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Sunday 3 July 2011

Glossary of terms for telescopes and binoculars


by NIPON SCOPE & OPTICS


Index

A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T. U. V. W. X. Y. Z.




Altazimuth Mount – This usually refers to telescope mount which allows movement in two directions: azimuth (horizontally) and elevation (vertically).

Aperture - The diameter of the binoculars' or scope’s objective lenses, measured in mm.

Apparent magnitude - This refers to how bright the star appears to the naked eye. The difference between the apparent brightness of two stars follows a logarithmic ratio of 2.512. Therefore, a star that is three magnitudes less than another is (2.512) 3, or about 16 times brighter. Using this system, stars can also have negative magnitude values, and these are the brightest we see in the sky. See also MAGNITUDE.

Aspherical Lens - A lens with flattened edges, useful for a clearer, sharper image.


Bak-4 Glass - Premium, high-density barium crown glass that minimises internal light scattering so the images seen through these lenses are sharper. See also “Prism Glass”.

Barlow Lens – An extra lens used in conjunction with a telescope’s eyepiece to increase the magnification, usually by 2 or 3 times. This is named after the English physicist Peter Barlow. View Barlow lenses in the Nipon Scope & Optics online store.

Binocular tripod adaptor - An L-shaped adapter that connects a binocular to the pan head of a standard tripod.

Bk-7 glass - Also known as "borosilicate" glass. Most optical prisms are made of BK-7 glass.


Cassegrain – A reflecting scope comprising a primary mirror with a central hole through which the light from the primary mirror is reflected to an eyepiece at the focus, the cassegrain focus, beyond the primary mirror. The design is often used in compact and portable telescopes.

Center-Focus binoculars - A mechanism that allows both eyepieces to be adjusted at the same time, useful for rapid focus. Centre focusing is the most common and convenient and generally the most preferred way of focusing. See also Diopter Adjuster and Individual Focus.

Central Focusing Wheel - A wheel mounted in the middle of the binoculars for focus adjustment.

Chromatic Aberration - This is a defect of optical lenses used in binoculars. Different wavelengths (producing different colours) are diffracted, or bent, at different angles and produce coloured halos around images.

Close Focus (Near Focus) – The closest you can be from an object and still get a clear, focused view through the binoculars or the scope. For example, the close focus of Nipon 10x50 binoculars is around 7m; the close focus of NIPON 26-78x78 is about 10m, suitable for birding at close range.

Coated / Multi-Coated Glass - Thin layer(s) of coating applied to the glass surface to help reduce light reflections. This coating reduces the amount of light lost as the light passes through the glass surface.

      Note - Types of optical coating:
  • Coated optics (C) - one or more glass surface is coated. 
  • Fully coated optics (FC) - all glass surfaces that have any vulnerability to air are coated. 
  • Multi-layer coated (MC) - one or more glass surfaces are coated multiple times. 
  • Fully Multi-Coated (FMC) - all glass surfaces susceptible to air are multi-coated. 
  • Broadband Anti-Reflective (AR) Coatings - this is a relatively new optical coating technology to provide anti-reflective properties over much wider spectral range for improved image quality. 
  • PC-3 Phase coating - this chemical coating is applied to the prisms to enhance resolution and contrast. It is found on some roof prism binoculars, but it would not provide an advantage on porro prism models.

Collimation – The process of aligning the optical system of a scope or binocular so that the light is brought to a focus at the correct position.

Compact Binoculars or Scopes – Small binoculars or scopes that can fit in a pocket or handbag and are convenient to carry around. Compact binoculars are roof prism binoculars or reverse-Porro prism binoculars. Compact scopes are those with Maksutov-Cassegrain System, such as the NIPON 26-78x78 scope model.

Compass Binoculars - Binoculars with a compass built in - perfect for finding your way back to the campsite after a long day of bird-watching or hunting.

Contrast – Good image contrast is desirable for viewing low contrast objects such as the targets in low lighting condition or the lunar surface and planets.

