The half flux diameter or HFD is a definition used by astronomers to define the star size in an astronomical image. Mainly due to the seeing, stars are not imaged as a dot but spread out like a Gaussian shape. [1] The half flux diameter defines the diameter of a circle around the bright center in which half of the star flux or energy is contained.

2015年6月12日 · Another measure for the star focus is the Half Flux Diameter (HFD). It was invented by Larry Weber and Steve Brady . The main two arguments for using the HFD is robustness and less computational effort compared to the FWHM approach .

HFD 2D contour. The star half flux diameters (HFD's) are displayed in a 2D contour. Dark areas indicate a lower and better HFD value. This will quickly visualise sensor tilt or other problems.

2020年6月14日 · The important thing to note about HFR (and HFD) is that the lowest value depends on your particular setup in terms of sensor pixel size and the effective focal length. The opening paragraph in the HFD wikipedia article explains this relationship well. So think of the light from a given star falling across a group of pixels on the sensor.

The star profile display shows the cross-section of the guide star along with measurements of its full-width-half-maximum (FWHM) and half-flux-diameter (HFD). HFD is generally a more stable measure of the star size since it doesn't require curve fitting or any assumption about the overall shape of the star image.

2022年5月14日 · The Half Flux Diameter ($HFD$) for a perfectly normal distributed star is $HFD_{norm-dist} = 2 \cdot \Gamma\left(\frac{2}{3}\right) \cdot \sqrt{2} \cdot \sigma = 2.50663 \cdot \sigma$ where $\sigma$ is the variance of the distribution. The result does not depend on $R_{out}$ and also not on the normalization factor of the distribution.

2018年6月4日 · FWHM is a measurement of the width (diameter) of a star where it is half as bright as it is at its peak measurement. HFD (diameter) or HFR (radius) is the width (diameter) or half width (radius) of a star at its statistically center of brightness.

The Half Flux Diameter (HFD) is a measure of the size of a star in a FITS image. Specifically, the HFD is the diameter of a circular aperture that contains half of the total flux or intensity of the star. In other words, it provides a measure of the size of the central part of the star's light distribution.

2022年5月3日 · “The HFD is defined as the diameter of a circle that is centered on the unfocused star image in which half of the total star flux is inside the circle and half is outside.” it should be easy to predict the expected outcome.

2021年10月30日 · A quick answer is that HFR has advantages when the star is far from Gaussian looking, possibly a donut or washer shape. Otherwise fwhm is much more useful, particularly for faint stars against a noisy background. A longer answer is that HFR/HFD are only used for stars in amateur software.