# Getting Data¶

The goodman focus value ranges from $$-2000$$ to $$+2000$$ the best practice (from experience) is to sample every $$200$$. If you want to refine you should not go below a $$100$$ step. If you already know the approximate focus value for a given setup, you don’t need to do the full range, just take enough samples so it is possible to make a fit or see the trends. At least five points.

Note

Always use the narrowest slit available

## Imaging¶

For imaging, an image of the slit is obtained, illuminated by an uniform light such as a quartz lamp. A special ROI is used for faster reading. This does not affect the focus of course.

## Spectroscopy¶

In spectroscopy a comparison lamp is observed and after every line is measured and fitted, an average is obtained with sigma clip rejection.