Using an optical instrument, magnifying glass, binocular or microscope is a daily routine in the curation and conservation world. Choosing such an important device to be our daily ally could be a tedious task.
Here’s a quick and easy guide to help you decide what’s best for you. (TL;DR this way)
Learn to look, look to learn
Observe, decide and work
In the conservation world, thorough observation of things will bring inputs on the state the looked-at object is in and to identify causes of its deterioration. It is the basis of condition or preliminary reports. The latter can then give educated treatment proposals.
When looking for an optic, beside the obvious need for an adequate magnifying power to see the smallest things, one also has to take into account seemingly mundane aspects such as practicability or ergonomics, to prevent eye and muscle fatigue. Never forget that one ! Sherlock Holmes’ loupe is handy for short observations, but you wouldn’t want to have to use it to look at your work while removing accretions with a scalpel for 8 straight hours.
Physics, Optics and the jungle of mercantile practices
“But, all I wanted was a nice magnifier !” did you just say ?
I’m surprised at your naïveté. Things are, of course, more complex than that. Have I taught you nothing ? Shame on me ! Take a deep breath, it will get bumpy at times, but I will be with you all the way.
Ready ? Let’s begin.
For a long time, even the simplest optical instrument was a rare and pricy thing. Industry processes developed during the XIXth and XXth centuries allowed for easier and cheaper access to those, along with a real increase in magnifying capacities. Customers can now choose among a plethora of items, all highly praised by a sometimes misleading over-present marketing.
To help you swim in those murky waters of magnifying abilities, keep three elements in mind: magnification, scale and dioptres.
Magnification
Magnification is a mathematically obtained number related to a specific optical instrument. Its value is given in the technical specs of said item in a standardized manner, for example “zoom 30x”. As such, it is a very useful tool to compare choices.
Remember well: it only defines a tool, never an image.
Scale
A magnified image is characterized by a scale ratio. It is also a mathematically obtained number, most often given in the form of a fraction. For example 1/50 or 1:50 gives you the information that 1 unit measured on the image equals 50 units in real life.
This time, remember this: a scale only can define an image, never the magnifying power of an optical device.
Dioptres
A dioptre is a surface between two environments with different refractive index.
Things are getting blurry ?
Let’s remedy that.
In a nutshell, your eye is a series of dioptres letting light enter from outside to its centre, the vitreous body. The water surface on your glass: dioptre. The same goes for your coffee cup. Windows ? A whole lot of dioptres! Passing from one dioptre to another modify the path the light uses.
From this idea was born the dioptre as a unit. I can see from your look that you’re smelling something fishy. How can this dioptre thing help you choose a magnifier ?
You’re absolutely right. In itself, it can’t. Until now, I have only mentioned half of the optical system you need. You are the other one ! The last piece of the puzzle is the distance between your eye and the lens. That’s what completes the image (pun intended) and allow you to benefit from the magnification power.
Dioptre as term has been coined in 1872 by Ferdinand Monoyer to standardly quantify a lens “power”. Fun fact: one of the arrays of letters your ophthalmologist can ask you to read to measure your visual acuity is called the Monoyer chart. It’s one of the tool that allows to pinpoint the ideal lenses for your glasses…measured in dioptres.
But something immediately springs to mind: all those standardized industrially processed things are well and good but your eye isn’t standard ! Therefore, bear in mind that all the technical specs makers will provide can only be approximates of the effect the instrument has for your sight.
You may now breath freely again, we’re done with the maths. You now have more insight into what you should look for and what isn’t relevant. No more fright when looking at specs !
Choosing the right tool
A practical approach to things: size doesn’t really matter, weight does !
If you’re reading these lines, chances are you’ve already tried to understand how to choose the right instrument to suit your needs.
Browsing through the numerous possibilities, you may have noticed small optics that were offering more magnification than larger ones. Let’s get rid of a cliché: for a magnifying need to better see elements ranging from a few millimetres to a few microns, an optic’s size isn’t relevant, its lens quality only matters. More often than not, its price will provide you with a more accurate input on that part.
To make an educated choice, you need to assert your needs. What do you expect from this optical instrument ? Is it to do field work ? Is it to have a better view of your work for a long period of time ? Would you like to be able to see pollens of a few microns or the intricate few millimetres of a fabric weave ?
Identifying your needs will speed your researching process by guiding you to specific optics, help find one to more accurately suit your expectations, and often reduce the expenditure.
