Understanding ISO In Digital Photography

ISO is one of the three pillars of the photography along with the shutter speed and the aperture. When we are talking about the camera with digital censor, ISO refers to the amount of amplification of the signal. It affects the exposure of the image by affecting the shutter speed and the aperture combination used in camera. ISO value indicates the camera's image censor's sensitivity to the light and gives us an idea of how sensitive the image sensor is to the light. High ISO value means image sensor is more sensitive to the light and similarly, low ISO value means sensor is less sensitive to the light. You can take pictures in a low-light condition when the ISO value is set to high in your camera. But at the same time, setting up high ISO value also introduces the digital noise in the picture because when we increase ISO value, artificial electric gain is added to the signal to provide more lights into the image. It's not coming from the natural light source but the light is being produced artificially and amplified by the camera using the signal booster.

When the ISO is set to Auto, camera’s metering system will automatically detect the light condition and increase or decrease the ISO value as needed. If you are using your camera into semi-manual mode or Manual mode (M), you can also manually set the ISO value to adjust the proper exposure under different lighting condition. Higher ISO value allows you to set the faster shutter speed so that you can freeze the motion when your aperture couldn't be more wider to allow more lights into the sensor. But you also have to consider the noise factor when increasing the ISO after certain value. Some cameras specially consumer level DSLRs are highly susceptible to the noise with higher ISO value whereas full frame cameras can take much higher ISO value without producing noticeable noise in the picture. When you have enough lights available, you should use lower ISO value and adjust the proper exposure using the combination of faster shutter and wide open aperture (smaller f value). Increasing or decreasing ISO value by double (from 200 to 400, 400 to 800 etc or reverse) is same as increasing or decreasing the exposure by one f-stop.

Focal Length - 50mm     Aperture - f/1.8     Exposure - 1/1.3 sec     ISO - 800

All of these pictures are taken in an Aperture Priority (A) mode with f/1.8 aperture and only changing the ISO value. The first picture was taken with ISO 800 and the camera adjusted the shutter speed to 0.769 seconds automatically to balance the exposure. This picture is almost noise free and much more cleaner than the second shot where the ISO was bumped to 6400 and then the camera accordingly adjusted the shutter speed to 0.0769 seconds to adjust the exposure. By increasing ISO value, I was able to shoot with much faster shutter speed but it produced the noise in the picture as well.

Focal Length - 50mm     Aperture - f/1.8     Exposure - 1/13 sec     ISO - 6400

I cropped the corner area of the second image to demonstrate the digital noise in the picture. If you look at the picture below more closely, you can clearly see the grainy noise all over the picture introduced by high ISO.

Focal Length - 50mm     Aperture - f/1.8     Exposure - 1/13 sec     ISO - 6400

Using higher ISO value allows your camera sensor to capture images at very low light condition but also produces noises (grains) in the picture. You won't probably notice it in a small size picture but if you enlarge the image, you can easily notice the effects of high ISO vs low ISO. It is always good practice to shoot with lower ISO value possible and increase it if you cannot get more lights by adjusting the Shutter speed and the Aperture value. But with more and more innovation everyday, modern DSLR cameras produce acceptable pictures quality even at higher ISO.

If you are looking for Nikon D90 specific ISO settings, please click here.

RAW Vs JPEG Picture Format

RAW files are the exact representation of your subject captured by the camera sensor without any modification. RAW format retains more detail information about the picture and camera setting which you can adjust later during post-processing. Every camera manufacturer has their own proprietary format to store RAW files. Nikon uses NEF format to store RAW files and Canon uses CRW into older camera models and CR2 into newer models. Usually, RAW format stores information into 12 to 16 bit data. Camera always captures the data into RAW format first and if you are using JPEG mode, camera processes it using built-in algorithm to handle the white balance, contrast, saturation, sharpness and other settings that is set into your camera and compresses it into JPEG format to produce a 8 bit of data (JPEG) file. That means you will loose some details during the compression, which is pretty obvious given the reduction of information. I once read Ken Rockwell's comment about shooting in RAW mode where he says and I quote, "I never shoot RAW. Why would I? Raw is a waste of time and space, and doesn't look any better than JPG even when you can open the files". Later he added, "Cameras all start with raw data and convert this data to JPG images with hardware in the camera. They then throw away the raw data since it's no longer needed. Some fancier cameras save this raw data so you can use software to do the same thing the camera's hardware did, later".

