20-60X zoom XF eyepiece for 65mm Pentax spotting scopes

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This Pentax zoom eyepiece is physically sized for use with the compact 65mm Pentax spotting scopes. It can also be used with the 80mm and 100mm Pentax scopes if the size and weight of the larger XW eyepieces normally used with them becomes an issue with those models. It has a 1.25" barrel, so it can also be used as a zoom eyepiece with astronomical telescopes accepting 1.25" eyepieces.

It has a variable focal length range of 19.5mm to 6.5mm. This provides a zoom range of 20x to 60x magnification with the 65mm Pentax scopes, to cover a wide range of birding and nature study situations. Its apparent field of view ranges from 42° at 20x to 60° at 60x. This provides an actual 2.1° field (110’ @ 1000 yards) at 20x and a 1° field (52.5’ @1000 yards) at 60x. (It provides a magnification range of 26x to 78x with the straight-through 80mm Pentax scope, 27x to 81x with the straight-through 80mm Pentax, and 32.5x to 97.5x with the 100mm Pentax.)

The usable eye relief ranges from 14mm at 20x to 10mm at 60x. These somewhat-short figures will vignette the field of view for those who must wear eyeglasses while observing due to astigmatism, particularly at the higher powers. Those who do not wear glasses will find the eye relief more than acceptable for unvignetted viewing, particularly when the rubber-rimmed twist-up eyecup is extended to block out ambient light and position the eye at the correct eyepoint.

The eyepiece barrel has a series of four grooves machined into the scope side of the barrel. When the eyepiece is first inserted into the scope, before tightening the eyepiece locking collar, the eyepiece should be twisted slightly until one of these grooves engages the pin in the bottom of the eyepiece receptacle. This will keep the eyepiece from twisting in place when the knurled power change collar on the eyepiece is turned to adjust the magnification.

All lens elements (a sophisticated 6 lens/4 group design) are fully multicoated with Pentax SMC (Super Multi-Coated) high transmission antireflection optical coatings for maximum light transmission and contrast. High refraction/low dispersion glass elements are used for excellent color fidelity. The eyepiece is specially sealed to be weatherproof under the worst observing conditions a birder might encounter, short of total submersion. Protective caps are provided for both ends of the eyepiece.

Field of view 1000 yards:
Eye Relief:
Eye relief is the distance from the last surface of the eye lens of an eyepiece to the plane behind the eyepiece where all the light rays of the exit pupil come to a focus and the circular image is formed, sometimes called the “Ramsden Disk.” This is where your eye should be positioned to see the full field of view of the eyepiece. If you must wear glasses because of astigmatism, you’ll usually need at least 15mm of eye relief or longer if you want to see the full field of view with your glasses on.

A note on our eye relief figures: Quite often, our eye relief figures will differ from those of the manufacturer. This is because we measure the “usable” eye relief, while the manufacturers specify their usually-longer (but technically correct) “designed” eye relief.

The eye lens of the eyepiece is normally recessed below the rubber eyeguard or rubber rim of the eyepiece to keep the lens from being scratched during use. An eyepiece might have a “designed” eye relief of 15mm (and the eye relief will truly measure 15mm from the eye lens to where the image forms). However, if the eye lens is recessed 3mm below the eye guard, the Ramsden Disk forms only 12mm above the eyepiece body (the 15mm “designed” eye relief, less the 3mm of eye relief made unusable by having the eye lens recessed into the body of the eyepiece). This “usable” eye relief of 12mm (measured from the rolled-down eyeguard – the closest point you can get your eye to the eye lens – to where the image forms) is the eye relief figure we would measure and list in this website.

Why is it important to list the “usable” eye relief? For those people who don’t wear eyeglasses while observing, a few mm difference between the eye relief they expect from the manufacturer’s literature and the shorter eye relief they actually get in real life doesn’t mean a lot. They can simply move a little closer to the eyepiece to see the full field, and never realize that the eye relief is a little shorter than they expected. However, some people must wear eyeglasses while observing, because of severe astigmatism. These observers can’t move closer to the eyepiece if the eye relief is shorter than expected because their glasses get in the way. For these people, the real life “usable” eye relief is more important than the technically correct but sometimes not fully usable “designed” eye relief. We measure and list the actual usable eye relief so that people in the real world can pick the eyepieces that will work best for them.

Focal Length:
This is the length of the effective optical path of a telescopeor eyepiece (the distance from the main mirror or lens where the lightis gathered to the point where the prime focus image is formed). Focallength is typically expressed in millimeters.

The longer the focallength, the higher the magnification and the narrower the field of viewwith any given eyepiece. The shorter the focal length, the lower themagnification and the wider the field of view with the same eyepiece.

Number of optical elements:
Barrel Size:
The industry standard diameter, as of 2011, is 1.25" and is the most common.  Other sizes available are .965" and 2".
The weight of this product.
8 oz.
Limited Lifetime
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Pentax - 20-60X zoom XF eyepiece for 65mm Pentax spotting scopes

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Pentax - 20-60X zoom XF eyepiece for 65mm Pentax spotting scopes
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Our Product #: PXFZ
Manufacturer Product #: 70530
Price: $289.00  FREE ground shipping - Click for more info
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MSRP: $319.00

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This 20x to 60x Pentax zoom eyepiece is physically sized for use with the compact 65mm Pentax spotting scopes, as well as telescopes using 1.25" eyepieces.

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