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EOS M50 high shutter speed dark bar along bottom


Dell-20230720--Illum--000027.jpgI am using this camera on a microscope, tethered to a computer.  Lately, I have noticed an uneven dark bar along the bottom edge of the images.  The darkest  bar is at 1/4000s, the fastest shutter speed with this camera.  Slower than 1/800 or 1/1000 the aberation is not especially noticeable.  I have some questions:

  1. Does this suggest the shutter is dying?
  2. Will limiting the usage to slower shutter speeds help extend the life, if #1 is the case?
  3. Does this mean replacement of the shutter, as some might suggest?

Interestingly, a fellow at a camera shop was able to take normal images, claiming he exposed at 1/4000.  I cannot understand why this would be the case, as in every case I have tried this shutter speed, the effect is noticeable.  I normally use Entangle, a GNU/Linux tethering software.  The camera has been attached using USB.  I have tried the following:

  • shorter USB cable
  • Canon software on an iphone via wifi
  • Canon software on a Windows computer

In every case, the same dark bar is visible at 1/4000s.

Can anyone suggest something I can do, say, cleaning or maintenance, short of replacing or repairing.  This camera was purchased used, but has been used by me for only about two years. 


Thank you for any suggestions.


Alan Davis



The software used and cable to connect to the computer wouldn't change anything.  This does appear to be a hardware issue with the shutter.  Especially since it is happening for shutter speeds below the maximum as you noted (1/800 or faster).

For the person you mentioned at the camera shop, did they use your camera to capture 1/4000 images?

Have you tried eliminating the microscrope from the equation and shooting images (outdoors in bright sunny conditions) at 1/4000? Do you see the same issue?   Here, I'm wondering if there's something about the light in the microscrope (flicker?)


EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L, 600EX-RT (x6), ST-E3-RT
EOS C70, RF 24-70 f/2.8L IS, EF-EOS R 0.71x


A fellow in college that took photos of algae on a microscope hanging drop slides with a film camera in the late 60s. He helped me get an
A in the class, BTW, did the guy at the camera shop take photos with the microscope to duplicate the situation?

Canon EOS T7; EF-S 18-55mm IS; EF 28-135mm IS; EF 75-300mm; Sigma 150-600mm DG


First reset the camera to default settings. It must be completely set back to factory settings. Now set SS to 1/4000 and go outside on a nice day and try it. Adjust the other settings to allow such a high SS for proper exposure.  If it is OK then we know the shutter is OK. If you still get the black area across the bottom the shutter is failing. This would not be unreasonable especially if you have continually used the M50 at 1/4000 for two years. IMHO, the M50 is a poor choice for this type of continuous dally work. People don't realize it but the forces required to start and stop a mechanical shutter to such high speeds are tremendous. Wear is consequentially high. 

If the M50 passed the outdoor test, then your problem is with your light source. If it is a flash the sync isn't correct. If it is LED or florescent or incandescent it could be flicker. Whatever, the light source has to be corrected.

EOS 1DX and 1D Mk IV and several lenses!