Technical Brief: USCAMEL 10x50 BAK-4 FMC Porro Binoculars

Product Description

• Brand Name: USCAMEL
• Model Number: UW004
• 10x50 Marine Binoculars with internal rangefinder scale and directional compass.
• Nitrogen filled waterproof & anti-fog floating Marine Binoculars.
• Porro optical system with BAK-4 prisms & FMC objective lens.
• Individual Focus Binoculars with fold-down eyecups.

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USCAMEL 10x50 Marine Binoculars.

Function

• Waterproof & anti-fog
• Durable non-slip rubber armored exterior
• Individually adjustable Left + Right Eyepiece Diopter focusing rings
• Rubber fold-down eyecups
• Distance & Object Size measuring dial on left objective lens barrel
• Illumination switch (with battery powered illumination for night viewing)
• Nitrogen filled: Yes
• Tripod adaptable: Yes
• Rangefinder: Yes
• Compass: Yes
• Floating: Yes

Specifications

Binoculars Optical System

Many current binoculars use convex lenses for the objective lenses and eyepiece lenses and a prism to erect the image. There are two types of prisms, Porro prism and Roof prism.

Porro prism binoculars have excellent optical properties and enables a bright, sharp field of view from low to high magnifications. You can tell Porro prism binoculars at a glance because they are offset. The objective lenses are not lined up with the eyepieces. The optical system has 4 times internal reflection (no refraction) through 3 optical faces, with 99.2% light transmission. Porro prism binoculars provide greater depth perception and generally offer a wider field of view.

Roof prisms are designed to be used in a straight line with the eyepiece lens and objective lens so their optical axis are all aligned. This makes it possible to build lightweight, compact binoculars with potentially better magnification in a smaller package. Roof prism binoculars have 5 times internal reflection (partial refraction) through 4 optical faces, with about 90% light transmission.

The USCAMEL 10×50 BAK-4 FMC Porro Binoculars with Porro prism system provides a broader field of view, using high quality BAK-4 porro prism for high-contrast, improved light transmission & image clarity.

Exit Pupil Diameter & Relative Brightness

The exit pupil diameter can be calculated by dividing the effective diameter of objective lens (mm) by the magnification (x). The larger the exit pupil diameter, the brighter the image will appear in the binoculars. As a rule, if the exit pupil diameter of binocular is larger than the pupil diameter of the human eye, then the image in the binoculars will appear bright.

The pupil diameter of the human eye changes significantly due to changes in brightness, and ranges from about 2 - 3mm in bright conditions to about 5 - 7mm in the dark. For this reason, binoculars with exit pupil diameter of about 2 - 3mm or more are good to use in bright locations (Figure 1), whereas 5 - 7mm or more are best for use in dark locations (Figure 2). The USCAMEL 10x50 Marine Binoculars have Exit Pupil specification of 5mm, and will produce a bright image even in low light conditions.

Binoculars Field Of View

Field of view describes the image area visible when looking through the binocular, and is measured in feet at a distance of 1000 yards. The USCAMEL 10x50 Marine Binoculars have a 10x magnification and the field of view is 396 feet at 1000 yards (132m at 1000 meters). When viewing a target at 1000 yards, an area of 396 feet across can be seen. Likewise, when viewing a target at 1000 meters, an area of 132m across can be seen. In angular terms, this corresponds to a View Angle specification of 5.6 degree.

Due to the magnification, distant objects will appear closer compared to actual distance. The apparent field of view is calculated by multiplying the actual field of view by the magnification.

• Apparent Field of View angle, θ2 = 2 x arctan { magnification x tan(θ1 / 2) }

For example, let's say you are looking through the binoculars and see a Tree that is 132m tall (Figure 3). Since our binoculars have a Field of View specification of 132m at 1000m, when looking at the Tree through the binoculars from a distance of 1000m the Tree will cover your entire field of view.

How To Use Rangefinder With Measuring Dial?

The binoculars have a built-in etched reticle in the vertical & horizontal axis of the optical system to allow you to measure angles in the field of view. Once you measured an angle, you can then use the measuring dial on the objective lens barrel to figure out the distance to the object (if you know the size or height of the object you are looking at), or determine the size of the object (if you know the distance).

• Step 1: Align the scale's horizontal reference baseline to the bottom of the object and measure the height density of the object. The scale gives the object size in MILs e.g. 3 as shown in the picture below.
• Step 2: Rotate the measuring dial to align the MIL number to the ANGLE index mark.
• Step 3: Locate the size of the object on the middle scale OBJECT SIZE e.g. 5 if the Tree is 5m tall.
• Step 4: You can now read the distance given by the lower scale DISTANCE i.e. the Tree is about 160 meters away.

How To Use Rangefinder To Calculate Object Size Or Distance?

The binoculars have a built-in etched reticle in the optical system to allow you to measure angles in the field of view. Once you measured an angle, you can then use formulas to calculate the distance to the object (if you know the size or height of the object you are looking at), or calculate the size of the object (if you know the distance). You can use any unit you wish since these equations are a ratio, but you must use the same units for Size & Distance whether in meters, yards, feet etc.

Formulas:

• Distance = 100 x Object Size / Rangefinder Scale Reading
• Object size = Distance x Rangefinder Scale Reading / 100

Examples:

• If you know a building is 70 metres tall and your scale measures the building's angular height density as 4 MILs, so you divide 70m by 4 then multiply by 100. This means the building is 1750m away.
• While at sea, you notice another boat is crossing your course. How far away is it? If you estimate the mast height of that boat to be 50 feet and the vertical scale reads 2.5, you can calculate the distance to be 100 x 50ft / 2.5 = 2000 feet.
• If an object is 500 meters away and the Rangefinder scale reading is 0.6, then Object size = 500m x 0.6 / 100 = 3 meter

How To Read The Directional Compass?

