Astro Focus (Bahtinov Mask) Guide
How the Bahtinov Mask Works
A Bahtinov mask creates three diffraction spikes around a bright star.
Center spike shifts left or right when focus is off.
With short focal lengths, diffraction spikes are subtle—requires more care.
Focus precision is still achievable—even at f/1.4–f/2.8—with the right steps.
Recommended Base Camera Settings
Mode: Manual (M)
Focus: Manual
Aperture: Widest (f/1.4–f/2.8)
ISO: 3200–6400
Shutter: 5–10 sec
Assist Tools:
Live View ON
10x Zoom / Magnify View
Focus Peaking ON (if available)
External Monitor (optional)
Step-by-Step: Focus with a Bahtinov Mask
Mount the mask gently over the front of your lens. Use elastic bands or a custom holder.
Find a bright star (magnitude 1 or brighter). Sirius, Vega, Arcturus = good bets.
Center the star in the frame using live view.
Zoom in digitally to 10x for diffraction clarity.
Adjust focus slowly until the center spike is perfectly between the outer spikes.
Confirm—slight changes can shift the spike: recheck after small tweaks.
Mirrorless Focus Tips
Use focus peaking to catch contrast edges—but confirm using diffraction spikes.
If using a tilt screen, angle it for ergonomic comfort.
External monitors or loupe magnifiers can boost clarity.
Use lens hood to block stray light while focusing.
Common Pitfalls & Fixes
Dim stars = faint spikes → always pick the brightest available.
Vibration or tripod bump while removing the mask = refocus!
Too quick to trust peaking → only diffraction confirms true sharpness.
Low contrast on screen? Boost ISO temporarily (e.g., ISO 6400–12800) to check focus.
Lock and Verify Focus
Gently tape the focus ring with painter’s tape or a rubber band.
Take a test shot and review at 100% zoom.
Zoom in on stars at the edge and center to confirm sharpness.
Don’t bump the lens when removing the mask.
Field Checklist
Manual focus + live view zoomed in
Bahtinov mask secured on lens
Bright star centered
Adjust focus until center spike is centered
Confirm with multiple exposures if needed
Lock focus (tape or band)
Remove mask gently
Review test shot @100% zoom
Pro Tip: Practice during twilight on Venus or bright stars to master spike alignment before heading out.
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