Design
WFPC2 was built by NASA's Jet Propulsion Laboratory, which also built the predecessor WFPC ("WFPC1") camera launched with Hubble in 1990. WFPC2 contains internal corrective optics to fix the spherical aberration in the Hubble telescope's primary mirror.
The charge-coupled devices (CCDs) in the WFPC2 detected electromagnetic radiation in a range from 120 nm to 1100 nm. This included the 380 nm to 780 nm of the visible spectrum, all of the near ultraviolet (and a small part of the extreme ultraviolet band) and most of the near infrared band. The sensitivity distribution of these CCDs is roughly normal, with a peak around 700 nm and concomitantly very poor sensitivity at the extremes of the CCDs' operating range. WFPC2 featured four identical CCD detectors, each 800x800 pixels. Three of these, arranged in an L-formation, comprise Hubble's Wide Field Camera (WFC). Adjacent to them is the Planetary Camera (PC), a fourth CCD with different (narrower-focused) optics. This afforded a more detailed view over a smaller region of the visual field. WFC and PC images are typically combined, producing the WFPC2's characteristic stairstep image. When distributed as non-scientific JPEG files the PC portion of the image is shown with the same resolution as the WFC portions, but astronomers receive a raw scientific image package which presents the PC image in its native, higher detail.
To allow scientists to view specific parts of the electromagnetic spectrum the WFPC2 featured a rotating wheel which moves different optical filters into the lightpath (between the WFPC2's aperture and the CCD detectors). The 48 filter elements included:
- A polarizing filter.
- A graduated filter, featuring a wide range of very narrowband filters. By positioning the target object at a precise part of the field, the operator can use an accurately picked narrowband filter (albeit over a very small part of the field).
- A number of different optical filters, allowing the operator to choose from a variety of different response characteristics.
Read more about this topic: Wide Field And Planetary Camera 2
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