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About Magnifiers

Why do we need Magnifiers ?

Human eyes only have the ability to properly focus to approximately 6-8"(focal length)  in front of them, as you closer then that the image gets distorted and blurred. If eye could focus closer magnifiers and loupes would not be needed. A Magnifier and Loupe assist in allowing your eyes to focus at a closer focal length at a distance beyond human eye capability. 

 

 Who invented the the first Magnifier ? What year was it ? 

Its generally accepted that the first Magnifier or Magnifying Glass was invented by English Philosopher Roger Bacon in year 1250 while he was at University of Oxford. It is also documented that thousands of years ago that Egyptians used chips of crystal to better view small objects.

 

Is it true that magnifier can be used as a survival  tool to ignite a fire ?

Yes a magnifier can been used to start a ignite a piece of paper, this done through refraction and  by concentrating the sun's rays into a tiny point. This occurs when the lens is held at exactly two focal lengths from the surface. (This should only be done with adult supervision and at your own risk.)

 

Have Magnifier lenses changed much over the years ? 

Simple lens designs haven't changed drastically in hundreds of years.  What has evolved over time is the evolution of single magnifier lenses into compound lens structures such as the doublets,triplets, galilean, and the compound microscope.
  

Why does my view sometimes flip when I use a Magnifier ? 

That can occur when you move the lens to twice the designed focal length of lens.


What is Magnification ? 

Magnification or Magnifying is the process in which something is optically enlarged in appearance and not actuality, and this is typically using a double-convex lens , spherical lens, or compound  lens and prism lens structure. The double-convex lens shape creates a magnified "virtual image" of the surface being viewed through the lens. The Lens focuses and disperses the light by means of refraction, the lens focuses the light to form a magnified image.

 

Do you make Magnifiers for both the consumer and industrial markets.

Magnifiers and loupes can be very use and application and industry specific and there are many designs that go well beyond general vision enhancement and are used for critical measurements and high power inspection. We have a large selection of both special use and general use magnifiers and vision tools. Contact us if you do not see what your needs require.

 

What is Depth of Field (DOF) ? 

Depth of field is the distance or depth of area in which the lens allows for the object and area  being viewed to stay in focus. As you move a lens in and out you will see the depth of field as the image goes from being sharp and in  focus to being out of focus and distorted. Generally speaking as the lens power increases the depth of field decreases and the lens must be held at a very steady and very specific distance as magnification increases. Most general use Magnifiers are 1.5x to 3.5x and as magnification goes up lens size goes down, this is essentially without exception and due to physics. 

 

What is lens distortion?   Flatness of Field ?

Distortion is an optical error or (irregularity) that occurs due to the convex nature of the lens, the convex shape of the lens results in a slight difference in magnification at different points within the image,due to that fact that your viewing through the lens itself.  Distortion generally increases as you move out from the center of the lens, it however usually isn't noticed until the very edge of the lens. Distortion is also what is commonly describe as the out of focus area towards the edge of the view image. This again is caused by the curved shape of a lens, and this problem is magnified as magnification goes up because , more magnification = more lens curvature. The viewed area which is in focus and undistorted is referred to as the "Flat Field", a multiple lens structure helps flatten the field and reduce this distortion. 

 

What does the term focal length mean?

Focal length is defined as the measured distance between the object being viewed and the lens surface, when the image viewed through the lens is clear, crisp and in sharp focus. The focal length of a lens is determined by the amount of curve on the lens "face" or surface. 

 

What does the term Field of View mean?

Field of view is described as the area that is viewed or seen clearly through the magnifying lens when it is at its focal length. As the lens magnification increases, lens diameter and thus the field of view decrease. This is a rule that is restricted by physics, again as magnification increases, lens size and field of view decreases. At (5x) magnification power the typical field of view is roughly 1.5 inches. At (10x) power it is about .6 inches. As you can see there is an inverse relationship between lens power and lens field of view. We recommended to use lower power lens for scanning or reading large surface areas and a high power lens for inspection and detailed scanning and inspecting very small areas.

 

What is  Eye Relief  ?  

This is the maximum distance between your eye and the magnifier lens that still allows you to see a full field of view through the lens. Generally speaking as lens size gets smaller eye relief goes down, which means as as lens size gets smaller and magnification goes up it requires you to get your eyes closer lens in order to have a full view through the lens.

 

Does lens size matter ? Why am I not finding large lenses with high magnification power available ? 

There is an inverse relationship between lens size and magnification that is due to physics, and there is no way to design around that fact.  The larger the lens the lower the magnification and the smaller the lens generally the higher the magnification. It all has to do with the convex nature of the lens shape. As magnification increases and the lens becomes more convex the field of view decreases.

 

Should I put my eye close to the Magnifier lens ? 

The Closer your eye is the lens and the more center focused your eye is on the lens, the wider the field of view you will see, this will also decrease eye strain and frustration, and will increase your reading speed, comprehension, and make it a more enjoyable experience. 

 

 

What  magnification is recommended for general reading ? 

Magnification needs will vary person to person depending on vision ability, however generally speaking a good magnification for reading or general use is 1.5x-4x magnification. This magnification is easy to use and provides for a field of view that allows mutiple words to be viewed at one time for easy reading. 

 

What Magnification is recommended for Coin collecting ? 

For inspection such as coin or stamp collecting and general grading a magnification power of at least 5x-8x is recommended. If your doing detailed coin grading you will want a magnification of 10x-30x. 

 

What is lens Diopter or Dioptre ? How can I convert Diopter to Magnification ? 

