Demystify the optical hocus-focus.
Updated: Jun 2, 2022
Are you about to buy a new set of loupes and are confused by all the optical terminology being thrown around? Not a professional microscopist or optometrist? Don't worry – we've got you covered! This post hopes to demystify some of the optical hocus-focus.
Working distance (WD)
Working distance is the distance from your eyes to the work area. This distance will be measured when you order your loupes in a variety of treatment positions around the head of the patient, whilst maintaining good posture and minimising excessive neck flexion or hunching.
Working distances will vary from 350mm for shorter operators up to 570mm for very tall operators.
Once set, the working distance cannot be changed without returning the loupes to the manufacturer for modification.
Depth of field (DOF)
The depth of field is the distance whereby the loupes remain in focus.
Say for instance you're wearing loupes with a depth of field of ±25mm (25mm either side of the object you're observing). When you're working on the 4.8. The 4.8 will be in focus but the 4.6 distal distal will be blurry.
Ideally you'd select a set of loupes where the depth of field is as large as possible whilst maintaining the other desirable optical characteristics. PENTAX PRISMVUE NF2 loupes are available with a field of view from 80mm-150mm
2x - ±75mm
2.5x - ±70.5mm
3x - ±60mm
3.5x - ±53mm
4x - ±49mm
5x - ±40mm
Field of view (FOV)
Field of view is the open observable area you can see via an optical device. Usually this is measured in degrees where there is no fixed working distance (like a security camera) or in mm diameter in the case of surgical loupes.
Typically, loupes will have an overlapping circular field of view, however PENTAX PRISMVUE NF2 loupes have an ellipsoid (squashed circle) field of view, which gives a wider and brighter image.
Declination angle and prismatic deflection
Declination angle is the angle that your eyes are inclined downward toward the work area when using Galilean loupes. This angle should be steep enough to help you attain a comfortable working position with minimal forward head posture (20 degrees or less). The farther the head is positioned forward to see through the loupes, the greater the strain is on your neck.
Prismatic deflection allows for even further declination angles without eye, neck or back strain. PENTAX PRISMVUE NF2 loupes deflect you vision down by 48 degrees, whilst maintaining a straight eyes-forward posture.
This one is easy - 5X means 5X larger and so on. BUT there are trade-offs.
The higher the magnification the lower the field of view. The reduction in the field of view from the naked eye is probably the biggest change to get used to when wearing loupes. A higher magnification is suggested to those who have worn loupes in the past and are confident with a smaller field of view.
You may also like to consider a higher magnification when treating a patient that requires endodontic treatment. A higher magnification allows canals to be found, accessed and mechanically prepared with far greater accuracy. Certain canals like the MB2 of upper first molars are near impossible to locate without magnification. It has been shown that the detection rates of MB2 canals increase with loupes magnification from 17.2% with the naked eye, to 62.5% with loupes and 71.1% with a microscope (if you'd like a microscope too, we sell those HERE).
Since you can't change the magnification of your loupes, it is generally a good idea to have more than one set of loupes to cover a wider range, or combine loupe and microscope use (obviously not at the same time) depending on the treatment you're providing to your patient.
Galilean or Prismatics (how the lens bends light)
When selecting loupes you may be given the choice of either Galilean or Prismatics.
Galilean loupes are the most popular style of loupes as they are lightweight and offer easier adaptability. Galilean loupes are generally offered in magnification ranging from 2.0X -3.0X making them the perfect choice for most dental procedures.
Osseo Group offers Prismatic loupes for far greater clarity and higher magnification levels. Additionally they are great for more detailed work like endodontics. PENTAX PRISMVUE NF2 loupes are available in magnifications from 2X to 5.0X
Exit pupil diameter
The exit pupil diameter is the diameter of the usable light that comes out the back of an optical system into your eyes. On a pair of binoculars it can be seen as the bright circle in the center of each eyepiece when you hold them about 30cm away from your eyes.
The larger the exit pupil diameter, the more light will be delivered to your eye and the less eye strain you'll experience. Our pupils only dilate to about 7mm, so an exit pupil diameter over 7mm is really an unrequired luxury when it comes to loupe selection.
PENTAX loupes are available in exit pupil diameters ranging from 4.2 -6.4mm making the PENTAX PRISMVUE NF2 loupes some of the brightest prismatic loupes on the market today.
2x - 6.4mm
2.5x - 6.4mm
3x - 6.4mm
3.5x - 4.6mm
4x - 4.3mm
5x - 4.2mm
BUT... There is always a but...
You may want a set of loupes with a 7x magnification, 100mm field of view, 100mm depth of field and a 6.8mm exit pupil diameter BUT you can't have everything you want. Each optical attribute is a trade off for another.
Greater magnification generally means: less field of view, exit pupil diameter and depth of field.
Lower magnification generally means: greater field of view, exit pupil diameter and depth of field.
Service, repair and care
In some cases, a loupe and light purchase requires servicing due to the high number of factors that go into custom-making loupes.
It is important to purchase from a company who can service your needs post-purchase. You'll be wearing loupes for extended periods and may sometimes discover that they need changes in working distances, adjustments to the frames to realign the oculars, frame corrections, and many other local services.
At Osseo Group, the specialist who measures you up for your loupes will be your go-to person for all things loupe related. You can also call us weekdays 9am - 5pm at 1300 029 383 or email us at firstname.lastname@example.org
Osseo Group is a licensed PENTAX repairer for most minor repairs, major repairs will be returned to PENTAX/HOYA Technosurgical in Japan for repair and recalibration.
It's also important to remember that your loupes are expensive, the repairs will be too, You're about to invest a lot of money getting the best surgical loupes for your practice and preventing damage through misuse or carelessness is the best way to ensure your loupes last a lifetime.
If you're in the market for a new set of loupes
and would like to demo our PENTAX PRISMVUE NF2 loupes
Click HERE to book an in-office demo or call us at 1300 029 383.