this week I'm going to test the long
exposure noise reduction feature in my
camera (the A7iii)
nowadays a lot of cameras have this
feature it's called long exposure noise
reduction what it does is reduce the
amount of noise in the shot I want to
see what difference this actually makes
what you'll find is when you turn this
function on it'll double the time you'll
have to wait so with a 20 second
exposure you'll be waiting for 40
seconds with a 2 minute exposure you'll
be waiting for 4 minutes so I've been
out and I've taken a load of shots some
of cityscapes and some of night scapes
I've taken shots with a noise reduction
on and the noise reduction off just to
see how it changes the image so let's
have a look so I'll start with the
cityscapes with these first set of
images I kept it to ISO 100 and then I
changed the shutter speed so at 30
seconds 1 minute 2 minutes 4 minutes and
8 minutes each time I had the noise
reduction on and then the noise
reduction off so if we start off at the
8 minute point you can see this is noise
reduction off at 8 minutes I've cropped
in on this section down here you can see
these little red green and blue dots
around this area here if I switch to the
same length exposure with noise
reduction pond you can see most of those
have gone so you can see the difference
that's with an 8 minute exposure so this
is noise reduction off this is noise
reduction on so it really helps when
you're shooting really long exposures
now let's go down to the 4-minute one
you can see those red dots are still
there they're less prevalent but they're
still there noise reduction on they've
gone now if I go down to a two-minute
exposure you can see those dots are
still there but they're less prevalent
so the longer the exposure the brighter
these hot pixels get and also the longer
the exposure the more of them there seem
to be so if we just compare 1 minute 2
minutes 4 minutes and 8 minutes from
this first set of images when your
exposures are 1 minute or longer the
long exposure noise reduction really
helps when it comes to removing these
hot pixels so when you're at the
location you
need to make the decision as to whether
you have this on or off if you're doing
really long exposures it means waiting
double the time the next thing I did was
ramp up the ISO to see if it affected
normal noise patterns or whether it just
affects these hot pixels I had to put
the ND filter on at ten thousand and I
shot at f/8 and at f/4 obviously it's
not a usable image but I want to see
what the noise reduction function does
at this high ISO so this is exactly the
same settings I didn't change anything
didn't change white balance or anything
so f/8 ten thousand you can see with the
long exposure noise reduction on the
exposure becomes a little bit more red
whereas with it off it was slightly
greener obviously like I said you can't
use these images but it's interesting to
see what happens so if I go in so that's
noise reduction on I'll go to this
section again down here you can see the
normal noise patterns you get at such
high ISO s what the long exposure noise
reduction seems to do is kind of smudge
everything out can see if you've got rid
of all of these dots the noise would be
a lot less than in this one it just
seems a little bit more fuzzy and at the
normal exposure you can see without it
it's very green and with it it's kind of
smudged in the Reds a little bit so it
doesn't affect high iso noise it affects
long exposure noise and that's these hot
pixels the next location I went to was
out in the desert underneath some night
skies it wasn't that dark there was a
fair bit of light pollution about but I
could see some stars and what I want to
see from this is whether the long
exposure noise reduction kills any of
the stars again I did the same test
starting at 30 seconds then I did one
minute two minutes and then eight
minutes you can see the stars are really
streaking and my object wasn't to get
clear crisp stars was just to see how
the long exposure noise reduction
effects the stars I'd like to try this
test
a tracker to do a four-minute exposure
and then see how it works and try one
with a tracker with long exposure noise
reduction on and long exposure noise
direction off just to see how it effects
the Stars and see if it actually deletes
any of the stars
but for now we'll have a look to see
what we've got I took shots both on the
a7 r2 and the a7 3 so this is at 8
minutes with noise reduction off and
noise reduction on so that's noise
reduction on and it looks quite clean
obviously the stars of streaking quite a
bit but I had to wait another eight
minutes for this to process one thing I
noticed with this is as I brought these
images into Lightroom when I first
looked at the images there was quite a
lot of noise on the ones without long
exposure noise reduction and I think
Lightroom actually processes them a
little bit and looks for these hot
pixels and just automatically gets rid
of them you can see here it's getting
rid of this little red pixel there on
the a 73 I took two underexposed shots
at f/8 8 minutes iso 100 this is noise
reduction half this is noise reduction
on this is a one by one crop now if I go
into develop a bump up the exposure you
can start to see that noise pattern
again and then if I select both and I
sync now you can see the difference so
this is noise reduction off this is
noise reduction on and it seems to do a
really good job of distinguishing
between the hot pixels and the stars
although it's not hard in this case
because the stars are really long
streaks again on the a7r what I've done
is come up to the top corner of the shot
I've bumped up the exposure so the
slightly darker area in the top corner I
brought the exposure up a little bit and
where the noise reduction is off you can
start seeing these red dots
and with the noise reduction on it's
gotten rid of all these red dots one
other thing I've noticed is it's really
affected by temperature
I was out shooting in the desert the
other week and it was around about 40
degrees I started getting this noise
from about 30 seconds onwards in colder
temperatures I've started getting it at
around about 2 minutes so here are the
conclusions I found that 4 exposures for
two minutes and longer you start getting
this long exposure noise it's mostly
visible in underexposed areas so it's
not too bad if you expose your image
properly but in the shadows if you want
to bump these up afterwards you'll
really see this noise appear it's really
affected by the ambient temperature that
you're shooting in it also seems to be
able to differentiate between stars and
hot pixels if you're taking shots longer
than two minutes long exposure noise
reduction is worth thinking about if you
don't have time to wait around in the
field you'll then have a lot of editing
to do in Photoshop especially in the
shadowy parts of your image as always if
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