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What is Dithering?

In astrophotography, to dither means to shift the pointing direction of your telescope (via the telescope mount) in random directions between each exposure.

This technique is a useful way to create images with a better signal-to-noise ratio by “canceling out” hot pixels, fixed pattern noise, and more. 

By moving the pointing direction of the telescope, dithering shifts the stars to a slightly different place in each frame. As you process your images, you will align (register) and stack individual frames based on the stars in each image. 

This subtle feature found in most camera control software applications (including Astro Photography Tool) can make a dramatic difference to your final image. 

dithering

Using Astro Photography Tool and PHD2 Guiding to dither between each image exposure. 

Jerry Lodriguss has written an extensive (and technical) description of the dithering process in this Sky and Telescope article. 

In the past, I have manually dithered my astrophotography images, by shifting the image frame slightly after a few exposures. This was done on a portable star tracker that was not utilizing autoguiding.

I used this technique when capturing images of the Carina Nebula from the resort I was staying at in Costa Rica. I was using short exposures, an aggressive ISO setting, and I needed to do something to help reduce the noise in my final image. 

wide field astrophotography

I manually dithered this image of the Carina Nebula using an iOptron SkyGuider Pro mount. 

Benefits of Dithering

There is a saying by professional astronomers; “dither or die.” It may not be quite that serious for amateur astrophotography, but dithering will improve your images tremendously. Have a look at what my good friend Dylan has to say about dithering:

Dithering improves the signal-to-noise ratio (SNR) and can remove artifacts like hot pixels and satellite trails. Images shot with a regular DSLR camera can benefit from dithering, by helping to decrease the amount of fixed pattern noise. 

Because the noise pattern is fixed, shifting the image frame between exposures allows your stacking software to isolate the signal from the fixed pattern noise and create an image with an improved SNR. 

I dither every deep-space image I take (on an equatorial telescope mount) whether it was captured with a DSLR camera or a dedicated astronomy camera. It is a simple way to improve the overall quality of your stacked image and is easy to apply using today’s image capture software. 

Triangulum Galaxy