Questions Techniques Fréquemment Posées

Multi-element magnifiers are required for larger magnification systems. They are also designed for better resolution and for correcting chromatic and spherical aberrations, as well as distortion. As a result, they have much better image quality and flatter fields. As more power and quality are needed, the required design starts to change from a magnifier to a microscope. Compound magnifiers are actually the basis for "simple microscopes."

This has to do with the physical limitations of a lens. Note from the magnifying power (MP) equations above, that the MP and EFL have a reciprocal relationship. In order to increase the MP, the EFL needs to be decreased. Because the approximation from the Lens Maker's Equation for a DCX lens is EFL=R1=R2, the radius of curvature (R) also needs to be decreased. In order to decrease the radius, the lens must be physically reduced in size. The result of a smaller lens diameter is a smaller field of view. Accordingly, as the magnifying power increases, the size of the magnifier is reduced.

A diopter is a measurement of power and has units of inverse meters.

Power (diopters) = 1/EFL where EFL = effective focal length of a lens with units of meters

For a thin lens element, the power is calculated below. Using the magnifying power (MP) of a magnifier or comparator you can calculate the power in diopters.

For the smaller magnifiers:

Power (diopters) = MP/0.25 where EFL is in units of meters

For the larger magnifiers:

Power (diopters) = (MP-1)/0.25 where EFL is in units of meters

Note that this should not be confused with prism diopters. This is also a measure of power, typically used with wedge prisms, that is defined as a 1cm deviation of an input beam at a distance of 1m from the prism.

Magnifiers form images that are not real and cannot be focused onto a screen for instance. The image is called 'virtual' and appears larger and un-inverted when compared to the object being viewed. The magnifying power (MP) of a simple magnifier (handheld magnifier, comparator, pocket magnifier, base magnifier or loupe) is the ratio of the angular size of the image seen with the magnifier to the angular size of the object viewed without the magnifier. The angular object size is the maximum value that the eye can see without any assistance. As an object gets closer to the eye, its angular size becomes larger. However there is a distance at which the relaxed eye cannot focus any closer, this is called the 'near point' and is generally accepted as 10 inches (250mm).

As an example, if a single positive (converging) lens is used as a magnifier and the object is placed at the lens' length (EFL) on one side of the lens, the image will appear to be an infinity. Your eye then focuses that image onto the retina. The generally accepted formula to determine the magnifying power of a simple magnifier is:

MP = 250mm/EFL

The above equation is for small magnifiers, i.e. base magnifiers and pocket magnifiers. The larger magnifiers are viewed so that the virtual image of the object is placed at the near viewing distance of the eye. This is the case for a single positive lens when the object is placed just within the lens' focal length (EFL) on one side of the lens. The image will appear to be formed at the near point distance from the lens when viewed from the other side of the lens. In this configuration the equation changes to:

MP = (250mm/EFL) + 1

Note that angular magnification and is used with magnifiers rather than lateral magnification.

The field number is the maximum field number of the eyepiece that they should be used with.  For infinity corrected objectives the maximum field number is dependent on the tube lens clear aperture and how far apart the tube lens is from the objective.

Both DIN (Deutsches Institut für Normung) and JIS (Japanese Industrial Standards) are industry standards for microscope objectives and eyepieces.

When referring to microscopes, a DIN standard eyepiece or objective uses a basic 160mm tube length. DIN microscopes begin with an object-to-image distance of 195mm, then fix the object distance at 45mm. The remaining 150mm distance to the eyepiece field lens sets the internal real image position, which is defined as 10mm from the end of the mechanical tube (which gives the 160mm tube length). DIN standard eyepieces have an international standard 23mm diameter. DIN standard objectives often times have "DIN" etched on the side and have a standard 0.7965" diameter thread, 36 TPI, 55° Whitworth threading.

A JIS standard system has a 170mm tube length. JIS standard eyepieces also have an international standard 23mm diameter, however JIS standard fixed the object distance at 30mm. JIS standard objectives also have a standard 0.7965" diameter thread, 36 TPI, 55° Whitworth threading.

Most microscopes are DIN standard. DIN and JIS standards are interchangeable from a mechanical point-of-view. Please note, however, that the magnification of a microscope is calculated by multiplying the objective and eyepiece power together. This is assuming you have the same standard microscope, eyepiece and objective. If your eyepiece, objective, or tube length does not conform to the same standard, then recalculation of the total magnification is necessary. Also note that non-standardized microscopes exist, so be careful when choosing an eyepiece or objective.

