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How to build your own illuminated sensor loupe for camera sensor cleaning (or other purposes).




It's cleaning time

There are many ways to clean your camera sensor, and plenty of products out there to aid you with the task. One of the challenges when cleaning a sensor is to determine when your sensor is actually clean. The typical recommendation you'll get in most articles on this topic is to shoot a clear sky or a white wall at the lowest aperture possible for your lens (say f/16 or lower), and then check the image on the PC to detect any dust spots. While this is good advice, and certainly works, it is quite tedious to do multiple checks as you go along. If you ever tried cleaning a sensor, you know that there's a fair amount of "trial-and-error" involved, so you usually have to repeat this process many times over. A faster and more convenient way to assert whether the sensor is clean or not, is to look at it with a specialized "sensor loupe" as this provides almost immediate feedback throughout your cleaning process. There are of course commercial products available for this purpose. Because mostly professional users get them, their price, while not exorbitant, is a bit out of proportion to what's actually inside these things. Check this one from Amazon for example. As of this writing, it sells for about $80. As you know, I am a proud "DIYer" (Do It Yourselfer; if that's a word), so when I saw that, I decided to make one myself, not only because it is much cheaper, but also because it is so much more fun! Here's how you can do it too.

Note: this project, though originally conceived for sensor cleaning, can also be used for a number of other purposes. I've found it very useful to examine small electronic components in PCBs for example. Any application where you need to inspect small objects and need some local illumination will benefit from this gadget...


What you'll need

* General Purpose Eye Loupes

I recommend buying a set like this (Amazon link) as it allows you to view the sensor at different magnifications. For sensor cleaning, I end-up using the 2.5x and 5x versions most of the time.

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Figure 1 - Eye Loupe Set

* 1 Camera Body Cap

In this case I used a Canon body cap (See Figure 2, Amazon link)  thought you could use the one for the camera brand you own. The advantage of this body cap is that it is made of relatively good quality plastic (oxymoron anyone?) and is already already designed to cover the camera lens mount, so the dimensions won't be very far off from optimal.


Figure 2 - Body Cap

* Three LR44 Button Cell Batteries

I already had these around the house. I extracted them from a laser pointer but they can be had at many stores (Amazon link, for example). Any dollar store will usually carry them (dollar stores are a good place to buy batteries). If they are not already taped in series as shown in Figure 5 (to yield a total of 3x1.5 = 4.5V) then you can use regular tape to construct a similar arrangement. You need three cells in series to get the desired 4.5V voltage.

* Three white LEDs

The specs for these LEDs are not very critical, as you won't be running them at full brightness. This increases battery life and reduces flaring. They can be purchased online (Amazon link for a pack of 25) or at Radio Shack if you don't want to buy that many. 

* Three 560 Ohm (or 470 Ohm) resistors

You can buy them at Radio Shack or at an online retailer if you don't have them already.

* Small ON/OFF switch

I already had a few and was able to repurpose it. You can also buy them at Radio-Shack, Frys or online.

* Wire and contact points, glue, etc.

Total estimated cost: about $15 (even less if you already have some of this stuff laying around, as I did).


Hot glue gun, soldering iron, drill with hole saw bit, Xacto knife. A Dremmel tool is helpful but not a must.


Start by marking the center of the body cap with a punch and drilling a small pilot hole. Use a 1 ¼ in hole saw to drill a circular opening in the body cap as shown in Figures [x and y]


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Figure 3 - Hole Saw Bit


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Figure 4 - Cutting the Opening


Next, cut a small opening in the inner circle of the body cap to accommodate the three batteries. Use an Xacto knife or a Dremmel tool with a cutting wheel. Leave some room (though not much) for the metal contacts (see next step).  

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Figure 5 - Battery Opening Cut


You'll need two small pieces of metal to make contact to the battery terminals. I used some pieces from an old lantern that I had saved and cut them as shown in Figure 6 and 7 . The advantage of this material (zink/copper?) is that you can use a regular electronics soldering iron to attach wires to it.


