Specifications for a general purpose imaging camera for ARC 3.5m

Rationale: want to provide design specs for general purpose imaging. These will not necessarily be optimal for some particular science program, but are meant to provide reasonable performance for a range of potential projects

Formulation: goals and requirements are presented. The requirements are things that must be achieved. Goals are things that we would like to have, but it is possible that not all goals will be achievable. The goals have associated priorities, so that if not all goals can be met, the ones with higher priority should be strived for more than those with lower priority.

ID	feature	requirement	goal	priority	comments
Optics
A.1	pixel scale	0.1-0.4 "/pixel	0.2" arcsec to optimally sample (across diagonal) best images available (taken to to be 0.6").	2	Can consider binning options
A.2	field-of-view:	>5 arcmin on a side	>10 arcmin; as large as possible within cost constraints.	2	Note that 4096*0.2" = 13.65 arcmin
A.3	image quality	90% encircled energy within 0.7" diameter aperture across field in each SDSS bandpass	90% encircled energy within 0.4" diameter aperture across field in each SDSS bandpass	2	insure seeing limited images across field (thus spatially constant to the level of seeing variations). Note 90% EE diameter corresponds to FWHM by E_90 = 1.82 FWHM for Gaussian PSF
A.4	scattered/stray light	scattered light in flats less than 0.5% across 5' field of view	scattered light in flats less than 0.5% across entire field	1
A.5	distortion	no greater than 10% across field, and calibrateable to better than 1%.	no greater than 5% across field, and calibrateable to better than 0.5%. Change in distortion no greater than 0.1% across field from 3700-9000A	1
A.6	Filter size	provide unvignetted illumination across detector with new SDSS filter set	provide 4.5' unvignetted FOV for 3" filters provide 3' unvignetted FOV for 2" filters	1
A.7	Filter bandpasses	provide SDSS filter set, with < 1% out-of-band throughput	SDSS filters transformable to standard SDSS system to better than 1%.	1
Throughput/sensitivity
B.1	sensitivity	>30% from 3700A-9000A, >70% from 4000A-7000A	>50% from 3700A-9000A, >70% from 4000A-7000A	1	Includes optics+detector, not filter or telescope
B.2	stability	throughput stable to better than 0.5% over course of a night. throughput stable to better than 5% over thermal cycling and seasonal variation	throughput stable to better than 0.1% over course of a night.	1
Detector
C.1	readout noise	sky limited on moonless night for 5 minute exposure in all SDSS bandpasses	sky limited on moonless night for 1 minute exposure in all SDSS bandpasses, and for 15 minute exposures for 25A narrow band filter at Halpha	1	note that the requirement on detector readout noise that flows from this depends on sensitivity and pixel size
C.2	charge transfer efficiency	loss no greater than 1% across maximum vertical transfers	loss no greater than 0.5% across maximum vertical transfers	1	requirement implies CTE>0.9999975 for 4000 transfers, CTE>0.999995 for 2000 transfers, CTE>0.999990 for 1000 transfers
C.3	stability	sensitivity stable to better than 0.5% over course of a night. sensitivity stable to better than 5% over thermal cycling and seasonal variation	sensitivity stable to better than 0.1% over course of a night.	1
C.4	Readout time	<60 seconds at rate where 60s broadband exposures are sky limited	<10 seconds at rate where 60s broadband exposures are sky limited	1
C.5	Dark current	90% of pixels <1 electron per pixel in 1 minutes (0.016 e/s)	90% of pixels <1 electron per pixel in 5 minutes (0.003 e/s)	1
C.6	Dynamic range	>5,000	>10,000	1	measured from max linearity electrons relative to readout noise
C.7	Fringing	<5% in SDSS i; less than 10% in SDSS z	<1% in SDSS i; less than 5% in SDSS z	1	Measured on moonless night
Opto-mechanics
D.1	shutter operation	shutter time must be repeatable and calibrateable to better than 0.5% across entire field for exposures from 0.5 to 3600 seconds	shutter time must be constant across field to better than 0.5% for exposures from 0.5 to 3600 seconds	1
D.2	shutter lifetime	Shutter should have expected lifetime > 5 years of normal operation	all mechanisms replaceable within 24 hours	2
D.3	Filter wheel repeatability	Must repeat position to within 5 pixels on detector	Must repeat position to within 2 pixels on detector	1
D.4	Filter wheel speed	Achieve any filter wheel repositioning within 10 seconds	Achieve any filter wheel repositioning within 5 seconds	2
D.5	filter wheel lifetime	Filter wheel should have expected lifetime > 5 years of normal operation	all mechanisms replaceable within 24 hours	2
Electronics/control/software
E.1	metrology	Electronics should provide metrology: filter/shutter location, dewar pressure/temperature, CCD temperature, etc.	Provide metrology on CCD to monitor for failures		CCD metrology probably depends on controller manufacturer
E.2	electronic/optical	Electronics should contribute no light to detector larger than 1 electron in any pixel in 5 minutes
E.3	ICC software	Software must support APO communication standard
E.4	ICC exposure commanding	software must support standard APO exposure command/reply set			ICC programmer should consult with Russell Owen before implementation
E.5	CCD configuration	Software should support configuration of all modes that CCD controller supports	ICC software should support windowing and binning as options to the exposure command (rather than as separate configuration commands)		What modes are available to normal user, e.g., through TUI, is TBD!
Mechanical/thermal
F.1	CCD thermal control	CCD must maintain constant temperature to 1K over seasonal usage
F.2	Vacuum	Dewar should require pumping no more than 4 times per year	Dewar should require pumping no more than once per year	2
F.3	Thermal output	Instrument must conform to observatory requirements on heat loads
F.4	Operating temperature	Instrument must be fully functional from -20 to 30 C ambient temperatures.
Documentation
Digital filter bandpasses for all new filters
CCD manufacturer data: AR coatings and QE, manufacturer spec sheet, Purchase Order, manufacturer acceptance tests
CCD performance data: QE, readout noise, gain, CTE??
Design philosophy and decisions, engineering notes, solicited inputs, design reviews presentations and reviewer notes. Copy of requirement document.
Optical: Zemax drawings of completed optical design, spot diagrams in raw format and pdf, Purchase order for all glass purchases, figuring information and coatings spec and as built performance data, all stray light and baffling analysis. Assembly/Disassembly instructions. Photos of optical elements
Electronics: Block diagram and location of instrument electronics, pin-out schematics for all cables, manuals for motors, sensors etc.. , PCB documentation schematics, Leach Control Theory of Operation
Software: low level command sets, keywords, and programming architecture , copy of source code
Hardware: complete SolidWorks assembly and as built shop drawings and models, in raw format and pdf, manuals or spec sheet for purchase parts. Copy of all FEA and load calculations. Separate section for any custom tools and tooling. Assembly/Disassembly instructions, listing of type and use of any lubricants.
Test Data: final lab test data for all subsystems, commissioning data with actual performance metrics versus requirements document.
User Manual (similar in scope to other APO Instruments)

High level goals

photometric precision: better than 1% across field. This is a top level requirement that requires:
• A.4 flat fielding to better than 0.5%, i.e. scattered light control in flats to better than 0.5%
• C.3 detector stability better than 0.5%
• B.2 throughput stability over the course of a night to better than 0.5%
• D.1 shutter time must be repeatable and calibrateable to better than 0.5% for exposures from 0.5 to 3600 seconds
• A.5 distortion must be calibrateable to better than 0.5%
• C.2 charge transfer efficiency