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I have just accidentally changed my lens over with the power on. In the manual it lists this as something you shouldn't do as a 'caution' . Can this cause damage? If so, what and how will I tell?

(I have an Olympus OM-D.)

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    \$\begingroup\$ I've never once turned off my DSLR for the purpose of changing my lens. Don't worry about it. \$\endgroup\$
    – dpollitt
    Commented Aug 16, 2012 at 13:50
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    \$\begingroup\$ @dpollitt same here, not problems. I think I had my 5D2 freak out once, and just turned it off and on again, and it resolved it. \$\endgroup\$
    – Fake Name
    Commented Aug 16, 2012 at 22:21
  • \$\begingroup\$ You still have the shutter covering the sensor. When you press the release button for the lens, the electrical contacts are powered down AFAIK. I guess you do more harm to the camera if you power it down each time you change a lens. Just make sure you don't change it while it is taking a picture (e.g. long time exposure). I did that already thousands of times, no problems. \$\endgroup\$
    – Andreas Huppert
    Commented Sep 25, 2013 at 16:30
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    \$\begingroup\$ If it was especially dangerous, free lensing would be an activity to seriously avoid. \$\endgroup\$
    – Joanne C
    Commented Sep 29, 2013 at 12:51

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The potential problem is that the sensor or the glass cover over the sensor is electrically charged whilst it is switched on, so if you take the lens off, it will attract dust.

Search the web for sensor cleaning, but it is a subject that divides photographers. Some only ever get their sensors professionally cleaned, others do it themselves quite often. http://content.photojojo.com/tutorials/digital-slr-sensor-cleaning/ contains more information, and a method for seeing how dirty your sensor actually is. Don't panic at this stage, you may have no dust on your sensor at all. Take a photo at f22 of a blue sky, uniform grey wall or similar and view at 100% to see how many specks of dust are on the photo.

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  • \$\begingroup\$ It happens that Olympus has one of the best built-in automatic sensor-cleaning systems (possibly the best, although it's been several years since I've seen a comparison). It's likely that this will clear up any dust issues from a one-time accidental powered-on lens change. \$\endgroup\$
    – mattdm
    Commented Aug 16, 2012 at 12:50
  • \$\begingroup\$ @Chris Better than one photo at f/22, take TWO photos and then swap to and from between them - either a displayed or zoomed in to variable extents. Dust that is in the sensor will be constant between shots. Other source of occlusion (if any) will "flicker" between shots. \$\endgroup\$
    – Russell McMahon
    Commented Aug 16, 2012 at 13:35
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    \$\begingroup\$ You can do a fair job of simulating an evenly illuminated surface by setting aperture to f/22 or smaller, adjust ISO or whatever until exposure is 2+ seconds, find a moderately uniform target, DEFOCUS onto something else, then point back at target and wave lens to and fro and in 'circles' while the exposure is occurring. The defocused waving gives you a uniform exposure (once you get the feel for the method). | \$\endgroup\$
    – Russell McMahon
    Commented Aug 16, 2012 at 13:38
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    \$\begingroup\$ This "wave the unfocused camera for several seconds (is he mad???)" method is also able to give you an emergency white balance reference when a suitable surface is unavailable or you need one urgently. Wave defocused image area over light source of interest for say 2 to 4 seconds. IF the light is "white" a grey card would be properly illuminated. IF the light is not white then you'll get the hue (more or less) that a grey card will see. Useful for eg end of reception dance with disco strobes. This vector sums the lights and gives you SOME hope of being approx right. Some :-). \$\endgroup\$
    – Russell McMahon
    Commented Aug 16, 2012 at 13:41
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    \$\begingroup\$ The statement "The potential problem is that the sensor or the glass cover over the sensor is electrically charged whilst it is switched on, so if you take the lens off, it will attract dust." has always been problematic for me since the sensor is usually covered by the shutter unless an exposure is taking place. Ring hollow for anyone else? \$\endgroup\$
    – BobT
    Commented Sep 23, 2013 at 18:10
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To directly answer your question, it introduces more variables that can cause damage.

Keep in mind the mechanics of an interchangeable lens camera. You have mechanical and electrical links between the camera and the lens. Having the power on means that there could possibly be gears moving or a current moving between the two and you'd be interrupting this link without affording the camera an opportunity to finish what it's doing. While most cameras don't have a problem with this, it's not the intended method of breaking the link. Powering off the camera will ensure that there isn't a link between the two.

As Chris mentioned, you will attract dust and this will indirectly introduce more opportunities to damage your lens as well.

That said, I've done hundreds, possibly thousands of hot swaps on my 7D and have not had any issues. Most cameras are designed to be able to hot swap. Possible signs of damage would be a failing auto focus or trouble recognizing the lenses.