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 Figure 6 - The Contact Material and the Switch


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Figure 7 - Contacts already cut


Figure 8 shows the layout of the project with the LEDs pointing towards the center. To install them, I drilled very thin holes through the inner plastic circle, just wide enough to fit the LED wires. You can also heat-up a needle and puncture the plastic if you don't have a small enough drill-bit.

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Figure 8 - Layout

Next you will need to make the electrical connections using a soldering iron. Figure 9 shows the conceptual schematic drawing. The circuit is extremely simple. There's a serial resistor with each LED to limit current. I purposefully limited the current to a pretty low level (about 2.5 mA per LED). This will ensure the battery lasts a long time. I also found that you don't need very bright light for the small area under examination. A very bright light may actually create flaring and be counterproductive. That said, should you wish to increase the brightness, simply reduce the resistor value to 220 Ohm for example.


Figure 9 - Schematic Diagram

Figure 10 shows a detailed view of the soldering process. Note the LEDs are already mounted through small holes. Leave a little bit of space between the LEDs and the inner plastic ring so you can later bend them down (so the light goes towards the sensor, not towards the loupe)..

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Figure 10 - Assembly Detail

Sony NEX-5N, OM Zuiko 50mm f/1.4


I glued the small switch to the inner wall with crazy glue first. Figure 11 shows a small clamp holding the switch while the glue dries..

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Figure 11 - Gluing the Switch


Figure 12 shows the final assembly. I filled the spaces with hot glue, both to isolate the soldering points, and to hold the wires down. Not a very pretty solution but we will cover it with black tape in the next step.

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 Figure 12 - Detailed View 

Figure 13 shows how I used black electrician's tape around the cap and then later bent it around to cover the ugly "hot glue" job. It's not the prettiest thing in the world, but bear in mind that this is the bottom of the project so it won't even be visible most of the time :)


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Figure 13 - Applying Tape


Figure 14 shows the final project mounted on a Digital rebel SLR. Notice how the three LEDs provide good lighting to the surface of the sensor. Bend them down slightly to optimize the viewing angle as needed.


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Figure 14 - Bottom View, Final

Now you simply use the loupe of your choice on top of the contraption as shown in Figures 15 and 16. Initially I thought of gluing the loupe to the cap with epoxy glue. However, I found this arrangement is actually more flexible as I can choose the right magnification for the job by swapping loupes as needed.


Figure 15 - Mouned on a Canon Rebel


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Figure 16 - Detailed View


Another (unplanned) but welcomed advantage of this arrangement is that you can actually insert the loupe "up-side-down" as shown in Figure 17. This configuration can actually work better depending on the distance to the sensor and the magnification needed.



Figure 17 - Loupe Mounted in Reverse


Finally Figure 18 shows the sensor loupe on a Sony NEX-5N mirror-less camera. The same device can be used with other cameras (you are not limited to Canon !).

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Figure 18 - Sensor Loupe on a NEX-5N


Final thoughts

I've been using this device to clean my Sony NEX-5N camera sensor and it has worked very well. It's actually a bit scary realizing how much dust the sensors gather over time. Don't panic though, since most of the times, all it takes is a small "rocket blower" to remove it. It's nice to be able to verify right away if you made matters better or worse:)

Note: cleaning sensors is not rocket science (pardon the pun), but if you don't feel comfortable with the risks, and there are some risks every time you open the camera, then please don't do it. There are services out there that will clean the sensor for you for a small fee.

There are some possible improvements to the project that I would likely implement if I was starting over. While the light generated by the three LEDs is adequate for the job, adding two more LEDs might make it a little more even all around the sensor. I would probably also paint the back of the lens cap white so it would reflect more of the LED light towards the sensor. These are improvements you might consider should you decide to make your own. Have fun removing all those dust-spots!

Comments, questions, suggestions? You can reach me at: contact (at sign) paulorenato (dot) com