How to Measure Backfocus Like a Pro

Tools You'll Need

• Ruler or caliper with millimeter precision
• Extension tubes or spacers (optional)
• Your telescope’s manual
• Camera or eyepiece holder

Step-by-Step Process

1. Check your telescope’s specified backfocus distance in the manual.
2. Point your telescope at a distant object and set the focuser to infinity.
3. Measure from the focuser’s mechanical flange to where your sensor or eyepiece achieves focus.
4. Attach your camera or eyepiece and confirm critical focus without overextending the focuser.
5. If needed, add spacers to reach the ideal backfocus distance.

Regularly verifying backfocus helps avoid blurry stars and ensures your astrophotography gear performs at its best.