Microscopes: Best Image Quality for Your Money
Having a good vision system is crucial to saving your eyes, avoiding fatigue, and eliminating guesswork when working on small electronics. I've spent many hours using top-quality stereo microscopes (such as from Vision Engineering). I wanted to compare my [good] experience with optical stereo microscopes to the usability of low-cost USB microscopes. This is not a product review, just an evaluation of how useful low-cost USB microscopes are for small electronics work.
I picked up this USB microscope for $35 because it's the #1 best seller on Amazon. The advertised specs are:
- 2 Megapixel
- 10X - 250X Magnification
- LED light ring
For those searching for the summary, here you go:
I'm happy to have it for $35 but might rather have something with better optics for 2-3x the cost. This microscope doesn't produce photo-quality results but it is a useful tool for enhancing your vision for pass/fail type inspection. The low frame rate makes controlling tools (soldering iron) difficult so it's best suited for static images. Also, for the typical setup the magnification maxes out at 40X, which is still good for electronics work. See below for image samples and alternatives that you might find suitable for occasional use.
A Real-World Test
The first thing I did is take a look at an actual problem I was had recently with a tiny DFN 3x3mm part. In the picture below you can see three pins. The left-most pin looks ok. My question was about the right-most pin. Did it reflow ok? Is it soldered well enough? You can see metal, possibly the edge of the pin or pad. However, even with this microscope, I can't see well enough to to make a judgement. This doesn't bode well.
Up and running in Linux
I'm using this microscope on Linux Mint (Debian). In the
v4l-utils package is the
v4l2-ctl utility, which will tell you resolution and frames per second (fps) of your microscope (or any camera). This one is 800x600, 20fps. The specs said 2 Megapixel, and it might indeed have a 2MP sensor, but the output image is only 800x600 = 480k pixels.
I'm using VLC to display the video and take snapshots (select "Open capture device" and hit "play").
To measure the magnification, I physically measure the component under inspection (such as a 0402 capacitor) and then physically measure the image as displayed on my monitor. I'm using a conventional low-DPI monitor (about 100ppi) and displaying the output image 1:1.
Change the working height
The microscope has one knob (focus) and you zoom by physically moving the microscope up and down, closer and farther from the subject. Getting closer to the subject increases magnification, but reduces the space you have to get tools (like tweezers or a solder iron) in there to do work.
The microscope has a built-in LED light ring which causes quite a bit of glare at higher working distances (when it has a wider field of view). High-end microscopes have a built-in polarizing filter to help eliminate glare.
Below are images of some 0402 capacitors. Notice how as the working height is increased, the magnification goes down and the impact of glare is greater.
0.050 inch working height, 35X magnification
Here the front of the microscope is touching the components. There's no way to get any tool to the components and this setup gives nearly maximum magnification. You can clearly see details about the solder flow, hole centering in pads, silkscreen details. Depth-of-field is about the thickness of a component (PCB is in focus and the top surface of the 0402 capacitor is getting fuzzy). This is useful, but the tip of the microscope is so big, it's hard to get this close to most components because there is often a connector or tall component in the way.
0.5 inch working height, 25X magnification
Glare starts to become visible at the edges of the frame. Some detail is lost. At 1/2 inch from the PCB, you might be able to sneak a soldering iron in there without melting the rim of the microscope.
1.5 inch working height, 15X magnification
Glare is covering a significant portion of the frame. You can clearly see it's caused by the 4 LEDs of the light ring. Also the brightness of the glare is effecting the auto-exposure control and it's beginning to darken the rest of the picture. With a 1.5 inch gap, you can get tools under the microscope to do work.
3 inch working height, 10X magnification
A 3 inch working height would be useful for a lot of applications. The depth-of-field is about 0.25 inch but the magnification at this height is reduced to 10X. Combine that with the intense glare and darkening from the auto-exposure control and this is not a very useful configuration. However...
3 inch working height, 10X magnification, external light source
This is the same configuration with the light ring turned off and an external light source applied. This allows you to position the light to move the glare. The light is uniform, no darkening. This is a useful configuration for inspection, but you can see the grittiness that comes with low quality optics.
Solder paste particle size measurement
Now we're just having fun. Since we know the magnification in a given configuration, we can measure other things. This is at (or beyond) the limits of this setup. Below is a picture of the tiniest dab of solder paste from the tip of a pin. I measured the size of the particles of solder in this solder paste to be about 0.001 inch (25 microns) diameter.
Also note the difference in quality of the silkscreen on this PCB vs the previous images. This PCB is from Itead.
The image below was taken from the onboard camera of my Nexus 5X phone. At a working distance of 3 inches you get 4X magnification. Not bad in a pinch.
Here's the setup: