High ISO demystified- part 2

We hope you enjoyed part 1 of this two-part post on using high ISO values for your wildlife photography. In this post, I will show a few examples of what happens when you underexpose, expose correctly (to the eye) and deliberately overexpose to capture the maximum amount of data on the right hand side of the histogram.

Two things to consider: Since mid-2012, I only shoot in FULL MANUAL mode for complete control. I have no need to use any other mode than Bulb (B) when shooting very long exposures during star trails or auroras. And if I get a few blinking highlights I will accept those, because the review image on the LCD is based on a jpeg file that is generated from the RAW file in the camera for review. In reality, the RAW file will be far more effectively managing the dynamic range of each image and I have found more often that those images with few blinkies will have no blinkies once I open them in the RAW conversion software.

I will now demonstrate with some images I took of one of my trusty dogs – Biscuit – on a dreary winter afternoon when it was dark and cloudy. I deliberately chose to shoot all images at ISO1600 with my Canon EOS 1DmkIIn camera body. Sure it’s a 1D series, but the principle remains the same for any digital SLR camera and should yield similar results overall. I took shots at five exposure correction settings in Av mode, using evaluative metering, which is my standard daytime operating method (EC = exposure compensation). One thing to remember, that I originally wrote this blog entry for my blog in 2012, well before Netra and I met, and even the pro camera bodies were nowhere near the level they are today when it comes to high ISO performance.

This is how the images looked in Canon Digital Photo Professional. See exposure compensation applied written in RED over each image. Exposure compensation applied during the capture is in red. From top, left to right: -1, 0, +1, +2, +1 2/3.

I will discuss the above images in more detail now. Let’s start with the one underexposed by 1 stop, that is expressed as -1EC (exposure compensation).

Look at that histogram accompanying the above shot. It is bunched up on the left really tightly against the left corner. That actually means that there is loss of detail in the black tones. Also, looking at the image overall, it appears underexposed; that is dark. This is a time when I have seen and heard or read of many photographers who resort to Adobe Photoshop to improve their exposure. I also believe that many may be very surprised at the sheer amount of digital noise that is in the dark areas of the image once they brighten it. The 100% crop will show you what happens to the image quality when you use high ISO, underexpose it then believe that Adobe Photoshop will be the panacea to your fundamental exposure error.

The 100% crop of the image here shows clearly that it is way underexposed.

Just to clarify, 100% crop basically means that you increase the viewing magnification to 100%, which will give you the detail that you need. In Photoshop just press CTRL + 1 to get to 100% view.

There is clearly digital noise that is visible already. Many people would now increase the exposure during the RAW file conversion process – rather than learn how to properly expose a RAW file. That is, I am assuming most photographers use RAW files, which is important if you want to capture the best possible detail and dynamic range.

Once the exposure was increased, I feel that the below image quality is really poor here. That is, due to the increase in exposure which in turn exacerbated the amount of noise. No wonder many folks complain that their cameras are noisy at high ISOs. They simply don’t know how to Shoot To The Right, that is overexpose then pull back in post.

This is how noise will appear when you underexpose a RAW file, then increase exposure during file conversion.

The next image below was taken with no exposure compensation applied (0EC). The histogram looks far better, but there is still an apparent loss of some of the blacks due to the histogram bunching up on the left hand side of the histogram. The right side is still empty so that indicates that the exposure can be pushed some more. However, most folks when seeing this image on the LCD will accept this image as well exposed. I am afraid that is not the case. It is not a transparency we are looking at, but a digital file.

Let’s see the 100% crop from this image. Still some noise, but not as severe as the image underexposed by 1 stop (-1EC).

While the below image – that was overexposed by 1 stop during capture (+1EC) – may look a little overexposed, the histogram next to it tells me otherwise. I am getting more data on the right side, with far less on the left. This is almost how I want it. And I feel it could be pushed even more.

Let’s look at what noise we can see when we view the image at 100% below.

There is hardly any visible noise in this shot. So the exposure is getting much better.

The final image was overexposed by 1 2/3 stops. This is about as far as I want to push the histogram to the right. See, it’s pretty much touching there?

100% crop of unchanged RAW file. Looks very good with not much noise at all.
Same image with exposure compensation applied during conversion. Looks pretty much perfect in my opinion.

We looked at images shot at -1, 0, +1 and +1 2/3 exposure compensation increments with the +2 being too overexposed with blown highlights. The histogram and its blinkies do not lie! Trust them.

To sum up the principle, I will compare the first image (taken with a -1EC) with the last (taken at +1 2/3EC). In both instances the exposures were adjusted in Canon’s Digital Photo Professional software to provide the visually correct exposures.

Underexposed by 1 stop (-1 EC) then exposure was increased during file conversion. Verdict: noisy, not very good at all.
Overexposed by +1 2/3 stops (+1 2/3 EC) then exposure was pulled back (reduced) during file conversion. Look at the difference in the two images!

We hope that this two-part blog post about the “mystery” of using high ISO has been useful to you. The important thing is that the more you push your ISO, the lower the dynamic range becomes, but that does not mean you can’t take visually pleasing images just because you are shooting high ISO. You can make some really exceptionally good quality images with the knowledge and techniques that you learn along the way.

Our O’Reilly’s adventure certainly introduces our guests to using this effective technique in the field, as we often shoot in low light forests to obtain our images. Check out our upcoming O’Reilly’s workshop on our Wildlife & Bird Photography page by clicking the link below.

Stay safe, and happy shooting.

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