ZWO EAF adapter for Samyang 135mm lens

This is an adapter system to mount a ZWO EAF electronic automatic focuser to a Samyang 135mm f/2.0 ED UMC lens for astrophotography.

This is similar to other popular EAF mounts for William Optics Redcat 51 telescopes, but specifically made to fit this lens. My design also is better balanced as the motor is symmetrical down the middle of the dovetail. The William Optics CAT-series mounting ring, as used on the Redcat 51, has an inside diameter of 70mm and is a perfect fit for the Samyang 135mm lens. My lens is a Canon EF-mount lens, but it should work on the Nikon F-mount lenses as well. The cinema lenses won't fit due to the aperture gear teeth. The aperture ring is covered by the mounting ring, so set it to the desired aperture before clamping it down or screw it aperture step-down rings to the front of the lens if you have those. This lens works so well, I've been shooting it fully open at f/2.0. Others prefer f/2.4 or f/2.8, which give you 18-point diffraction spikes on bright stars.

I've tried this on William Optics Dual-Sided dovetails, both 210mm and 245mm and it works well. I've also used it on a cheaper SVBony 210mm dovetail and it works equally as well, but the bolts are different length. Actually, the spacing of the SVBony dovetail gives more mounting option.

I chose to mount the ASIair pro on the end, but there isn't enough room on the William Optics dovetails to use the center 1/4" thread, so I used one of the four offset M4 threads, which needs one of the dovetail bushings to fit. The SVBony dovetail is shaped different and has a different part.

If you have a filter wheel, you can reposition the riser at the end of the dovetail to allow the filter wheel to freely rotate, and put the ASIair up at the front, but I didn't want the heat to rise up and affect the images. Also, I use a T-Link TL-WR902AC mini travel router to extend the Wi-Fi range and use Jaewook Chung's mount adapter https://www.thingiverse.com/thing:4621599 to attach the TP-Link router and power supply to the top the ZWO ASIair Pro. That would be too high if mounted in front. I've made my own mount for the TP-Link router up at the front, and use his clips to hold the router and power converter to my adapter.

The single-piece focus ring is a slight interference fit - carefully slide it on the focuser on the lens. There is adjustment on the EAF adapter, so once you slip the belt on, just slide the EAF down and tighten the bolts to tension it.

You will need the following parts to install this on your lens:
William Optics CAT-series mounting ring
William Optics CAT-series handle bar (optional)
2GT 16-tooth timing pulley with 5mm bore (20-tooth will also work)
2GT 308mm length x 6mm width timing belt
2X M4x8 socket head cap screws (SHCS) to mount EAF to adapter with or without washers. Screws come with EAF.
3X M6 hex nuts - two for EAF adapter and one for TP-Link adapter

If you use a William Optics Dual-Sided 210mm or 245mm dovetail plate, use the following bolts:
2X M6x60 SHCS for riser
2X M6x20 SHCS for EAF adapter
1X M4x16 SHCS for ASIair Pro
1X M6x16 SHCS for TP-Link adapter
I didn't use washers with the William Optics dovetails

If you use a SVBony Vixen-style dovetail plate, use the following bolts:
2X M6x55 SHCS for riser
2X M6x16 SHCS for EAF adapter
1X M4x12 SHCS for ASIair Pro
1X M6x12 SHCS for TP-Link adapter
I did use washers with the SVBony dovetail except for the ASIair Pro

I printed the riser with 100% infill and the other parts with 50% infill.

Designed in Fusion 360