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  • \$\begingroup\$ In this case it's a mirrorless interchangeable lens camera, not an SLR, but the same basic things apply. \$\endgroup\$
    – mattdm
    Commented Aug 16, 2012 at 14:05
  • \$\begingroup\$ Thanks, @mattdm, I updated my answer to remove the SLR note. \$\endgroup\$
    – AndyML
    Commented Aug 16, 2012 at 14:09
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    \$\begingroup\$ Wow, do I feel anal retentive! I have never done a 'hot swap', in fact, I shut off the image stabilization on the lens, then power down the camera EVERY TIME I swap lenses. I guess I'm paranoid of spurious signals, too slow/too fast contact closures, IS being powered on uncontrolled... the sort of things that engineers don't pay rapt attention to when they specify in the manual that swapping lenses must be done on an electrically dead camera. "Hot Swapping" sounds suspiciously like Russian roulette to me. \$\endgroup\$
    – Therealstubot
    Commented Aug 16, 2012 at 18:12
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    \$\begingroup\$ I almost always hot swap. And I do have to clean the sensor more often than some report. \$\endgroup\$
    – Russell McMahon
    Commented Aug 16, 2012 at 18:33
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It really depends on the camera being used and how it is designed. There are certain things that the camera should do before a lens is removed such as ensuring the mirror is down to protect the sensor and potentially disengaging mechanical links to drive aperture and focus (though these are generally designed to be self-disengaging when you remove the lens.)

Many cameras, however, can tell when you push the lens removal button and can do this process by the time you actually unscrew and remove the lens. The best advice is follow the manual, if it cautions against doing it, then you are best off to listen to the manufacturer that designed your camera. If they don't object to it, you should be fine.

Personally, I use a Canon 5D Mark iii and have no problems with removing the lens on the fly and reattaching a new one. I've even done this in relatively dusty environments without a problem yet (over the course of a year). The only thing it specifies is that if you are going to use a teleconverter, you should attach it to the lens first so that the correct information is available when you attach the lens assembly to the camera.

As far as damage that could occur, the most likely issue would be that something could happen to the sensor or mirror as the mirror moves to try and cover the sensor as you are removing the lens or if the mirror doesn't move at all, leaving the sensor directly exposed to outside contaminants (such as dust). There could be other issues specific to your camera body though and depending on lens design, it could be possible (however unlikely), for example for the mirror to collide with part of the lens. This would do substantially more damage and possibly break the mirror, rendering the camera effectively useless until repairs can be made.

While I can't prove it, if the sensor having a charge actually could draw in dust, then why on earth wouldn't camera makers cut the power to it when the lens is removed. If they can do it when the camera is powered off, they can do it when the lens is removed too and it would be bad design not to (either that or it simply is an old wives tail that it's a problem).

One final thought, it may actually be worse to power off for a change. While there isn't any evidence of dust attracting being an issue, powering off and powering on does potentially result in extra self-cleaning cycles as well as other power off and power on activities. These activities have a much higher chance of causing wear and tear on the camera and resulting in eventual damage than the remote possibility that it might attract dust (which could simply be cleaned off). I doubt that either of these is even a measurable contributor, but if I had to gamble, I'd gamble that turning off for every lens change is actually more harmful (by an insignificantly small amount.)

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    \$\begingroup\$ This is the only answer so far to mention that the lens release button is not only a mechanical function but is also sending an electronic signal to the camera about a lens removal. \$\endgroup\$
    – Esa Paulasto
    Commented Nov 9, 2013 at 11:47
  • \$\begingroup\$ The lens release button theory sounds good, but it is incorrect, at least on Canon EOS cameras. You can hold the LRB all the way down and shoot with full camera functionality. You can even rotate the lens and shoot in manual exposure mode (you'll lose control of the aperture - it will stay set where it was when the power contacts were disconnected - but the camera will take a photo). You can even take an exposure when there is no lens attached to the camera at all. \$\endgroup\$
    – Michael C
    Commented Dec 21, 2016 at 1:14
  • \$\begingroup\$ "While I can't prove it, if the sensor having a charge actually could draw in dust, then why on earth wouldn't camera makers cut the power to it when the lens is removed. If they can do it when the camera is powered off, they can do it when the lens is removed too and it would be bad design not to (either that or it simply is an old wives tail that it's a problem)." \$\endgroup\$
    – Michael C
    Commented Dec 21, 2016 at 7:00
  • \$\begingroup\$ While it is not perfectly clear you are saying such, it seems you are at least indicating that you think that the camera has a sensor that detects when the lens release button is pushed. Canon cameras don't have such a sensor. The camera detects a lens is being removed when the electrical power contacts between the body and lens are no longer touching, and even then the sensor is still energized and the mirror, etc. operate exactly as they would with a lens fully attached. The only difference is that the camera won't attempt AF or Av control. \$\endgroup\$
    – Michael C
    Commented Dec 21, 2016 at 7:03
  • \$\begingroup\$ Actually, there's one other small difference. If a Canon DSLR camera is in live view mode and has an electronically active lens attached, when you start to remove the lens, it treats that communication failure as evidence of lens removal and drops the mirror to protect itself. You can probably put it back in live view mode with a manual lens (I've never tried), but it definitely kicks you out. I'm not sure what it does if you try that in video mode. \$\endgroup\$
    – dgatwood
    Commented Nov 29, 2017 at 20:22
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I don't think any manufacturer officially supports this, but you can hold down the depth of field preview button to set the aperturer before removing the lens to add an extension tube or reverse adapter and for this to work the power must be kept on while the lens is removed. So far I haven't had any issues and this entire technique relies on this hot-swap step so you should be mostly safe in doing so.

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