Hello, i just bought a Asi 2600 mc air (it has the same connection of asi 2600 mc duo)with m54 filter drawer, m54m-m48f-2 adapter and m48-m48 16.5mm spacer. This is the scheme  recommended by zwo and the only one to achieve a backfocus close to 55mm. This way you get to 56mm. When I want to shoot with only the UV-IR filter included with the 2600, what should I do? I don’t use any filters, so 56mm is too much, and there is no way to decrease bacfocus with the zwo equipment.