How to minimise noise at high ISO settings
Today I am going to tell you why high ISOs don’t always mean more noise and why sometimes you should be increasing your ISO to decrease your digital noise! Confused? Don’t be!
I love today’s episode because this is something I didn’t realise for WAY TOO LONG and those are the tips I love to share the most.
This episode has been born from seeing lots and lots of you struggling with noisy images. Sometimes I look at them and I can quickly see that the noise was inevitable but sometimes I look at them and see that it could have been drastically reduced.
Before I start talking about ISO and noise, there are two things I need to address first. Number one is that I am not going into the basics of ISO here so if you need those first you can find them in episode 5. The second is inextricably linked to almost everything I talk about in this podcast but it is especially relevant today.
What I am talking about is ‘light’.
You can take all the advice given to you about making good use of your camera settings and exposing your images well but it will all mean nothing if you fail to select good light to take your photographs in.
Light, light, light. I can’t talk about it enough. The number one reason for learner photographers being disappointed in their images is that they did not think about or understand the light they were shooting their subject in.
So before I help you with noise reduction and ISO selection I want to make that super clear. If possible, choose great light to work in. If you do that you will have a much easier task when it comes to noise in your images.
However, today’s show is not about teaching you how to recognise good light (although there is some help on that front in episode 26). The purpose of today’s show is to help you understand how to minimise noise in your images when the light you have available is not quite enough for low ISO settings.
Because let’s get real for a moment. Sometimes you don’t have the luxury of fabulous light, do you?
For example, you might be taking photographs in a church at a wedding. The light may be terrible but you still want or need to capture those moments! Most churches will not allow you to use flash inside so you have no choice but to increase your ISO and shoot.
Or maybe you have selected decent quality light to work in but there is not an abundance of it. For example, you have chosen to shoot beside a window but it is very overcast outside. You have a nice pool of light by the window but there is not a lot of it.
Remember, just because there isn’t quite enough of the light you are shooting in doesn’t mean it is not ‘good light’. ‘Lots of light’ and ‘good light’ are not the same thing.
If you are confident using flash and you have all the kit – the speedlights, the triggers, the softboxes and the stands – then you can add your own light to most situations. If you are adding your own light then you can afford to keep your ISO lower than those of us who are not.
But there is no getting away from the fact that we all have to raise our ISO at times.
But how do you raise you ISO and keep your image as noise-free as possible?
We need a good scenario for this so I want you to imagine this one;
You have the whole family together for once and you decide to take a big group photograph. It’s freezing cold and windy outside and you have some elderly relatives present so you decide indoors will be best on this occasion. If you have listened to episode 26 then you know that the first step would be to go around the house to find the best light to shoot this in.
Let’s say you find a good area of light in the living room coming from a big window. There is no direct sunlight entering so the light you have found is quite even and no one is going to be squinting. You move a couch into this light because that is where you are going to sit your group for this photograph. You move back to the window and make sure that you are going to be able to fit everything into your frame.
I want you to imagine you have a good crowd so you are going to have some people sitting on the couch, some sitting on the floor at their feet, some to the sides and some at the back. So there is depth to this group portrait and you can’t create a lot of distance between you and them because you are indoors.
You need your depth of field to be right. You definitely won’t get away with a very wide aperture here. In order for you to get everyone in focus you will need to narrow it down a little. All photographers are different but I would probably select an aperture of around f/4 or f/5.6 for such a shot (you might go narrower).
But let me tell you what I would do next. I would not go and start arranging everyone just yet. I would find just one person and ask them to help me get my exposure right. The reason for that is you want everyone sitting around for as little time as possible. You want to get yourself prepared before you have an audience. It just makes sense. I would sit my volunteer pretty central to wherever the group is going to be positioned and I would meter the light from their face.
(If much of this is a foreign language right now, you are the perfect candidate for my FREE ‘Auto to Manual for Beginners’ course – sign up here.)
And here is where it gets interesting…
Before you meter the light in manual mode you need to have selected two of your exposure settings. You have decided on an aperture of f/5.6 so that you have decent enough depth of field to capture everyone in focus. And let’s say you start with an ISO of 800.
N.B. You could start with any ISO you want but it is a good idea to use your common sense. If you are indoors with just window light to use and you are not shooting with a wide-open aperture then the chances are, a low ISO of 100 is not going to be possible for this shot.
So all that is left is to spot meter the light from your test subject’s face to find the shutter speed you are going to need to expose this photograph. Let’s say you do this and your light meter tells you that to expose this you will need a shutter speed of 1/60 of a second. You take a shot with these settings and you are very happy with the exposure.
However, you know that in a group shot there is always going to be someone moving, right?, especially if kids are involved. So you decide that you would prefer a faster shutter speed than 1/60.
Let’s think about the choices available to you.
You need a faster shutter speed which is going to let in less light so you need to increase the light in another way. You could widen the aperture to allow more light to enter but, remember, you need that depth of field so that everyone is in focus. So widening the aperture is not an option.
The second option is to increase your ISO and make your camera sensor more sensitive to the light. Let’s say the next ISO setting on your camera is ISO 1600.
But you are just not happy with the idea of ISO 1600. You know that by increasing your ISO you are increasing the noise in your image and you don’t want that.
So you think to yourself, to get around increasing my ISO I will just shoot this with a faster shutter speed but keep the ISO the same! This means that the photograph will be a bit underexposed but I can lighten it up on my computer later and I will have kept the digital noise to a minimum.
Seems reasonable, right?
Have you ever done that? Have you ever deliberately underexposed an image so that you can keep the ISO down and decrease noise?
Here is why it simply doesn’t work like that.
Noise doesn’t just come from increasing your ISO. It comes from lack of light. And in fact, lack of light creates more noise!
So, in the scenario I have just described, if you decided to keep your ISO low and shoot the image darker (with a view to increasing the exposure using your editing software later) then you would find that there would be more noise in the dark areas of your image than there would have been had you increased your ISO to 1600 and exposed your scene properly.
Take a look at the images of my son below taken just after sunset so it was getting dark.
The thing about ISO is that as long as you have enough light getting to your sensor then your digital noise will be minimal.
Don’t take my word for it though, try it out for yourself. Choose an area of good light and compose a scene in it. E.g. outdoors in open shade or indoors next to a very large window. Expose the scene with the lowest ISO possible and then gradually increase your ISO right up (you will, of course, have to balance the light by increasing your shutter speed or narrowing your aperture as you do this). You will see that, as long as you are correctly exposed, the noise, even at high ISO settings, is minimal.
Then do the same again, but this time underexpose each time. As soon as you reduce the light like this the noise becomes so much more apparent and unsightly.
What I want you to take from this is not to be afraid to ramp up your ISO. Allow your sensor to receive the maximum light it needs – don’t hold any back just to keep your ISO low because high ISO settings is only one part of digital noise. Lack of light is the main culprit.
Embrace your camera’s ability to increase light sensitivity – it’s a fantastic thing!
I’d love to hear from you. Have you been guilty of keeping your ISO as low as possible to avoid noise, even if it meant underexposing slightly? I know I have!