Ricoh/Pentax Pentax Eyepiece SMC XW 16.5

Pentax Eyepiece SMC XW 16.5 – 85° apparent field of view with 20 mm eye relief

The Pentax SMC XW 16.5 eyepiece delivers the widest apparent field of view in the XW series. With an 85° field and 20 mm of eye relief, it gives observers a broad, comfortable view that is particularly well suited to observing nebulae and star clusters.

Key features at a glance

• Apparent field of view of 85°, the widest viewing angle in the XW series, suitable for observing nebulae and star clusters.
• A new optical system with 7 elements in 5 groups that surpasses the conventional XW series to obtain sharp star images all the way to the edge of the field of view.
• Original multilayer coating for outstanding light transmission efficiency.
• Advanced light-shielding technology for improved image contrast.
• Weather-resistant (JIS Class 4) construction for all-weather viewing (note cannot be used under water).

Optical design and image quality

The eyepiece uses a 7-element, 5-group optical system. This design produces sharp star images right to the edge of the field of view. In addition, Pentax selected lanthanum glass elements with high refractive power and particularly low dispersion. As a result, the eyepiece produces a balanced image with minimal aberrations.

Moreover, the design specifically reduces the blackout effect. It compensates for spherical aberration of the pupil, which helps maintain a steady, evenly illuminated field during observation.

Coatings and light transmission

All air-exposed lens surfaces receive Pentax's original multi-coating. Meanwhile, all laminated surfaces use an innovative partial coating. Together, these treatments raise light transmission to more than 90% across the visible spectrum and achieve an estimated peak transmission of 96% at 550 nm. Therefore, the eyepiece delivers bright images while preserving color and contrast.

Contrast and stray light suppression

Pentax applies advanced computer simulation to place a light-shielding diaphragm in the most effective position inside the eyepiece. Consequently, this reduces internal reflections and dramatically improves image contrast. Observers will notice a clearer view with fewer stray light artifacts, which is especially helpful when viewing faint deep-sky objects.

Construction and durability

The eyepiece features weather-resistant construction rated to JIS Class 4. Thus, you can use it in damp or inclement conditions for reliable field use. However, note that the eyepiece is not suitable for underwater use.

Specifications

FAQ

Question: What makes the SMC XW 16.5 ideal for deep-sky observing?
Answer: Its 85° apparent field of view combined with 20 mm eye relief gives you a wide, comfortable view that is great for scanning nebulae and star clusters. The optical design and coatings maintain sharpness and brightness to the edge of the field.

Question: How does the eyepiece handle contrast and internal reflections?
Answer: Pentax uses a light-shielding diaphragm positioned through computer simulation to limit internal reflections. This improves contrast and reduces stray light, producing a cleaner view of faint objects.

Question: Are the coatings effective at transmitting light?
Answer: Yes. All air-exposed surfaces have original multi-coating and laminated surfaces have partial coating. Together they deliver more than 90% transmission across the visible spectrum and around 96% at 550 nm.

Question: Can I use this eyepiece in poor weather or underwater?
Answer: The eyepiece has weather-resistant JIS Class 4 construction, so it withstands damp and adverse conditions. However, it is not suitable for underwater use.