Back Focus Spacers / Adapters

Back Focus Spacers & Adapters

If you have a Celestron SE, Evolution or CPC mount and want to use it with a camera and the Celestron 6.3X focal reducer you will need a way to avoid the camera crashing into the mount as the optical tube approaches zenith. Below are 4 different configurations I have detailed along with all of the parts needed to enable reaching zenith without crashing into the mount. These are all parts that I have purchased and confirmed work. Links are affiliate links which means that I can earn a small commission which helps defray the cost of this web site. If you have questions on these or other products email me at [email protected].

The Celestron 6.3X focal reducer requires a back spacing, that is the spacing from the back of the focal reducer to the sensor in the camera, of 105mm. The spacing is measured from the back most surface of the focal reducer. I have outline 4 solutions below with the parts needed in each case. Links are provided for my two preferred astronomy equipment vendors, Agena Astro and HighPoint Scientific. Just pick the setup you want and the vendor you prefer and use the links to assemble the entire back focus setup you need.

Agena Astro Celstron 6.3X focal reducer bit.ly/3IEeMc5
HighPoint Scientific Celestron 6.3X focal reducer bit.ly/3Uet5Iq

Straight Through Solution - rail extension not shown in the photo

Agena Astro Links:
SVBony Rail Extension amzn.to/3QB5ssj
or Celestron Universal Mounting Plate for CG4 bit.ly/3QCSvyi
Celestron 50mm SCT-T Adapter bit.ly/3BVmmLo
Blue Fireball 37.5mm Extension bit.ly/48tFsrl
or Baader Varilock 46 T2 Variable Extension bit.ly/3rztlZb
ZWO M42 Female to Female 11mm Adapter bit.ly/3QSoqfE

HighPoint Scientific Links:
SVBony Rail Extension amzn.to/3QB5ssj
or Celestron Universal Mounting Plate for CG4 bit.ly/412fJCQ
Celestron 50mm SCT-T Adapter bit.ly/3BVmmLo
Celestron M42 Spacer Kit (30 + 7.5mm = 37.5mm) bit.ly/3ukdZ8B
or Baader Varilock 46 T2 Variable Extension bit.ly/3Rpf77f
ZWO M42 Female to Female 11mm Adapter bit.ly/49YFeZI

Straight Through Solution with a Filter Drawer - rail extension not shown in the photo

Agena Astro Links:
SVBony Rail Extension amzn.to/3QB5ssj
or Celestron Universal Mounting Plate for CG5 bit.ly/3QCSvyi
Celestron 50mm SCT-T Adapter bit.ly/3BVmmLo
Blue Fireball 7.5mm Spacer Ring bit.ly/3MFZ0iS
Blue Fireball 10mm Extension bit.ly/47uF7mC
WO M42 Female to Female 11mm Adapter bit.ly/3QSoqfE
ZWO Filter Drawer M42 Male to M48 Female bit.ly/49tbTX7
ZWO M48 Male to M42 Female Adapter bit.ly/3stkt7E

HighPoint Scientific Links:
SVBony Rail Extension amzn.to/3QB5ssj
or Celestron Universal Mounting Plate for CG5 bit.ly/412fJCQ
Celestron 50mm SCT-T Adapter bit.ly/3upIHNC
Baader 7.5mm T-2 Extension bit.ly/3Rnufll
Apertura10mm Extension bit.ly/47CQHwx
ZWO M42 Female to Female 11mm Adapter bit.ly/49YFeZI
ZWO Filter Drawer M42 Male to M48 Female bit.ly/3RiRRaN
ZWO M48 Male to M42 Female Adapter bit.ly/413ZEwD

Right Angle with a Diagonal Solution

Agena Astro Links
Baader Ultra-Short SCT F to T2 M Adapter bit.ly/47qmoJ0
Baader T-2 90-deg Prism Star Diagonal bit.ly/3POOSVv
Blue Fireball 18mm Extension bit.ly/47tE7zm
SVBony 24-35mm M42 Variable Extension amzn.to/3ME1azA
ZWO M42 Female to Female 11mm Adapter bit.ly/3QSoqfE
You could substitute the Baader Varilock 46 T2 Variable Extension bit.ly/3rztlZb for the Blue Fireball 18mm & SVBondy 24-35mm if you want less components

HighPoint Scientific Links
Baader Ultra-Short SCT F to T2 M Adapter bit.ly/47Tz4s4
Baader T-2 90-deg Prism Star Diagonal bit.ly/4a1QX9Q
Apertura 10mm Spacer bit.ly/47CQHwx
SVBony 24-35mm M42 Variable Extension amzn.to/3ME1azA
ZWO M42 Female to Female 11mm Adapter bit.ly/49YFeZI
You could substitute the Baader Varilock 46 T2 Variable Extension bit.ly/3Rpf77f for the Apertura 10mm and SVBondy 24-35mm if you want one less component

Right Angle with a Diagonal and Filter Drawer

Agena Astro Links
Baader Ultra-Short SCT F to T2 M Adapter bit.ly/47qmoJ0
Baader T-2 90-deg Prism Star Diagonal bit.ly/3POOSVv
SVBony 24-35mm M42 Variable Extension amzn.to/3ME1azA
ZWO M42 Female to Female 11mm Adapter bit.ly/3QSoqfE
ZWO Filter Drawer M42 Male to M48 Female bit.ly/49tbTX7
ZWO M48 Male to M42 Female Adapter bit.ly/3stkt7E

Alternatives to the SVBony 24-35 Variable Extension
Blue Fireball 18mm Extension bit.ly/47tE7zm + Blue Fireball 6mm Extension bit.ly/478vJFs
Optional Components to Vary the Back Focus Spacing Baader T2 Delrin Spacer Ring Set bit.ly/49yhbko
Blue Fireball Additional Spacers bit.ly/49tNReL

HighPoint Scientific Links
Baader Ultra-Short SCT F to T2 M Adapter bit.ly/47Tz4s4
Baader T-2 90-deg Prism Star Diagonal bit.ly/4a1QX9Q
SVBony 24-35mm M42 Variable Extension amzn.to/3ME1azA
ZWO M42 Female to Female 11mm Adapter bit.ly/49YFeZI
ZWO Filter Drawer M42 Male to M48 Female bit.ly/3RiRRaN
ZWO M48 Male to M42 Female Adapter bit.ly/413ZEwD

Optional Components to Vary the Back Focus Spacing Baader T2 Delrin Spacer Ring Set bit.ly/3sXVj1e