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How much should you charge for a photograph?Equivalent exposures
Equivalent (or 'synonymous') exposures, explained in as few words as possible...
It can be useful to think of the three variables in an exposure as a set of sliders.
Changing, say, the aperture on your camera changes things beyond the amount of light that gets into your camera. As such, you might decide that you want a smaller aperture, in order to get a greater depth of field. A smaller aperture means that less light comes in to the camera. How do we solve this?
Your camera has three different adjustments for exposure: Shutter speed, aperture, and ISO. If you adjust one so the exposure would be brighter, you can adjust another one to compensate for the additional light captured.
For example: Let’s start with an exposure taken at 1/100 second, f/4.0 and ISO 200. Now, you can change your camera settings to 1/200 second. That would let half the amount of light into your camera compared to 1/100 second, because the shutter is only open for half the duration. Your photo will now be darker. If you change your ISO to 400, the sensitivity of the sensor is doubled, and the photo will come out looking more or less the same, from a brightness point of view, as with your original exposure.
You can change any of the settings to compensate for any of the other settings: A smaller aperture can make up for a higher ISO, a faster shutter speed can make up for a larger aperture, and a lower ISO can make up for a slower shutter speed.
Other effects of exposure changes
Of course, ISO, Aperture and shutter speed don't just affect the brightness of the image... Here's a handy reminder for what else they affect:
Easy peasy!
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Comments
Nice graphic. You could also annotate the tops and bottoms of the bars with `noise', `motion blur', `DoF' accordingly :)
That's a mighty good point! I might just do that.
http://woofie3.pixiq.com/files/brighter_darker_600.jpg
There are 2 errors in this graphic. One is a basic one, "darke" instead of "darker". The second is a slower shutter speed doesnt give less motion blur, it gives you more, and likewise a faster shutter speed doesnt give more, it gives less.
Do'h! It turns out that it's a lot harder to make little infographics than to just type information out. I've updated the graphic so it should now be correct.
Thank you for your vigilance!
Do'h! It turns out that it's a lot harder to make little infographics than to just type information out. I've updated the graphic so it should now be correct.
Thank you for your vigilance!
wasn't fast shutter speed supposed to avoid motion blur?
Do'h, stupid mistake on the graphic. Updated! Thanks for noticing!
In your first graphic you really don't have it right either. Instead of lighter and darker it would probably be more accurate to simply say under or over exposed.
In your second graphic you again talk about images being lighter or darker. All three of your examples should result in the same amount of light being recorded. As you say, Equivalent Exposures, but not lighter or darker.
A good way to look at this is to use the old exposure value (EV) metering that cameras like Hasselblad used to use. This used exactly this concept.
http://en.wikipedia.org/wiki/Exposure_value
`Instead of lighter and darker it would probably be more accurate to simply say under or over exposed.'
No! Under- or over-exposure are purely relative to the photographer's intent. When he says lighter or darker, he means lighter or darker.
re: No! Under- or over-exposure are purely relative to the photographer's intent
Not really. This is not a discussion of intent, style or fashion. It's how the three elements, f-stop, iso and shutter speed interact to provide as the title says, "Equivalent Exposure".
Consider simply photographing a standard 18% gray card. Then the only question about the picture is if the card is rendered accurately and if it's accurate as you change the elements. As long as you maintain the same exposure value, they should.
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