#56-073 Mitutoyo MT-L Accessory Tube Lens is similar in mechanical construction to #56-864 MT-L4 Accessory Tube Lens. In other words, the same basic mounting will work for both.

We offer a #66-027 Mitutoyo MT-L/ MT-L4 C-Mount Adapter to make integration much more simplified. From the C-mount image plane to the MT-L (and MT-L4), you need 176.4mm of space. Factoring in the flange distance of a C-mount camera (17.56mm) and the length of #66-027, you only need 150mm of C-Mount Extension Tubes to fill this space. Since the tube lens does not attach directly to a Mitutoyo objective, #55-743 Mitutoyo to C-Mount 10mm Adapter needs to be attached to the objective (this adapter adds 10mm of length and adapts the M26 thread to a C-thread). This leaves roughly 57mm of space between the tube lens and the objective, which can be filled with extension tubes or other items such as beamsplitters, filters, polarizers, etc.

You can use the spacer rings to compensate for little irregularities of the position of the intermediate image plane on the MT-1/MT-2 C-Mount Adapter. They are extremely useful when trying to properly align a setup as the can easily correct for slight misalignment anywhere in the system.

Since infinity corrected objectives, like the Mitutoyo objectives, are designed to form images at infinity - when using them with a camera, a tube lens is needed to form the image onto a sensor. Most Mitutoyo products have M26 threads or no threads at all, unfortunately, making them difficult to use with most C-mount (1"" x 32TIP) cameras. On the bright side, Edmund Optics® has Accessory Spacer Tubes and Adapters and C-Mount Extension Tubes to make this process as simple as possible.

#54-428 MT-4 Accessory Tube Lens:

Use #56-992 Mitutoyo to C-mount Camera 152.5mm Extension Tube to connect the MT-4 Tube Lens to a C-mount camera. This extension tube is M26 on one side to attach to the tubes lens and C-thread on the other to attach to a C-mount camera. The MT-4 Tube Lens attaches directly to a Mitutoyo objective.

#54-774 MT-1 OR #56-863 MT-2 Accessory Tube Lenses:

This one is a little tricky. #58-329 Mitutoyo MT-1/ MT-2 C-mount Adapter can be opened up and the MT-1 or MT-2 Tube Lenses fit inside. Since the tube lenses themselves have no threads, this adapter provides the necessary C-threads on both sides. Between this adapter and the C-mount camera, you will need an additional 190mm of extension tubes. Since the tube lens does not attach directly to the objective, #55-743 Mitutoyo to C-Mount 10mm Adapter needs to be attached to the Mitutoyo objective (this adapter adds 10mm of length and adapts the M26 thread to a C-thread). An additional 76.5mm of space between the tube lens and the objective is optimal, but really you only have about 56.5mm of space between #55-743 and #58-329 since each adapter adds about 10mm of space. With this 56.5mm of space, you can use extension tubes or add other items such as beamsplitters, filters, polarizers, etc (this is the benefit of using the MT-1 and MT-2 tube lenses.

Please note that 76.5mm is the recommended distance since these objectives are infinity corrected. However if the distance is too short, you risk vignetting, and if the distance is too long, the resultant image will be dim because of insufficient light. So, from the top – it is a C-mount camera, 190mm of extension tube, MT-1 or MT-2 Accessory Tube Lens inside #58-329 Adapter, 56.5mm of extension tubes, #55-743 adapter, and then the Mitutoyo objective.

Only if your microscope is designed to work with an infinity-corrected objective. Due to the design of the infinity-corrected objective (see above question), they will not work in a DIN or JIS standard microscope. An infinity-corrected objective on a DIN or JIS standard microscope will not focus. Please also note that the threading for our infinity-corrected objectives is not a DIN standard threading and the objectives are physically not interchangeable with DIN or JIS objectives.

An infinity-corrected objective is a microscope objective designed to be used in conjunction with an infinity-corrected tube that will give you a longer working distance than a normal DIN-type objective. In most microscopes, the tube length is empty and all the magnification is done using the lenses in the eyepiece and the objective. The image from an infinity-corrected objective is collimated (parallel light) prior to being imaged by the secondary lens assembly. With an infinity-corrected system (objective and tube), a lens system is actually contained within the tube, which is required in order to form an image from the objective. This allows the objective and the entire microscope to be placed farther away from the sample, allowing users the added room to maneuver the sample being viewed. The major disadvantage of using infinity-corrected objectives is that you must have a tube lens or the system will not focus.

