Z o plates that were available at the time. While these photographs reveal the larger, more obvious albedo features, the human eye was able to see much more detail just looking through an eyepiece in a smaller telescope. The Palomar photographs suffered from the effects of "seeing".

Unlike deep sky photography of stellar and nebulous objects in which the camera can be placed at the prime focus of the telescope, planetary photography requires some amount of "eyepiece projection", so that the image falling on the photographic film is large enough for the film to record planetary detail with satisfactory resolution. To achieve this projection, an eyepiece is placed in front of the camera, using a tele-extender between the camera and eyepiece so that the camera's film plane is some distance from the eyepiece, thus projecting an enlarged image on the film. Jupiter is a bright object and we normally do not have much difficulty observing it visually at moderately high magnifications. But when the image is enlarged to project onto film, the act of enlarging the image spreads out its light and also reduces its brightness. This dimming requires us to lengthen the exposure time to capture an acceptably bright image on the film. And there's the rub. When we lengthen the exposure time, we give the effects of poor seeing a chance to blur our photographic image. The exposure time required to capture an enlarged image of Jupiter can range from 1 to 3 s, and perhaps longer. During the 3 s or more of exposure, the waviness of the currents in the air smears the fine detail that we want to record. There are modern, fast films available that can reduce exposure time, but normally the faster the film the coarser the grain of the emulsion. This coarseness will reduce the film's ability to record fine detail.

Donald Parker, world-renowned amateur planetary imager, used film successfully into the late 1960s before the advent of CCD cameras. Don produced some of the best film based photographs of the planets taken up to that time and yet, he was not able to capture all that could be seen with the human eye.

Astrophotography with film has always been an exciting endeavor for me, and every amateur astronomer should give it a try. I have seen some surprisingly good film images taken of Jupiter by a few amateurs with near perfect seeing conditions. But be prepared for disappointment and a lot of darkroom work trying to improve contrast in the final print to squeeze out as much detail as possible. There are many good books on the subject and you should certainly have a few of them in your own library. Remember that the same information recorded when a drawing is made of Jupiter should also be recorded for the photograph, including information about the film, camera, and exposure.

Fortunately, technology marches on and advancements have led to a solution for the problems with planetary photography through the use of CCD cameras and web cams.

Was this article helpful?

0 0
Telescopes Mastery

Telescopes Mastery

Through this ebook, you are going to learn what you will need to know all about the telescopes that can provide a fun and rewarding hobby for you and your family!

Get My Free Ebook

Post a comment