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) | |||||