Notes Regarding Trinocular Microscopes

In this post I am looking to discuss setting up a Trinocular Microscope for use with photography and video, covering my own experiences in getting the thing working and aspects that are not covered in the fairly useless manual. The type I am using is sold as an Industrial Inspection Microscope giving a magnification range of 3.5X to 90X depending on the installed optics. These look to come from a single factory in China and are distributed under various different brands by a variety of shops on the internet and in places such as ebay and Amazon.

In my electronics work I have been moving across to SMD (Surface Mount Devices) components, these can be rather small and fiddly for which a microscope is just the business. I chose a stereo microscope over the cheaper monocular microscope camera as this gives me a binocular depth of field view so when micro-soldering components I can make out the distance of the iron tip in relation to the board and component. In the past I have tried similar with a camera and monitor setup and this did not work for me.

Parts of the Microscope

Parts of a Trinocular Microscope

Clockwise from the top:

  • Eyepieces, to look through, with rubber cups – these make the scope easier to use. The eyepieces fitted here are WF10X/20, I’ll talk about the magnifications later
  • Ocular Tubes, the eyepieces mount into these and are used to set the dioptre – fine tune the focusing
  • Interpupillary Adjusters – to set the distance between the eyepieces
  • Objective Lenses – there are two of these
  • Focusing Knob – as you change magnification, you will need to re-focus.
  • Magnification Knob – for zooming in and out of your object
  • Trinocular Lever – pull this out to enable the camera view, when enabled the left eyepiece is blacked out. Simul-Focal microscopes do not have this.
  • Trinocular Port – camera mounting – the microscope shown comes with a C-mount adapter, here I have attached a C-mount to Fuji X-Mount adapter.
Objective Lenses on a Stereo Microscope

Other Parts
An essential addition to the microscope is some kind of illumination, an LED ring light is an excellent place to start, this mounts onto a slot on the barlow lens or a screw in adapter. You will be wanting one thats both adjustable, really bright and gives and even spread of light, look for those with at least 144 bright white LED’s.

LED Ring light

Barlow Lenses fit below the objective lenses, they are used to either reduce the magnification slightly to increase the working distance, or to add additional magnification.

Barlow Lenses

With the 0.5X barlow fitted the working distance can be raised from 9cm to around 15cm, I have not yet found any real use for the 2X barlow.

I have also fitted a 48mm UV (plain glass) filter from a camera shop, this is to simplify cleaning up the various emissions created when soldering, to this I have added a 48-52mm stepping adapter ring to give a place for the LED ring light to attach to as the 0.5X barlow lens does not have a suitable slot.

The objective lenses Magnification is shown on the right hand magnification knob, from 0.7X to 4.5X, the eyepieces are 10X and the barlow is at 0.5X the zoom is calculated by multiplying all the magnifications:

    \[total\ magnification\ = objective\ lens \times eyepiece \times barlow\ lens \]

Generally I am more concerned about the image size being appropriate for the work I am doing, but when specifying a scope you need to know what it can do, these inspection microscopes are excellent for electronics but completely useless for extreme closeups such as seeing the cells from a layer of onion.

The Field of View is shown on the eyepieces, it is the second part of the code: WF10X/20 this field number is the diameter of your objective view in millimeters at 1X magnification, the formula is:

    \[FoV\ \diameter in\ mm = \frac{field\ number}{objective\ magnification \times barlow\ lens\ magnificatoin} \]

Types of Stereo/Trinocular Microscope

These trinocular microscopes have two main types, those that are simul-focal and those that are not. As mentioned before, the standard (for want of a better name) have a lever on the left side which needs to be pulled to enable a view for the camera, this in turn disables the left eyepiece, this becomes a problem if you wish to video while you are working, for photography is is less so. These standard microscopes are a bit cheaper, around £80 – £100 than the simul-focus ones and the image quality from the optics is just the same.

I first started with a standard microscope, in the photo at the top of this page, the small stand makes it very stable for photography, and although it does not have a reducing barlow lens I have successfully used it for a few electronics projects. I have now moved onto a simul-focal microscope with a long boom arm, this is the AmScope SM-4TPZ, this type of microscope is popular among the independent repair shops on YouTube (see the links below), the boom arm and barlow lens makes it more flexible to use.

Microscope on Dual Boom Arm

Setup and Focusing

Setting up for eye focus or for camera focus is relatively straight forward, but getting the camera and the eyes to be working in the same focus can be tricky. The eyes are much more tolerant and have a greater depth of field than the camera, the following steps should give you the results you are looking for (with a 0.5X Barlow Lens, knock 5cm off the height if you don’t have one):

  • With the focus knob turned so that the scope support (the bit that goes up and down when focus is turned) is flush with the part attached to the support upright hold the microscope and loosen the upright knob at the rear, set the height of the scope so that the objective lens is around 15cm above your work surface.
  • Set the interpupillary distance to something comfortable, with your eyes hovering above the rubber cups, not in them, I use the bridge of my nose to fix the distance you should see a whole clean circle, and black shading around the sides means you are off centre.
  • Rotate the ocular tubes, dioptre, so that they are just above halfway distance in their range. Set the magnification to its lowest, 0.7X (I’m not including the magnifications of the other lenses).
  • With a specimen like a coin or ruler under the objectives, close your left eye and adjust the dioptre on the ocular tube for your right until the focus is sharp.
  • Repeat with your left eye, closing the right and adjust the left diopter. Its not unusual for your eyes to have different focal distances.
  • Now zoom in, as you increase magnification adjust the focus knob to suit, micro-adjust the dioptres as required. Once correctly set up, adjusting the focus should be minimal while zooming through the range.

