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I got a quick video for you today.
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I wanted to talk about
shooting at ISOs lower
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than the base or native ISO in log
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on cameras that allow you to
do that, like the Sony cameras
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and I think there's other
brands that do as well
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but some brands don't.
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Some brands, when you
try to go below the base
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say it's ISO 800, it just switches to auto
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and you can't choose the lower
sort of pseudo extended ISOs.
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On the Sony cameras, you can tell
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because these are the ones with the lines
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on the top and the bottom
here, let me show you.
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So here I've got an a7S
III and if we go into ISO
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then we can see that the
native ISO in log is 640
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and we can increase that up to
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well quite high on an a7S III.
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But you'll notice that
there's also a few ISOs
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below 640, 500, 400, 320, 250,
200, and 160 that basically
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two stops below that all
have lines above and below.
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And these are the ISOs
that we're talking about.
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Like I said, not all cameras
even let you choose these.
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So what happens if you were to shoot
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at 400 or 200 or something like that?
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So first off, I just
have some Xyla 21 charts
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because I wanted to test the dynamic range
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because generally when
you shoot in those lower
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than native ISOs, you are
giving up dynamic range.
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So I wanted to see exactly how much
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but before I give you the scores,
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take a look here on the waveform.
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So at 640 we can see that
it's clipped right here
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and then how many stops we get moving down
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and then we can see the noise floor.
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And this is gonna be important as well.
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And I want you to look
at these lower stops here
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as we go through.
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So if we switch to ISO 400,
which is now one of the
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lower than base ones, we can
see that what happened was
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the clipping point, the maximum
point went down a notch.
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And with that, if you look
at this sort of fuzzy line
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at the bottom here, the
noise also went down.
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It's not as noisy anymore.
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And if we compare to an extreme example
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which is this one over here at ISO 160,
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we can see that the noise
is very, very thin now
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compared to the 640 and 160,
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much, much thinner amount of noise.
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But the way that the stops
are kind of peeking up
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we can see that it sort of stops here
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and we can't see anything past this.
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But if we go to this one
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there are remnants, they're very noisy,
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but there are remnants of
stops that move past this.
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So any stops that are more
mixed into that noise floor
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are going to kind of disappear.
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And if we look at the Imatest results
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so the actual scores from
these, we can see this.
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So if we start here and we look at ISO 640
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and then we look over at this section here
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where it says slope-based DR,
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this number 14.6 is the
total amount of stops
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that it can see regardless of noise.
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And then as we go down
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these are varying qualities
based on the signal to noise ratio.
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So usually we look at
something like medium
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which is a signal to noise ratio of two.
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12.6 is telling us we get 12.6 clean stops
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but the camera can see 14.6 total.
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But if we were to move
down to ISO 400 here,
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by the way this plus 88,
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that's the clipping point in camera.
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If you were to set your Zebras
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to what level to be the maximum white now
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based on that new lower ISO,
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that's what it'll be is plus 88.
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I'll show you in the camera in a minute
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once we're done here.
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So now the total dynamic range,
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the total amount of stops it can see
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drop to 14 from 14.6.
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But the medium and low
scores, they stayed the same
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at 12.6 for clean and 13.6
for, you know, pretty clean.
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If we moved to ISO 200 though,
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which now has a plus 79
for maximum clipping point,
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the total amount of stops
we can see drops to 13.2
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which also is affecting the low now.
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It's not affecting the medium,
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it says it went up a little bit,
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but just it's probably margin of error.
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But the low is now being limited by that
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which means the stops that
were sort of noisy before
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but not as clean as medium.
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Those used to be 13.6 all the way through.
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But now we can only see 13.2 of them
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because there's only 13.2 stops total.
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But we still get our 12 and
a half ish in the medium.
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And then finally, if we move
all the way down to ISO 160
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which is the lowest we can set the ISO,
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the total amount of stops that
you get to work with period
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is 12.8 which means that
the low is also 12.8
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and the medium, again,
could be up to 12.8 maximum.
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And what's interesting is
that they're all the same now
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which makes me think that it's
kind of calibrated probably
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so that when you set the
ISO as low as possible
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that it's gonna give you only the stops
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that have a signal noise ratio
of two, like the clean stops,
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which is what the medium is showing here.
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So you can just sort of trim off the
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extra noisy ones, reduce the noise,
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and get rid of those stops if you want,
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by lowering the ISO down.
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And the lowest clipping
point for ISO 160 is plus 76.
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Let me show you what
that means in the camera
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if say you use zebras to
expose on these Sony cameras.
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Okay, so as you can see in
the bottom of the frame there
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it's ISO 640 and if we go into our zebras
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where it says lower limit 94 plus
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that is the correct clipping point
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for S-Log three, each gamma is different,
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and you can always tell which one it is
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by just moving up and down.
