Abdul Thomas Jnr avatar

Hi. I’m just wondering which filter thickness to get between Baader High Speed 6.5mm or 3.5mm Narrow Band CMOS Optimised. Set up will be the Rasa 8 and Zwo 294mm pro camera. I know the 3.5mn are more expensive but I just want the best for this setup. The guy from the astro shop recommended the 6.5mm but it looks like most people are using the 3.5mm with the Rasa. Thanks in advance

andrea tasselli avatar
Abdul Thomas Jnr avatar

The Rasa is at F2, won't the F3 filter makes a difference?

andrea tasselli avatar
You won't see much of a difference in terms of out-of-band shift between the nominal f/2.3 and an actual f/2.
Well Written
Abdul Thomas Jnr avatar

Okay. So is the 6.5mm at F2 not good enough?

andrea tasselli avatar
The 6.5nm filters are good enough if high-speed versions otherwise the out-of-band shift is too much to make them worthwhile for a f/2 telescope with a CO of 35% or worse (e.g., a RASA). If you want the absolute best of contrast and your skies aren't that dark then the more expensive variants are your best choice, if you are willing to spend that much (I wouldn't but that's me).
Abdul Thomas Jnr avatar

Okay thank you for your time. I will get the 6.5mm high speed ones. Those are the ones I was gonna get anyway