ASI 294MM Pro to filter distance

Valmount

Hi,

if I use EFW 8x1.25" with ASI 294MM Pro, what will be the distance between the sensor and a filter? Is it 10mm?
if so, a calculator shows me, that for 600mm F/4, I need the opening of the filter 25.32mm, and so 1.25" filter will work, am I right?

Tech@ZWO

For 294, if telescope >F3.7, which is your case, you can use 31mm filter.
1.25" filter only work when telescope >F7.

m32guy

Hi, can you clarify? I thought 1.25 filter could be used with telescope >F5 with the 294mm? I have an Esprit 100 at F 5.5 and do see some vignetting and and also may be picking up a reflection off of the mounting rings. Curious whether 31mm might solve.

FYI, I have doublechecked backfocus.

Tech@ZWO

m32guy

Hello
Recommend 31MM and larger filter for 294MM
31MM would be fit your F5.5 telescope（no vignetting）