TBPJr Loc: South Carolina

Don't bother, UNLESS your manual instructs you to do so. I have never concerned myself with turning the camera off when swapping lenses because I didn't recall any such instruction in the manual that came with my camera (or the updates). Just as in the discussion of whether to power down while changing cards, it does not appear to be necessary.

I read all the responses until just before now (with time out to recheck the manual to my Canon 5D Mark III)--nowhere could I find a suggestion or direction to power down the camera to change lenses--I was pretty sure this would be the case when I started because I have read it several times and I am picky about complying with the instructions on use and care (I did break one of the rules--I dropped the camera a little over a month ago, but that was nothing I tried to do). Despite all of the statements of our UHH crowd, I see no reason to turn the power off to change lenses--none the reasons for doing so that have been offered in this thread are echoed in the manual from the manufacturer and none of the concerns are addressed as issues in the manual. I generally have little patience with proscriptions offered without a basis in actual knowledge--like those for obtaining permission to photograph in public places--and none of the reasoning here is discussed in the manual for my camera, not "the sensor is charged," the "contacts will rub and may spark," "any electronic device should be powered off to work with it," or any of the others. Of course, other cameras well may have such requirements--one should follow the instructions in the operator's/owner's manual.

John8385 Loc: Leesburg, Fl

Thanks TBPJr . . . this has been an interesting thread and forum. I've seen pros and cons both ways. I think I may still turn mine off seeing I work with electrical all day and see the importance of powering down some equipment while others it doesn't matter. Almost like the discussions in this thread. I was just a little concerned on the wear and tear of the off/on switch and possibly some damage to the electronics if it wasn't powered down.

TriX Loc: Raleigh, NC

A

If you remove the lens from your 5D3, you will notice a series of spring loaded contacts on the body that mate with the stationary contacts on the lens. Now when you initially mount the lens before rotating into the locked position, you’ll also notice that the flange of the lens is flush with the flange of the body. Soooo, when you rotate the lens into the locked position, each of the contacts on the lens touches each of the contacts in the body, but not until the lens is completely locked do all the contacts line up CORRECTLY. That means that as you rotate the lens the last contact patch on the lens touches the first contact on the body, and as you continue to rotate the lens until locked, it touches every contact before finally touching the correct contact when locked. Not only does this mean that almost every contact on the lens touches the WRONG contact at the body while rotating, but that the contacts on the lens MAY be able to bridge two adjoining contacts on the body. The only thing that MAY save you is if the camera automatically shuts off power to the lens within the first few degrees of rotation either way - locking or unlocking, and Canon MAY have built this in as a safety feature, but I’m certainly not risking my 5D3 on that possibility. But if you want to, feel free, but I think that’s bad advice for other owners unless you can document such a safety feature. If you cannot, the advice to shut off power BEFORE changing lenses stands, at least on EOS mount bodies and lenses.

John8385 Loc: Leesburg, Fl

TBPJr Loc: South Carolina

Horsefeathers! If any of that made any difference at all, don't you think Canon would have warned its customers in the owner's manual? It includes such instructions as "This camera is a precision instrument. Do not drop it or subject it to physical shock." and "Do not touch the camera's electrical contacts with your fingers. This is to prevent the contacts from corroding. Corroded contacts can cause camera misoperation." The omission of the warning you are attempting to rationalize would be a great lapse; I have never read any discussion of a repair or malfunction attributed to any failure to follow your imagined precaution.

No one should have to be told not to drop his camera, yet Canon included that explicit instruction. The omission of a requirement to to power down the camera to change lenses is a pretty clear indication that Canon either designed its camera to deal with changing the lens without powering down or knew it made no difference to the equipment to do so without any such precaution. Creating new safety procedures out of thin air does nothing for the camera, the lenses, or a photographer.

Read the manual; follow the instructions.