When you look into the eyepiece, you will see a compass window with figures and lines below the field of view. The compass shows orientations as angles: North is 0°, East is 90°, South is 180° and West is 270°. The compass scale is in one degree increments. Between numbers, each line represents 1°. Position the binoculars so that the object is aligned with the rangefinder scale in the center of view, and then read the compass. When using the compass bear in mind the local variation between magnetic North and true North.

The compass has an accuracy of 2 degree and is illuminated by a lighting window. You can use the built-in lighting in the binoculars by pressing the illumination switch at night to read the graduations on both rangefinder & compass in the dark. It uses two LR936/AG9 or equivalent 1.5V button cell batteries. Rotate the battery cover at the front of the binoculars to open it and install the batteries.

How To Use The Compass To Locate Your Position?

You can use these binoculars together with a chart and protractor to locate your position on a map. For example, if you are on a boat sailing within the map’s area, follow the steps below using the compass to determine the location of your boat.

• Step 1: From the boat, use the binoculars to locate the buoy shown on the chart (Figure 1). In this example, the compass would show that the buoy is located 190° from the boat.
• Step 2: Use this information to determine the direction from the buoy to the boat. To do this, subtract 180° if the bearing is 180° or greater, or add 180° if the bearing is less than 180°.
  Thus, Direction from buoy to boat = 190° (direction from boat to buoy) - 180° = 10°.
• Step 3: On the map, draw a line from the buoy extending in a 10° direction (10° from magnetic north). You now know your boat is somewhere along this line (Figure 2).
• Step 4: To determine your boat’s exact position, use the binoculars to locate a second object, the lighthouse. The compass will show that the direction from your boat to the lighthouse is 300°.
• Step 5: Then calculate the Direction from lighthouse to your boat i.e. 300° - 180° = 120°.
• Step 6: Finally, draw a line extending 120° from the lighthouse (Figure 3). Your boat is located at the point where the two lines intersect.

Terminology

• BAK-4 prisms. This is a specification for the prism glass. BAK-4 prism is superior to BK-7 or K9 glass and gives a sharp image that has high contrast. BAK-4 prisms are made of high density barium crown glass with high refractive index & higher levels of image quality.
• Minimum Focus Distance. The minimum focus (or close focus) distance is the shortest distance you have to be away from an object for the binoculars to focus on it. Typically, as magnification is increased, the minimum focus distance also increases. If you need shorter minimum focus distance, look for binoculars with larger objectives lens & lower magnification.
• Diopter adjustment. Found in individual focus binoculars, the diopter adjusters can be used to make small focal adjustments by rotating the eyepiece. This will correct for any differences in your left and right eyes, and thus changes the minimal focal distance.
• Eye relief. This is the distance from the outer surface of the glass to where the final image is projected above the ocular lens or eyepiece. You need to locate your eye at that distance from the eyepiece to obtain the full viewing angle. Eye relief is especially important for those wearing spectacles.
• Exit pupil diameter. Exit pupil is the size of the focused light that hits the eye. It is obtained by dividing the objective lens diameter by the magnification. The larger the exit pupil diameter, the brighter the image in the binoculars will appear. It should equal the typical diameter of the dilated iris of a human eye. A large diameter is important as it helps to pick up an image from a moving deck and for night vision when pupils are fully dilated. You can see the exit pupil by holding the eyepiece about 8 - 10 inches away from your eye and looking into the lens. It appears as small dot of light in the center of the eyepiece.
• Field of view. Field of view describes the image area visible when looking through the binocular, and is measured in feet at a distance of 1000 yards. It is related to the view angle specification which describes the angular view. Wide angle binoculars are ideal for tracking fast-moving action across wide areas such as football fields, racetracks and wilderness terrain.
• Fixed focus or focus-free binoculars. Also called Individual Focus Binoculars, these do not have a central focusing mechanism. Instead, they come with dioptic correction rings on each of the eyepieces to calibrate to your eyesight. This type of binoculars are designed to focus on distant objects with a very long depth of view. Everything from its minimum focusing distance of around 20 meters to infinity will be in focus, which makes them extremely easy to use.
• Interpupillary distance. The interpupilary distance varies between different people depending on how far apart their eyes are. Binoculars with adjustable hinge can rotate the eyepieces to set the barrels of the binoculars to match the distance between your eyes.
• Lens coating. Light lost through reflection at each optical surface would make the image lose contrast, appear hazy, and dim. Lens coating are films applied to lens surfaces and have antireflection properties to increase light transmittance & contrast, and help make colors look more vivid for a brighter & clearer image. Fully-multi-coated (FMC) optics consist of multiple coatings of all lens surfaces.
• Magnification. Magnification produces a larger image in the field of view. With 10x magnification, distant objects will appear closer, as seen from 1/10 actual distance. The larger the magnification, the smaller the field of view.
• Objective lens. These are the front lens of the binoculars facing the object. Larger objectives not only allow more light to pass through them to produce brighter, sharper & clearer images, but also gives a larger field of view.

Links

• [ Product Page ] USCAMEL 10x50 Marine Binoculars
• [ Blog ] Featured Product: USCAMEL 10x50 BAK-4 FMC Porro Binoculars
• [ Video ] How to use Rangefinder With Measuring Dial?
• Binoculars Basic Knowledge