T2i Remove a lens while the camera is on?

[dishan]

I'm considering using my native EOS Tamron lens with an adapter on a GH2. But since the adapters can't control the aperture, someone recommended setting it on the Canon body, set the aperture, then removing it while the camera is in DOF preview so the aperture stays.
First of all, I assume the DOF previiew button is that little one next to the EOS mount, right under the lens release button, right? I've never had to use it before so I'm not sure.

Secondly, does this advice make sense? I mean, I always thought removing a lens while the camera is on (and therefore exposing the sensor) is a really bad idea! Is this safe to do? And why does the DOF button need to be pressed? Will the iris go back to default otherwise?

 

[Jordan Scott Price]

No idea about the DOF Preview stuff...

But it's not cataclysmic to remove the lens while the camera is on. DSLRs with mirror boxes protect the sensor when you turn it off, so you can turn it off to shield the sensor if you wish, but cine cameras don't have anything to protect the sensor unless the lens or port cap is in place. Typically, the best strategy is to just work quickly and put a new lens or the port/body cap on the camera.

There is a thread discussing the potential for problems when removing smart (electronic) lenses, however...let me find it...

Edit: Damn, I don't know what forum it was under. I thought it was on the FS100 subforum. Basically, some people were airing some fears that removing a lens that communicates electronically with the camera while the camera was on is a problem. However, since you're using a dumb adapter, it shouldn't matter.

 

[Kin Lau]

Yes, the whole point of using DOF preview is to cause the lens to stop down since there isn't a mechanical means of doing so.

By using DOF preview, the sensor is not exposed at all... the shutter is still closed, not to be confused with Liveview or video mode.

BTW, exposing a sensor in a relatively clean env is fine.... that's how we clean the sensor using a swab.

 

[dishan]

Yes, the whole point of using DOF preview is to cause the lens to stop down since there isn't a mechanical means of doing so.

By using DOF preview, the sensor is not exposed at all... the shutter is still closed, not to be confused with Liveview or video mode.

BTW, exposing a sensor in a relatively clean env is fine.... that's how we clean the sensor using a swab.

Hey, you know I always wondered what that little button was for (but apparently not enough to actually look it up or try it). That's really cool! So, apparently when the camera is off the iris defaults to wide open. Removing the lens from the camera in video mode turns the camera off instantly, and defaults the iris before it is fully disconnected. That's why I didn't understand how this works.
But if I flip the camera mode to Aperture priority (and keeping live view off), I can set the desired aperture with the dial, then remove it from the body while holding down the DOF preview button. I can see that the aperture blades are in fact still in place after I do this, so cool!

So technically, if I'm shooting with this and the GH2, I can set the aperture if needed on the canon body first, then put it on a micro 4/3rds adapter (and hope I won't need to change the F-stop during the shoot).

No idea about the DOF Preview stuff...

But it's not cataclysmic to remove the lens while the camera is on. DSLRs with mirror boxes protect the sensor when you turn it off, so you can turn it off to shield the sensor if you wish, but cine cameras don't have anything to protect the sensor unless the lens or port cap is in place. Typically, the best strategy is to just work quickly and put a new lens or the port/body cap on the camera.

There is a thread discussing the potential for problems when removing smart (electronic) lenses, however...let me find it...

Edit: Damn, I don't know what forum it was under. I thought it was on the FS100 subforum. Basically, some people were airing some fears that removing a lens that communicates electronically with the camera while the camera was on is a problem. However, since you're using a dumb adapter, it shouldn't matter.

Well, no- it would matter. The dumb adapter does not get involved until after this step. I'm taking about a native lens being removed from a Canon body. Its an EOS EF-S version of the Tamron that I originally bought for my Canon, so I'm discussing using a Canon t2i body to set the F-stop. The dumb adapters can't interface electronically, so this is the only practical way to do it that doesn't involve electronic adapters that cost a bloody fortune.
That's why I chose to place this topic here and not in the GH2 section- I'm asking about the Canon lens and body, and if removing a lens while the camera is powered on is somehow bad for it. If it is, that's something I need to be concerned about.

However, after Kin Lau's explanation I tried it again here and think I have a better understand of how it works. When pressing the live view button, it holds down the aperture in its current setting so you can see in the optical viewfinder. However, doing that appears to essentially disengage any other communication- light metering stops, you can't focus, etc... everything seems to be "on hold" electronically until you let go of the button. The sensor is surely still protected during this, and there doesn't appear to be much interface going on with the camera at that time (other than obviously sending the signal to stop the iris down). Interestingly enough, I noticed that taking the lens off the camera during like this does NOT shut the camera down (as it would in live view mode). Rather, it just displays F/00 just like it would if I were shooting with vintage glass or some other glass that doesn't interface electronically.
Reattaching the lens, it suddenly updates all information in real time (metering, F-stop, etc). Almost as if the camera was designed to work this way... makes me start to wonder, is that what photographers do? When shooting with primes, you may have to swap lenses relatively quickly. In this mode, is it designed so that photographers can quickly swap out their primes?

Either way, I think I'm going to try out one of those EOS to M43 adapters now that I get how this is supposed to work.

Thanks for the help and interesting insight, guys!