Carnac Loc: Las Vegas

I have been using Canon DSLRs for years. 30D, 50D, 5D II, with anywhere from 7 to 12 lenses. Sometimes the camera is off when I change lenses, but most of the time the camera remains on during the change. With hundreds (probably thousands) of lens changes - never had a single problem with a Canon lens. I had a couple of problems with third party lenses, and I attribute that just to the third party lens.

Do what you want, but I wouldn't (don't) sweat having the camera on or off when changing a lens. More likely that the on/off switch will break from excessive switching before there is a problem with the lens.

Jim

torchman310 Loc: Santa Clarita, Ca.

Your camera's instructions should tell you. But any way, turn it off before switching lenses. You can short circuit the electronics in the body if you don't. Better safe than sorry.

Anhanga Brasil Loc: Cabo Frio - Brazil

It is on my T6 manual: "Turn off the power before changing lenses".
And I do.

Tomcat5133 Loc: Gladwyne PA

Of course shut down when opening camera by exchanging lens.
I also shut the camera off when switching cards or putting new one in.
Good luck.

TriX Loc: Raleigh, NC

With all due respect, the fact that the prohibition isn’t in the manual is a pretty poor counter arguement against the facts that I just presented. Let’s say that the camera turns off as soon as one of the contacts is opened as you rotate. Now disregarding that there may be current flowing through the contact(s) at the time and may cause a small arc/spark which over time will damage the thin gold plating or create a transient that may damage a semiconductor device or corrupt data in memory; considering how close the contacts are, the time until it hits the next contact is minuscule, and as you undoubtedly know, the camera doesn’t shut off instantly even when done intentionally. So if you are willing to risk a 3K$ body on a possible omission in the manual, then God bless and carry on, but I have read most sections of that particular manual MANY times, and I can think of several omissions, so I’ll keep turning mine off. This is one occasion where we’ll need to agree to disagree.

TBPJr Loc: South Carolina

The problem is that you cited exactly no facts, just speculation based on zero knowledge about the circuits, the electrical currents, the charges, or anything else (I do not have that detailed technical knowledge, either). Your preference to do as you see fit with your camera is entirely yours--as you said, you should do as you please (as will I). But it is another thing completely to answer the questions of someone seeking information with pronouncements about things you only imagine. I, like Carnac, have been using Canon products for years (my DSLR experience is only with the 20D and the 5D Mark III)--with thousands of lens changes (and maybe hundreds of memory card swaps), I have never encountered any problem or heard of one caused by leaving the camera powered while making the change. My 5D Mark III is over six years old; Canon routinely updates its manuals (it has added information about what lenses autofocus at what f-stops with which focus points for updated lenses, for example); if there were an issue associated with the power status of the camera and changing lenses, I am confident we owners would know by now (provided we registered and follow updated information at all).

After reading Anhanga Brasil's comment, I was curious, so I checked the T6 manual online, and then a lot of the other manuals for Canon DSLRs. What I found was that the manuals for the T6-series, the T7-series, and some others (generally older, but not including the xxD series or the 5D series--they began to run together after a while) include the instruction to turn off the camera power while changing lenses only in a section about avoiding shooting problems (unspecified), i.e., not in any caution against things that might cause equipment damage or in other safety warnings. That specific instruction is not reflected in the step-by-step procedure for attaching and detaching a lens in any of the manuals; that alone indicates that the status of the power switch is unimportant for the camera and the lens, even for the cameras whose manuals contain the instruction at all. All of that is pretty strong evidence that the "omission" in the 5D series manuals is deliberate, and not an oversight, because the power status of the camera does not matter when changing lenses (or memory cards).

My advice is still the same: do what the manual for your camera recommends. Precautions based on imagined issues are like every other superstition--useless.

As for possible omissions in the owner's manual, I could easily believe that--Canon's technical writers are certainly not the best at clear communication. However, I have seen nothing to persuade me that the omissions extend to issues that could damage the camera or shorten its life--the omissions are much more in the areas of explaining how particular menu settings work and how they affect other settings. What specific omissions did you find?

