Pentax XL 8-24mm Zoom

Pentax XL 8-24mm Zoom

  (2 Reviews)
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About this product

Model:  PentaxXLzoom
Part Number:  70509

This premium quality six-element zoom eyepiece with ED and Lanthanum glass can be used in any telescope that accepts 1.25" accessories.

Mechanically and optically this is a benchmark zoom eyepiece! 

Zoom eyepieces enable the observer to match magnification to changing lighting or seeing conditions. This together with Pentax-grade optics results in an exceptionally useful eyepiece for terrestrial or astronomical observing. 

For astronomical use, the zoom is usable for medium to high power observing with telescopes of all optical designs – from long focal ratio refractors down to fast f/4.5 Dobsonian reflectors. 

Like most other Zoom eyepieces the FOV varies across the zoom range (from 38° at 24mm, to 60° at 8mm). 


  • Premium optical design with six lenses in four groups.
  • ED (extra low dispersion) glass lens elements that include Lanthanum glass minimise chromatic aberrations and astigmatism. The result is very high contrast and centre resolution, with very little ghosting.
  • All air-to-glass surfaces are fully multi-coated with proprietary Pentax SMC (Super Multi-Coated) anti-reflection coatings for high light transmission.
  • For optimum contrast, lens edges and interior mechanical surfaces are all blackened to minimise reflections and ghosting.
  • A rubber eyecup twists in and out of eyepiece body to optimise shield your eye from ambient light.
  • The knurled rubber grip is turned to change magnifications.
  • When the twist-up rubber eyecup is fully retracted for eyeglass use, the eye-relief ranges from 18mm (at 8mm setting) to 22mm (at 24mm). This enables observers with eyeglasses to see the entire field of view at low magnifications. When observing at high magnifications while wearing eyeglasses some vignetting of the outer field will occur (at these high magnifications you will likely be observing smaller objects that do not fill the FOV so minor edge vignetting is rarely a concern).
  • The barrel of the eyepiece is marked in both magnifications (when used an 80mm Pentax spotting scope) and in focal lengths for astronomical observing. An index mark shows the power in use.
  • The 1.25" nosepiece is threaded to accept 1.25" astronomy filters. 
  • JIS-4 weatherproof construction for protection against wet weather and night-time dew.

Weight: 550g (1.2lb)
Length: 114mm (4.5")
Width: 69mm (2.7")

Customer reviews

Average Rating (2 Reviews):  
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Rating (max 5):  
Big Zoom, Big Performance, Big Price!
19 April 2016  | 

Having owned several Baader 8-24mm zooms, and having always hankered after a premium Pentax one, I finally took the plunge in early 2016.

FLO service was excellent, as always and I received the eyepiece 24 hours after ordering it.

First impressions, (with all too few later sessions due to weather and work commitments):
Size: This is a Big zoom, considerably bigger than the Baader, but looks fantastic and comes with branded eyeglass cover and bomb proof bolt case for storage.

Build quality - superb, exemplary:
Zoom mechanism is quite stiff, due to the O Seal JIS waterproofing, but it does ease off and I have found that the best results come when using a Baader Click Lock 1.25" adapter in my 2" scope focuser. This holds the ep rock solid and enables plenty of torque to allow the smooth rotation of the zoom mechanism. A real, tangible step up on the build of the Baader zoom.

Optics: The optics are very, very good for a zoom. In comparison to a world class Meade Japan UWA 14mm, I would say the Meade ever so slightly edged it in terms of faint stars visible, but it was a very slight advantage: from darker skies than mine this might disappear as a factor, and a tiny price to pay for having several eyepieces in one unit.

Stellar images are pinpoint to the edge in my F7.7 apo doublet, with very good contrast.

Field of view. The range of this zoom is 24mm, at which the specs say the view is 38degrees, going up to the highest 8mm power, at which the view is 60 degrees. On the face of it, the 24mm setting is quite narrow, but it never feels tunnel like, and the quality of the views are excellent. I have a wide 68 deg 24mm for that purpose anyway, so I do tend to look at this (and Baaders are the same fov) as an 8mm-20mm eyepiece. At 20mm the field is approximately 45degrees, and at 16mm about 50 degrees (same as most plossls). But, unlike many cheaper fixed eyepieces, the whole field of view is very sharp right to the edge. At 14mm and above, the field increases steadily up to the very healthy 60 degrees at 8mm. And, of course, you can increase or decrease the magnification in very small increments/decrements as conditions dictate.

The zoom is NOT 100% parfocal. As you move from the 24mm setting to the highest 8mm setting, you need about a 2mm further in-focus setting on my focuser to achieve perfect focus. This is not a deal breaker at all for me, but just something to be aware of.

Perhaps the best feature optically of the Pentax zoom is it's versatility. On any given night the seeing can vary quite significantly, and, when using fixed length eyepieces it can be very tiresome to have to keep swapping eyepieces to get the best view at a given moment.

With the Pentax, you just dial in the magnification that gives the best view, simple, with just one eyepiece. So, you can observe for longer and see more.

This is not a cheap eyepiece. But, it is of superb quality in all respects, and will last you a lifetime if you want it to. The Baader is an excellent unit to be sure, but in my honest opinion the Pentax has it comfortably beaten on all counts. And, at about twice the price of the Baader, so it should!

Highly recommended.

Rating (max 5):  
King of Zooms
09 May 2011  | 

This is simply the best Zoom Eyepiece I have tried at longer than 6mm focal length. The field of view is good and sharp to the edges and the focal shift through the range from 8mm to 24mm is so small that I can't detect it at all. The construction is very sturdy and oozes quality.

This lives up to the Pentax brand and although pricey at least backs it up with performance!


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