DeltaOptical orange filter #21 1.25″
Want to get the most out of planetary observation? The DeltaOptical orange filter #21 for 1.25″ eyepieces is an excellent tool that significantly improves contrast and visibility of surface details when viewing Mars, Jupiter, Saturn, and the Moon. Thanks to its characteristic orange tint, it transmits light in the range of approximately 530-700 nm while effectively suppressing the blue and green portions of the spectrum.
What does the orange filter #21 reveal in the sky?
The number 21 orange filter is one of the classic color filters with a long tradition in planetary astronomy. Here is what it brings to each object:
- Mars - noticeably enhances dark surface features, polar ice caps, and dust storms by increasing contrast against the surrounding terrain.
- Jupiter - helps render atmospheric belts and zones more clearly by suppressing bluish cloud tones and emphasizing warmer hues.
- Saturn - makes cloud structures in the atmosphere easier to observe.
- Moon - reduces glare while preserving rich surface detail.
Design and mounting
The filter is set in a precisely machined metal cell with a standard thread for 1.25″ eyepieces. Mounting is straightforward - the filter simply screws onto the bottom of the eyepiece and is immediately ready for use. The optical element features anti-reflection coatings that minimize unwanted reflections and ensure the cleanest possible image.
Recommended aperture and use in astrophotography
With a light transmission of approximately 46%, the filter is suitable for medium and larger telescopes - from an objective diameter of approximately 100 mm and above. With a smaller aperture, the image might be too dim for comfortable visual observation.
For photographers, this is an excellent tool for imaging Mars and also for shooting with wide sensors, as it significantly suppresses chromatic noise.
Technical specifications
| Parameter |
Value |
| Filter number |
#21 |
| Color |
Orange |
| Eyepiece fitting |
1.25″ |
| Transmission range |
approx. 530-700 nm |
| Light transmission |
approx. 46% |
| Recommended min. aperture |
100 mm |
| Cell material |
Metal |
| Coating |
Anti-reflection (AR) |
Quality and durability of DeltaOptical filters
DeltaOptical filters are manufactured with an emphasis on optical quality and long service life. Precision-ground optical glass, high-quality anti-reflection coatings, and a robust metal cell with a thread precisely matching the 1.25″ standard guarantee reliable and repeated use without any loss of performance.
DeltaOptical focuses on astronomical accessories for demanding observers who do not want to compromise on quality. Whether you are an experienced planetary observer or just beginning to explore the solar system, the DeltaOptical orange filter #21 is an investment that pays off from the very first look through the eyepiece.