A reticle is a clear glass disc marked with scales or patterns that is placed in a microscope eyepiece at a particular position that superimposes the pattern with the image viewed through the microscope. A scaled reticle is a microscope eyepiece reticle designed to be accurate for a specific objective magnification. Most reticles are specified for a 1X magnification and are not scaled for the objective power of any particular microscope, making a conversion factor necessary. Stage micrometer scales are designed for not only calibrating microscope eyepiece reticles and objective powers, but also for determining the conversion factor from an eyepiece reticle scale designed at 1X to the true measurement as objectives, eyepieces, or reticles are interchanged. Stage micrometers are placed on the microscope stage and are similar in format to microscope slides. Please note that for a zoom microscope the reticle is only scaled at one objective power position. In this case, repeating the scaled position may be difficult.

This depends on the magnifying device being used. In order to view the reticle and the object through a simple magnifier, the reticle is placed directly on the object plane. The base magnifiers are machined to accept a given diameter reticle. Simply select the reticle diameter that is accepted by the magnifier. The reticle in a direct measuring or pocket microscope is placed at an intermediate image plane and is scaled according to the power of the objective. These reticles are generally not interchangeable.

There are some eyepieces, however, which will accept reticles. In this case you would just match the reticle diameter to the reticle acceptance diameter of the eyepiece. Please note that reticles have different types of scales in order to accommodate different applications. Additionally, the correct eyepiece size must be selected to match the microscope. If a microscope has a removable eyepiece, then it can be exchanged with a similarly sized eyepiece that can accept a reticle. Note however that replacement eyepieces that can accept reticles are not necessarily the same length as the original eyepiece. This causes a height difference between two eyepieces for a binocular microscope, for example. If there is a large eye relief difference, you may have to also change the second eyepiece.

Another difference between magnifier and microscope reticles is the size requirements. The thickness for most magnifier reticles is larger than the thickness of a microscope reticle and will not be able to fit in a microscope eyepiece. Also, diameter tolerancing is an issue. The diameter tolerance of our microscope reticles is +0mm/-0.1mm, meaning that the diameter of the reticle will not be larger than the catalog specification. This assures that the microscope reticle will fit inside the eyepiece tubing. Our magnifier reticles have a diameter tolerance of ±0.05mm, meaning that the diameter of the reticle might be as much as 0.05mm larger than what we list in the catalog. As a result, there is a chance that a magnifier reticle will be too large to fit in the eyepiece tube, even though it matches the stated diameter reticle needed for that eyepiece.

In a binocular microscope, there is one optical path originating from the microscope objective. The optical path is then split into two paths that are then brought each eye. If your microscope has two eyepieces, but one objective, then chances are it is a binocular microscope. A trinocular microscope works the same way, but the optical path is split into three paths- two for your eyes and a third port usually for a camera connection. In a stereo microscope, there are two paths originating from the microscope objective that travel essentially parallel up to the eyepieces. The advantage of using a stereo microscope over a binocular microscope is in the depth perception. Having two separate optical paths makes depth perception and three-dimensional viewing of an object possible. Using a binocular microscope, you will see only a flat field and will not be able to discern any height differences on the object that you are viewing.

Edmund Optics offers two major types of microscopes: zoom microscopes (where the magnification factor can change smoothly over a range) or non-zoom microscopes (where the magnification factor is set at one or two fixed values). The choice of which one suits your need depends upon your application. The major advantage of using a zoom microscope is a smooth change in magnification and field of view over a specific range. For example, our Edmund Optics Zoom Inspection Microscope Heads can obtain any magnification value between 7.5X to 30X or 25X to 100X depending on the specific model, while a non-zoom microscope only offers a fixed magnification i.e. either a 10x/30x or a 20x/40x magnification. The major disadvantage of using a zoom microscope is cost. Zoom microscopes tend to be many times more expensive than non-zoom microscopes.

No. All of our Direct Measuring Microscopes have non-removable and non-interchangeable reticles. When using a direct measuring microscope, you must have a scaled reticle designed and calibrated for the specific magnification (see above question on Scaled Reticles). Our direct measuring microscopes contain reticles that are designed and calibrated specifically for those microscopes and as such, cannot be removed once installed.