Atik 4000 Filterwheel C11 Edge Moonlite backfocus

[Edward Orlando Wiley]

I have a C11 edge and trying to figure back focus. As I understand, the critical distance is 146mm to the chip. Can someone on the forum give me some feedback on my calculations?

1.   The Moonlite unit has two flanges. What I term the “inner flange” connects to the baffle lock nut. The other is the “focus flange” that connects to the body of the Focus unit and then to the "inner flange."
2.   The distance between the baffle lock nut and the surface of the “inner flange” that mates with the “focus flange” is 20 mm.
3.   Distance from the inner face of the “focus flange” to fully retracted outer edge of the draw tube = 75 mm. With draw tube about ½ out the distance  = 90 mm.
4.   Filter wheel = 22 mm, with filter add 1mm = 23 mm.
5.   Back focus of Atik 4000 = 16-17 mm (nominal 16.5 mm)
Total with focus unit at ½ position is 150 mm and this can easily be compensated with the draw tube.
I would love feedback. Calculations sound reasonable?

[vince]

Hi,

It does all sound reasonable. Set the system up as you list, then rough foucs with the C11's focuser and fine focus with the Moonlite.

Best regards
Vince

[laperuz]

I use the similar setup. My Scope is EdgeHD 14", the same 146mm distance, though. I also have Orion's ultra-thin guider that adds about 10mm. Overall it works fine, no star elongation at the edges. Although with "smallish" Atik 460EXM chip. Not sure  how it would play out with full frame chpis (11000 or 4000).
Hope this helps,
Ian