Nikon Digital Camera Series
|Nikon D2x - Understanding ISO and Noise Reduction Settings
|© Darrell Young|
One thing that makes a digital camera exciting is the fact that one can change the “sensitivity” of the image capturing sensor at any time.
A film user must carry rolls of film with different ISO numbers and waste film when it's necessary to change the ISO before the end of a roll. A digital camera can, instead, use AUTO ISO for automatic sensitivity adjustments, or one can adjust the camera manually for a different ISO on each shot. When one combines flexible ISO with the ability to change color saturation levels on the fly, a digital camera allows great adaptability to various light and color conditions.
Why write an article on the humble act of changing ISO settings? Well, the Nikon D2x has more than the usual amount of flexibility in its ISO system. When one adds in things like Noise Reduction, and modifiable ISO stepping (1 step vs. ½ steps) the D2x has some things to consider, and some decisions to make.
The International Organization for Standardization (ISO) is a worldwide federation of national standards bodies from some 140 countries; one from each country. They do not create standards but, as with ANSI, provide a means of verifying that a proposed standard has met certain requirements for due process, consensus, and other criteria by those developing the standard. So, in short, they are the central body for formation and dissemination of industry standards for all other national standards bodies. Here is a link to their website.
An ISO number, such as 100 or 400, in one's camera, is an agreed on sensitivity for the image capturing sensor. Virtually everywhere one goes in the world, all camera ISO numbers will mean the same thing. With that fact being established, camera bodies and lenses can be designed to take advantage of the ISO sensitivity ranges they will have to deal with. Standards are good!
In the D2x the ISO numbers are sensitivity equivalents. To make it very simple, ISO “sensitivity” is the digital equivalent of film speed. The higher the ISO sensitivity, the less light needed for the exposure. A high ISO setting allows higher shutter speeds and smaller apertures.
Why not get your D2x and manual, and we'll look over the ISO and Noise Reduction settings. Even if you think you understand ISO and NR settings, this will be a good review, and you might even learn something. ISO is covered on pages 52 and 53 of the D2x manual.
Here, in Figure 1 to the left, is the image I use below as a test image for all the illustrations.
I took a picture of the D2x logo on the edge of the D2x camera box, using my D2x and an AF 60mm Micro Nikkor lens.
The small red rectangle is the actual area of the picture we'll examine in the other images below, at 100%, to see the ISO sensitivity noise changes.
Next, we'll look closely at images from the D2x at various ISO settings. In Figure 2 below, examine the images taken with the D2x and an AF Micro Nikkor 60mm lens. This is the same subject, as seen in Figure 1 above, and the images are at 100% cutout with no post processing applied. All RAW file to JPEG conversions were done using Photoshop CS ACR.
To save web space the images in Figure 2 below reflect full 1 EV steps from 100-3200 ISO. This will allow you to judge the noise levels from increasing the ISO, with no additional noise reduction applied. Basic noise reduction is always applied to HI-1 and Hi-2 settings, even if you have noise reduction turned off in your D2x. If you turn noise reduction ON, then even more than “normal” will be applied to the HI-1 and HI-2 settings.
Here, in Figure 3 below, is a full frame JPEG view of an image at 100 ISO, and the same image at 3200 ISO (HI-2) with no noise reduction.
In examining the two images in Figure 3 , the JPEG compression tends to smooth the apparent differences. But, surprisingly the differences aren't that great. The colors are more muted in the HI-2 image, and somewhat grainier, but much less so than equivalent film images would be.
The D2x is very flexible in the number of increments allowed while adjusting the ISO sensitivity. According to how you have Custom Setting b2 set, the ISO numbers can be adjusted in 1/3, 1/2, or 1 EV steps. Below is a chart that shows the ISO ranges for all the Custom b2 settings:
1/3 EV Step ISO Range (b2 Factory default)
1/2 EV Step ISO Range
1 EV Step ISO Range
As seen above the ISO sensitivity can be set between values equivalent to 100-800 ISO in 1/3, 1/2, or 1 EV steps. HI-1 is roughly equivalent to 1600 ISO, and HI-2 to 3200 ISO. The “HI” steps are always simply 1 step apart, with no in-between settings like with the 100-800 ISO range.
Below, in Figure 4 , you will see the menu screen series to select the ISO Step Values.
I leave my D2x set to the 1/3 step default, because I like to be able to use small increments when needed. Some may prefer larger EV increments, and they are there if desired.