Crosshairs - Also known as reticle, it is a system of cross wires, dots, or rings in the focus of a finder scope or eyepiece for target centring purposes.


Declination – A system for measuring the altitude of a celestial object, expressed as degrees north, or south, of the celestial equator. Angles are positive if a point is North of the celestial equator, and negative if South. It is used, in conjunction with Right Ascension, to locate celestial objects.

Depth of Field – This refers to the distance from “near” to “far” that is in focus at a certain setting of the focus or at a certain distance. In a given system, as the magnification increases, depth of field decreases. Depth of field also changes with the distance observed, usually reducing in depth as the distance decreases.

Dew shield - A covering of ABS plastic wrapped snuggly around the tube assembly and extending beyond the aperture of a telescope to prevent dew from forming on the objective lens of a refractor or correcting plate of a Schmidt-Cassegrain or Maksutov telescope.

Diagonal, correct-image - A 45° or 90° diagonal used primarily for terrestrial viewing because it renders images as the unaided eye sees them — upright and left-to-right. Some resolution is lost when using a correct-image diagonal, so it is generally not recommended for astronomical viewing.

Diagonal, mirror - An accessory that fits into a telescope's focuser and diverts incoming light at a right angle. This is for viewing at a more comfortable angle when using a refractor or catadioptric telescope. Mirrors are used to redirect the light within the diagonal.

Diagonal, prism - An accessory that fits into a telescope's focuser and diverts incoming light at a right angle. This is for viewing at a more comfortable angle when using a refractor or catadioptric telescope. Prisms are used to redirect the light within the diagonal.

Digital Camera Binoculars - Binoculars with a digital camera built in - useful for taking clear, magnified pictures.

Digital Eyepiece – A digital eyepiece can be attached to a scope using a specially made eyepiece adapter to take pictures and even video footage through the scope. One example is digital eyepiece EE300.


Diopter Adjuster - A separate eyepiece-focusing tool, usually on the right lens, that allows the user to adjust the lenses separately to allow for eyesight differences.

Dispersion - The breaking of white light into its component colours when it passes through one medium, like air, into another medium, such as glass. Dispersion is what causes chromatic aberration in lenses.


ED glass - Short for "Extra-low dispersion", an optical glass that has superior refractive properties compared to standard optical glass. Lenses made with ED glass typically exhibit less chromatic aberration than lenses made with standard glass.

Erector Lens – Certain combinations of objective and ocular lenses yield an inverted image. An erector lens incorporated into the system serves to reorient the image right side up. In binoculars and scopes, prisms are often used to ‘erect’ the image.

Exit pupil - The amount of light rays that enter the objective lens and exit the ocular lens (eyepiece) to form a magnified, circular image. The measurement is achieved by dividing the lens aperture by the magnification. For example: In the NIPON 10x50 binoculars, the exit pupil is 50mm/10=5mm. A higher exit pupil means the binoculars will work efficiently in dim light. For well-lit surroundings, an exit pupil of 2.5 to 4 is sufficient. If you hold a pair of binoculars away from your eyes and look through the eyepiece, you'll be able to see the clear circular exit pupil.

Eyepiece – Sometimes known as an ocular. This is a system of lenses closest to the eye. Its purpose is to magnify the image at the focus of the scope. The magnification of an eyepiece can be obtained by dividing its focal length into that of the scope.
      Note: There are various types of eyepiece designs, such as Kellner, Orthoscopic, Erfle, and PLÖSSL. Amongst them, PLÖSSL eyepieces are considered to be a good compromise and offer the best all-around price and performance. According to the scope manufacturer, a set of these PLÖSSL eyepieces with 16mm, 26mm and 32mm focal length would serve a wide range of observation purposes.

Eyepiece Sizes – There are three sizes of scope eyepieces, i.e., 0.965”, 1.25” and 2”. The sizes are determined by the diameter of the eyepiece barrel that fits into the telescope. 1.25” is regarded as a standard eyepiece size and almost all telescopes are designed to be used with 1.25” diameter eyepieces.

