In Search Of ISO
• ISO Settings And Exposure Compensation
ISO Settings And Exposure Compensation
Q) My SLR offers ISO settings in 1?2-stop increments. Is the range of light control insufficient or as good using exposure compensation?
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A) This is a case of the camera designer giving you more options than before. A camera’s ISO setting controls the degree of apparent image sensor sensitivity—apparent because the sensitivity of the sensor really doesn’t change. You’re adjusting the amplification of the signal coming off the sensor. One thing to keep in mind is that when you amplify a signal, you also amplify the noise that’s in the signal. So, as you increase the ISO, you increase the amount of noise in your image.
Your digital camera’s ISO values are the same as those used for film sensitivity and typically are given in “one-stop” increments: 100, 200, 400, 800, etc. A change from ISO 100 to 200 represents a doubling of sensitivity—the camera becomes twice as sensitive to light. This is different from exposure compensation, which is about how much light is let into the camera.
To give you even more control over ISO, the camera designer has given you steps between the steps—hence your comment about 1?2-stop increments. Instead of the ISO going from 100 to 200, it would go to 140 (I know you’d think it should be 150, but the math involves logarithms). If the camera offered 1?3-stop increments, the ISO would go 100, 125, 160, 200.
Using exposure compensation and adjusting ISO are two different methods for tweaking exposure. If a particular image is coming out dark, you might use exposure compensation to “open up a stop.” Depending on what exposure mode you’re using, this may mean using a slower shutter speed or a wider aperture.
If you adjusted the ISO one stop more “sensitive” instead, your image still would be dark. This is because you’ve changed the sensitivity of the camera to allow a different shutter speed or ƒ-stop that’s automatically chosen by the metering system. So the camera would adjust exposure to compensate for the “faster” ISO setting.
So you set ISO to control sensitivity of your camera to different light levels. You set exposure compensation to affect the actual exposure of a scene, making it brighter or darker.
When choosing an ISO setting, consider this:
•?Set it to the least sensitive setting possible for the conditions; this minimizes noise in your image. But the noise reduction done in-camera these days is phenomenal, so don’t let high numbers scare you, either.
•?Don’t sacrifice image clarity to minimize noise. If you find yourself using slow shutter speeds and handholding the camera because you’re using a low ISO, your images will suffer. True, they might not have noise, but they’ll have blur, which will be more noticeable.
•?Set the ISO for the environment and use exposure compensation (or aperture/shutter speed in manual mode) for each image. When I walk into a room, I decide which ISO I want to use, then check the camera to see if the meter tells me I’m in the range of aperture and shutter speed I want. Once ISO is set, I leave it alone and use either exposure compensation, or if the meter is in manual mode, aperture or shutter speed to control exposure.
Q) I recently began shooting only RAW images and I’m close to starting my own photography business. If I only shoot in RAW, will I be able to put images on disc and take them to a local camera store for developing? If this isn’t feasible, how do I save the images in a different format for developing purposes?
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A) Most labs or local camera stores want to work with either JPEG or TIFF files for a number of reasons, including that these files always can be opened and they’re “developed” compared to RAW. Since you’re starting up your own photography business, I recommend that you talk to the camera store you want to use. While I can tell you what file would be most widely accepted (JPEG, with minimal compression), it’s important that you establish a good relationship with the person who will do your printing. He or she may have suggestions about your process that will help produce the prints that you want.
Think about RAW, and you can see why others don’t want to work with a photographer’s own RAW files. When you download your RAW files to your computer, you go through a series of steps to get them to look right. Some call this “developing” or “processing” or a term analogous to developing film. Others take the analogy a bit further and refer to RAW as your “digital negative,” but that may take it a bit too far.
If you think about film, once it’s processed, there isn’t much you can do to it until you move into printing. But if you sent me a RAW file, for example, I could change your negative-white balance, saturation, contrast or a whole host of other parameters! So you wouldn’t want to send your camera store a RAW file, since it could “adjust” your image, too!
In actuality, when you’re “processing” a RAW file, you’re just changing metadata; you aren’t changing the image itself. If you want a film analogy, consider the RAW file a “latent image” you need to develop. If you want to “freeze” this image so it’s developed the way you want, you need to turn it into a file type other than RAW. The new file type might be the native format of your image editor, or if you have no additional editing to do, it might be some format you’ll then use as your master file.
Quite a few RAW conversion programs let you batch-process RAW files to TIFF or JPEG files. The manufacturers usually will tell you that on their websites.
I want to mention a technology I recently used on a trip to Europe. I needed to travel light and couldn’t bring my laptop, but I still needed to check in at various points. Throughout the trip, I was able to find and use Internet-connected computers, but they were configured for the user’s native language. Getting around in a web browser or e-mail was a potential problem.
Before I left the U.S., I set up a USB drive (SanDisk Cruzer Micro) with U3 technology, including a browser with all of the bookmarks I needed. When I traveled, I simply plugged in the USB to the computer, and I could use my web browser in English on each computer that was configured in a foreign language. Plus, I was able to download documents and take advantage of the storage on the drive.
If you have questions, please send them to HelpLine, PCPhoto Magazine, 12121 Wilshire Blvd., Ste. 1200, Los Angeles, CA 90025 or firstname.lastname@example.org.