This filter is placed between the telescope optics and my Canon T3i modded camera.
My telescope is a 80mm doublet with a focal length of 480mm at f/6
Images were cropped
Left: no filter, almost no red nebulosity (Hydrogen alpha)
Right: ZWO 2" Duo-Band Filter $149 (Ha and OIII) WOW!
(Note: click on the image for an uncluttered view)
In addition to providing an inexpensive entry point into the field of narrowband imaging, this filter also offers a pragmatic solution for imagers in a city with even light pollution and natural sources such as moonlight, and also helping minimze the effects of artificial sources such as street lamps.
The filter was well worth the money!
