DeltaOptical Blue Color Filter #80A 1.25″
The DeltaOptical Blue Filter #80A is a specialized optical accessory designed for observing Solar System objects through any standard 1.25″ eyepiece. By effectively reducing red, yellow, and infrared wavelengths, this filter dramatically improves contrast and reveals subtle surface and atmospheric details on planets that would otherwise remain hidden to the observer.
Key Features
- Fits all standard 1.25″ eyepieces and focusers
- Filter designation: #80A (medium blue)
- Blocks red, yellow, and longer wavelengths
- Transmits blue and blue-green light for enhanced planetary contrast
- Fully coated glass optical element
- Threaded aluminum cell for secure, shake-free attachment
- Suitable for observers of all experience levels
Technical Specifications
| Parameter |
Value |
| Filter color |
Blue (#80A) |
| Barrel size |
1.25″ |
| Thread type |
Standard 1.25″ eyepiece filter thread |
| Recommended minimum aperture |
6″ (150 mm) for most planets; 8″ (200 mm) for Mars and comets |
| Primary use |
Planetary and lunar observation |
| Brand |
DeltaOptical |
Performance by Observation Target
Jupiter
The blue #80A filter is one of the most effective tools for Jupiter observation. It sharpens the boundaries between the reddish equatorial belts and the adjacent bright zones, enhances the visibility of fine atmospheric structures in the upper cloud layers, and makes it significantly easier to locate the Great Red Spot as well as festoons and other intricate features within the belts.
Saturn
When observing Saturn, the filter increases contrast between the planet's various bands and zones, including the polar regions. Details that would normally blend into the bright disk become clearly distinguishable, making extended observation sessions considerably more rewarding.
Mars
The blue filter is particularly valuable for Mars observations. It improves the visibility of surface albedo features, local dust storms, water-ice clouds, and morning or evening mists at the limb. It is especially useful during the rare phenomenon known as the "Violet Clearing" - a still unexplained event during which the Martian atmosphere, normally appearing as a uniform bright violet disk due to scattering of shorter wavelengths in the thin atmosphere, becomes transparent to blue and violet light. This reveals large dark surface features that are otherwise completely hidden. A telescope with a minimum aperture of 8″ (200 mm) is recommended for these observations.
Venus
Observing Venus with a blue filter is one of the most scientifically interesting applications of the #80A. The filter can reveal subtle cloud shadings and faint structural patterns in the upper layers of the Venusian atmosphere - details that are entirely invisible without filtration and which are considered valuable even by experienced planetary observers.
Mercury
The filter proves useful when observing Mercury during twilight, when the planet is low above the horizon and atmospheric dispersion makes observation difficult. The blue filter helps reduce the effects of atmospheric color fringing and improves the definition of the planet's small disk.
The Moon
As a lunar filter, the #80A increases contrast against a dark sky background and improves the distinction between different terrain types. It performs best with telescopes of at least 6″ (150 mm) aperture, where it brings out subtle tonal differences across the lunar surface.
Comets
The blue filter allows observers to achieve the highest possible resolution of gas tails (ion tails) in telescopes with an aperture of 8″ (200 mm) or larger, providing unique and striking views of these dynamic Solar System visitors.
About DeltaOptical
DeltaOptical was founded by astronomers for astronomers, with a clear focus on quality, functionality, and accessibility. Every DeltaOptical product undergoes rigorous testing to meet demanding standards for optical precision and durability across a wide range of observing conditions. The brand offers a broad range of astronomical accessories - from basic color filters to advanced optical components - all built around the philosophy that high-quality equipment should be within reach of every enthusiast. Through continuous product development and active engagement with the observer community, DeltaOptical has established itself as a trusted partner for amateur and semi-professional astronomers worldwide.
Who Is This Filter For?
- Amateur astronomers interested in planetary detail
- Visual observers who want to get the most out of their existing telescope
- Observers looking to explore phenomena such as the Martian Violet Clearing or Venusian cloud structures
- Anyone using a 1.25″ eyepiece system who wants to expand their accessory toolkit