Now that the eyes have been setup, its time for the camera. The smaller the cameras sensor the further away it needs to be:

  • Zoom back out to 0.7X and set the focus back to its central position, as you started with before
  • Mount the camera on the Trinocular Port and adjust the height so you see an in focus image.
  • Now as before, increase the magnification in steps 1X, 2X etc. and check the focus of the camera and eyes, put the camera into focus with the focus knob and adjust the diopters for the eyes, these should be micro-adjustments.

With everything in place, you should have a stable in focus range of around 3cm from your work surface where for a particular magnification nothing but the focus knob needs to be changed.

Photography

When taking photographs using the microscope my camera of choice is a Fuji X-Pro2. This is a mirrorless camera with an APS-C sensor, the reasons for this are: its lighter than most DSLR’s, an old fashioned mechanical plunger type cable release can be used, because the sensor size is smaller it crops out much of the tunnel effect caused by looking down a long tube, and the live view has a manual focus assist which can be used to zoom the live view display and help take a nice sharp image.

Camera attached to Microscope

The camera sensor size makes a huge difference, to illustrate this here are two photos, one with the Fuji and another with a Canon DSLR full-frame both uncropped:

Fuji APS-C sensor
Canon Full Frame Sensor

Normally I would crop to a square inside the image.

The depth of field is rather shallow and there is no aperture to change. To get around this I have used Image Stacking/Focus Merge, where you take a series of photos starting at the top of your object and focusing slightly further down, each image being a slice, I then use Affinity Photo to create a fully focused image.

Image Stacked Daisy

I set for a low ISO, around 100-400 and being lazy I use auto-exposure. Despite the bright LED light exposure times are generally quite long, 40th-60th of a second and bumping up the ISO to grainy makes little difference, cropping in post can make high ISO grain more apparent. I have made a suitable mount for a macro flash from the lid of an old spray can, a resize ring, small bits of wood and plenty of epoxy (I should have documented this).

One thing you may see in your images is a white dot in the centre of the photo, this is most obvious when fully zoomed in and is caused by light bouncing around the trinocular tube leading to the camera:

With the dreaded White Dot, and fixed

this is simply fixed by inserting a tube of matte black card running the length of the camera mount, in this case 40mm:

Cardboard inserted into trinocular mount

Video

I use a dedicated microscope camera for video, the photo cameras while I am sure they would work well have a built in time limit for recording and need attention, I also want to record directly on computer. The camera I use is a generic nameless blue box bought of ebay, on the computer it has the name “H1400 USB Camera” and I have it on a USB 2.0 port outputting 1080p at 30fps in to Open Broadcaster without any problems, it can also do HDMI and can take still images at 14 megapixels (apparently).

Video Camera for the Microscope with a 0.5X reduction lens

The big drawback with the camera is that the sensor used is tiny compared to those used for photography, this appears to be common among almost all video cameras designed for microscopes. To partly fix this a reduction lens can be fitted to the Trinocular Port, I use an AmScope FMA050 (aka RU050) 0.5X reduction lens which I got of ebay. You can see the cameras view in the sketch drawn on 5mm graph paper below, with the magnification set to 0.7X the outer circle is what I see through the eyepieces, the rectangle is what the video camera supplies to the computer:

Microscope limited video camera view

These cameras would also benefit from being able to provide an image in the old 4:3 aspect ratio as that is much more square than the 16:9 widescreen. The view to your eyes in the microscope will always be substantially better than that presented by the camera.

To Conclude

For a trinocular microscope suitable for micro-soldering I would recommend a simul-focus, its only little extra money for the functionality with the 0.5X barlow lens. AmScope do cheat the magnification a bit, not pointing out the need to swap barlow lenses round to get the advertised 3.5X to 90X range, but with the 0.5X barlow attached it goes upto 22.5X or without it is 45X, on the electronics for most of the time I work at around 15X only zooming in close for inspecting bad soldering and showing off.

As I live in the UK, buying through Amazon UK has the advantage that import duty is paid at checkout, AmScope ship from the USA (a well traveled Microscope, made in China) using UPS, this prevents holdups in customs and UPS’s hefty tax collection fee, ebay have a similar Global Shipping Programme.

Using the microscope for the first time is an odd experience, its interesting how your fingers adjust to the micro-distances, finding the occasional need to wave the soldering iron about until it appears in your field of view and looking at dead insects under the microscope, while eating, is probably best avoided.

Crows Feather

Links and References

Microscope Suppliers

  • AmScope – USA, also available on Amazon UK and ebay
  • GT Vision UK Supplier, also on ebay

YouTube microscope users – Independent Repair Shops, mostly iPhone and Apple Macs

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