Eyepiece Adapter (Adaptor) – Eyepiece adapters are used to adapt from one eyepiece size/format to another. This device will make it possible for the same scope to use different types of eyepieces. For example, with a specially designed eyepiece adapter, both the Nipon 20-60x70 spotting scope and Nipon 26-78x78 scope can be fitted with a digital eyepiece or other standard 1.25” eyepieces (eg. the PLÖSSL eyepiece set) for a wider range of applications.

Eyepiece, Zoom - Provides a continuous magnification range and hence the option of using a single eyepiece versus switching from one to another. The less expensive zooms sometimes suffer from internal reflections, unless they've been properly coated and their internal barrels blackened or glare-threaded.

Eye Relief – The distance images are projected from the ocular lens to their focal point, measured in mm. This is the distance a binocular or scope can be held away from the eye and still present the full filed of view. The eye relief of a binocular can vary from 5mm to as much as 23mm. A typical range of eye relief is 8-13 mm which is considered to be appropriate to enable eyeglass wearers to see the whole field of view.

Eyecups (or eyeguard) - Cups on the eyepieces of binoculars that allow for positioning of the eyes and provide optimal eye relief. It improves viewing comfort and helps block extraneous spripheral light. Some eyecups come in a rubber version that the user can fold down to accommodate eyeglasses. Other binoculars use cups such as 'twist-up' or 'pop-and-lock' that are more adjustable for any user.


Field Glass - A type of binocular that uses a second lens (instead of a set of prisms) to magnify an object. Field glasses are more durable than prism binoculars, although the magnification strength tops out at about 5x.

Field of View (FOV) - The size of the image you can see while looking through binoculars or a scope. It is defined by the width in feet or metres of the area visible at 1000 yards or metres. It can also be defined as an angle in degrees (1 degree of field=52.5 ft/1000 yards).
      Note: A wide FOV is better for following fast-moving target or scanning for wildlife. In general, the higher the magnification, the narrower the field of view.

Filter, colour - Glass filters, each of a specific colour, which screw onto eyepiece barrels for enhancing lunar and planetary detail. Various colour filters reduce other interfering or scattered wavelengths that blur certain wavelength-specific features. Red filters, for example, bring out Martian surface detail while green increases contrast of Jupiter's Red Spot. Also called planetary filters.

Filter, light-pollution - A filter that threads on to an eyepiece or rear cell of a Schmidt-Cassegrain that blocks wavelengths of light pollution sources such as mercury vapour and high-pressure sodium, but pass wavebands specific to deep-sky objects, such as hydrogen alpha, hydrogen beta, and oxygen III.

Filter, moon - A glass filter in an aluminium cell that threads onto an eyepiece barrel and reduces the Moon's glare so that it can be comfortably observed. Without the eye being overwhelmed by moonlight, more lunar detail becomes apparent.

Filter, planetary - Glass filters, each of a specific colour, which screw onto eyepiece barrels for enhancing lunar and planetary detail. Various colour filters reduce other interfering or scattered wavelengths that blur certain wavelength-specific features. Red filters, for example, bring out Martian surface detail while green increases contrast of Jupiter's Red Spot. Also called colour filters.

Filter, solar - A glass filter that fits snugly over the aperture of a telescope and allows the photospheric surface of the sun — sunspots and solar faculae — to be observed comfortably and safely. A good solar filter blocks some 99.99% of the sun. Observing the sun without a solar filter may cause serious damage to the eye.

Filter, Variable-polarizing - Variable-polarizing filters act as dimmer switches to bright celestial objects, including the Moon or a planet. The filter, which threads on to 1.25" eyepiece barrels, consists of two pieces of polarized glass mounted in an aluminium cell that, depending on how much it is rotated, varies light transmission from 1% to 40%.

Finder (or Finder Scope/Finderscope) – A small telescope, with a wide field of view, mounted on the main telescope tube to enable an observer to easily locate celestial objects, and place them within the field of view of the main telescope.
      Note: In the ‘red dot finder scope’, you see a LED red dot in the centre of the finder’s visual field, which helps to locate the target.

