17mm 70° field AF Series eyepiece, with dual 1.25" and 2" barrels

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The 17mm focal length of this Astro-Tech 70° Field AF Series dual-barrel eyepiece is designed for unsurpassed wide field observing with any telescope type, under virtually any seeing conditions – from fair to superb. It is truly excellent for medium magnification lunar, planetary, and globular observing with long focal length refractors, reflectors, or catadioptric scopes. Contrast is very good, rivaling that of orthoscopic and Brandon eyepiece designs, but with a substantially wider field of view than either. Its high contrast also makes it a good choice for resolving detail in planetary and emission nebulas, while its sharpness across the field makes globular clusters vivid and nearly three-dimensional.

An f/4.5 Dobsonian will yield a 3.88mm exit pupil, getting into the rich field observing range for bright images of nebulas and galaxies and scanning the star clouds of Sagittarius. Even with the larger short focal length refractors, such as the Astro-Techs or TMBs, it’s a low to medium power eyepiece. With the 777mm focal length 4.4” Astro-Tech AT111EDT triplet apo, for example, it provides 46x, a 2.42mm exit pupil, and a 1.53° field. With the 910mm focal length 5.1” TMB-130 Signature Series triplet apo, it provides 53.5x, a 2.43mm exit pupil, and a 1.3° field. On both scopes, the fields are two and a half to three times as wide as the full Moon. These figures are all very usable for observing the more compact nebulas and large globular clusters, which will fit nicely into the field of view, with a framework of black velvet around them to set off their subtleties.

With its dual barrel design, the 17mm Astro-Tech 70° AF eyepiece can be used in both 2” and 1.25” focusers and star diagonals with no adapters needed.

The 17mm eye relief of this 17mm Astro-Tech is ideal for those who must wear eyeglasses when observing due to astigmatism. Vignetting will be minimal for eyeglass wearers, although the very wide field may require some moving of the head from side to side to see the entire field, even for those who don’t wear glasses.

This Astro-Tech comes with both 1.25” and 2” barrels, dust covers for both ends of the eyepiece, and a plastic bolt-type eyepiece container.

The optical performance of this 17mm Astro-Tech would be exceptional at any price. At its actual (and very sensible) price, it is truly outstanding. Well corrected for all aberrations, high in contrast, flat and sharp across its entire 70° field, it is an extraordinary value. We feel that this Astro-Tech 70° Field AF Series eyepiece equals or surpasses the performance of exotic designs costing twice its very reasonable price. It would be a welcome addition to any astronomer’s observing kit.

Field of view:
The field of view (FOV) is the amount of observable world one can see at any given moment.
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.
16 oz.
2 years
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Overall Product Rating: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics(5.00)   # of Ratings: 4   (Only registered customers can rate)

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Showing comments 1-4 of 4
1. Wes on 5/21/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
I had a chance to use this eyepiece at the Texas Star Party with my
160mm, f7 refractor. Previously I had use a 17mm Nagler type 4 and liked the FOV, so I purchased the Astro Tech 17mm. In the dark, I had several people ask me what eyepiece they were viewing with because they were impressed with what they saw. When I told them, they told me how it was not sharp to the edge; a classic example of
letting brand preference override reality. The eyepiece is not sharp
to the edge= but it is sharp at least 90% of the way. And in "normal"
viewing, the edge distortion is not noticeable due to the wide field.
What we all saw was sharp stars, accurate color shading, and the central object being framed nicely (66X). I am very pleased with it and recommend it as a cost saving alternative to other eyepieces with
only a slight change in performance.
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2. Jeffrey on 5/1/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
Love the eyepiece. I had looked long and hard at a set of titans, but was put off by some negative reviews, and saw a very positive review about the 22mm af, and put myself on the waiting list. In the meantime, i picked up the 17, which ive heard isn't quite as good as the 22mm.. I have been very pleased with the 17, I use it with a 10 inch meade sct, with which it excels, a 4 inch f/6 refractor, and it does very nicely, although not quite as nicely as it does with the longer f/r SCT. I once had some naglers, and some pentaxes, and this ep is not quite to that standard, but i have a kid now, and can't afford those, and this eyepiece is a very viable alternative, with a very high bang/buck ratio.
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3. Robert on 3/3/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
Nearly as good as the 22mm version. Similar field curvature. Doesn't sharpen up at the extreme edge quite as nicely. The outer 5% to 10% suffers from some astigmatism making pinpoint focus impossible. Bright stars at the edge show a small rainbow comet tail pointing to the center at sharpest focus, though no where near as bad as the 13mm version. The center is extremely sharp out to about a 60 degree AFOV. Out to 65 degrees is nearly as good. Compared to a 17mm Nagler Type 4, it is at least as sharp in the center losing out only at the edges. It snaps into focus more easily than the Nagler. The eyecup screws off the same as the 22mm. With it removed, it is just as easy to take in the view as with a Pentax XL or XW, with just a few less mm of eye relief, but still easy with glasses. Barlows as nicely as the 22mm, nearly removing the astigmatism and field curvature. No problems holding the exit pupil, either. Highly recommended for the price.
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4. Matt on 10/27/2012, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
Excellent EP. Clear, sharp views. Dark background.
This eyepiece is the first I have used that has allowed me to see spiral arm definition in Andromeda galaxy from my light polluted urban back yard, with a nearly full moon as well! I have used many EP's on Andromeda on many nights and in all kinds of viewing conditions and this was the best view yet!

The wide FOV is excellent for open and globular clusters as well.
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Astro-Tech - 17mm 70° field AF Series eyepiece, with dual 1.25" and 2" barrels

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Astro-Tech - 17mm 70° field AF Series eyepiece, with dual 1.25" and 2" barrelsImage showing the fixed 1.25" barrel and the removable thread-on 2" barrel of the Astro-Tech 17mm AF Series 70° field eyepiece.
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This 17mm Astro-Tech AF Series very wide 70° field dual-barrel eyepiece is usable for crisp and contrasty medium power observing with any telescope type, under virtually any seeing conditions – from fair to superb . . .

. . . our 36th year