Aurel Ashgrove lunar filter 1.25 in, premium grade

Specifications

Description

The Ashgrove lunar filter is a neutral-density filter in a 1.25 in threaded cell, designed to reduce the brightness of the Moon at the eyepiece. It transmits about 18 percent of incident light across the visible spectrum, which lowers the glare of the lunar surface without shifting its color. Because the attenuation is broadly even across wavelengths, the filter keeps the natural tones of maria and highlands, so you can judge albedo differences and crater floors as they appear.

Full moon and near-full phases put a large amount of light into a telescope, and at high magnification the glare can wash out fine detail along the terminator and on bright ejecta rays. A neutral-density filter reduces the total light entering your eye, which helps to preserve contrast and to ease eye strain during longer sessions. Many observers find it most useful in telescopes of 100 mm aperture and larger, where the lunar image is brightest at high magnification.

The filter threads onto the barrel of any 1.25 in eyepiece or the nosepiece of a 1.25 in diagonal. Handle the glass by its cell, avoid touching the optical faces, and store it in its case when not in use. Because the filter reduces light, the view may appear darker at the eyepiece, so focus at a lower power first and then add the filter if the image is too bright.

Lunar filters do not improve planetary or deep-sky observing, since they remove a significant share of light from those targets. Inserting it into the optical path can shift focus slightly, so refocus after installing it. Sharp focus is easiest to achieve by focusing on the bright lunar limb with the filter already in place, then making fine adjustments as the Moon moves through the field.

About this configuration

This listing covers one configuration of the Aurel Ashgrove lunar filter 1.25 in, defined by its grade, coating, case, and edition year. The premium grade uses polished glass with tighter flatness tolerances, which helps at high magnification. Premium grade filters are checked for the position of the passband before they leave the factory. With anti-reflection layers on both sides, less light bounces between the filter and the eyepiece or camera sensor.

The filter ships in a clear plastic case that keeps dust off the glass between sessions. The 2025 edition keeps the same transmission figures as the earlier years of the Ashgrove line. The transmission figures in the specifications apply to every configuration of the Ashgrove line.

What's in the box

• Lunar filter in 1.25 in threaded cell
• Plastic storage case
• Plastic storage case

Compatibility notes

• Threads into 1.25 in eyepieces, diagonals, and filter wheels (M28.5 x 0.6).
• Most useful in telescopes of 100 mm aperture and larger at higher magnifications.