There is however a common element to all the situations that only depends on yourself: eyes health. Too many times ignored, visual comfort will effectively be the only element deciding whether or not you will use your newfound optic. Maybe you’re not comfortable with the too small window of the utterly powerful jewellers’ loupe you just bought. Despite its hefty price, it will remain in a drawer from now on. Maybe you’ve been seduced by the look of the head-worn binocular magnifier, only to realize it gives you nausea (and believe me, it will) so the poor thing is now hanging somewhere gathering dust (they all do). Your eyes are one of your most important assets in this line of work, be gentle with them.
Portable items for field work
Portable items are every optics you can easily have on you at all time. They’re light, small, efficient and allow swift and precise observations while doing field work. Their fields of view are limited, and they are not fitted for long observations.
Be extra careful as to the weight of these items: you have to be able to hold them as close as possible to the material you’re looking at without weariness. Gorgeous copper and wood loupes are very chic on a desk but bordering on dangerous to use while balancing a ladder, one hand also occupied with a flash-light… True story.
Those optics can be:
- Loupes, magnification loupes or jewellers’ loupes: ranging from 2x to 10x, these are the most versatile tools. From botanical identification to crystal observation, they exist in an impressive number of variations for a very reasonable price. Choose the one you like ! Some of them have integrated rulers visible when looking through them. It has proven useful to properly document observations and characterize elements.
- Smartphones cameras and complement optical apparatuses, lens attachments or “microscopes”: ranging from 10x to 100x, as advertised by producers, these are only recently available. Their qualities may vary, but they are useful though not always fast and easy to put in place. Advantages: their fields of view are huge compared to small loupes, and therefore visual comfort is matchless. They also allow taking pictures of what you are looking at, always handy to include in a report. Huge drawbacks: this make for a very heavy tool ! The longer you hold the phone and attachment combo, the more muscular tension arises, putting the object you’re looking at risk if you drop it (not to mention damaging your phone). Using a tripod of some sort is rarely an option. It can also be difficult to make for proper lighting whether to look or take pictures. It is not easy to determine a scale for said images and allow for size determination of the elements.
- USB or Wi-Fi microscopes for phone or computer: ranging from 40x to 1200x, this technology is sometimes stubborn and the marketed automatic connections not so automatic. For a reasonable price, these items are very interesting. They go steps further lens attachments and have their own incorporated LED lighting. Sizing elements on images can be tricky, particularly on phones. On the contrary, the dedicated apps on computers can make the whole process a breeze. Computer usage limits the observation to smaller pieces where you can install a makeshift base camp and have the objects alongside.
Lab or Workshop items
Lab items are the items too heavy or too big to be used for field work. Those optics are more suited for long observations. Carefully selected, they can generate only minimum strain on muscles and eyes.
- Magnifying glass (desk or floor version): ranging from 2x to 10x, most of the time with an inbuilt lighting system, these tools provide the more versatile solutions to work for long hours on a precise work. However, two elements must be considered. First the quality of the lighting (colour, heat generation, dimmer and flickering) and then the real dimensions of the field of view. Be extra careful with this: most sellers will give you the top window dimensions, not the actual field of view size. The lenses used tend to be rapidly blurry, restricting vision to a few centimetres in the centre.
- Magnifier Visor: ranging from 1.5x to 4x, this is the tool used in the classic representation of lab-coated conservators, painstakingly working on some unidentified oil paintings in an immaculate white lab, probably listening to a piano concerto. Don’t be fooled, reality is way more messy !
These optics must be chosen with the utmost care. They must be fully adaptable to your morphology (lens distance, lens orientation, headband) and be very lightweight. They are associated with conservation mostly because they were historically the most reasonable option. In truth, they are not well-liked in workshops and only useful in limited situations. And they will get you nauseous.
Be aware that they are not suitable for people suffering from common visual defects like astigmatism, even at a small degree.
- Binoculars: ranging from 10x to 50x, look for models with large sole and high column to be able to slide the piece underneath. Magnification is exceptional on most planes but these optics generate visual and muscle fatigue after a while. Remember to stretch and move your back and neck regularly.
- Microscopes, analog or digital: ranging from 1000x to 2000x and more. Those optics are not really useful for the needs described in this article. They can be used in the conservation field during preliminary phases or for a full study to identify elements to be able to accurately select a treatment. Images created by optics like scanning electron microscopes are usually done by independent labs that carry this somewhat heavy and pricey machinery. Don’t get me wrong, most lab or workshop has an old analog microscope somewhere on the shelves, most of the time used briefly to identify fungi or the odd algae.
Recap
Manufacturers sometimes give conversion table between magnification and dioptres. Remember anyhow those specs are average data for a standardized eye…
