Tech Talk: Rating Your Sensor

Greetings, volks. Welcome to Hohenfels Volks, THE place for our place! WOW! The annual Hohenfels Volksfest was a great time and the weather was perfect. Now the clouds are puffing up some, and that makes for great outdoor photos that include the sky!

Today we’re going to introduce rating and EI.

Your camera has a range of ISOs you can choose from, most likely running from ISO100 to ISO3200 in third stop increments. Camera and film manufacturers used the International Standards Organization methods to set the speed, or ISO, of your sensor or film. They generally are set to favor overexposure, as underexposure is harder to correct. Therefore, in test conditions ISO 100 performs at ISO 80-100 to get you exposed at the general target for the contrast and exposure standards set by the organization. This used to be referred to as a film’s “box speed.” For digital work, I’ve come to think of it as “nominal.” Therefore, when I say I shot it at ISO 125, that’s what I was set and exposed for.

The ISO recognized that most scenes deviated from test conditions, as did developing or processing. A film may be rated at ISO 100, when developed in a certain developer for a specific time, but not for any other combination. Film shooters would “rate” their film at different speeds for their methods, including exposure and development controls. For instance, some would shoot FP4+, which is ISO125 in Ilford’s ID11 developer, rated at EI80 developed in Kodak D-76 for their preferred method of exposing and developing a standard shot.

EI, or “exposure index,” is what you rate your film at for your methods, and usually refers to speed rating assigned that’s different from the film's actual speed. Generally, when you shoot with your digital SLR, you shoot maybe at ISO 100, and edit it in your manufacturer’s provided application and get decent results. You are shooting and making your shot at nominal speed, or box speed with film.

You may find that in high contrast scenes at nominal speed, you are getting shadows that are clipped to black and whites that are blown and have no detail. In that case, it’s time to change your EI, or rate your speed different. To do this correctly, you should test your camera, and we’re going to cover the procedures to do that for YOUR best results. Since this test is based on your equipment, metering, and editing, someone else will get different results using the same equipment. This test is based on your style and methods, which others may not follow. Keep that in mind when “rating” your gear, you can recommend your “rating” to others with the same camera, they will most likely appreciate the information, but each “rating” is subjective, and will work best in your hands.

This testing becomes especially important when shooting at extremes of lighting. In very low light, like that in most old buildings, noise is a real concern when trying to increase your image brightness during editing, and in bright daylight lit landscapes skies and clouds can become just blotches of white without any detail.

The procedures for setting your EI involved a gray card, meter, and your camera. You should be set up for this in light conditions that match your intended shooting conditions to effectively use this method.

Step 1, set up your gray card in lighting that matches your shooting conditions. Step 2, set your desired ISO reading on your camera, and select RAW mode. Step 3; set your camera to f/8 or f/11 and AV mode. Step 4, meter your gray card, use spot metering and fill as much of the frame as possible with the gray card. Note the shutter speed. Step 4, set your camera to manual mode, and enter the shutter speed metered in step3, which should give you an 18% gray image. Step 5: compose your test shot. You can pull back some, including other elements. I have a test screen that includes black and white pieces and collapses nicely into a camera bag, and prefer to use that to check contrast ranges while doing this test. Step 6, take the following series of shots- at the metered reading obtained previously, -1/3 stop, -2/3 stop, -1 stop, +1/3 stop, +2/3 stop, and +1 stop. Step 7, load the images onto your computer. Then open your image editing application. Step 8, Open each image in turn, and find the one that is MOST CLOSELY identical to the gray card in exposure for your set up. Make sure to perform absolutely no adjustments to the images, as we are looking for the most closely identical image. Take note of the settings used for this shot. Step 9, this is your EI for that type of scene with that ISO selected. For example if –1/3 stop produced the best rendition for ISO100, then your EI would be 125 or EI125. You will effectively be rating your ISO100 shots at 125, and removing 1/3 stop on all your shots in those conditions. To accomplish this, when shooting at ISO100 simply remove 1/3 stop exposure, either by increasing your shutter speed 1/3 stop or closing down your aperture 1/3 stop.

