We take cryptocurrency — so the coins you hold can buy real hardware.Pay in crypto, spend it on real hardware. Free insured shipping worldwide over $399. Plain, unbranded boxes, sent from Germany.Free insured shipping over $399. Your rate is locked for 30 minutes once checkout opens.Rate locked 30 minutes. Every item sealed, serial-checked and covered by a 24-month warranty.Sealed, 24-month warranty.

Saved items Sign in
Round 2-inch astronomy filter with black anodised metal ring and neutral-tint glass

Baader Planetarium

Baader Planetarium Semi-APO Filter 2 inch

SKU CH-65FK-WTS5G

A 2-inch filter that reduces violet fringing in achromatic refractors for sharper, higher-contrast astronomical images

  • Minimises violet fringe for sharper planetary detail with Semi-APO coating
  • Boosts contrast on nebulae and galaxies via Neodymium substrate
  • Cuts glare and scattered light for comfortable long sessions
  • Maintains natural colour balance while suppressing chromatic aberration
  • 2-inch thread fits standard focusers and diagonals directly

Semi-APO Filter for 2" Focusers

The Baader Planetarium Semi-APO Filter threads into a standard two-inch focuser or diagonal to suppress the violet fringe that limits sharpness in achromatic refractors. It combines a strengthened Fringe Killer coating with a Moon & Skyglow Neodymium substrate in a single glass element. The filter is aimed at visual observers and astrophotographers who want cleaner colour correction without stacking multiple cells.

Sustained Session Performance

During extended observing runs the filter maintains a neutral colour balance while continuously rejecting scattered short-wavelength light. The coated substrate resists dew buildup longer than uncoated glass, so contrast remains stable across temperature drops. Eye strain is reduced because the background sky stays dark without dimming the target object.

Upgrade Path and Limits

This single filter replaces a separate Fringe Killer plus Moon & Skyglow stack, saving back-focus and reducing vignetting risk. The improvement is most noticeable on fast achromats below f/7 where violet halos are strongest. It does not correct spherical aberration or field curvature, so users needing full apochromatic performance will still require a true APO refractor.

Highlights

  • Minimises violet fringe for sharper planetary detail with Semi-APO coating
  • Boosts contrast on nebulae and galaxies via Neodymium substrate
  • Cuts glare and scattered light for comfortable long sessions
  • Maintains natural colour balance while suppressing chromatic aberration
  • 2-inch thread fits standard focusers and diagonals directly

Specifications

No published specifications for this item yet.

Questions about this item

Does the Semi-APO Filter run hot or draw power during long imaging sessions?

The filter is a passive optical element with no electronics, so it generates no heat and requires no power supply during extended use.

What must my telescope or camera already have to attach this 2-inch filter?

Your equipment needs a standard 2-inch filter thread on the eyepiece barrel, diagonal, or camera adapter to screw the filter in place.

Will the filter work with my older achromatic refractor that shows strong violet fringing?

Yes, it is designed specifically for achromatic refractors and combines a strengthened Fringe Killer coating with a Neodymium substrate to suppress most violet aberration.

Also in this aisle

People compared these

Same shelf, same checkout — eight coins and a 30-minute rate lock.