Pentax
Pentax 70538 XW40-R Telescope Eyepiece 40mm
★★★★★
Explore the Universe with the PENTAX XW40-R Telescope Eyepiece The PENTAX XW40-R is a high-performance 2-inch eyepiece designed for telescopes, offering an extra-wide 70° apparent angle of view and exceptional image quality. Perfect for viewing nebulae, planets, and exploring the night sky. Det...
$451.00*
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*Price sourced from Amazon.com. Last updated:Jul 14, 2026.Price and availability are subject to change.
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Overview
Explore the Universe with the PENTAX XW40-R Telescope Eyepiece
The PENTAX XW40-R is a high-performance 2-inch eyepiece designed for telescopes, offering an extra-wide 70° apparent angle of view and exceptional image quality. Perfect for viewing nebulae, planets, and exploring the night sky.
Detailed Specifications:
- Focal Length: 40mm
- Apparent Angle of View: 70°
- Eye Relief: 20mm
- Optical Design: High-Refraction, Extra-Low-Dispersion Lanthanum Glass Elements
- Lens Coating: PENTAX Original Multi-Layer Coating
- Weatherproofing: JIS Class 4
- Adapter Mounting: Built-in Adapter-Mounting Screw (43mm Diameter, 0.75mm Pitch)
- Included Accessories: Front Cap, Rear Cap, Plastic Case
Key Features
IDEAL FOR ASTRONOMICAL TELESCOPE: The XW40-R is the perfect eyepiece for viewing the nebula, planets and exploring the night sky.
CLEAR, COMFORTABLE VIEWING: XW40-R eyepiece features an extra-wide 70° apparent angle of view and an extra-long 20mm eye relief to deliver an exciting image with a wide-perspective.
HIGH-GRADE OPTICS FOR EXCEPTIONAL IMAGE QUALITY: The high-performance XW40-R's 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 for the spherical aberration of the pupil.
SMC COATING: 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: Thanks to PENTAX’s advanced computer simulation technology, XW40-R features a light-shielding diaphragm at the most effective position to drastically reduce internal reflections for a brighter, higher-contrast image.
ALL-WEATHER CONSTRUCTION: The XW40-R features JIS Class 4 weatherproof construction, making it possible to use it in drizzle or under night dew.
BUILT-IN ADAPTER-MOUNTING SCREW: When the rotatable eyecup is removed, it also offers an adapter-mounting screw/thread (43mm in diameter with a 0. 75mm pitch).
PENTAX SPORTS OPTICS SINCE 1938: Bringing together technology cultivated through the development of a wide variety of cameras and lenses, Experience the clarity made possible by trusted optical performance and revolutionary coating techniques. Discover a new way of seeing with PENTAX sports optics.
WIDE RANGE OF XW SERIES LINEUP: With a wide range of magnifications to choose from, the XW series accommodates a wide range of both casual and specialized applications.
WHAT'S IN THE BOX: Includs front cap, rear cap and plastic case
Specifications
Focal Length
40mm
Apparent Angle of View
70°
Eye Relief
20mm
Glass Elements
High-refraction, extra-low-dispersion lanthanum glass
Coating
SMC (Super Multi Coating)
Light Transmission Efficiency
>90% (96% at 550nm)
Light Shielding
Advanced computer simulation technology
Weather Resistance
JIS Class 4
Adapter Mounting Thread
43mm diameter, 0.75mm pitch
Pros & Cons
👍 Pros
- Ideal for observing nebulae, planets, and exploring the night sky with its versatile design.
- Features an extra-wide 70° apparent angle of view for an immersive, wide-perspective viewing experience.
- Offers an extra-long 20mm eye relief, ensuring comfortable viewing, especially for those who wear glasses.
- Incorporates high-refraction, extra-low-dispersion lanthanum glass elements for minimal aberrations and well-balanced images.
- Utilizes SMC coating on all air-contacting lens surfaces, achieving over 90% light transmission efficiency across the visible spectrum.
👎 Cons
- While weather-resistant (JIS Class 4), it is not designed for underwater use, limiting use in very wet conditions.
- The included adapter-mounting screw/thread (43mm in diameter with a 0.75mm pitch) might not be universally compatible.
- Specific details on the materials of the lens housing are not provided, only the weather-resistant quality.
- The term "minimal aberrations" is subjective and could be interpreted differently by experienced astronomers.
- Offers only one focal length (40mm), which limits magnification options without purchasing additional eyepieces.
Frequently Asked Questions
What kind of celestial objects is the Pentax XW40-R eyepiece best suited for?
The XW40-R is ideal for viewing nebulas, planets, and for general exploration of the night sky, offering clear and comfortable wide-field observations.
How wide is the apparent field of view with this eyepiece?
This eyepiece features an extra-wide 70° apparent angle of view, providing an exciting image with a broad perspective.
Is this eyepiece comfortable for people who wear glasses?
Yes, it offers an extra-long 20mm eye relief, which allows for comfortable viewing even while wearing eyeglasses.
What optical technologies contribute to the image quality of the XW40-R?
It incorporates high-refraction, extra-low-dispersion lanthanum glass elements to minimize aberrations and uses SMC coating for over 90% light transmission efficiency.
Does this eyepiece have features to reduce internal reflections?
Yes, the XW40-R features advanced light-shielding technology with a diaphragm at an effective position to drastically reduce internal reflections, leading to brighter and higher-contrast images.
Is the Pentax XW40-R eyepiece weather resistant?
Yes, it features JIS Class 4 weatherproof construction, making it suitable for use in conditions like drizzle or under night dew.
Can accessories be attached to this eyepiece?
Yes, when the rotatable eyecup is removed, it reveals an adapter-mounting screw/thread with a 43mm diameter and a 0.75mm pitch.
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