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  3. Large Observatories

Palomar 48" Schmidt Camera

The 48” Oschin Schmidt Camera is located on the grounds of Mount Palomar Observatory. This instrument is only designed to take photos with no visual use possible. It was started in 1938 but was not completed until 1948 due to the interruption from World War 2. The 20 foot long tube and fork mounting weigh about 12 tons. The instrument has a 48 inch diameter corrector lens in front, and a 72 inches inch diameter mirror in the back. This combination provides a 120 inch (3 meter) focal length at f/2.5. This is the largest Schmidt Camera in the World and it’s used to map the sky and find objects for other telescopes to study. These photos were taken in 1992.
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01, The Schmidt Camera is mounted in a 48 foot diameter dome about a half mile from the 200 inch Hale telescope dome.
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01, The Schmidt Camera is mounted in a 48 foot diameter dome about a half mile from the 200 inch Hale telescope dome.

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  • 01, The Schmidt Camera is mounted in a 48 foot diameter dome about a half mile from the 200 inch Hale telescope dome.
  • 02, The rear cover has been removed from the 20 foot long tube. The tan colored tube on top of the Schmidt Camera is a 10 inch diameter refractor used to guide during long exposures. That has been converted to an auto guiding system.
  • 03, The large diameter circle at the base of the fork mount is a cover that houses the polar drive gear. Control panel is the blue cabinet to the right.
  • 04, The counter weight system is shown in this view of the rear of the telescope. There are 18 lever and weight mechanism that are designed to accurately support the 72” diameter mirror no matter what position the telescope is in so the mirror is not distorted by gravity.
  • 05, The image plane for a Schmidt Camera is literally in the middle of the telescope tube. The night technician is demonstrating how a film plate is loaded into the telescope. The 14” and 10” square plates must be flexed to a radius of 241” to stay within the curved image plane of a Schmidt Camera. Each plate is pretested by flexing it about 150% greater than needed before it’s loaded into a film holder to make sure it doesn’t break when it’s loaded into the instrument.
  • 06, This shows the mechanism used to transport the film plate from the side of the tube to the center of the tube where the image is located. This is a closer view of the previous image. Note the outline of an access hatch at the very top of the photo. See next photo for view through this hatch.
  • 07, The night technician was kind enough to open the access hatch seen in the previous photo to give me a view inside the 48” Schmidt. There was no room to fit both my head and the camera so I just stuck the camera inside and took this photo (looking toward front of tube). The red rectangle in the upper right is the location of the film plate during exposures.
  • 08, This is a wide angle shot looking from the front to the back of the tube where the mirror is mounted. The black ring with handles is the Schmidt Corrector Lens Mount. The mechanism for the clamshell shutter can be seen just behind the lens at the bottom of the tube in the middle of the photo.
  • 09, Taking a few steps back with the wide angle lens this shows the clamshell shutter part way closed. There is a note at the top of the black ring holding the corrector lens, “420 lbs”. My guess is this is the weight of the lens and lens holder combined.
  • 10, It takes several seconds to close the shutter all the way. The shutter is located just behind the corrector lens so it's easy to remove the lens for maintenance or add attachments to the front of the lens.
  • 11, For many years astronomers have been Hyper-sensitizing film (call Hypering) to make the film more sensitive and reduce the effects of reciprocity failure. This process involves heating the film in a hydrogen atmosphere (this can be exciting if it blows up). This building on the grounds of Mount Palomar Observatory is called the “Hindenburg”. This is where they were storing the hydrogen. Today the 48” Schmidt has been converted over to digital. There are 112 CCD arrays used to record the image and the whole telescope is automated and remotely operated.
  • P54, The Pleiades Open Star Cluster: This is a photo of a 14” square film plate (converted to a positive image) that was exposed in the 48”Schmidt Camera. The Pleiades star cluster has dust surrounding the stars and it’s this dust that reflects star light to produce the wispy light around the larger stars.
  • P55, The Vail Nebula: This is a positive image of a 14” square plate showing the remnants of a supernova that exploded about 5000 to 8000 years ago. The image covers an area about 5 X 5 degrees of the sky.
  • P56, Andromeda Galaxy: This is our largest neighboring galaxy.
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