Match your setup to your seeing

Optimise your gear to get sharper astrophotos whatever your sky conditions

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The quality of your astro images isn't just down to your processing skills. Key is the relationship between your telescope's optics, your camera's imaging chip and your local atmospheric 'seeing' conditions. Locations with steep temperature gradients and turbulent air – such as urban areas – usually mean poor seeing conditions that distort starlight and blur images.

While you can't do much to reduce poor seeing – short of opting to image higher-altitude targets – you can optimise your setup for your local environment by understanding your image scale and image sampling rate. Here's how to match your gear to the sky for sharper, more detailed results.

Find your ideal scale

Seeing conditions can be summarised as the 'full width at half maximum' (FWHM) of stars, and are measured in arcseconds. This indicates how much the starlight is being spread out due to turbulence before it hits your camera sensor. A lower FWHM value indicates good seeing conditions and sharp stars, while a higher FWHM value implies poor seeing conditions. Typical FWHM values are: 2–4 arcseconds in average seeing conditions; 1–2 arcseconds in better-than-average conditions; and closer to 5 arcseconds for poor seeing.