TBPJr Loc: South Carolina

It is in your manual--I looked online, then I became curious. The instruction to turn off the camera when attaching or detaching lenses is in the T6-series, the T7-series, and some other, older series; that instruction is marked with the symbol that indicates one should follow it to avoid shooting problems, and is found only after all the other discussion about detaching and attaching a lens. There is nothing in any of the other places one finds cautions that address safety, whether for equipment or the user; it's also not in the step-by-step instruction for attaching and detaching a lens. Whatever the issue is, Canon does not say, that I can find, at least.

Do what your manual advises--I certainly try to do what mine says.

TriX Loc: Raleigh, NC

The facts I referred to are my physical examination of the arrangement of the various contacts on exactly the Camera you are referring to - the 5D3, which I have owned for a number of years. I also checked to see if perhaps the flanges did not touch until the last few degrees of rotation (thus keeping the contacts separated until the final tightening), but that was not the case. You are certainly correct that neither of us have schematics, but we can be assured that there is a motor that drives the lens for AF and an actuator that drives the aperture and that both of these actuators require voltage and some current to drive. I have not measured the voltage on the contacts with the lens detached (but I may), but I think it’s safe to assume it’s likely in the 3-6 volt range and the actuators (USM motor for the AF) draw more than a few ma of current while autofocusing or changing aperture - probably in the 10s of ma. I think it’s also safe to assume there is at least one ground pin. Further, unless the camera is off, it’s certainly possible the the lens is changing aperture or focus while we’re detaching the lens. Thus, it’s not only possible but likely that at least one or two of the pins are hot with respect to ground. Now it MAY be that either (1) the first pin to disconnect and the last to connect is the supply rail, thus no danger of inadvertently shorting to ground, or (2) there may be a sensor or switch that doesn't make until the lens is locked in position, preventing power being applied until locked, or (3) some other unknown safety mechanism, and I grant this is a possibility.

Like you, I have owned multiple Canon bodies for about 60 years (starting with an AE-1P and F1N) and my last two DSLRs have been the 7D and 5D3, which I still have. My entire working life has been in electronics, so having seen every failure you can imagine including ESD damage in the most benign circumstances (even on circuits with specific protection), my general rule is to always power down before making or removing any type of connection unless I know that the circuit has been specifically designed for “hot swap”. So regardless of the fact that you (and many others as far as I can tell) rarely power down when changing lenses without damage (at least until now), I would personally never do that or advise others to out of an abundance of caution - it’s just too easy to simply turn off the switch. I do note btw, in researching this, that many Nikon cameras specifically warn against changing lenses with power on, so my guess is that this is brand and lens-to-Camera interface specific. As I said in my last post, this is a case where we can agree to disagree.

Edit: Here is the pinout for the EOS lens interface. Note that there is battery voltage for the focusing motor on Pin 1, VDD on pin 3, and grounds on pins 2 and 7:

Pin
Number Pin
Name Description
1 VBat Focusing motor power
2 A_GND Motor Ground (this contact pad is bigger then others)
3 VDD Lens Difital power
4 Dout SPI camera digital output
5 Din SPI camera digital input
6 Dclk SPI clock
7 D_GND Lens digital ground

Cheers

williejoha

All the arguments that TBPJr is posting is from a technical standpoint total garbage. If you want to change with the power on go for it.
WJH

rmorrison1116 Loc: Near Valley Forge, Pennsylvania

Unless you are pressing the shutter button or whichever button you designated to activate the camera, there is no communication going on with the lens. It's just that simple. The cameras power switch may be in the on position but that doesn't mean the camera is active, it simply means power is available. Nothing is doing anything until you half press the shutter release or whatever button you have assigned that function to.
I have changed lenses on all of my Canon and Nikon DSLR'S with the power switch in the on position numerous times with absolutely no I'll effect. If anyone wants to turn the power off, that's absolutely fine.