DECam Characteristics

Main Characteristics of Focal Plane

Field of View 3 square degree (2.2 degree field of view)
Pixel scale 0.2637 arcsec/pixel (center), 0.2626 arcsec/pixel (edge)
Detector 62, 2048x4096 pixel red-sensitive science CCDs from LBNL, 520 megapixels total (570 Mpix including guide and focus CCDs)
Read-out noise 7e-
Read-out time 20 seconds
Dark-current ~
QE 40% at 400 nm, 70% at 520 nm, then around 90% until 920 nm, falling to 40% at 1000 nm, 10% at 1050 nm
Dynamical range 16 bit
Inter-CCD Gaps 3.0 mm (201 pixels) along long edge (e.g., between S4 and N4); 2.3 mm (153 pixels) along short edge (e.g., between N4 and N5)
Cosmetics Good to excellent. On average, each CCD has 0.05% bad pixels and the worst CCD has 0.39% bad pixels.
Filters 8 filters now available (ugrizY, wide VR, narrow N964)
Gain 4 e-/ADU (typica)
Non linearity, For normal observing, keep level below 100,000 e-, 22,000 ADU
Raw data format FITS (with extensions),1 GB/file, ~600 Mbyte/file compressed
Instrument F ratio f/2.7
Available filters u g r i z Y VR N964

The figure below shows the orientations on the sky and spatial footprint of the focal plane array.

The 2k x 2k CCDs labeled as "F" are used for focus and alignment control; those labeled as "G" are used for guiding. The detector position numbers (e.g., "S4" or "N4" near the center of the field) are useful for identifying specific CCDs to look at in the multi-extension images, like "display DECam_00153116.fits[N4]"). Note that CCD N30 is not functional. CCD S30 was not functional 2014-2016.

When working with the data, both at the telescope (real time display) and off disk (default ds9 view), the images are often displayed in "pixel orientation". The figure below shows the orientation of the field and CCDs in pixel orientation.

Example images can be downloaded from the NOIRLab Astro Data Archive.

Current gain and readnoise values for all CCDs/Amplifiers can be found in either the image headers or here.

Here is the pixel scale distortion map (courtesy Mischa Schirmer).Compared to most prime-focus systems. DECam has very low distortion.

Further information can be found in the DECam Data Handbook.

Updated on May 26, 2021, 5:22 am