Astronomik UHC-E Filter – This filter was designed for the visual observation of emission and planetary nebulae with (mainly) smaller scopes, but also works well for imaging these objects if used with an IR block. The IR block can be inbuilt, as with a DSLR, or in combination. The Astronomik L3 type luminance filter gives particularly good results and colour balance. Price includes delivery.
The Antlia 2″ 4.5nm SHO Filter Set is extremely good and represents great value at the price point. Only far more expensive filters, such as Chroma, will give better results.