High ISO demystified – part 1

People often shy away from using high ISO. In fact, many still don’t like to go over ISO400 in case they get noise in the RAW file. However, it’s these photographers that want to photograph birds in a low-light situation that then complain they cannot get “the shot”. Funny that! These days with the camera technology at a point once thought impossible, it is possible for the skilled photographer to use very high ISO values and obtain very good quality images. You just got to understand the technical aspects of the capture. If you kept your ISO at 400 for the below image, that is 7 stops of difference from 51,200.

Stop 1 – 51,200 to 25,600

Stop 2 – 25,600 to 12,800

Stop 3 – 12,800 to 6,400

Stop 4 – 6,400 to 3,200

Stop 5 – 3,200 to 1,600

Stop 6 – 1,600 to 800

Stop 7 – 800 to 400

Now do the maths with the shutter speed for 7 stops slower when using the same aperture of f/13. The steps are: 1/30th, 1/15th, 1/8th, 1/4th, 1/2 second, 1 second, 2 seconds. You would have had to hold your camera STILL for 2 FULL seconds. No chance!

An Eastern Yellow Robin photographed in the early morning at O’Reilly’s. Being so close, I wanted as much depth of field as possible, hence the small aperture. But check out the other specs. OM-1, M.Zuiko 300mm f/4 Pro lens, ISO51,200, f/13, 1/60th, hand held. The image is amazing considering I shot this at ISO51,200. That is no marketing gimmick at all from the OM System Brand. High ISO shooting is truly achievable if you know what you are doing with your gear!

Firstly, there are a number of things to consider with photographing birds.

Birds move about a lot when they are living their lives, that is; feeding, courting, flying, fighting, fleeing and so on. This means that low shutter speeds often don’t give an opportunity to freeze motion. You would need a relatively fast shutter speed, depending on what kind of behaviour you are trying to photograph. If you think of a scenario with a bird in a forest environment in the morning hours, when light is low and even with fast lenses you would only get a slow shutter speed. You will quickly appreciate, that there must be ways to increase your opportunity to take a keeper shot. This is even more critical when using hand-held equipment, rather than tripods. Unless you have some physical limitations or you are photographing from a hide or a set-up scenario, then tripods are completely unnecessary with today’s modern camera and lens stabilising technology and the ability to shoot at very high ISO values. Use your gear like a pro and you will be guaranteed to get good quality files.

This is a demonstration of an image of this Straw-necked Ibis I shot back in 2013 with my then back-up camera (my first DSLR) the Canon EOS 30D, released almost 20 years ago. It was a sloth compared to today’s stuff. Yet, I still managed a high quality image shooting ETTR (see explanation further down in this blog post). ISO1600 was not something considered useable by people back in the 2000s and early 2010s with these old cameras. Yet with technique and understanding I was managing just fine.

You probably ask now, what is a fast lens? Fast lenses are generally those with a maximum aperture of f/2.8. Lenses with a maximum aperture of f/4 are still pretty fast, but the extra stop of light with an f/2.8 lens makes a big difference in low light. Lenses with apertures of f/5.6 or smaller are considered slow lenses and make image taking in low light much more challenging.

The only unfortunate thing is, that most bird photographers who use full frame cameras will prefer a 500mm f/4 or 600mm f/4 lens for the extra reach rather than a 300mm f/2.8 or 400mm f/2.8 lens, which are obviously faster, but generally not as useful for most bird photography in the field, except from a hide or with cameras that have so many megapixels that you can comfortably crop your image by 60-70% and get a high quality image. In my opinion, cropping that much simply defeats the purpose of bird photography, as what’s the point of having so many megapixels if you don’t actually use them because you are a sloppy shooter who just wants to crop excessively because you haven’t developed the field craft required to be a good bird photographer.

Though remember, the big lenses are all heavy to some extent, but with a relatively average fitness one can hand hold one for a day as long as it’s not pointing at something constantly for the day.

How do you minimise digital noise? Well, read on and learn.

Make yourself familiar with the ETTR theory. What is that you ask? Expose To The Right is what what ETTR stands for. It means you push your digital exposure as far right (on the histogram) as you possibly can, making the image look overexposed, then pull that exposure back during post processing. This method of RAW file capture really reduces the amount of digital noise generated during the image taking process. It won’t necessarily remove it all, but it will make further processing more effective and less visually overpowering. You just need to be careful to not blow the highlights, although in some situations with strong backlighting, that cannot be avoided.

Rainbow Lorikeet in our backyard. OM-1, M.Zuiko 300mm f/4 Pro lens, ISO6400, f/11, 1/500th. Smaller aperture used to increase depth of field. Nothing has been cropped from the original image.
This is the brightness of the RAW file that I captured to use the ETTR method. There was little light and the image on top represents the real low light level at that time.

If you consider the bird in a dark forest scenario above, you want to use high ISO when the light is low, so you can get a fast enough shutter speed, even if it’s just to be able to hand hold your super telephoto lens and take a beautiful low-light portrait of your subject. How does your sensor record the light? It is covered in millions of photons (pixels) that capture light, which the camera then converts into a colour image. That is truly putting it in very simple terms. Noise will be more visible in dark areas of the image where there is less light and more amplification of the signals, especially as you push ISO higher and higher. 

Digital sensors record data in a number of stops, usually seven in 12-bit
mode recording 4,096 tonal values (2 to the power of 12). Although, you now have cameras that can capture 14-bits of data, which is enormous! However, from what I have read having 14-bits over 12-bits does not
give a huge advantage. In fact, it slows down your image making process. That
is because the camera has to process more data than in 12-bit mode, 4 times as
much actually. That is, 16,384 tonal values! Phew! That’s a ton if you ask me. No wonder your processing power slows.

Most of your good data is on the right side of the histogram, illustrated by the below image. The old saying shoot for the highlights and the shadows will take care of themselves kind of rings true here. 

This shows you the transitions between tonal values from darkest (left) to brightest (right) side. The transitions should be smoother, but I could not replicate in the top section of the illustration.

    Whilst you might think that each of the seven stops in the range of the sensor record an even number of tones throughout the dynamic range, you would be mistaken. F-stops are logarithmic in nature meaning that each stop records half of the light of the previous one. Practically, this means that the brightest stop records half of the possible number of tones, i.e. 2048, the second stop records half again (1,024), the next half again (512) and on and on until you reach the seventh stop that records a measly 32 tonal levels. Here is the news! If you underexpose an image and correct the exposure during in post processing, the tonal transitions in the darker areas will not be as smooth, and the risk of degrading your image quality is much higher. If you overexpose your image, by pushing the histogram to the right, you will capture much more tonal information that results in much better image quality when correcting the exposure in post processing.

    I will post another part to further discuss our techniques for shooting high ISO and managing noise during capture and post process next week. Check back on Tuesday morning, when the next post will be up following on from this one.

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