In my view, shooting in either RAW format or JPEG format is your personal choice but the only difference is, if you shoot RAW, you have the flexibility to adjust settings later on the computer but in case of JPEG format, camera already did that job for you and you have to trust it’s algorithm for your final image since there is very less room left for further adjustment due to the loss of data. It is up to you whether you want to spend your money on getting software and use your time for further processing of your image on the computer or let your camera do that job for you. RAW mode is designed for someone who wants to do experiment with the photograph by applying different settings during editing. And if you are a professional wedding photographer for example, shooting in a RAW mode might be a no-brainer. You can't re-shoot the wedding once its done. And if you need to adjust something later on the picture without loosing details, you can do so with a greater flexibility if you shoot in a RAW mode. One thing you might want to consider while shooting in a RAW format is a memory. As we discussed earlier, RAW file uses 16 bit data format compare to the 8 bit format for JPEG file. RAW format takes almost double the size of JPEG format. If you are shooting all day event (using RAW format) capturing hundreds of photos, you might have to consider the memory size of your camera as well. It is always a good idea to carry an extra memory in your camera bag but if you are shooting in a RAW mode, that might become a necessity.

In my opinion, if you are smart enough to use a post-processing software for editing pictures, it is a good idea to shoot in a RAW format. But if you are not confident enough on using computer software to edit the pictures, it's better to believe in your camera and let it process for you. If you really want to see the differences between two formats, you can also use RAW+JPEG mode (most of the modern DSLR camera supports dual mode) which saves both files; one in JPEG format and another in RAW format. And later, you can try processing both formats using software and see the difference yourself. Reminder - since it keeps both file formats of the same image into your camera memory, you will have to be more careful about the memory space.

Personally, I shoot JPEG Fine for the most of the friends and family events. But I also shoot RAW when I do night cityscapes, fireworks or landscape photography and use Nikon Capture NX2 for post-processing. Please feel free to share your experience and tell us about views on shooting RAW Vs. JPEG.

Update : I switched from Capture NX2 to Adobe Lightroom in 2017

FX Format Vs DX Format DSLR

I have got many requests from the readers to talk about FX vs DX format DSLR camera. They also asked me to briefly discuss whether the FX and the DX camera bodies and lenses can be used with each others or not. In short, FX is a full-frame camera which uses bigger censor (36x24 mm) like in the film camera to produce lower pixel density or high quality pictures. This kind of camera is used to produce highly pixelated full framed picture under the low light condition by increasing ISO sensitivity without affecting much on the picture quality. In the current market, Nikon D3X, Nikon D700, Nikon D3S and Nikon D3 are FX format camera from Nikon. Whereas DX format DSLRs use censors that are usually 2/3 of the size (almost 24×16 mm) of the FX censors. That is the main reason DX cameras are cheaper than the full framed FX camera and also they are more sensitive to lights than the full frame camera. Nikon D40, Nikon D60 and Nikon D90 are the examples of DX format camera.

Now the question is, can I use the FX format lens with the DX format camera body or the DX format lens with the FX format camera body? The simple answer is, in case of Nikon, you can use either DX lens or FX lens on the DX camera or the FX camera but same is not true for Canon cameras. You have to have a FX format lens for the FX format Canon body. Lots of photographers think this is the strength of the Nikon camera that you can use either FX lens on DX body or DX lens on FX body (even though there are some limitations on cross combination). You may not want to use DX lenses on the FX camera because, since the lens won't fill the entire frame, the corners of your picture will come out dark. Similarly, if you mount the FX lens on the DX camera body which has a smaller sensor size, only the center of the lens's image circle is captured. The edges are cropped off,  which is equivalent to zooming in on the center section of the imaging area. To be more precise, 1.5 x crop factor will be applied when you use the FX format lens with the DX format body. That means if you mount the 50mm FX format lens on the DX format camera body, it will work as a 75mm (=50mm x 1.5) on the DX body. Actually, this technique is very much popular among the wildlife photographers to reach the long distance subjects by taking advantage of this crop factor.

There are also other pros and cons of both body types. The main advantages of DX sensors are compact wide-range zooms, and you can reach farther with the FX telephoto lenses. You will also have a greater working distance for the close-up or macro shots with the DX sensors. The advantages of the FX sensors are you can shoot with the less noise even at the higher ISO and get the good wide-angle shot with certain type of lenses. If you have something to add or comment, please let me know using the comment box below.

Happy Shooting!