PlaneWave FSCT8 image train sections

Camera on the left, scope on the right. Every part is drawn at one scale, 5 px per mm, for both length and radius. The backplate, Snowflake plate and camera body are cut short where marked.

Train 1, SFW5082.35 mm10.9 mm too long

Train 2, SFW50S80.35 mm8.9 mm too long

Fit A, ETA, no rotator70.35 mm1.1 mm of rack-out

Fit B, rotator, no ETA69.35 mm2.1 mm of rack-out

Fit C, rotator, guide scope64.85 mm6.6 mm of rack-out

Sensor must sit at59.5 to 71.5 mmfrom focuser face, 2 mm filter in path

Part you listed Required spacer or adapter you did not list Diameter not confirmed Rotator motor box, clearance unverified Reachable focal plane

Trains as requested

1. ASI2600MM, SFW50, OAG-L, ETA, Rotator Mini

With the focuser fully racked in, the focal plane reaches 71.5 mm behind the mounting face. The sensor sits at 82.35 mm, so this train cannot focus. The 15 mm standoff between rotator and ETA is what breaks the budget.

2. ASI2600MM, SFW50S, OAG-L, ETA, Rotator Mini

The slim wheel saves 2 mm and the sensor still lands 8.9 mm past the reachable range. SFW50S accepts 50 mm unmounted filters only, so it does not take the 2 inch mounted Antlia set.

Trains that fit

ETA and rotator cannot share this focuser, so each option drops one. All three use the SFW50 for the 2 inch mounted filters.

A. ETA and OAG-L, no rotator

Keeps automated tilt and off-axis guiding. The 9 mm standoff keeps the OAG-L helical focuser off the PlaneWave flange. The two 2 mm Snowflake spacers put the guide prism back at the 41 mm ZWO geometry so the ASI220MM Mini reaches focus. Sensor at 70.35 mm leaves 1.1 mm of rack-out. If the guide camera focuses without the spacers, the train drops to 66.35 mm.

B. Rotator and OAG-L, no ETA

The layout PlaneWave suggested, with the missing parts counted. The OAG-L needs a ZWO M54 tilt plate to carry a thread and a 2 mm M54 coupler to reach the rotator. Sensor at 69.35 mm fits with 2.1 mm of rack-out. Tilt is set on the focuser. Risk: the guide prism sits about 37 mm from the sensor, 4 mm short of the ZWO geometry, and adding the Snowflake spacers pushes the train to 73.35 mm, which is too long.

C. Rotator and guide scope, no OAG, no ETA

Most margin. Without the OAG-L the train is only 46.85 mm, so an 18 mm M54 spacer brings the sensor to 64.85 mm, the middle of focuser travel. The spacer sits ahead of the rotator to give its motor box room. Tilt is set on the focuser and guiding moves to a separate guide scope.

Fitting options compared

Option	Total	Rack-out	You give up	Extra parts	Open risk
A. ETA and OAG-L	70.35	1.1	Rotator. The SecureFit clamp turns by hand.	PW adapter, 9 mm M54 male to male, two Snowflake spacers from the box	Only 1.1 mm from the racked-in stop. Standoff length depends on measured helical focuser position.
B. Rotator and OAG-L	69.35	2.1	ETA. Manual tilt on the focuser.	PW adapter, ZWO M54 tilt plate, 2 mm M54 male to male	Guide camera may not reach focus. Rotator motor box clearance.
C. Rotator and guide scope	64.85	6.6	ETA and OAG-L. Manual tilt on the focuser.	PW adapter, 18 mm M54 spacer, 2 mm M54 male to male, guide scope	Rotator motor box clearance. Guide scope flexure at 568 mm.

Reference

Thickness by part

Optical thickness is the back focus the part consumes, face to face. Mechanical envelope is the longest axial dimension of the part including motors and protrusions.

Part	Optical	Mechanical envelope	Notes
ZWO ASI2600MM Pro, tilt plate off	12.5	90 dia body	Sensor is 12.5 mm behind the bare front face, 17.5 with the tilt plate fitted. Sensor drawn at its 28.3 mm diagonal.
Wanderer Snowflake SFW50	16.0	36 at motor box, plate 219 dia	Takes 2 inch mounted filters. Aperture sits about 70 mm off the plate centre. Motor box faces the camera, beyond the cut in the drawings.
Wanderer Snowflake SFW50S	14.0	36 at motor box, plate 219 dia	Takes 50 mm unmounted filters only.
Snowflake spacers, 2 x 2 mm	4.0	4.0	Supplied with the SFW50. Used in option A to restore guide focus.
ZWO OAG-L	17.5	17.5 body, 46.2 at helical focuser	No threads on either face. Helical focuser overhangs the camera face by 15.05 and the scope face by 13.65. Its radial position, 54 to 91 mm off axis, is scaled from the ZWO drawing.
ZWO M54 tilt plate	5.0	5.0, 90 dia	Gives the OAG-L a thread when the ETA is not fitted.
Wanderer ETA M54	5.0	about 33 at motors, 130 x 150 triangle	Bolts to the OAG-L front in place of the tilt plate. Motors stand 12.6 mm toward the scope and hang 16 mm toward the camera, 65 to 75 mm off axis. Fine travel 1.2 mm.
M54 male to male spacers	2, 9, 15, 18	same	15 mm clears the ETA motors ahead of a rotator. 9 mm clears the helical focuser ahead of the PlaneWave flange. 2 mm couples two female threads.
Wanderer Rotator Mini V2 M54	10.0	11.8 body, 51.5 at motor box, 100 dia	M54 female both sides. Motor box is 39.7 deep on one side, 54.6 to 93.6 mm off axis.
PlaneWave SecureFit to M54 adapter	6.35	11.4 with thread boss, flange 120.65 dia	SKU 600389. PlaneWave confirmed SecureFit by email, no drawing yet.

Clearance points the drawings show

ETA motors need 16 mm behind the ETA before anything wide. The OAG-L supplies 17.5 mm, which leaves 1.5 mm to the Snowflake plate, or 5.5 mm with the spacers in option A.
The OAG-L helical focuser must point toward the short side of the Snowflake plate and sit between two ETA motor lobes.
The rotator motor box is drawn facing the scope. In trains 1, 2 and B it reaches 35 mm forward of the focuser face while the racked-in focuser body is 29.2 mm long, so it may reach the backplate. In option C the 18 mm spacer moves it back to 17 mm forward. Facing the camera instead, it meets the helical focuser or the Snowflake plate. These figures are read from drawings and need measuring.
The focuser body diameter is not published. It is drawn at the SecureFit flange size, 120.65 mm.
Focuser window uses the figures PlaneWave emailed: 70.79 mm racked in and 12 mm of travel, plus 0.67 mm for a 2 mm filter.