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