40mm 1.25" Value Line Plössl

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This Astro-Tech 40mm Value Line Plössl is a good quality low power long eye relief eyepiece at a price that’s substantially lower than competitive Plössls. The eye relief is designed to be 31mm, and is claimed as such by similar eyepieces, and this is technically correct. However, because the eye lens (from where the eye relief is normally measured) is deeply recessed within the body of the eyepiece, the usable eye relief (the distance from where the image forms to the rolled-down eyecup, the closest point you can get your eye to the eye lens itself) measures 20mm. This is still long enough for essentially unvignetted eyeglass use.

The Astro-Tech 40mm Value Line Plössl has a good 40° apparent field of view, designed for the big picture of emission and reflection nebulas, for seeing entire open clusters like the Pleiades in one field, and for scanning nebular remnants like the Veil. Similar eyepieces may claim a wider field of view, some wider than is physically possible in a 1.25” eyepiece, but we choose to use a more realistic and accurate 40° value.

This Astro-Tech will work well with any telescope type (with the exception of fast focal ratio Dobsonian reflectors), at any focal ratio from f/6 and up. It works particularly well from dark sky sites where light pollution won’t reduce the contrast in its bright image. A knurled rubber ring on the body provides a secure grip when changing eyepieces in cold or damp weather.

Field of view:
The field of view (FOV) is the amount of observable world one can see at any given moment.
40°
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.

20mm
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.

40mm
Number of optical elements:
4
Barrel Size:
The industry standard diameter, as of 2011, is 1.25" and is the most common.  Other sizes available are .965" and 2".
1.25"
Weight:
The weight of this product.
5.5
Warranty:
2 years
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1. Ken on 7/19/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
Surprisingly good quality for the price. Crisp, clear image. Easily rivals the premium brands.
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52mm x 80mm eyepiece container
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Astro-Tech 40mm Standard Plossl
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Astro-Tech - 40mm 1.25" Value Line Plössl

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Astro-Tech - 40mm 1.25" Value Line Plössl
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With a long eye relief that’s good for eyeglass wearers, this low power 40mm Astro-Tech Value Line Plössl gives you the widest field possible from a 1.25” eyepiece for the big picture at a very little price . . .





. . . our 34th year