The UltraBlock filter is tuned to achieve maximum contrast on emission nebula, including favorites such as M1, M42, M8, M16 & 17, M27 and M57. The list goes on. Using an UltraBlock filter, it becomes possible to see these faint delights even from light-polluted locations.
Please note this filter is for SCTs only. It screws onto the visual back of your scope, and your diagonal screws onto the filter, a simple operation easily performed in the dark. This places your scope in "nebula mode" - allowing eyepiece changes without swapping filters around, and eliminates the need to own both 2" and 1.25" filters.
See the details on p.55 of your Orion catalog. (It's next to your favorite chair.)
Condition is pristine. The "stuff" you see on the filter in the picture are stars from the chart below it.
Price is $90, shipped in ConUS.
Prefer PayPal, but will accept money orders.