Rating your sensor or speed before shooting can save a lot of time editing and the heartbreak of a shot that doesn’t live up to your expectations. It’s not perfect, and varies based up taste, style, and personal preference, but it will bring you closer to achieving your vision. It’s definitely something to try in conjunction with this week’s exercise on contrast and contrast control. Combine it with M+ and M- exposure placement for even better results. By exposing properly, you can keep your contrast in the desired range, and make it easier to achieve your vision in your final processing stage.

For those interested in more information about film speed, Wikipedia has a great article. It includes formulae and details about how box speed and nominal are attained.

I’m looking forward to seeing your results and hearing from you. Let me know what you think and how you’re using your camera! Share your thoughts here or at the Hohenfels Volks Facebook page. Of course, commenting on both Facebook and here is always appreciated, too! Don't forget, we're on Google+, too!

Ambience...

Greetings, volks. Welcome to Hohenfels Volks, THE place for our place! This time of year in Hohenfels starts seeing some awesome photo opportunities springing up everywhere, I hope you’re seeing some!

First, let me apologize for the sporadic posting, an emergency has left me somewhat distracted. Such is life; I’m making lemonade from those lemons as we speak!

I hope everyone is enjoying the exercises we’ve been sharing. I’ve been shooting mostly film again as I develop a new way of looking at values and value control in digital photography. Today we’re going to cover a couple tips when shooting with ambient light.

Ambient light covers a lot of ground, from the living room lit only by the fireplace to the bright sunlit beaches of the Med. We’re going to focus on the darker side here to make this short.

The first and most important thing to be said about low ambient light shots is that a tripod is required! Without a tripod, you’ll never get a truly spot on level of sharpness that sets an image apart. A shot handheld with a 55mm lens at 1/30 with IS turned on will still be less sharp than a 55mm on a tripod at 1/25 with IS off. You’ll still get something you can use, and be proud of, but nothing like you’d get when you stick it the ground!

Second, consider how dark it is and how much light is available. You will need an ISO that will prove sensitive enough for your range of luminance, yet low enough to prevent excess noise to become a problem.

The third thing to consider is metering and exposure. In case you haven’t noticed, I’ve become big on using the meter to aid in getting things to levels I visualized. Your camera has a built in meter, so let’s put it to use. Do you want to use a small aperture or a faster shutter speed? To control the DOF, go to AV mode and set your desired aperture. To shoot something with more speed, go to TV and set your desired shutter speed. Before you meter, you need to decide where your want your levels to be. For a brighter image, you’ll need greater exposure in the shadows, and conversely less exposure for a darker image. Once you determine that, meter for your intended image. You’ll have a little leeway in editing, but remember that increasing your brightness in editing can introduce some seriously unsightly noise.

Another thing is your composition. You want to compose your image in a way that maximizes visual and emotional appeal. Move around to find that shot, try moving your subject. You may be able to move your light source. Zoom in or out to cover what you envisioned, and you'll notice some interesting things happen, and this ties in to our exercise on shooting only 1 focal length. Remember how you had to move around to get the shot?

Here are a couple more tips for low ambient light shooting. First, use a cable release. This will provide an even steadier platform. Second, if your camera has it, enable mirror lock-up. This locks your mirror in the up position, preventing the mirror vibrations from introducing shake into your image. A lot of cameras let you compose the image, activate the shutter button to lock the mirror, then wait for another shutter activation to actually expose the scene. Third, try to introduce balance into the composition between light and shadow. This allows you to create something that has fewer bright distractions against your main subject. Lastly, this is incredibly important, if your shooting at night or anywhere there is some risk of accident or injury, take a light and play it safe!

I know this all over simplified, but learning your gear and using these simple tips will help improve your low light and ambient light shots. It will also help you get that shot you visualized and not feel like your time was wasted.

Enjoy the week and keep on shooting.

Don’t forget to post any of your images you’d like to see here at the Hohenfels Volks Facebook page. Of course, commenting on both Facebook and here is always appreciated, too! Don't forget, we're on Google+, too!