Focal Length – The distance between the objective lens (or primary mirror) and its focus (or focal plane).

Focal Plane – The plane where the image formed by the lens or lens system is in sharp focus. In a camera, the focal plane is the sensitised surface of the film.

Focal Point - This is a point where the light rays from an image come sharply into view after passing through the binocular or scope.

Focal Ratio (f-ratio) – Defined as f value. This is the focal length of a lens (or mirror) divided by its diameter. A focal ratio of 8 is written as f/8.

Focusing Range – All binoculars or scopes have the ability to be focused for infinity. So a primary point of distinction between product models is the minimum focus range (see “Close Focus”).

Focusser – The mechanism which holds the eyepiece and allows adjustment for focussing the image.

Folded Light Path - A combination optical configuration using lenses and mirrors to create a total scope length much shorter than the total focal length of the system. This provides a compact design yielding long focal length performance.

Full Size Binoculars – In comparison with compact binoculars, full size binoculars offer better light gathering ability because of a relatively larger objective lens. For example, a 10x42 binocular is a full-sized binocular, while a 10x25 binocular is considered as a compact binocular.

Fully Multi-Coated Optics – Binoculars or scopes that have fully multi-coated optics have multiple coatings on all air-to-glass surfaces. See also “Coated/Multi-Coated Glass”.


Haze – Light scattered by particulate matter in the atmosphere, such as dust or moisture droplets. Haze lens a foggy or cloudy appearance to distant objects or scenes, subduing colours and contrast.
     Note: Haze effects are more apparent when using high magnification optical instruments than when viewing with lower-power optics, and are more pronounced at long range than short range under a given set of atmospheric conditions.


Image-Stabilized - Binoculars with a self-steadying feature, designed to counteract any hand-shaking of the user.


Individual Focus - Unlike centre-focus binoculars which adjust both eyepieces at the same time, individual-focus binoculars focus each eyepiece separately. This allows for extra-precise focus adjustment for each eye.

Infrared (IR) Illuminator – This provides a light source for the optical system to amplify, yielding enhanced images in very low light conditions (such as with night vision systems) where no ambient light is available for amplification.

Inter-Pupillary Distance (IPD) - IPD is the distance (in mm) between the centers of the pupils in each eye. This measurement is sometimes provided in binoculars descriptions to define a range of user populations the binoculars can fit. For British adults (5th-95th percentile, 18-64 years old), the IPD measurement is in a 54mm-68mm range , with an average value of 61mm.


Light-Gathering Power - The light-gathering power of a binocular or scope is determined by the surface area of its objective lens.

Light Transmission - The ratio of the total amount of light passing through the objective lens to the eye. Better coatings on the optics increase the amount of light that reaches the eye.

Light-Gathering Power - The ability of the binoculars to collect light. This measurement is directly proportional to the size of the objective lens of the binoculars.

Limiting Magnitude – The faintest object that can just be detected by a telescope.


Magnification (Power) - The power of the binoculars or scopes. It tells you how many times bigger an image can be seen through the scope (or how many times the target can be ‘brought’ closer) than you would see it with the unaided eye.
      Note: the stronger the magnification, the smaller the field of view.

Magnitude, Absolute - A measure of a star's true or intrinsic brightness. Essentially, astronomers decide this by gauging how bright the star would appear to the eye if brought to a standard distance of 10 parsecs, or 32.6 light-years. Alnitak, the easternmost star in Orion's belt, has an apparent magnitude of 2.05 but an absolute magnitude of -5.9, because that's how bright it would appear if it lay 10 parsecs away. The Sun, with an apparent magnitude of -26.7 has an absolute magnitude of 4.8.

Maksutov (MAK) - A catadioptric reflecting telescope similar to a Schmidt, except that it employs a deeply curved full-aperture lens called a meniscus to correct for spherical aberration. Maksutovs utilize spherical mirrors and can be designed with a Cassegrain configuration, in which they are called Maksutov-Cassegrains, or as Newtonians, in which they are called Makstutov-Newtonians (or MAK-Newts, for short).

