Basic Troubleshooting

This page collects some commonly seen external flash related problems and their solutions. It is not meant to be complete and will be updated frequently.

My External Flash Does Not Fire!

This is a very commonly seen problem. There are a number of possible causes:

1. Check to see if you have turned on your external flash
   This is nearly a stupid answer; but, all of us frequently forgot to turn on our external flash before shooting!
2. Check the Batteries
   In many occasions, we simply keep shooting and assume that the external flash can keep us our shooting pace. In reality, it is usually not the case. Fully charged and fresh batteries may be able to keep up our pace; however, after some shots, we have to give the external flash sufficient time to recharge. The time needed for recharging the external flash is directly proportional to the number of shots that have been taken. More shots means longer recharge time. If we take a shot while the external flash is charging, either the flash does not fire or can only provide minimal output. Both cases will yield results similar to no flash. A rule of thumb is that change batteries if it takes more than 20 seconds to recharge the flash.
3. Check the hotshoe to make sure the external flash has been properly mounted
   Sometimes we stop pushing the external flash into the hotshoe hard enough when we sense some friction. This is a major mistake. We have to push hard enough so that the flash foot completely fits into the flash hotshoe. Otherwise, the center contacts are not aligned properly and the external flash may not be able to detect the triggering signal from the camera. The following shows an example that the flash does not completely fit into the hotshoe.
   

My Shots Are Over-Exposed

There are a number common causes of over-exposed flash images.

1. Check the ISO settings, Apertures and Flash-Subject Distance
   This is usually the first step. Make sure the apertures and ISO values used on the camera and flash are the same (if you are a beginner). If they are the same, then make sure the subject is within the flash-subject distance calculated using the GN and aperture. In the automatic mode, if the subject is closer to the flash than the minimum flash-subject distance calculated via the flash exposure table, over-expose is guaranteed. Keep in mind that with the automatic mode, the actual flash-subject distance can be shorter than the calculated one as the flas sensor will adjust the output power. In the manual mode, since the flash always puts out its maximum power, the tolerance between calculated and actual flash-subject distances is smaller than what you can expect.
2. Do You Have a High GN Flash?
   Many of us prefer to buy a high power flash in the hope that someday we can use its power. Unfortunately, a high power flash will have a higher minimum power as well. If the flash-subject distance is not large enough, the flash may not be able to tone down its output to below its minimum power, and, as a result, over-exposed results are likely. If this happens, move away from the subject, use a smaller aperture, use a lower ISO, or any combination of these three.
3. Check the Flash Sensor!
   If the over-exposed results were obtained using the automatic mode and if you have tried the best to maintain the flash-subject distance and lens and flash apertures, then check the flash sensor. If the sensor is covered by dirt, it will not be able to accurately measure the scene illumination and incorrect exposure is likely.
4. Check the Flash Contact!
   If the flash is not mounted properly, it may act strangely and incorrect exposure is always possible.
5. Did You Forget to Set the Flash to the A or M Mode?
   Keep in mind that in the manual mode the flash will send out its maximum power. Therefore, if you "think" the flash is in the automatic mode in which power may be cut off early, you may get some over-exposed results. Some flashes may also send out maximum power if it is set to use TTL mode but the camera can only support the ISO standard.
6. Check the Background
   In the automatic mode, if the background is dark and far away from the main subject, since the flash sensor will not be able to pick up the reflection from the background, it will "think" the scene is not illuminated properly and continues to put out its maximum power. Consequently, it is possible that the background will be illuminated to some degree (but still under-exposed) while the main subject will receive too much illumination and is over-exposed. Should this happen, either recompose to minimize the proportion of the background in the image or use manual mode.

My Shots Are Under-Exposed

There are a number common causes of over-exposed flash images.

1. Check the ISO settings, Apertures and Flash-Subject Distance
   This is usually the first step. Make sure the apertures and ISO values used on the camera and flash are the same (if you are a beginner). If they are the same, then make sure the subject is within the flash-subject distance calculated using the GN and aperture. In the automatic mode, if the subject is located at a distance larger than the maximum calculated flash-subject distance, under-exposed results are very likely. Keep in mind that with the automatic mode, the actual flash-subject distance may be shorter than the calculated one. In the manual mode, since the flash always puts out its maximum power, the tolerance between calculated and actual flash-subject distances is smaller than what you can expect.
2. Check the Battery!
   If the battery power is weak, the flash may not be recharged fully before your next shot. Consequently, the flash will not be able to discharge the needed power for a particular aperture, flash-subject distance, and ISO sensitivity.
3. Do You Have a Low GN Flash?
   If the flash-subject distance is too large, the flash may not be able to reach that far in the automatic or manual mode, and, as a result, under-exposed results are likely. If this happens, move closer to the subject, use a larger aperture, use a higher ISO, or any combination of these three.
4. Check the Flash Contact!
   If the flash is not mounted properly, it may act strangely and incorrect exposure is always possible.
5. Does the Background Include Glass or Mirrors?
   As we all know, glass and mirrors reflect lights. In the automatic mode, the reflection can fool the flash sensor to think the scene is bright and well-illumination and cut its power prematurely. The result is an under-exposed image. The left image below were taken with the automatic mode in front of a mirror that fooled completely the flash sensor, while the right image below was taken in the manual mode. Now, you can see the difference. Therefore, if you cannot avoid glass and mirrors in the background, use manual mode or shoot from a different angle so that flash light reflection will not enter the flash sensor directly.

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