Safety shift is the helping hand for many EOS cameras that keeps exposure in check when the light changes, either unexpectedly or gradually.
Let me give you a scenario… you choose to shoot some action shots and know that the right shutter speed is key to capturing motion. If that means you turn the mode dial to Tv then safety shift is the guardian angel for your exposure.
Start your day be selecting 1/2000s and ISO 400. The light is relatively good, so your camera selects a suitable aperture of f/5.6. At some point in the shoot the clouds roll in and it slowly gets darker. You don’t really notice until the aperture display in the viewfinder or on the LCD starts flashing at f/2.8 – the widest your lens allows.
In the photo above, there’s a tree adding shade over the track for the foreground rider and the one behind is in brighter light, requiring different exposures.
Flashing aperture display
Most people don’t read the manual enough to know that the flashing aperture display means the camera cannot open the aperture any wider, and underexposed shots are the result.
It can happen the other way too, but somehow photographers rarely suffer from “too much light” 🙂
That flashing aperture was your cue to raise the fixed ISO or choose a slower shutter speed. However you want a little helping hand and that is the whole reason for you to know about safety shift.
Most modern EOS cameras in the mid-range and advanced categories have safety shift. Cameras including the EOS 70D/80D/7D and full-frame cameras. Though EOS 250D also has a limited safety shift too.
The brightness changed as the rider moved from the lighter open part of the track to the more densely tree covered shaded part during this jump.
Safety shift custom function
There are three settings for safety shift in many cameras.
- Disable
- Shutter speed / aperture
- ISO Speed
So no surprise that if you choose disable, or don’t choose something, as this is the default, then you’re going to experience photos getting darker as the light level drops.
Way back in the beginning of time photographers used film cameras, and the film in use determined the ISO available. So safety shift handily offered the choice to adjust the selected shutter speed (or aperture value if using aperture priority, Av mode). The whole reason for using shutter priority is often to freeze action, so if the camera slowed your 1/2000s to 1/1000s you might be ok, but what about 1/250s?
EOS 250D has the shutter speed / aperture option, but not the ISO one below.
With digital cameras, and recent ones in particular, the ability to use higher ISO values has less of an impact on the pictures. If like me, you follow the “sharp with a bit of noise is better than blurry but clean” approach, you’ll welcome your fixed ISO speed being automatically changed for a correct exposure.
ISO limits for safety shift
Your camera’s limits for auto ISO are the range of ISO that can be selected if you use ISO speed safety shift. Some of the advanced cameras allow you to separately set a limit for ISO auto to the range you can manually choose.
Aperture priority (Av)
Safety shift applies to aperture priority too, it is most likely to be helpful if you are in the habit of taking portraits with fast lenses at wide apertures in bright light. In such cases once the shutter speed is maxed out, then the ISO will be reduced if possible. However when ISO is at the minimum, shutter speed at the maximum and you still persist in taking photos in bright light, then you’re going to see a flashing shutter speed indication. That’s your cue to close the aperture a little, fit an ND filter or go somewhere with less light. Even in full sun through a huge glass window I only reached 1/2000s at f/1.2 for the shot above. Clearly I’m going to need a different country to test safety shift in bright light.
Program (P) mode
If you’ve chosen safety shift with ISO speed, it also intervenes when needed while using program mode with a fixed ISO, as you can see explained in the help from the EOS R above. Though maybe if your mostly using program mode, custom functions are possibly not on your radar yet…
EOS R/RP – Flexible priority mode
Safety shift won’t help you out if you use flexible priority mode as if it was shutter priority with a fixed ISO.
Hi Thanks, I understand how to use safety shift but would like to know if exposure compensation reverts to zero when safety shift is active. I always set exposure compensation to underexpose by a third or two thirds in a variety of situations. Will this setting be affected if safety shift becomes active when shot taken. Many thanks, Cheers , Don , 5D mk 4
Nice question Don. But the answer is easy to see when you check on the camera. I’ve set my camera to Tv mode, chosen 1/1000 shutter speed and set the ISO to 100. Half press the shutter and the ISO jumped to 3200. Then keeping the camera in the same place I changed the exposure compensation to +1, then half-pressed the shutter and the ISO went to 6400. Dialled in -1 exposure compensation and the ISO went to 1600. I did this on both the EOS 5D Mark IV and the EOS R.
The one thing that will cause problems is where the ISO auto range is such that the camera cannot set a suitable ISO to give the intended exposure.
Brian/p4pictures