The Riddle of Intermediate ISO Settings

I guess today is a “blow your mind” Friday, because we have a guest post here by Iliah Borg, the person behind the RawDigger software that is used to analyze RAW images. I had a chance to engage in a conversation with Iliah when discussing the noise performance of the Nikon Df, where he not only proved me wrong on my assumption that the Df had exactly the same sensor as the D4 (turns out that they are similar, but not exactly the same), but also shared some incredible information about testing procedures, data analysis and other crazy, mind-boggling stuff! The learning curve with photography never ends, especially when you get into the whole sensor and image processing pipeline side of it. I must warn our readers though – the below article is very technical and is not intended for beginners! Hope you enjoy it! Nasim.

If one is shooting raw, they might be interested to know if there is any benefit in using intermediate ISO settings like ISO 125, 160, etc. There is no single answer to this question, because it depends on implementation of these intermediate ISO settings in the particular camera. Sometimes they are implemented the same way as the main ISO settings, but other times they are a result of certain manipulations, like digital multiplication.

To demonstrate how this can be determined, we will first analyze the so-called Masked Pixels (often called optically black area, or simply OB), which is a portion of the sensor that we normally do not see in our images. It is covered from light, so it can be a good indicator of the lowest possible noise of the sensor, while noise is what we analyze to learn how to use a given sensor optimally. We are taking a series of shots at varying ISO settings, from the lowest to the highest and, of course, using all intermediate ISO settings available. The subject of the shots can be anything – you can even shoot with a lens’ cap on.

Next, bring the first shot of the series into RawDigger and set RawDigger preferences to display the black frame (Display Options, Masked Pixels checkbox, checked) and not to subtract black Level (Data Processing, Subtract Black checkbox, unchecked).

RawDigger Preferences 1

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Nikon Df vs Nikon D4 ISO Performance

In my previous articles comparing the Nikon Df to other cameras like D800, D700 and D610, I posted images from the D4 as if they were from the Df in the articles (note that I clearly pointed out that the images were from the D4), because I was pretty sure that the Df had the same sensor. Some of our readers criticized me for doing that, arguing that Nikon’s sensor technology and the imaging pipeline might have changed since the introduction of the D4. I received the Nikon Df last week, so one of the first things I did was compare its performance against the D4 to see if I could spot any differences. Below is a detailed comparison between the two, which shows that both cameras utilize the same or similar sensor technology. So my previous comparisons are still valid and can be referred to for comparing between the different Nikon DSLRs.

Nikon Df Nikon D4

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Understanding ISO, Shutter Speed and Aperture – A Beginner’s Guide

It is difficult to take good pictures without having a solid understanding of ISO, Shutter Speed and Aperture – the Three Kings of Photography, also known as the “Exposure Triangle”. While most new DSLRs have “Auto” modes that automatically pick the right shutter speed, aperture and even ISO for your exposure, using an Auto mode puts limits on what you can achieve with your camera. In many cases, the camera has to guess what the right exposure should be by evaluating the amount of light that passes through the lens. Thoroughly understanding how ISO, shutter speed and aperture work together allows photographers to fully take charge of the situation by manually controlling the camera. Knowing how to adjust the settings of the camera when needed, helps to get the best out of your camera and push it to its limits to take great photographs.

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Understanding ISO – A Beginner’s Guide

It is challenging to take good pictures without a good understanding of how ISO works and what it does. Camera ISO is one of the three pillars of photography (the other two being Aperture and Shutter Speed) and every photographer should thoroughly understand it, to get the most out of their equipment. Since this article is for beginners in photography, I will try to explain ISO as simple as I can.

Before we go any further, you should first understand how DSLR cameras work.

1) What is ISO?

In very basic terms, ISO is the level of sensitivity of your camera to available light. The lower the ISO number, the less sensitive it is to the light, while a higher ISO number increases the sensitivity of your camera. The component within your camera that can change sensitivity is called “image sensor” or simply “sensor”. It is the most important (and most expensive) part of a camera and it is responsible for gathering light and transforming it into an image. With increased sensitivity, your camera sensor can capture images in low-light environments without having to use a flash. But higher sensitivity comes at an expense – it adds grain or “noise” to the pictures.

Take a look at the following picture (click to open a larger version):

ISO 200 and ISO 3200 Comparison

ISO 200 and ISO 3200 Comparison

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