Diopter is a measuring unit for measuring the optical power and the curved nature of
convex lens.

 Magnification Power equals =(Diopter/4) + 1

 

Diopter        Magnification  1x=Zero Magnification/Actual Size

 

3                         1.75x

5                         2.25x

7                         2.75x

9                         3.25x

10                       3.5x 

13                       4.25x

14                       4.5x

18                       5.5x 

20                       6x

24                       7x

32                       9x

36                      10x

48                      13x

 

 

What is working distance ? Why is it important ? 

Working distance is the distance between the lens and the object when the view is in focus. Working distance is most often requested for headband magnifiers or magnifiers or loupes worn on the head by people that use them for long periods of time or for their occupation. The working distance dictates the distance you must maintain between the lens and the object your viewing in order to see it in focus. 

 

Below are examples of the relationship between magnification and working distance

 

Magnification             Working Distance

 

1.75x                                    13inches 

2.75x                                      5.5inches 

3.5x                                        4inches 

4.25x                                      3inches 
6x                                           2inches 


Why are most quality Magnifiers made with optical Acrylic instead of conventional glass lens ?

The most common reasons for using acrylic instead of glass are, clarity, lighter weight and durability. Acrylics are highly resistant to warping, shattering, cracking, salts,pollutants, non-oxidizing acids, and most light home and industrial solutions that are not damaging to the skin. grade acrylic also has exceptional color clarity, high impact resistance, and is resistant to the damage of UV rays, these benefits have over time made optical acrylic the standard in the industry. 

 

What is an aspheric lens ? is it better than a conventional lens ?

An Aspheric lens is specially designed with non-spherical surfaces, corrected to minimize the spherical irregularities of a convex lens, the aspherical design allows for less distortion, improved edge to edge focusing and improved collimating accuracy. 

 

What is the difference between a conventional lighted magnifier and an LED magnifier ? 

A lighted magnifier typically has one of two types of magnification, an conventional bulb or an LED (light-emitting diode). A led bulb is typically more expensive and has a very long bulb life as well as produces much less heat then a conventional bulb. Because it produces less heat, the bulb is more efficient as it uses its energy for light production and less energy is wasted in heat production. LED's typically have a whiter or more blue colored light then a conventional bulb, a conventional bulb light is typically view as a "warmer" colored light. An LED is generally more durable and can stand up to shock because there is not a fragile filament. 

 

A Small lens magnifier or a large lens magnifier ?

There is a trade off, there is an inverse relationship between lens size and lens power. As the lens power increases lens size decreases. A large lens is much easier and forgiving to use, a small high powered lens has to be used very carefully and held at a very specific focal length to maintain focus. If you are unable to hold a magnifier very still and steady you should not purchase a high powered Magnifier. 

 

Why do some magnifiers and loupes have multiple lenses/elements ? 

Most low power/diopter magnifiers have a single lens structure which works well with lower power. Higher power magnifiers and loupes benefit by having multiple lenses with allow for improved edge clarity, resolution,  it also helps with Chromatic Aberration which helps to more closely converge light colors to focus at the same convergence point. Multiple lenses also help flatten the field of view by helping to compensate for the natural distortion that occurs as you move outward from center on a lens due the physics of a curved lens shape. 

 

What is Color Distortion ? Achromatic lens ? 

Color distortion is a caused by different wavelengths (colored light) converging (focusing) at slightly different points which will cause for inaccurate viewed colors. This is correct by using a achromatic lens, which is simply two lenses (one positive lens and one negative lens) fused together , this creates a lens that transmits and focuses the different colored light waves to focus at the same point. 

 

What is a fresnel lens, how is the image quality ? 

A fresnel lens is a flat plastic lens approximately 1mm thick. The Fresnel lens has concentric ring shaped lenses/prisms that does not have a curved surface of a conventional lens. These series of concentric grooves are molded or etched into the surface of a thin, lightweight plastic sheet, making the lens very thin, almost sheet like. This design creates prisms that magnify and was often used in lighthouse lenses to magnify and focus the light. The tiny grooves are optical prisms that act ot magnify the image. The etch grooves act as tiny light/image prisms that magnify the image and the incoming light. These groves create an image quality is not anywhere as clear as a conventional lens due to the etched nature which can be seen through the fresnel lens. Increase etched density of the prisms can create higher quality images however they will appear more distorted or blurred then a conventional clear convex lens. A fresnel lens is a compromise between efficiency, low price, and reduced image quality, however the slim nature of the lens makes it ideal for a wallet magnifier or cheaper magnification tool.

 

Why does an image become out of focus when lifted to high over viewing image ? 

A magnified image or surface will go out of focus and become every distorted as you move the lens beyond its designed ...“focal length.”  This can happen if you go to close to or "fore" the focal length or "aft" the focal length. The best image is created when the lens is held at or near its focal length. 

 

What does a bifocal lens means ? What are the features and benefits of a bifocal lens?

A bifocal lens describes a lens design that has more than  one magnification powers or lens surfaces molded within one overall lens. This concept and design is similar to bifocal eyeglasses which have more than one magnification designed into a single lens... one surface for distance viewing and one surface used for up close viewing. In a typical lens design a large portion of a bifocal lens has one magnification, and the smaller lens (the bifocal) has another and its usually located in the outer corner or bottom center of the lens in order to not interfere with the horizontal field of view. The is Bifocal is created and molded as an integral part of the larger lens, the most common bifocal strength is 4x-5x magnification.