ZWO Filter

The 7nm half-width indicates the narrow band of light the filter allows through. This is tight enough to block most light pollution and moonlight, which significantly boosts the contrast of faint nebulae, but wide enough to keep exposure times manageable for most deep-sky setups.

No, you shouldn't need to. These filters are designed to be homofocal with standard L-RGB sets, meaning they share the same optical thickness. This allows you to switch filters during an imaging run without having to pause for refocusing.

Yes, these are excellent for city environments. Because they only transmit specific wavelengths emitted by nebulae, they effectively filter out the broad-spectrum light pollution common in urban areas, allowing you to capture deep-sky detail that would otherwise be washed out.

These filters are designed specifically for astrophotography. Because they block so much light, they will make the view through an eyepiece appear extremely dark, making them ineffective for visual observing.

Yes, these are standard 1.25-inch mounted filters. They are compatible with almost all standard filter wheels and filter drawers designed for 1.25-inch accessories.