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If you have your zebras
set too high like this
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the zebras won't show up.
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So you can bring 'em down one at a time
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make sure you're pointing
at something that's clipped
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like pointing at a
bright light or something
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and you bring it down one at a time
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and as soon as you get the 94
plus the zebras will appear.
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So that's how you can sort of
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find out what the clipping point is
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for the gamma that you're on.
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What's the highest number that the zebras
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will appear on and if they
disappear going up one,
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bring it back, that's the clipping point.
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But if we had this set
to, so say we go in here,
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and we lower ISO down to 500 for example,
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there's a quick and easy
way to remember this.
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As you go over to this
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you have to drop it by three points.
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Each one-third stop of ISO
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requires you to lower your
maximum clipping point
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in your zebras by three points.
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So then now it would be like
this 92 would not show zebras
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and then 91 the zebras
would magically come back
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when you were at ISO 500.
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If we lower the ISO down to
400, same thing, it's a pattern.
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We're gonna go over here, here now 88,
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If we lower the ISO down to 320,
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again, same thing 85.
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If we lower the ISO to 250.
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And again, if you have
a camera that starts
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at a different base ISO,
a Sony camera that is,
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so say it's 800, the
same principles apply.
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It's just that you're
gonna start ticking down
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from 800 and you'll still end
up at the same bottom point
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but your bottom will now
be ISO 200 instead of 160.
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Okay, so now let's take
all this information
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and apply it to an actual
scene so we can see how
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it works when you're
actually shooting something.
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So in this clip here, the area right here
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that I'm pointing at with my finger,
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this zone right here is clipped,
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it has zebras on it when I
shot it, but over here is fine.
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The rest of the building just right there.
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And if we look at the waveform
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we can see what I'm talking about.
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The rest of it is just below the line.
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And then this bit right here is clipped.
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If you were to try to shoot
this building, let's say,
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and this is at ISO 800,
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and then you brought it down to ISO 400,
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what's gonna happen?
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Are you still gonna be clipped here
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or all of a sudden you're
not gonna be clipped?
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Because if you moved
from say ISO 1600 to 800
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you would no longer be
clipping that section.
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But are you still clipping it
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if you move down from ISO 800 to 400?
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The answer is yes, you are.
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However, the clipping point is now lowered
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like we talked about, you
don't recover any highlights.
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And I think that's important
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for you to remember is
if you turn down the ISO
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below a native ISO, you
don't recover highlights.
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You would if you were
shooting higher than native
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if you went from 600 to 800
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you would bring some
highlight information back
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but not if you go from 800 down to 400.
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All that's happening is
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the whole scene is being pushed down.
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So what would be the reason
for actually doing this?
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Well, if you were to monitor this shot
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or grade it or you knew what
your intention was in post
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you can see that the ISO 200,
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once I apply the standard Sony Rec 709 LUT
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is now really nicely exposed.
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Again, the spot is still gonna be clipped,
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it's not gonna change
anything but the scene
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as it was seen on the
day, like as it should be,
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as it should be shown.
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But as you can see, the
ISO 400 and the ISO 800
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are overexposed now with the LUT applied
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and they don't look good at all.
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So you have to go in and
you have to apply an offset
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manually before the LUT to
reduce them to equal exposures.
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And when you do that, now the shots are
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pretty much the same.
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So what if instead we expose
for middle gray perfectly.
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What's happening to the stops
at the top and the bottom?
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I showed you the dynamic range
if we expose to the right
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and see how many we can
see into the shadows,
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what happens if we expose
perfectly in the middle?
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So if we look here, this
is ISO 800 and I exposed
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for middle gray to be
the middle of the chart.
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And then we can see when
it clips off to the left,
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like at what stop it clips, and
what happens in the shadows.
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And so let's take a look
at the waveform there.
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We can see that there's four stops
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on the brighter side that are clipped
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and then we can see the rest of the shape
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and how it curves down.
But if we look at ISO 400
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now there's an extra stop that's clipped.
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So bringing it down ISO 400, like I said,
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doesn't preserve any highlights.
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If you expose to the middle
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those building shots were
also exposed to the right.
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So keep that in mind, okay?
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But now we're exposed to the middle.
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So when you exposed to the right
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you don't bring any more highlights back.
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If you expose to the middle
and you bring down the ISO
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you actually have fewer highlights
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to work with because of the fact that
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the maximum clipping point
is moving down on you.
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So again, ISO 800 we can get this stop.
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ISO 400, that stop is gone.
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The rest of the curve that
you'll notice is pretty similar.
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And I'd say it maintains that
here just we lose this stop.
