Can I use my Canon T5i and close-up filters as a low-power microscope for PCB soldering?
Asked 10/18/2019
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I’d like to use my Canon T5i as a live-view magnifier for PCB soldering instead of buying a dedicated microscope. I have an 18-135mm kit lens and a 50mm f/1.8 STM, and I can mount the camera above the work and send video to a monitor.
My main concern is working distance and depth of field. I need about 6–8 inches of clearance between the lens and the board. Would cheap macro/close-up filters make this practical, and how would they affect focus range? For example, if I add a close-up lens, what happens to infinity focus and the maximum focus distance?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
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"Infinity" focus will be mapped to a finite distance. That distance is the inverse in meters of the lens strength in dioptres. If you aim for a maximum distance of 8" (roughly 0.2m) for infinity distance setting, that gives you a maximum strength for a closeup lens of 5 diopters.
A "set of cheap macro filters" will essentially be garbage with dubious sharpness and chromatic aberrations as you move from the center. Due to the limited zoom factor, you'll be able to move farther away and get better depth of field and magnification with a small-sensor superzoom (pitching for 600mm-800mm) and a moderate closeup lens (very preferably achromatic) of 3 dioptres or so.
Note that you'll also want continuous lighting sufficient for stopping down aperture as far as possible.
There is a non-zero probability that you'll be better off just taking that lighting and the intended closeup lens and mounting the closeup lens at a suitable distance between object and eye. Not going through the photographic plane will actually be a big boon with regard to things like depth of field and the impact of aberrations.
Originally by user87543. Source · Licensed CC BY-SA 4.0
user87543
6y ago
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It’s only partly practical. A close-up filter changes the lens so that “infinity” focus becomes a finite maximum distance: approximately 1 / diopters in meters. So a 5-diopter close-up lens puts the far focus limit around 0.2 m (about 8 in).
For your goal, cheap close-up filter sets are not ideal: image quality is often poor, especially away from the center, with softness and chromatic aberration. Working distance is also a problem. With a strong close-up lens on a 50mm, real-world working distance can be around 3 inches, which is too short for soldering.
Depth of field at high magnification will be very shallow. To improve it, you’ll need strong continuous light or flash so you can stop the lens down.
If you want to experiment cheaply, a reverse ring or extension tubes can give much higher magnification, but they usually reduce working distance even more, so they’re not a great fit for soldering clearance.
Bottom line: using the T5i as a PCB inspection setup is possible, but your required 6–8 inch working distance makes cheap macro filters on your current lenses a poor solution.
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AI6y ago
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