Negative Achromats consist of two optical components, a crown and a flint glass lens, cemented together. The crown is usually a bi-concave lens. As is true to all Achromats, they are corrected for color and on-axis spherical aberration. They are used predominantly to extend focal lengths in combination with positive achromatic systems or CCD lenses.
| Diameter | Dia. Tolerance | CT Tolerance | Centering | Irregularity | Surface Quality | Bevel |
| 6.00-25.00 | +0.00 / -0.10 | ±0.2 | < 3 minutes | 0.50 Waves | 40-20 | 0.25 x 45° |
| 25.01 - 50.00 | +0.00 / -0.10 | ±0.2 | < 3 minutes | 0.50 Waves | 60-40 | 0.50 x 45° |
| Dimensions | MM | |||||
| Clear Aperture | CA >= 90% of Diameter | |||||
| Coating | 1/4wave MgF2 @ 550nm (See Coating Chart for Available Options) | |||||
| Design Wavelength | 587.6nm | |||||
| Focal Length Tolerance | ±2% | |||||
| Edge Thickness | Reference | |||||
| * All dimensions are in mm | ||||||