Mirage – Optical phenomenon that occurs when air near the ground is significantly denser than the air above, creating visible reflected images of distant objects or targets.

Monocular - A single "pocket-sized" telescope used as a handy spotting scope.


Near Focus – See “Close Focus”.

Nitrogen-Purged (or nitrogen filled) - The atmospheric air inside the binocular or scope tubes is replaced with nitrogen, which prevents mildew, mold or acid inside the tubes. Nitrogen-Purged binoculars are commonly known as water & fog-proof, as with the Nipon 10x42 binoculars.
      Note: In rare situations such as extreme humidity and elevation changes, some internal fogging may occur, though the fogging usually clears on its own after a few minutes.


Objective Lens - The large lens at the end of the binocular or scope away from the eyepiece. This lens gathers light into the eye. The larger the objective lens, the more light that enters the scope and the brighter the image.

Ocular Lens - An alternate term for eyepiece.

Optical tube assembly (OTA) - The main tube of a telescope including the primary mirror or objective lens, focuser, and finder scope. The optical tube assembly does not include a mount or tripod.

O-Ring Sealed - A special sealant on binoculars that makes them waterproof.


Parallax – Apparent shift in position of a viewed object attributable to the difference between two separate and distinct points of view. In a scope sight, parallax can cause an aiming error, or parallax error, when the target image is not formed in the same plane as the reticle.

Phase Correction - A coating applied to the prisms of roof prism binoculars to prevent the light beam from splitting into two out-of-phase beams of light. This enhances colour fidelity and reduces image contrast and gives a clearer view.

Porro Prism – The objective or front lens is offset from the eyepiece (as opposed to the aligned roof prisms). Porro prisms have objective lenses spaced wider than roof prisms, and can provide greater depth perception and generally offer a wider field of view. Good examples are Nipon 7x50 and Nipon 10x50 binoculars.

Power - This refers to a telescope's magnification (i.e., 80x can be referred to as 80 "power").

Primary Mirror – The principal light gathering mirror in a reflecting telescope.

Prism Glass
- A solid glass figure cut with flat surfaces. Most optical prisms are made from borosilicate (BK-7) glass or barium crown (BaK-4) glass. BaK-4 is a higher quality glass yielding brighter images and high edge-to-edge sharpness.

Prism Systems - The prism system turns what would otherwise be an upside-down image right-side-up.

Prismatic Binoculars - Binoculars that use internal prisms instead of a second lens to magnify an object. These binoculars aren't ideal for heavy-duty use, as the prisms can be broken or knocked out of alignment due to rough handling. However, the magnification strength of prismatic binoculars is much better than that of traditional field glasses.


Rack-and-Pinion Focuser - A device into which an eyepiece is inserted and adjusted to bring a telescopic image to focus. A focuser can be as simple as a manual drawtube, but the more efficient type is the "rack-and-pinion" design, whereby a threaded axle affixed with knurled knobs at each end meshes with a threaded drawtube, enabling it to be moved up or down through the focal plane.

Rangefinder Binoculars - Binoculars with a rangefinder built right in. It is a tool used to calculate the exact distance between you and the object in focus.

Reflector – A telescope in which the main light gathering element is a mirror.

Refractor – A telescope in which the main light gathering element is a lens, known as the objective lens.

Relative Brightness – This is a term to quantify the “brightness” of scope sights and binoculars to facilitate comparison. The relative brightness number is the square of the diameter of the scope’s exit pupil, expressed in mm.

Resolution (Resolving Power) – Resolution or definition is the ability of a binocular or spotting scope to distinguish fine detail and retain clarity.

Reticle – In a rifle or handgun scope, the reticle is an aiming reference consisting of crosswires, dot, pointed post or other distinct shape that appears superimposed on the field of view. The reticle is positioned within the optical system to coincide with the plane of focus of the objective lens.

Rich-Field telescope - A short focal-length telescope designed for sweeping very large regions of sky such as star fields (hence the name "rich"). Also known as wide-field telescopes.

