Instrument Overview

The NOAO CCD Mosaic is a wide field imager having 8192 x 8192 pixels. At the 4­m, where the pixels are 0.27" on the sky, this provides a field of view of 36.8 arcmin on a side.

The CCDs are read in ~2.5 minutes through 4 Arcon controllers to a data taking computer (currently known as ctioa0), which serves as an intermediary data gateway. The pictures really end up on a much faster computer (ctio4m) where you can display and examine the data, perform full reductions, and tape the data much more effectively. Ctioa0 should be used only to do the minimal work required to take observations because the data rate through it is tremendous and nearly pegs the CPU at 100%.

Pictures are 135 Mbytes each. A typical night of ~70 pictures produces about 10 Gbytes. Be aware that processing this data, even just reading it, is a major task for the computing systems that most astronomers have access to. We recommend using a DLT tape drive (our DLT 7000 will write the lower density and cheaper DLT 4000 cassettes if you prefer, although currently there is a problem with the low density mode); however, we provide Exabyte 820 (8505XL compatible) and DDS3 drives for those who do not have DLTs. Provide enough time to tape your data each night. With the Exabytes, a picture takes 3 minutes to tape, so 70 pictures will take nearly 4 hours even without a verification pass. DDS3 writing with mscwfits take about 90s for each image , and the DDS3 tapes hold 12Gbytes (uncompressed). To summarize, DLT IV TAPE + DLT7000 drive holds 35 GB and writes one 135 MB image in 50 seconds.

The Mosaic requires large (5.75 inch) filters to avoid vignetting. We can provide an adapter for 4 inch filters, but using them makes poor use of the Mosaic's wide-field.

Despite the data volume and the unusual computer arrangements, using the Mosaic is still not very different than observing with our other CCD systems.


Philosophy and Structure of Manual

This manual is intended for an observer planning to use the NOAO CCD Mosaic imager. It is not intended to serve as a hardware or software reference document describing the inner working of Mosaic, although some details at that level may appear to help the observer plan observing strategies. Also, we assume that the observer is already familiar with CCD cameras, observations, and data reductions.

Two very brief summary pages are at the front of this manual. If you've read this far, and don't plan to read any further, be sure you understand those 2 pages.

This manual is an edited version of the KPNO manual, kindly made available by G. Jacoby. We have adopted bald-faced plagarism as our philosophy, and kept the structure and much of the text of that document. We have made changes were the systems are clearly different or where we have direct measures relating to the performance of our system. We will update this version as improved information becomes available.

Development of the Mosaic system is a continuing process, although only very minor adjustments are being made at this time. Throughout the lifetime of the instrument, filters will be added, old ones replaced, and software enhanced. This manual represents the status as of the date on the cover page. We expect to revise the manual occasionally to include information gained during engineering runs, as well as to reflect new filters.


Supplemental Information: Other manuals and Web pages to look at

Other useful information regarding the use of Mosaic, CCDs, and observing and reduction software can be found at:

Direct Imaging Manual  (


Various Publications (SPIE, ADASS, ...)

Mosaic Data Handling System (Valdes 1998, SPIE 3355, 497) (

CCD Detector upgrade for NOAO's 8192 x 8192 Mosaic (Wolfe 1998, SPIE 3355, 487) 

What is better than an 8K x 8K Mosaic? (Muller 1998, SPIE 3355, 577) (


This section was last updated on August13, 1999
Please send comments or questions to rschommer

Updated on June 5, 2021, 7:57 pm