The drop in shutter speed could become an issue if you are already shooting near your limit handheld, so you would want to open your lens up to correspond, use a tripod, etc.
 
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I didn't know that sharpness is decreasing at less iso than 100
This would be news to me also. Is it possible Scott Kelby is stating that going lower than base ISO (which is 100 on many cameras, but not all) sacrifices sharpness? I find it hard to believe that engineers would bother to design and produce a sensor that is just 1/3 stop slower (ISO 64) unless using that lower ISO achieves better image quality (both sharpness and dynamic range).

In any case, I think it is a moot point when three more pressing requirements for sharpness exist:
1. Achieving critical focus on the intended target
2. Sufficient shutter speed to freeze subject movement
3. Sufficient support (tripod, etc.) and/or stabilization (IBIS, VR, etc.) to prevent or mitigate camera movement
 
Joined
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Messages
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I think Kelby is wrong to state that sharpness decreases below ISO 100. There are plenty of things that can cause you to fail to capture the highest acutance possible, but deviating from an arbitrary ISO number isn’t one of them all by itself.

Going below base ISO (which is not always ISO 100) just means that the camera over exposes and then decreases the exposure in the image data to compensate. It is a built-in ETTR mode. There’s nothing about the ETTR method that would affect sharpness. The drop in shutter speed could become an issue if you are already shooting near your limit handheld, so you would want to open your lens up to correspond, use a tripod, etc.
Thank you for your answer.
In the chapter of tricks to make waterfalls soft and nice, he talks about extending the exposure time (several sec/tripod of course), even if the sharpness and contrast decrease. Pol/ND filter etc.
 
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Thank you for your answer.
In the chapter of tricks to make waterfalls soft and nice, he talks about extending the exposure time (several sec/tripod of course), even if the sharpness and contrast decrease. Pol/ND filter etc.
Increasing the exposure time alone will not affect sharpness or contrast. At a certain point slow shutter speed will make sharp images unlikely when hand-holding the camera (image stabilization can help here, but there is a limit). Mounted on a tripod, your exposure time can stretch into minutes or far longer without affecting sharpness or contrast. In extreme cases very long exposures can lead to noise or other artifacts due to heat buildup or other phenomenon, but for most of us it never comes into play.

Of course, much depends on how you achieve the longer exposure once ISO bottoms out. Stopping down a lens eventually causes diffraction to affect sharpness, but that is an optical issue. ND filters are generally employed so that a lens does not need to be stopped down so much (or at all); poor quality filters can have negative impacts, too.
 
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...but for most of us it never comes into play.

Of course, much depends on how you achieve the longer exposure once ISO bottoms out. Stopping down a lens eventually causes diffraction to affect sharpness, but that is an optical issue. ND filters are generally employed so that a lens does not need to be stopped down so much (or at all); poor quality filters can have negative impacts, too.
Thank you again for your answer.
Speaking of sharpness. I am oldschool. When I was younger I used Sinar 4x5" / 5x7" with Rodenstock lenses and I "just" stopped down to f:45 or even f:64 and I was good to go ;). Some b/w portraits I created.
Now a days I'm surprised/disappointed the decrease of sharpness at f:16 using my 24-70 VR or my 70-200 VR.
I am retired and now it is only a hobby (what a relief I don't have to hide all my mistaken shots), so it doesn't matter (almost :sneaky:).
Thank you again to you and all the other replies.
 
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