Roof Prism – The prisms overlap closely, allowing the objective lenses to line up directly with the eyepiece (as opposed to the off-set porro prisms). This result in a slim, streamlined shape of binocular or scope. The top models of the roof-prism and porro-prism binoculars are now generally considered to have equal optical quality.

Ruby Coatings - The objective lenses of a binocular with ruby coatings will be a bright reddish-orange. Since red light is reflected the colours seen through binoculars with ruby coatings are skewed to the cool end of the spectrum.
      Note: Another result of using ruby coatings is a shortened colour spectrum which may increase the contrast and resolution of a binocular.


Schmidt – A wide field reflecting telescope which uses a special mirror and correcting plate instead of a parabolic mirror. Mainly used for photographic sky surveys.

Spotting scope - A small, portable telescope used primarily for terrestrial observing, such as nature study and bird watching. Most spotting scopes use prisms to provide an image that matches the naked eye.

Spyglass – This is another term for handheld telescope.


T-Adapter - A camera adapter that attaches to the body of a 35mm camera (without the lens) and then connects to the focuser for prime-focus astrophotography.

T-Ring - Converts the lens mount on a camera body to a standard "T-thread" that can accept a T-adapter or universal camera adapter for either prime focus or eyepiece projection photography.

Terrestrial - Refers to bird watching, landscape or seascape daytime observing with a telescope, binoculars, or spotting scopes. A terrestrial scope is used during the day or in low light to observe terrestrial fields of view. Applicable to birding, sightseeing, and nature study.

Transmittance – As light travels through binoculars or scopes, a certain percentage of that light is lost through absorption and reflection at each air-to-glass surface or inside the prism system itself. The term used to describe this percentage of light that is not lost through the optical system is transmittance. See also “Light Transmission”.

Tripod - A three-legged stand with a swivel or pan head upon which a camera, spotting scope, or binocular can be attached. (Also see 'binocular tripod adaptor')

Twilight Factor – Most often associated with binoculars, this is a numerical expression of the telescope effect in dim light. It may also be calculated for scope sights.
      Note: The twilight factor is derived by multiplying the magnification by the useful objective diameter (mm), and then extracting the square root. This factor assumes realistically that in dim light, all other factors being equal, viewing instruments with higher magnification and larger objective lenses will outperform those with lower power and lesser light gathering capability.


UD Lens (Ultra Low Dispersion lens) - A lens made of special optical glass possessing optical characteristics similar to fluorite. UD lens elements are especially effective in correcting chromatic aberrations in super-telephoto lenses.

Universal Digital Camera Adaptor - It holds your digital camera next to your telescope's eyepiece so that you can take pictures of an object through the scope. The adaptor can be adjusted in 3 directions for different camera sizes and for camera lens positioning. See some typical universal camera adaptors.


Variable Power (Zoom Lens) – Variable-power scopes or binoculars have a control that allows the user to adjust the magnification over a predetermined range.


Waterproof / Fogproof – The binoculars or scopes that are sealed with O-rings and nitrogen-purged for waterproof and fogproof protection. These products are able to withstand complete immersion and remain dry inside.

Wedge – A device used to attach a fork mounted telescope to a tripod.

Wide-Angle Binoculars - Binoculars with a wider field of view (generally described as greater than 6.5 degrees). For example, NIPON 7x50 binoculars have a wide field of view at 7.5 degrees (130m/1000m), convenient for target search.


Zoom Lens – See “Variable Power”.

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Prepared by NIPON SCOPE & OPTICS

www.nipon-scope.com


Please send your comments or suggestions to: support@nipon-scope.com

Thank you!

Recent user feedback about using the Nipon 350x70 Refractor scope for Archery, with an additional 40mm eyepiece

I have tried the Nipon 350x70 Refractor scope out today and it is really fantastic, I can even read at over 200 feet the small letters on the target through the 40mm eyepiece even without the added Barlow, so I am very well pleased and would recommend this scope to any archer. (Message from John to Nipon Scope & Optics on 23/6/2011).