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But in exchange, again, go back to 800
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look how thick the noise is.
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You can see right here and
at 400, a lot less noise.
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So we're basically trading off this stop
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for less noise. And at ISO 200, we
lose another stop yet again.
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So now we have six stops that are clipped
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but the noise becomes even less so.
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But the curve here remains the
same throughout each of them.
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So what does that mean
then if we shoot a scene
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exposed to the middle that
has different values in it.
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So here as you can see, this is my scene
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shot at ISO 800 and I
exposed to middle grey to 41%,
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which is the buy the book
way to expose S-Log3.
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And if we move to ISO 400
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very little is changing and
there's a reason for that.
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Those extreme stops
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that are getting clipped
in the Xyla 21 test,
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they don't really show
up here because remember
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we still get 12 and a
half stops to work with.
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The noise is the biggest difference.
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Let's go to ISO 800 and
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we'll zoom in right over here.
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This is usually hard to show on YouTube
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so I'm gonna punch into
a crazy percentage.
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So we're like 400% or 500% now.
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Do you see the sort of pattern here?
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Watch as I click to ISO
400 and then ISO 200,
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you see how there's less of it.
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And obviously if we play a little bit
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versus play a little bit over here,
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this is the regular noise level,
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this is ISO 800, this is
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the native ISO and then 400 and then 200.
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So 200 is a very, very low noise,
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much lower than 800 and it's
actually lower than the noise
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if you do the typical overexposed
and bring it down trick
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which I thought was the most interesting.
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So here is two shots,
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this is ISO 400,
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and just use a LUT and
you grade it a little bit
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and then this is ISO 4,000,
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which is way, way, way overexposed
like maximum over exposure
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and then brought down
and then graded that way.
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So same deal, we're
gonna zoom in over here,
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really, really, really far zoomed in.
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So this is ISO 4,000.
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It's very, very clean.
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And then ISO 400 is
slightly worse, but it was
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the closest comparative I
could find was sort of one stop
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below the native is similar
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to massively overexposing.
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Flip back and forth you can
see that the 400 slightly worse
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but the 200, two stops below
native is slightly better
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than the 4,000 ISO extreme over exposure.
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So I thought that was interesting.
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Now, if we try to wrap all
this up and conclude with
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what do I do with this
information then practically?
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Basically just know the
limits, know what you're doing.
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So can you lower the ISO
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below the native and get away with it?
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Yes, of course.
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In fact, if you're shooting
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in a controlled setting where you need
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12 stops or fewer
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it's not gonna be an issue,
unless all your stops are,
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you need to be way up
in the clipping point
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then you're gonna wanna
expose to the right.
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But if you expose neutrally
and you and your whole scene
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will fit in that five, six
stops, above and below,
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then it really doesn't matter.
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You can just lower the
ISO to get a darker image
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and less noise and it works.
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There is less noise in the image.
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The trade off obviously is that for
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each stop of noise that you reduce
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you're losing a stop of highlights,
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which kind of makes sense and
it seems like a fair trade off
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but you'll never lose more
than the amount of clean stops
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the camera can see anyway at
a signal noise ratio of two,
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which in the case of the
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a7S III is that 12 and a half stops.
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Which I think is kind of
interesting that you'll never lose
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more than the 12 and a half stops.
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And then you'll just have to expose
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with how much light you're
letting into the camera
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to light the scene the way that you want.
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And like you saw in the
case of the sky here
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sometimes it can make
your workflow a lot easier
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because maybe you're
monitoring and you're like,
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oh, I didn't bring an ND or whatever,
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okay, I'll just drop my ISO down to 200
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and you've got the LUT applied
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so you're proving the LUT,
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you're like, yeah, looks good,
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okay. I don't see any issues with that
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because I'm not really worried
about liking in my shot
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with the sky and a building.
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The shadows are slightly
different in that corner
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because maybe we're
starting to encroach beyond
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the 12 and a half stops
and we're starting to see
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some of the more noisy stops
being allowed in there.
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But that's the type of difference
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that we're talking about
here. Is this versus this.
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Like, yes, you can see a slight
difference in the shadows
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but it is slight.
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So basically I just think
it's a tool you can use
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and know when and how to use it.
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And it's great to know that,
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while yes, you are
giving up dynamic range,
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some of the old things I read of like,
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"if you shoot below the
native ISO, your camera's just--
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throw it in the garbage
basically." It's not that bad.
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You are giving up dynamic range,
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but you're never giving
up more than what your
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clean signal to noise ratio of two
stops is going to be anyway.
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And I think that's pretty good.
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That's a good result.
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So I don't know, do
with this what you want.
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I hope that it was helpful.
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Yeah. (sighs)
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Alright...
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I'm done.
