20mm Orion Sirius Plossl Telescope Eyepiece

User level:

User level

Beginner Level - Suited for a wide range of uses, these products are simple to operate and set up. Some initial assembly may be required depending on the type of product. Optical instruments with this rating will have very good optical and mechanical quality. Great for families, young people, and folks who don't want to mess with equipment and complexity. Beginning level telescopes will show you countless lunar craters, Saturn's rings and a myriad of star clusters and nebulae! Referring to the manual is recommended.

Intermediate Level - These products offer higher performance and more advanced features than Level 1: Beginner models. They typically take a bit longer to learn and need some set-up or adjustments. But anyone with the slightest technical bent will have no problem getting familiar with these models. Referring to the manual is recommended.

Advanced Level - These products provide the best performance but may require more skill to master and appreciate. Optical instruments with this rating have exceptionally fine optics and mechanics. Some are easy to use but might be on the large or heavy side. Some are intended for specialized uses. These products will appeal to the more technically inclined. Referring to the manual is highly recommended.

Beginner
Design:

Design

Different eyepiece designs allow for a wide range of features, depending on the needs of the observer. Orthoscopic and Plossl designs can provide a great quality image with a standard field of view, but may be difficult to use at higher powers while wearing glasses due to the short eye-relief. Long eye-relief designs have more elements and can be more expensive, but work very well with glasses, even at higher powers. Wide angle designs provide a larger view of the sky at the same power as a standard eyepiece. More complex designs can combine all these attributes together in a single eyepiece.

Plossl
Eyepiece focal length:

20.0mm
Barrel size:

1.25"
Apparent field of view:

Apparent field of view

The edge-to-edge angular diameter of the image displayed in a binocular as seen by the eyes of the observer. It is an inherent specification for a given binocular design. The "angular diameter" of an object is defined as the angle an object makes (subtends) as seen by an observer.

52.0°
Eye relief:

Eye relief

The distance, measured in millimeters, between the observer's eye and the eyepiece lens in which the entire field of view remains visible. Eye relief varies with the optical design but generally increases with decreasing magnification. Long eye relief is advantageous for observers who wear glasses, as they don't have to put their eye directly on the eyepiece to see the entire field of view, nor do they have to remove their eyewear.

13.0mm
Coatings:

Coatings

Binocular lenses and prisms are often coated with anti-reflective material to minimize light loss as light travels through the multiple optical surfaces of a typical binocular. Coatings help maximize the amount of light transmitted through each glass surface of a binocular, so as much light as possible reaches the observer's eyes to provide a bright and sharp image.
Good lenses are at least "fully coated," with a single layer of magnesium fluoride coating applied to each air-to-glass lens surface. Multiple layers of coatings are even more effective; the term "multi-coated" means one or more air-to-glass lens surface has multiple coatings. "Fully multi-coated" optics are even better, meaning all lens surfaces have multiple layers of anti-reflective coatings applied for maximum light transmission and optimal image quality.

Multi-coated
Number of elements:

4
Filter threads:

Yes
Parfocal:

Parfocal

Parfocal refers to an attribute of an eyepiece set where little to no focusing is required when swapping out one eyepiece for another.

No
Field stop diameter:

Field stop diameter

The field stop is a mechanical ring in the eyepiece which provides the sharp edge to the field of view when looking through the eyepiece. The field stop diameter greatly affects the apparent field of view of the eyepiece; the larger the field stop diameter, the larger the apparent field of view is.

17.1mm
Barrel security recess:

Barrel security recess

The barrel security recess is a shallow groove or depression cut into the 1.25" or 2" barrel of the eyepiece. In the event the thumb screw holding the eyepiece in the focuser becomes slightly loose, the eyepiece will not fall out because the tip of the thumb screw will catch on the lip of the security groove.

No
Blackened lens edges:

Blackened lens edges

Blackened lens edges in eyepieces and refractor lenses prevent unwanted light scatter inside the tube. This results in higher image contrast.

Yes
Rubber eyeguards:

Yes
Body material:

Aluminum
Case:

No
Weight (oz.):

3
Dimensions:

2.2 in. x 1.3 in.
Warranty:

Warranty

This warranty gives you specific legal rights. It is not intended to remove or restrict your other legal rights under applicable local consumer law; your state or national statutory consumer rights governing the sale of consumer goods remain fully applicable.

One Year

User level

Design

Apparent field of view

Eye relief

Coatings

Parfocal

Field stop diameter

Barrel security recess

Blackened lens edges

Warranty