Friday 29 April 2011

I shoot old military guns at distances up to 1000 metres and need to see the bullet holes in the paper targets. Will the Nipon 350x70 scope allow me to do this nice and clearly?

To answer this question, we need to establish the level of magnification that is required in order to see a small target such as a bullet hole over that distance.

Someone with ‘normal’ 20/20 or 6/6 vision (visual acuity) is just able to decipher a letter (eg. E) that subtends a visual angle of 5 minutes of arc (5') at the eye. What this means is that if you draw a line from the top of a 20/20 letter (E) to the eye and another line from the bottom of the letter to the eye, the size of the angle at the intersection of these two lines at the eye is 5' of arc. It does not matter how far away something is from the eye, as long as it subtends an angle of 5' of arc at the eye, then a person with 20/20 visual acuity will just be able to distinguish what it is.

For shooting range up to 1000 metres, the bullet diameter is assumed to be about 0.45” or 11.43mm. If we know how far an individual with 20/20 vision can see an 11.43mm bullet hole with naked eye, we can then work out how many times the same target should be brought closer from 1000 metres (i.e., times of magnification).

Here is a calculation on how far one can see this 11.43mm target, where:

  • The bullet hole’s visual angle subtended at the eye is 5' of arc (5 minutes of arc), one-half of which is 2.5' of arc (this is to form a right angle by the line of sight and the plane of the target);

  • "d" is the distance along the line of sight, from the eye to the target, and

  • "h" is one-half the height of the 20/20 letter in mm.




  • Visual acuity angle calculation


    The simple trigonometry is calculated as:

    (1). 2.5’ of arc / 60=0.04167 degrees
    (2). Tangent 0.04167 degrees=h/d=5.72mm/d (note: 11.43/2=5.72)
    (3). d=5.72mm/0.00072=7944mm=7.944m

    This means that an individual with normal vision will be able to read a letter with 11.43mm height (i.e., to identify the direction of letter E) at about 8 metres. In fact, to see a round bullet hole is much easier than reading a letter. A field test has indicated that an 11mm white dot on black background (or black on white) can be seen by people with normal vision at 10m or slightly further. In other words, if the same target is placed 1000m away, it needs to be magnified (or 'brought closer') 1000/10=100 times.

    For the Nipon 350x70 scope, with the K9mm eyepiece and 3x Barlow lens included, it can achieve a 120x magnification which is within the power required for this purpose.

    If a target is located at 150 yards (140m), with a 0.22” (5.69mm) bullet, the required scope magnification can be calculated as: 140÷(5.69÷2÷0.00072÷1000)=35x

    It needs to be understood that magnification is only one basic aspect which needs to be considered in this example. There are other factors that also play important role in target observation, such as the size of the objective lens and optical coatings of the scope, which affect image clarity.

    Wednesday 12 January 2011

    UK Scopes and Binoculars Blog: How to connect a digital SLR (DSLR) camera to telescope for digiscoping?

    UK Scopes and Binoculars Blog: How to connect a digital SLR (DSLR) camera to telescope for digiscoping?

    Why do I only see a white image when I try to take pictures of the Moon using my Nipon digital eyepiece/camera?

    The Nipon digital eyepiece can be used to take pictures of distant objects through a telescope. You can see on the PC screen what you would see through the telescope's eyepiece and take that picture (or video footage) through your computer. However, if you point your telescope to the Moon, you may only see a spot of bright light on your computer screen, rather than the details of the Moon surface. This is because that the brightness of the Moon has exceeded the exposure limit of the camera's hardware chip. You may get a similar result when trying to take pictures of the moon using some other types of digital cameras.

    A solution for this: add a Moon Filter to the eyepiece holder of your telescope, before putting the digital eyepiece into the holder. You will get a better image of the moon. This should also help your astronomical observation and digiscoping on stars in the night sky.

    User experience with the Nipon digital eyepiece/camera (Model EE300) for digiscoping under Windows Vista system

    A customer has recently provided some feedback about his experience in using the Nipon digital eyepiece on his laptop computer which runs the windows vista system. This information should be useful for others who are interesting in digiscoping.

