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I'm using a Nikon D5100 with a shutter count pf only around 7k. Now when I use it with the pop-up flash, only the thin top part or thin bottom part is flashed, the rest would be black or dark.

I tried manually adjusting the flash sync, tried updating my firmware, also tried cleaning the body, still don't work.

Photos without flash are great and I have no issues with it.

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    \$\begingroup\$ Did you try shutter speed 1/200 or slower? \$\endgroup\$ Nov 1, 2023 at 12:07
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    \$\begingroup\$ Do you mean that you are using the built in flash? \$\endgroup\$ Nov 1, 2023 at 12:13
  • \$\begingroup\$ Yes sorry, I am using the built in flash \$\endgroup\$ Nov 1, 2023 at 12:26
  • \$\begingroup\$ I tried other shutter speeds, and it randomly work on 1/30 \$\endgroup\$ Nov 1, 2023 at 12:27
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    \$\begingroup\$ @MarcNarciso, please provide example photo. And what do you mean by " randomly work on 1/30"? \$\endgroup\$ Nov 1, 2023 at 12:29

2 Answers 2

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In a DSLR the shutter is a double curtain. Initially the first curtain covers the sensor. To take a shot, the first curtain is opened, then after the set exposure duration the second curtain follows.

Below a given speed/above a given duration (usually around 1/200s) the first curtain is completely opened before the second curtains starts, to the whole sensor is exposed to light at the same time.

At higher speeds, the second curtain starts before the first is completely opened, so you get a moving slit across the sensor, and the whole sensor it never entirely exposed to light. If you get a flash during the exposure, it will only enter that part of the sensor which is behind the open slit, and the rest of the picture will be dark.

So usually when using a flash, you keep the exposure long enough to have the whole sensor exposed. This is known as flash sync speed.

There are flashes that support High Speed Sync, where the flash emits a burst of small flashes during the exposure to overcome this when the exposure is shorter than the flash sync speed.

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  • \$\begingroup\$ If the issue is using a shutter speed faster than sync speed without an HSS capable flash, dark banding would be at the top/bottom of the frame [in landscape orientation], not the middle. \$\endgroup\$
    – inkista
    Nov 1, 2023 at 21:08
  • \$\begingroup\$ @inkista AFAIK the flash is triggered when the first curtain is fully open (standard case) so that would be a slit open at one end (2nd curtain almost down) or just before the 2nd curtain starts ("2nd curtain" option) with the the 1st curtain still way up so that would be a slit at the opposite end. \$\endgroup\$
    – xenoid
    Nov 1, 2023 at 21:22
  • \$\begingroup\$ I don't think there's "a slit at the opposite end". \$\endgroup\$
    – inkista
    Nov 1, 2023 at 21:37
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As xenoid said in their answer, at any shutter speed faster than sync speed there is not a single moment when the full frame is exposed, that's why sync speed is usually the fastest speed for flash to work correctly (so that it can fire the short pulse exactly when all the frame is exposed). All cameras typically limit the shutter speed as soon as you pop the flash.

You said you are having issues even at 1/30 which is very certainly the speed at which the flash should work correctly and there are no settings which would cause your problem.

Therefore your camera is malfunctioning, the sync between the flash the shutter and flash is not maintained. You need to service it.

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    \$\begingroup\$ I agree that the camera must be malfunctioning. Normally the camera will not allow the built in flash to function with incorrect settings, and will not allow for high speed sync with the built in flash. Also, a black band at the top of the image is the typical x sync/SS issue; but a black band at the beginning would be the flash firing late. \$\endgroup\$ Nov 1, 2023 at 16:07

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