Pentax 3.5mm XW extra wide angle eyepiece


Availability: In stock

This very short focal length Pentax eyepiece has a wide 70° field of view combined with a long 20mm eye relief for eyeglass use . . .
Our Product #: PXW03
Pentax Product #: 70511
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Product Description

This very short focal length Pentax eyepiece has a wide 70° field of view combined with a long 20mm eye relief for eyeglass use. It's a combination of virtues you won't find in any other eyepiece in its focal length range. It uses eight lenses in five groups to provide outstanding high magnification observing with short focal length refractors and fast focal ratio/short focal length Dobsonian reflectors. The wide and flat field of view allows longer undisturbed viewing with a Dobsonian. This allows several people to observe before an object has to be recentered in the field, a help for family viewing or star parties. Its long eye relief is particularly helpful if you must wear eyeglasses while observing, although all observers will benefit from its wide field and sharp images. Using it with an 820mm 4" f/8 Takahashi FS-102 fluorite refractor, for example, will result in 234x (58x per inch of aperture) and a 0.44mm exit pupil (about 1/50th of an inch across). Both of these figures are very close to the generally-accepted maximum values of magnification per inch of aperture and exit pupil size for usable observing under good to very good seeing conditions for a reasonably experienced observer.

Tech Details

Barrel Size 1.25"
Eye Relief 20mm
Field of view 70
Focal Length 3.5mm
Number of optical elements 8
Weight 14.3 oz
Warranty Limited Lifetime


Review by:
I purchased one of these quite a while ago for a short focal length refractor from a different distributor (sorry Astronomics), and the quality of the optics and hardware is outstanding. It is actually one of my favorite eyepieces. It has a decent f.o.v. with bright contrast images and a flat edge to edge field without any visible aberration or astigmatism. Something I should also note is that images appear brighter with less light scatter through this compared to other really short focal length eyepieces from other name brand manufacturers I own. Also, If you wear glasses (like me), viewing with them on isn’t an issue due to it’s longer eye-relief. Another nice perk is that it does come with a lifetime warranty. As others have mentioned, it does have a small exit pupil, but for the short focal length, is completely acceptable. Yes, it is an expensive eyepiece, but in my personal opinion it’s quality is well worth it. (Posted on 7/27/2019)
Review by:
Given my light polluted suburban skies, I concentrate on planetary and double star viewing. I purchased the Pentax XW 3.5mm eyepiece for use with my 10" f/6.6 Newt of excellent optical quality, yielding a magnification of 479x. The wide apparent field of 70 deg would be important for an observer lacking sidereal tracking but that is not my case. For me the key to this eyepiece is the outstanding eye relief of 20mm, allowing me to wear my eyeglasses even with the short eyepiece focal length. Throughput is excellent and internal reflections are effectively non-existent, which is important for bright objects. However, and this will be true with ANY eyepiece of such short focal length, be aware the exit pupil in my case is 0.5mm, which tends to bring out the "floaters" drifting about in my aging eyeballs. I give this eyepiece five stars. (Posted on 1/7/2019)
Review by:
Super sharp and contrasty right out to the edge. No signs of astigmatism, either. Great for planetary observations or for diving into the heart of dense globular clusters. The tiny exit pupil with many scopes does make for a dim view with some eye-floater issues, but it is nice to have for those fleeting moments of excellent seeing. Very easy to use with eyeglasses with no blackout issues. It is a bit long, but not as long as a barlow/eyepiece combination. Once you have 5mm to 40mm covered, consider getting this eyepiece, but not before. (Posted on 8/4/2017)
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