    When the digital eyepiece is connected to your PC through a USB slot, the computer should be able to automatically recognise this device and install the software driver. There is no need to install anything from the software CD which comes with the digital device. You should then be able to see a camera icon in "My Computer" programme. This is true when your PC runs Win 2000, Win XP or Win 7. However, in Windows vista, the camera icon becomes invisible. In fact, it has been reported that Win vista does not show other types of digital cameras in the "My Computer" programme. This is one of the problems with win vista.

    A solution for this is to install the software programme which comes with the digital eyepiece and to take digital pictures or video recordings from your PC using that software programme. This should achieve the same function as you would otherwise be able to do using a simpler "My computer" programme under win xp or win 7.

    How to connect a digital SLR (DSLR) camera to telescope for digiscoping?

    Digiscoping is becoming increasingly popular nowadays as people try to combine the function of powerful telescopes with advanced digital photographic technology. We have been frequently asked on how to connect a certain type of digital SLR cameras to a particular telescope model. This technical note is prepared to address some of the common aspects regarding digiscoping using DSLR cameras.

    There are basically two methods to connect a DSLR camera to a telescope. The first method is to attach the SLR body without the camera lens directly to the scope using a DSLR camera adaptor. In this way the scope can effectively become a telephoto lens of the camera. Traditionally, this is achieved by using two separate components, a T-adaptor and a T-ring (also known as T2 mount). The T-ring is connected to the DSLR camera in place of the camera lens, and the camera is then connected to the scope’s eyepiece holder through the T-adaptor. There are different types of T-rings for different types of DSLR cameras, but the T-adaptor is designed to fit a range of T-rings. For those who are new to digiscoping, there can be confusions as to what type of T-rings should be purchased to fit a DSLR camera, and what T-adaptor can then fit the T-ring and the telescope.

    More recently, a new type of
    DSLR camera adaptors
    has become available, which combines the T-ring and T-adaptor into one component. Such an adaptor is available for those widely used camera brands such as Canon and Nikon. A major advantage of these new adaptors is that they can fit a wider range of products (eg. the Canon adaptor can fit almost all Canon SLR cameras with up to 135mm lens and almost all types of telescopes with a standard 1.25” eyepiece holder), and you only need one of them for digiscoping.

    The second method of connecting a digital camera to scopes is to use a
    universal camera adaptor.
    These adaptors enable you to attach a digital camera (including both SLR and non-SLR cameras) to a scope’s eyepiece. You do not need to remove the camera’s lens in this case, but the image quality is often not as good as using the first method.

    Monday 3 January 2011

    What are advantages and disadvantages of using a Barlow lens?

    Some major advantages:


  • Achieve higher magnifications.




  • Provide flexibility of magnification levels with your existing eyepieces. For example, if you have 2 Plössl eyepieces with 16mm and 26mm focal length and use them on a telescope with 800mm focal length, you have a 800/16=50x and 800/26=31x magnification levels respectively. With a 2x Barlow lens, you will get 100x and 62x magnifications as well.




  • Increase eye relief (distance of exit pupil from eye lens). Many eyepieces have an eye relief which is directly related to its focal length. For example, the eye relief of a Plössl is 0.73 x its focal length. Therefore, for these eyepieces, there will be a greater eye relief with a Barlow than without one.



  • Disadvantage: a major disadvantage of adding a Barlow is a slightly decreased brightness in the produced image.

    What is a Barlow Lens?

    A Barlow Lens can multiply the power of the eyepiece by a specified magnification factor. For example a 2x Barlow lens will double the magnification and a 3x Barlow will increase the magnification by 3 times. A Barlow lens is placed between the objective lens and the eyepiece.

    The magnification/amplification factor of a Barlow is a function of its position in relation to the eyepiece and the objective lens. This factor can be increased by increasing its separation from the eyepiece using an extension tube. There are compact shorter tube Barlow lenses and longer tube Barlow lenses, both can achieve the marked magnification results.