Science Buddies: "Ask an Expert"

Will shutter speed effect the pixel intensity of a photo? I already finished my project and won the science fair and am doing extra credit to find out why my experiment turned out the way it did. Any help? Thanks!

Great job! Glad to see some post research initiative.

You can help us "experts" by providing info about your experiment set up and results. Also, if you have a specific question about the results, that would be a big help as well.

Look forward to hearing from you.
theborg

Well, I actually got the idea for this project from Science Buddies and I just changed the question. To do my experiment, I took my digital camera which was a Canon (any digital camera is fine) and went on my roof. I then set it up on a tripod so that when I took the pictures, the camera wouldn't move. I set the ISO to 200 and the aperture to 3.5/f or as wide as possible. I then took a series of pictures changing the shutter speed each time. I went down by a factor of 2. For example, I started at 8s and ended 1/1,000s. After analyzing all the pictures I took using an image processing program called Image J, it turned out that the shutter speed DOES effect the pixel intensity of each photo because it alters how much light is able to be captured. Here's the link to the original experiment:

https://www.sciencebuddies.org/science- ... p022.shtml

What I really would like to know is why my experiment came out the way it did. Thank you theborg!

You need to do some basic reading to understand how shutter speed, aperture, and "film speed" (your digital ISO setting) are related to the exposure of the image (your pixel intensity). The owner's manual for your camera may provide a starting point (look under Manual Exposure Control).

Photo.net is another excellent resource and has a whole section devoted to learning. Here is a link to a great article on exposure http://photo.net/learn/making-photographs/exposure

Additional thoughts...

You didn't specify what you were taking a picture of. However, from your post title "Astronomy/Astrophotography" I assume you were imaging the sky vs objects on the ground. The reason this is important is that objects on the ground would be stationary relative to you, but the stars would appear to move across the sky due to the rotation of the Earth. If you were imaging the sky without some sort of tracking mechanism on your tripod, i'd expect to see some slight "bluring or streaking" of the stars, especially at the slower shutter speeds, as the pixels obsorbing light energy changes position/orientation relative to them.

If you're trying to test the effect of shutter speed on pixel intensity. Shutter speed becomes your independent variable and pixel intensity is your dependent variable. Everything else, lighting, object brightness, position relative to the camera, temperature, etc... should be controlled to the best of your ability.

To give an example of what i'm talking about: The Earth is a spheroid with an approximate radius of 6,378 km that rotates about 15 degrees/hr toward the East. This means that objects on the surface (such as yourself and your camera) actually have a velocity toward the East dependent on your Latitude on the Earth. So at the equator (0 degrees Lat) there is a rotation speed of approximately 1,035 mi/hr (1,518 ft/s). At 33 deg N. Lat (Southern USA) that speed is approximately 870 mi/hr (1,276 ft/s). At 48 deg N. Lat (Northern USA) that speed is approximately 695 mi/hr (1,019 ft/s). So if you were near the 33 degree N. Lat, for example, during your 8 second exposure, you and your camera would actually have moved Eastward about 10,208 ft. For perspective, that is about 34 football fields.

As we walk around, we're usually hardly aware of this motion, but it could significantly skew your results. Keep this and those items Craig_Bridge mentions in mind as you set up further testing.

Good Luck,
theborg