I'm about to start exploring the world of long exposure shots, using my Canon EOS M. The camera has a standard max exposure time of 30 seconds, but in bulb mode I can keep the shutter open indefinitely (using a wireless remote to control the shutter.)

How long can I leave the shutter open without running the risk of prolonged exposure to light damaging my sensor?

For the purposes of this question assume I'm shooting in summer daylight, so that we can go by the worst case.

  • 3
    \$\begingroup\$ Part of this will depend on how much light is coming in through the lens. \$\endgroup\$ Apr 3, 2014 at 11:00
  • \$\begingroup\$ Makes sense, much less risk of damage at night. I'll update my question to align on it on the worst case. Thanks for the help @RowlandShaw \$\endgroup\$
    – CLockeWork
    Apr 3, 2014 at 11:04
  • 1
    \$\begingroup\$ Just out of curiosity, why would you use bulb mode in daylight? don't you get a very over exposed image? \$\endgroup\$
    – Yao Bo Lu
    Apr 3, 2014 at 11:06
  • \$\begingroup\$ In this case, why do you want bulb mode? \$\endgroup\$
    – Morpho
    Apr 3, 2014 at 11:08
  • 5
    \$\begingroup\$ not an answer to the actual question, but an additional suggestion. For long exposures in regular daytime light, you can use ND filters to reduce the amount of light hence giving you a longer exposure time before the image starts getting burnt out and less likely for your sensor to be damaged \$\endgroup\$
    – Darko
    Apr 3, 2014 at 11:28

3 Answers 3


As long as you aren't pointing the camera at the sun, lasers etc. (see this question)

You should be ok, at worst you'll get a completely over exposed image and the camera may give an over heating warning or the battery will run flat.

This is based on the general consensus (google to the rescue):

Almost certainly if your final result is correctly exposed you have nothing to worry about.

  • \$\begingroup\$ So overheating is mroe of a risk than actual sensor damage? That first link was awesome by the way, clearly I need to get better at Googling :( \$\endgroup\$
    – CLockeWork
    Apr 3, 2014 at 11:56
  • 2
    \$\begingroup\$ @CLockeWork It is a risk in the sense that it may add artifacts to the final image, reduce quality, prevent you from achieving your creative goal etc. It isn't a risk in that it will damage the camera, the camera should just end the exposure and possibly shut down. \$\endgroup\$ Apr 3, 2014 at 12:01
  • \$\begingroup\$ I left a 60D with its shutter opened overnight and at some point before the battery died the shutter will close and the image gets saved. Camera was fine but the picture was really weird. \$\endgroup\$
    – Nelson
    Feb 20, 2015 at 10:18

If you're shooting in summer daylight with very long exposure times, regardless of whether you damage your sensor or not, you're going to get a completely blown out image, with no recoverable data. If you want very long exposures in bright light, your only real choice is to cut the amount of light going through the lens. For this, you'd normally use a Neutral Density filter of appropriate light-cutting ability.

As with all things photography, the prices of these can vary from a few dollars to many hundreds. When looking at an ND filter, the most important thing to consider is how much light it cuts. See this for information on how ND filters are rated.

There are also variable ND filters of varying quality available. With the cheap ones, using them on a wide-angle lens can result in cross-shaped banding on your image, though this often goes away when shooting at longer focal lengths. The best ones don't suffer from this, but are breathtakingly expensive (a quick search on Amazon shows one selling for $450!).

You can also make a ~10-stop ND filter using welding glass, though these often lend a colour cast to your image, which may or may not be desirable. If you shoot RAW, this is fairly easy to correct (though you'll still lose some colour information).

  • \$\begingroup\$ Thank you for this answer, very detailed and I will indeed be looking into ND filters. I have accepted Richard's answer instead because he more directly answered my question, but this has been extremely helpful :) \$\endgroup\$
    – CLockeWork
    Apr 3, 2014 at 12:20

Sensor damage solely depends on the number of photons that hit an individual pixel on a sensor. Every pixel in a sensor has a well-depth. This is the number of electrons that a pixel can hold. When the well-capacity/depth is exceeded the electrons bleed into other pixels, which causes damage to the sensor.

So, any time you are over-exposing the sensor and see pixels bleeding into other pixels (looks like vertical or horizontal streaks) you are damaging the sensor.

It doesn't matter if it's a laser, the sun, or indirect light, occurs over a millisecond or occurs over 4 days, damage is damage.

That being said, try to damage it as little as possible in terms of electrons and duration.

  • 2
    \$\begingroup\$ I've never heard of overexposure damaging the sensor - source? \$\endgroup\$
    – rfusca
    Apr 3, 2014 at 19:51
  • \$\begingroup\$ I worked for a scientific camera company that worked with CCDs, EMCCD's, and sCMOS censors. By overexposure, I don't mean long exposure, simply long enough to fill the well-depth of the pixels. Unless the sensor somehow bleed off extra electrons they have to go somewhere \$\endgroup\$
    – TruthOf42
    Apr 3, 2014 at 19:59
  • 3
    \$\begingroup\$ I think that we're talking about the same thing - but it happens fairly frequently with no apparent ill effects, nor do I see any credible examples of it with a google search. Can you provide any written or documented sources? \$\endgroup\$
    – rfusca
    Apr 3, 2014 at 22:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.