Now, let's look at the two ways to set the ISO number in your D2x. It can be done from within the menus, or by simply holding down the ISO button and turning the main command-dial on the back of the D2x.
ISO Selection Method One : Notice that, in Figure 5 , there are two Shooting Menu screens used to select an ISO number:
Find the Shooting Menu, scroll down to ISO, and toggle right to the ISO selection screen. You'll notice that the ISO selection screen displays all ISO values in 1/3 EV step increments. Simply select your desired ISO and toggle to the right.
ISO Selection Method Two : The second method of selecting ISO is by far the easiest and fastest method.
Using Figure 6 as a guide, hold in the ISO button while rotating the Main Command-Dial. The ISO Sensitivity Readout on the small LCD will change as you rotate the dial. This is a very fast and easy way to change the ISO value, and most will use this method.
If you have previously set Custom Setting d5 to “Exposures Remaining” your ISO Sensitivity Readout number (Figure 6) will only show up when you have the ISO button pressed. (see page 196 in the D2x manual). The factory default is for the ISO number to show in the small rear LCD, so, if you can see it, Custom Setting d5 has not been changed.
The higher the ISO sensitivity is set, the more likely the image is to have random “noise” appear. This noise is randomly-spaced pixels that do not reflect the accurate colors of the surrounding pixels. The effect is not unlike “grain” in a film image. With the D2x it is not possible to add noise reduction until you reach 400 ISO, and even then only if YOU think it needs it. The D2x does a great job with noise all the way up to 800 ISO, and even beyond.
I generally don't use extra noise reduction because it tends to lower the sharpness of the overall image. Others use Noise Reduction frequently. I've found that most people are used to seeing a little bit of grain in an image and don't really notice digital noise unless it is very bad. The D2x defaults to a “normal” amount of noise reduction after you set your D2x to any ISO value 400 or above. We'll discuss this in more detail in a moment.
Let's look at a few pictures without and with noise reduction, and you can decide what looks best.
In Figure 7, 8, and 9 below, you'll see images without and with noise reduction, and with Photoshop CS sharpening set to 100. Figure 7 is at 400 ISO, Figure 8 is at 800 ISO, and Figure 9 is at 3200 ISO (HI-2):
Here, in Figure 10, are the series of menu screen used to set HIGH ISO Noise Reduction. (See also page 173 of the D2x manual):
Select the Shooting menu, scroll up or down to find High ISO NR, scroll right and select NORM, HIGH, or OFF.
NORM is the factory default, and provides whatever Nikon thinks is a normal amount of noise reduction to images set to ISO values between 400 and HI-2. There is also a HIGH setting, which provides even more noise reduction. The images in Figures 7-9 are shown with HIGH noise reduction enabled.
Finally, there is the OFF selection which applies NO noise reduction at all in the range of 400-800 ISO.
Remember that the D2x always applies some noise reduction in HI-1 and HI-2 modes, even if you have noise reduction turned OFF. And, even with noise reduction enabled there is NO noise reduction applied to any images below 400 ISO.
The D2x has a feature commonly found on point & shoot cameras, like the Nikon CoolPix line, namely, Auto ISO. This is turned on using Custom Setting b1. Here are the screens, in Figure 11, to set the ISO to Auto:
This mode can be used when you want the D2x to automatically adjust the ISO to the best possible setting without you doing anything. If you set the ISO to 100, the D2x may change that at any time to a higher ISO setting if the light gets darker. You may have the setting at 100 ISO and the D2x may switch it internally to a higher ISO number without warning, if it thinks the light is too low for a good exposure at the selected ISO. There doesn't appear to be any change in the ISO number recorded in the EXIF data included with the image. The ISO number you have selected is what the EXIF data reflects, even though the D2x might have switched to a different number.
If you want to set your D2x camera to be a point and shoot, you can do it. Simply set it in Programmed exposure mode, Auto White Balance, and Auto ISO. Now you have a giant, high-quality, very fast CoolPix. In point and shoot mode, maybe we could call it a “CoolD2x.”
All silliness aside, the noise reduction, variable ISO stepping, and excellent ISO range make the D2x, D2h, D100, D70, and even the humble D50, superior performance cameras.
Gone are the days when we were limited by whatever film type we had in our cameras. Now we can change ISO “sensitivity” on the fly to meet whatever light conditions we find ourselves experiencing. Learn to use the ISO settings on your D2x, and take better pictures for your trouble!
Keep on capturing time…