Semi APO filter

[OJ87]

Hi everyone,

As I mentioned before I'm new  to astrophotography. I bougt a Baader semi APO filter 1,25" for eyepiece. But mainly I thought it more useful for imaging (using canon 77D). Now I bought also Skywatcher coma corrector (telescope side 2" and camera side M48).

Do I need this filter for imaging? If yes should I buy the bigger 2" and attach it to the telescope side of coma corrector? 

Best regards,

[Cornelius Varley]

It will depend on the type of telescope. Semi Apo (hate that phrase) filters are designed to reduce the about of chromatic aberration (blue fringing around bright objects) found in achromatic refractors. Apochromatic refractors and Newtonian reflectors don't require any additional filtration to remove CA  because is doesn't occur in those types.

[OJ87]

11 minutes ago, Cornelius Varley said:

It will depend on the type of telescope. Semi Apo (hate that phrase) filters are designed to reduce the about of chromatic aberration (blue fringing around bright objects) found in achromatic refractors. Apochromatic refractors and Newtonian reflectors don't require any additional filtration to remove CA  because is doesn't occur in those types.

Thanks, my telescope is Newtonian Skywatcher Quattro 10S , 1000mm, f/4. That means I don't need this filter at all.