Some upper tier Canon cameras allow you to set the length of time the viewfinder display remains active when no buttons are pressed. A quick look at the EOS 70D Instruction Manual indicates this is not an option with the 70D. You can adjust the time exposure information is actively displayed while in Live View.
There are a few ways to keep the viewfinder display active for longer:
- Keep the Shutter Button half pressed. The viewfinder will remain active as long as you do so. If you have locked exposure it will also remain locked as long as you half press the shutter button.
- Keep the AE Lock button pressed. As long as you hold it down the exposure will remain set at the values current when it was first pressed. This is the case even through multiple exposures.
- Keep the AF-ON button pressed. As long as it is pressed the viewfinder will remain active. If the AE Lock button was pressed first to lock exposure and you press the AF-ON button while the viewfinder is still active the exposure setting will also remain locked as long as the AF-ON button is pressed.
Of course all of this assumes you have the default values selected for each of the buttons on your camera. If you have used the Custom Controls section of the Custom Functions menu, then you would need to use whatever button has been assigned the above functions.
There are also several ways to use the Custom Controls Menu to allow you to do what you want. Here are just a few of them:
- Set the shutter button for "Metering Start" only, without AF. This means AF will only be active when you hold down the AF-ON button on the back of the camera. Many refer to this as "back button AF". By separating AF from the half press of the shutter button, you can hold the shutter button halfway down (to keep the viewfinder active and preserve an exposure setting locked in using the Exposure Lock button on the back of the camera) while allowing you to control AF via the AF-ON button. This works particularly well with "One Shot" AF that locks the focus once AF is achieved. Each time you press the AF-ON button the AF will focus again and will then hold that focus setting (even after you release the AF-ON button) while you can recompose.
- Set the shutter button for "AE Lock (while button is pressed)". This works the same as above, except that metering is done and exposure locked in when you first half-press the shutter. You would also need to press the AF-ON button to use AF. But there is no need to press the AE Lock button at all! If you wish to change the exposure, you only need to release the shutter button and then half-press it again. You can even maintain the exposure lock for multiple exposures as long as you maintain a half-press of the shutter button between the full-press needed to take the photo.
- Leave the shutter button as is set by default to "Metering start/AF start" and set the AF-ON button to "AF Stop". This works particularly well with "AI Servo" AF. In this scenario you would press the AE Lock button to set exposure, then depress the shutter button halfway to begin AF. As long as you hold the shutter button halfway the exposure value will remain locked in, AI Servo AF will be active, and the viewfinder will remain on. If you wish to focus and recompose then place the active focus point(s) over the desired target and depress and hold the AF-ON button (that has been converted to AF-OFF) to lock in the focus, and then recompose before fully depressing the shutter button to take the shot. Exposure would not be locked from one frame to the next.
- Set the AE Lock button to AE Lock (hold). A first press of the button will lock in exposure. A second press of the button will release the exposure lock. The main disadvantage here is that if you have exposure locked in and wish to lock in a different exposure for a different framing you must press the AE Lock button twice to do so. It's also easy to forget exposure is locked after taking a shot and then recomposing and taking another shot of a different scene without pressing the AE Lock button to release the locked exposure value(s)!