Castell CLEAR filter for 1.25" eyepieces

They are intended to use as a protective window. Or using in a filter wheel the system will not lost parfocal position with other filters.

The UV/IR cut filter is recommended in many cases:

• at least one lens is used in the light path which is not corrected to infrared light (most of the lenses are optimized for visible light)
• when taking images without an IR blocking filter in the camera
• when the Sun is still above the horizon or close to it (dawn/dusk lasts more in IR light) 
• if there's a strong IR light source next to the target object

GSO's filter is affordably priced and provides 90% transmission.

Baader's filters have a transmission of 97% between 420 and 680nm.

Astronomik's IR blocking filter are similar to Baaders but filter for Canon EOS APS-C cameras are also available.