Filter DeltaOptical Red #25 1.25″

DeltaOptical red filter #25 1.25″

If you want to get the most out of your telescope when observing planets, a well-chosen color filter can make a remarkable difference. The DeltaOptical red filter #25 with a 1.25″ thread is a classic tool for planetary observers and astrophotographers - it transmits the red portion of the spectrum while suppressing blue and green light, dramatically increasing the contrast of surface details on selected planets.

What does the red filter #25 enhance?

Filter #25 is a strong contrast filter with a relatively narrow transmission band in the red region of the spectrum (approximately 580-700 nm). This makes it an excellent choice for a variety of planetary targets:

• Mars - the filter enhances dark albedo surface features, polar caps, and helps cut through the atmospheric haze of the planet.
• Jupiter - boosts the visibility of the Great Red Spot and equatorial belts.
• Saturn - improves contrast of atmospheric bands.
• Moon - dramatically improves surface detail rendition at high brightness, reduces glare and increases contrast in bright regions during full moon or waxing phases.

Light transmission and recommended aperture

Filter #25 is a fairly dark filter in terms of light transmission (approximately 14-25%, depending on the manufacturer). For visual observation it is recommended for telescopes with an objective diameter of approximately 150 mm and above. For astrophotography using sensitive cameras or CCD sensors, it can be used advantageously on smaller instruments as well.

Construction and compatibility

The filter is set in a precision-machined aluminium cell with a thread compatible with standard 1.25″ eyepieces. The optical glass is ground and polished to ensure it does not degrade image sharpness - this aspect is essential for astronomical color filters, as any substandard optics in the optical path of a telescope will immediately affect fine planetary surface details. The filter simply screws into the bottom of the eyepiece and is ready for immediate use.

Combining with other observation techniques

The red filter #25 can be combined with other observation techniques, such as using high magnification during stable seeing conditions, or as part of a set of supplementary filters for systematic study of planetary atmospheres. Photographers and videographers will particularly appreciate it when working with the lucky imaging method using planetary cameras - the filter suppresses atmospheric dispersion at shorter wavelengths and contributes to the sharpness of the final image.

About DeltaOptical filters

DeltaOptical filters are popular among amateur and advanced astronomers alike for their excellent quality-to-price ratio. The DeltaOptical brand places emphasis on precision optical surface finishing and consistent filter characteristics, ensuring each unit meets its declared specifications. A wide range of color, lunar and narrowband filters allows you to build a complete set for various types of observation. The 1.25″ threaded design guarantees compatibility with the vast majority of eyepieces on the market, so the filter will work regardless of which telescope or eyepiece you are currently using.

Technical specifications