Back in the day (or should I say night?), astronomers used to ride in the Hale Telescope at prime focus to collect their data just as this person is posed in this photo from the Google LIFE image archive.
They would ride up there all night and capture their images on glass photographic plates. This second photo from the same image archive shows a close up of an astronomer loading a photographic plate into a prime focus camera. Note the guiding eyepiece that was used to ensure that the telescope maintained the proper pointing during the night.
Those times have passed. No one has shot a glass photographic plate with the 200-inch since 1989. The first digital images with Charged Coupled Detectors (CCDs) were captured here in 1976 and that is the imaging standard now.
Here is a photo of the detectors within the Hale Telescope's Large Format Camera. The dark rectangles are the 6 CCDs that form its imaging array. This visible-light camera coupled with the Wide-Field Infrared Camera are the two most commonly used instruments at prime focus now.
Of course no one rides in prime focus any more. The astronomers sit in a comfortable warm room during the night. Technicians (at Palomar they are called "Electronicers") use the daytime hours to perform the instrument changes and keep them cooled with liquid nitrogen.
So how do the modern detectors compare to the old glass film plates? They are vastly more sensitive and they allow our astronomers to be much more productive. Of course another way to compare the old and new instruments is to look at how much sky they can see with a single exposure.
Palomar Skies reader (and Friends of Palomar Observatory member) W. Van Doran has certainly done his homework and made this graphic to compare the fields of view for the old film plate holders and the modern electronic detectors. Have a look at what he has done and be sure to click on it to see it in full size:
Thanks for your great graphic which bridges the old and the new at Palomar!