Northern Arizona Astronomy: astronomical observing, comparing the camera and the eye

March Sky Chart.  (Graphic/Barry Malpas)

March Sky Chart. (Graphic/Barry Malpas)

WILLIAMS, Ariz. — As with any science, astronomers must be knowledgeable of the equipment they are using. What are the strengths and the weaknesses? How are some telescopes better for certain applications than others? And also, how are digital cameras better than observing with the human eye, and vice versa?

This last question is often glossed over by many amateurs assuming there is little to be learned by visual observing. However, since Galileo first peered through a telescope, to relatively recent times, the human eye was the only device capable of detecting and discerning structural details of the often faint fuzzies known as Deep Sky Objects (galaxies, nebulae and star clusters). Even today, many amateur astronomers find it interesting, educational and enjoyable at what can be observed visually through a telescope once the basic techniques have been mastered.

Although it may seem logical to compare the eye as being equivalent to a camera, since the eye’s retina is almost the same size as the sensor on a full frame 35mm DSLR camera. After that, however, almost everything is different. Firstly, the retina is curved along the back surface of the eyeball, not flat like the CCD camera sensor, with the advantage that the edges of the retina are always about the same distance from the lens as the center. On a flat CCD sensor the edges are further away from the lens and the center closer.

The advantages of the human eye compared to the camera get reduced when the image is transmitted from the retina to the brain. A camera sends all the data from the CCD sensor to a computer chip for processing. However, the optic nerve that carries the information to the brain has only 1.2 million fibers, so less than 10 percent of the retina’s data is actually transmitted to the brain at any given instant.

The eye effectively transmits a constant feed of individual images, which are then processed by a part of the brain into what we see, where the signals from both eyes are then assembled into 3-D images, and then sent on to another part of the brain for image recognition and further processing. All this is done for each image in about a tenth of a second, and then cleared for the next image. Hence, the human eye is video, not photography. And here in lies the great advantage of the camera over the eye. The camera has the capability of building up an image over long periods of time, where the eye clears its images 10 times a second. This is why when we look through a telescope at galaxies and nebulae we tend to see them as fuzzy grayish objects with little to no hue, instead of those magnificently colored photographs that NASA gets from the Hubble Telescope.

Though the eye may be very sensitive, it did not evolve to build up images over time the way a camera can. With a digital camera the photographer can expose the object of interest to several minutes, or even hours, collecting the light to build up an image over time. Since the human eye clears its images every 1/10th second, we would not be able to see things in every-day life as we moved since everything would become a built-up blur.

Still, observing visually through a telescope can be a most enjoyable and informative avocation where the average person can see details on the moon, planets and even deep sky objects, as well as make discoveries that the professionals occasionally miss.

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