Brand: Ricoh

Pentax 16.5mm XW Series 2" Eyepiece (70540)


Brand: Ricoh

Pentax 16.5mm XW Series 2" Eyepiece (70540)


Pentax XW eyepieces are cult classics. They show extraordinary clarity and detail and are the most comfortable eyepieces we've ever used. We love all the eyepieces we sell, but these might be our favorites.
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Product Description

Clear, Comfortable Viewing Assured by 85° Apparent Angle of View and 20mm Eye Relief.

All SMC PENTAX XW-series eyepieces feature an extra-wide apparent angle of view and an extra-long 20mm eye relief to deliver an exciting, wide-perspective image.

High-Grade Optics for Exceptional Image Quality.

The high-performance XW-series optics incorporates high-refraction, extra-low-dispersion lanthanum glass elements to produce a well-balanced image with minimal aberrations. It is particularly designed to reduce the disturbing blackout effect by effectively compensating the spherical aberration of the pupil.

PENTAX-Original Multi-Layer Coating for Outstanding Light Transmission Efficiency.

All lens surfaces that come in contact with air are treated with the original multi-layer coating, while all laminated surfaces are treated with the innovative partial coating, to offer the light transmission efficiency of more than 90 percent (an astonishing 96 percent at 550nm) over the visible light spectrum.

Advanced Light-Shielding Technology for Improved Image Contrast.

Thanks to PENTAX’s advanced computer simulation technology, the XW series features a light-shielding diaphragm at the most effective position to drastically reduce internal reflections for a brighter, higher-contrast image.

A Choice of Six Magnifications to Meet Specific Applications.

With many different magnifications to choose from, the XW series accommodates a wide range of both casual and specialized applications.

Weatherproof Construction for All-Weather Viewing.

The XW series features JIS Class 4 weatherproof construction,* making it possible to use it in drizzle or under night dew.

* The XW-series eyepieces are not designed for underwater use and should not be submerged under water.

Standard Eyepiece Sleeve and Built-In Adapter-Mounting Screw

The XW series provides a choice of two installment diameters: American-standard 1.25″(31.7mm) version, and 2″ (50.8mm) version. When you remove the screw-on eyecup, the XW30-R and XW40-R models provide a screw thread with a 48mm diameter and a 0.75 pitch, while other models provide a screw thread with a 43mm diameter and a 0.75 pitch.


XW16.5 XW23 XW30-R XW40-R
Eyepiece Lens:
7 elements 7 elements 7 elements 6 element
Lens Structure:
5 groups 5 groups 6 groups 5 groups
Focal Length: 16.5mm 23mm 30mm 40mm
Apparent Field of View: 85˚ 85˚ 70˚ 70˚
Eye Relief: 20mm 20mm 20mm 20mm
Attachment Diameter: 2” (50.8mm) 2” (50.8mm) 2” (50.8mm) 2” (50.8mm)
Filter Diameter: -- -- 48mm 48mm
Field Stop Diameter: -- -- 36.2mm 46.5mm
Eyepiece Ring: Helicoid type Helicoid type Helicoid type Helicoid type
Height & Width: 3”x5.6" 3”x4.9" 4.8”x3.0” 4.6”x3.0”
Weight: 26.3 oz. (745g) 27.2 oz. (770g) 26.1 oz. (740g) 24.7 oz. (700g)

Customer Reviews

Based on 2 reviews
Stunning 16.5mm Pentax XW

I bought this eyepiece a couple of months ago. It is easily the best wide field eyepiece I have ever viewed through. I already own a complete set of Pentax XWs and the 16.5mm surpasses all of these! It provides the perfect combination of wide field (85 degrees) and eye relief.

The 16.5mm XW displays tack sharp stars across the entire view even at F/4.4 in my 16-inch dobsonian when combined with a Paracorr coma corrector. Colour rendition, transmission and contrast are excellent. For the first time in my life I saw red in the Orion nebula!

I found Nicholas to be very helpful and reassuring which was important to me as the eyepiece needed to be shipped from Canada to the UK.


I extensively tested this astonishing Pentax 85degree monster and except for my Nagler 20mm Type2 eyepiece i have never used such a fantastic optic and at the 24Xish that my F/6.45 telescope works at it gives an image beyond etched. I am so glad i saved and spent the cash for this eyepiece and the 20X the Nagler gives may seem trivial and it essentially is but at my F/9 optic its at 54.5X and the Naglers at 45X so summer sweeping and finding something interesting gives me the proverbial 50X power need but just a bit better under and over so an accomplished sweeper will be well served !!

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