Advice on spacer needed for optical train

[Filroden]

I have a Skywatcher Esprit 80 with flattener. I can already use my Canon 60D for imaging but would like to try the ZWO ASI224 (uncooled) as I already have one. What spacer would I need so that I get the right back focus? Ideally, I would like to retain the 6mm spacer that comes with the flatterer as it can take a 2" filter.

According to ZWO, the sensor distance on the 224 is 12.5mm. I have a 6mm spacer with the flattener. According to the Skywatcher manual, the distance I need is 61mm. If my maths is right do I need a (61 - 6 - 12.5) = 42.5m spacer? And with a female M62x1 thread at the flattener end and a male M42x0.75 at the camera end?

Just want to make sure!

Many thanks

Ken

 

[MattJenko]

As a raw calc that is right, but filters can change the focus distance required, depending on the filter. A variable T ring, like the Baader ones, or some Delrin spacers to add/remove a mm here and there is worth getting in. Not sure of the flattener connections so can't advise on that I'm afraid.

[Filroden]

Thanks for that Matt. I'm glad I checked as I didn't know the effects of adding the filter. I'll take a look at the variable spacer.