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8.6 Summary of FOC Accuracies

The following table summarizes the kinds of accuracies you can expect when analyzing FOC data. Note that many of these numbers come with qualifications and that you should check the relevant sections of this handbook for details.

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Final Accuracies Expected in FOC Observations

Procedure

Estimated Accuracy

Notes

Calibration (flatfielding)

Flatfielding

<5% rms large scale

5-10% rms small scale

"Clean" areas

Up to 90%

On reseau marks, scratches

Geometric Correction - f/96

0.3 pixel rms

Geometric Correction - f/48

0.5 pixel rms

Full format, central area only.

Relative photometry (f/96 only)

Repeatability:

~2-3% rms

As long as statistical errors are not important, target in same place on detector.

Background determination

~1-2%

Depends on aperture size, but generally not a dominant contributor to overall error.

PSF/focus effects, small apertures

Up to 50%

1 pixel aperture, UV wavelengths.

PSF/focus effects, large apertures

~2-3%

Aperture size >10 pixels radius

Absolute photometry

Sensitivity - f/96

~6% rms for most filters

~10% rms for uncalibrated filters

Sensitivity - f/48

~30% for most filters

Astrometry

Relative

0.005" rms (after geometric correction)

Absolute

1" rms (estimated)

Spectroscopy (f/48 only)

Wavelength Calibration

~0.5-1 Angstrom rms

First order only - higher orders not calibrated.

Spectrophotometry

~10% rms

First order

~30% rms

Higher orders

**Final Accuracies Expected in FOC Observations**
Procedure	Estimated Accuracy	Notes
Calibration (flatfielding)
Flatfielding	<5% rms large scale
5-10% rms small scale	"Clean" areas
Up to 90%	On reseau marks, scratches
Geometric Correction - f/96	0.3 pixel rms
Geometric Correction - f/48	0.5 pixel rms	Full format, central area only.
Relative photometry (f/96 only)
Repeatability:	~2-3% rms	As long as statistical errors are not important, target in same place on detector.

Background determination	~1-2%	Depends on aperture size, but generally not a dominant contributor to overall error.
PSF/focus effects, small apertures	Up to 50%	1 pixel aperture, UV wavelengths.
PSF/focus effects, large apertures	~2-3%	Aperture size >10 pixels radius
Absolute photometry
Sensitivity - f/96	~6% rms for most filters
~10% rms for uncalibrated filters
Sensitivity - f/48	~30% for most filters
Astrometry
Relative	0.005" rms (after geometric correction)
Absolute	1" rms (estimated)
Spectroscopy (f/48 only)
Wavelength Calibration	~0.5-1 Angstrom rms	First order only - higher orders not calibrated.
Spectrophotometry	~10% rms	First order
	~30% rms	Higher orders

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