Pentax 20mm XW extra wide angle eyepiece


Availability: In stock

This medium focal length Pentax provides sharp and very wide field images for both terrestrial and astronomical observing . . .
Our Product #: PXW20
Pentax Product #: 70516
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Product Description

This medium focal length Pentax provides sharp and very wide field images for both terrestrial and astronomical observing.

Terrestrially, it is an excellent medium power wide field eyepiece for detailed close-in or wide field nature studies with the 80mm and 100mm Pentax spotting scopes in overcast and sub-par light conditions, dawn to dusk.

Astronomically, its six lens/four group design makes it an excellent high-contrast choice for medium power deep space observing with long focal length refractors, reflectors, or catadioptric scopes. It is a superb low power eyepiece with short focal length refractors and fast focal ratio reflectors. An f/4.5 Dobsonian reflector, for example, will yield a 4.4mm exit pupil, excellent for detailed images of emission nebulas and galaxies. Its sharpness across the field makes globular clusters and nebulas vivid and nearly three-dimensional. The 650mm focal length TMB-105 triplet apo refractor provides 32.5x, a 4mm exit pupil, and a 2.15-degree field (over four times as wide as the Moon). These figures are all very usable for observing open clusters such as the Pleiades; large nebulas such as the Lagoon, Veil, and Orion; and large globulars such as M-13 and Omega Centauri. All will fit nicely into the field of view, with a generous framework of black velvet sky around them to set off their subtleties.

The long 20mm eye relief is ideal for those who must wear eyeglasses while observing due to astigmatism. Even those who do not wear glasses will find the long eye relief a comfortable change from the cramped eye relief that is typical of the usual short focal length eyepiece.

For terrestrial observing . . .
With an 80mm straight-through Pentax spotting scope this eyepiece provides 25x magnification and a huge 147' field of view at 1000 yards, which are the values given in the specifications to the left.
With the 80mm angled Pentax spotting scope this eyepiece provides 26x magnification and a 141' field of view at 1000 yards.
With the 100mm aperture Pentax spotting scope this eyepiece provides 32x magnification and a big 115' field of view.

For astronomical observing . . .
The field of view of 70° degrees given in the specifications to the left is the apparent field of view. The actual field of view will be equal to that apparent field divided by the magnification of the eyepiece/telescope combination.

Tech Details

Barrel Size 1.25"
Eye Relief 20mm
Field of view 70
Field of view 1000 yards 147'
Focal Length 20mm
Number of optical elements 8
Power 25x terrestrially
Weight 12.6 oz
Warranty Limited Lifetime


Review by:
This is the eyepiece I use most in my 290mm Classical Cassegrain. It hits the sweet magnification of 196x, just short of where local seeing usually falls apart. But the view is broad enough that I can also use it as a wide field eyepiece in my 6" f/8 Newt. Very comfortable and easy to use, no lateral color. I've stopped using my TV 25mm Plossl in favor of this eyepiece. (Posted on 8/14/2019)
Review by:
I've used the Pentax 20mm with both a 115mm APO and a 260mm reflector and found it to be my most used eyepiece; over the past 10 years, it has performed flawlessly. (Posted on 7/22/2019)
Review by:
I have used several high end eyepieces and this one measures up very nicely. It is compact and well made giving excellent views. Very crisp with high contrast. (Posted on 10/17/2018)
Review by:
This is my favourite eyepiece. I have a Celestron 6se, and I do wear glasses, so the eye relief is really nice. I've had no complaints from the non-glass wearing folks that have looked through it. It is super sharp and a joy to look through. I love this EP! (Posted on 8/4/2017)
Review by:
The 20mm XW often is criticized for suffering from "field curvature". However, I have used the 20mm XW with a 120mm f/8.3 achromat and a Vixen 140 Neo-achro Petzval refractor and found that the field curvature is not signficant with these scopes. The 20mm XW is extremely comfortable and the AFOV feels bigger than the 70 degs. When I compared it with an 82 deg AFOV eyepiece with similar FL the 20mm XW didn't feel like it had a smaller AFOV. The 20mm XW has excellent coatings and provides nice bright views of nebula and galaxies and precisely rendered pinpoint stars in clusters. It also handles a barlow extremely well. I've tried every XW FL except the 3.5mm and 5mm. The 20mm XW is easily my favorite XW. Personally, I do not like XW's for lunar observations. I think there are other eyepieces that give sharper lunar views - among both simpler and widefield designs. But as a deep sky eyepiece the 20mm XW is about as good as it gets. I also had some of the best views I've ever had of Jupiter with the 20mm XW. (Posted on 8/4/2017)
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