Correction Filters

What does a UV/IR-cut filter do?

A UV/IR-cut filter is a correction filter that blocks ultraviolet and infrared light while letting visible light pass through. Your eye does not see UV and IR, but a camera's sensor does. Without a filter, this results in bloated, less sharp stars in your photos.

When do you need a UV/IR cut filter?

With a color camera or a modified DSLR without a built-in filter, this is the first filter you need. Check with your astrocamera whether there is already a UV/IR cut filter in front of the sensor.

At a refractor infrared light refracts differently than visible light. That causes purple or red edges around bright stars. A UV/IR cut filter largely removes that.

Also when filming planets, blocking infrared results in a calmer image with more contrast.

What should you look for when choosing a correction filter?

Most astrocameras and Barlow lenses have 1.25-inch filter threads, so a 1.25-inch filter often fits directly onto the nosepiece of your camera or barlow lens.

The filter must transmit visible light, from approximately 400 to 700 nm, almost completely, including the H-alpha line at 656 nm. Then you no longer need to expose for a longer time.

If you are working with a monochrome camera and LRGB or narrowband filters, you usually do not need this filter. Look instead at the imaging filters.