Over the days leading up to the 25th of December I’d like to give something to everyone who stops by my blog. These tips cover camera settings, flash, lighting, software and gear. I’ll be providing a pair of tips each day until 25th December.

#31 – keep the same exposure for a new aperture

same exposure new aperture

Many lenses change their maximum aperture when you zoom from the shorter focal length to the longer one, or you will lose 1-stop or 2-stops of light when you add an extender to a lens. Also you might switch lenses from one with a fast aperture to a slower one. There’s a custom function found in advanced EOS cameras that ensures that even if you are shooting in manual, your exposure will be consistent as you zoom, add an extender or change lenses. It’s called same exposure for new aperture.

same exposure new aperture

Let’s imagine you are photographing birds with an EF100-400mm f/4.5-5.6L IS II USM lens. At 100mm the aperture is f/4.5, but as you zoom to 400mm, the aperture drops to f/5.6, about 2/3-stop. This amount might be possible to recover when processing your shots, but if an extender was added the amount would be more.

Alternatively you might be shooting portraits, and switch from an EF 85mm f/1.4L IS USM lens to an EF 70-200mm f/2.8L IS III USM lens. Now your aperture has been reduced by two whole stops, so this tip is not just for wildlife photographers.

same exposure new aperture

This custom function allows the camera to adjust either the ISO, or shutter speed, to maintain the same brightness. Personally I use the ISO setting, as I’m less concerned about a change from ISO 800 to ISO 1,250 than I would be with a drop in shutter speed from 1/1000s to 1/640s when I zoom to a longer focal length.

same exposure new aperture

If it’s so dim that you were almost at the limit of ISO, then you might get a drop in shutter speed too.


#32 – Zoom your off-camera Speedlite

zoom your speedlite

When working with a an off-camera Speedlite, the head of the remote/slave is automatically set to 24mm. This might be just what you need to fill a softbox, but you can also choose to zoom to a different setting.

zoom your Speedlite

Firstly, as you zoom in the light becomes more concentrated, so your effective power increases. At 24mm the guide number of the 600EX-RT is 27m @ ISO 100, but when you zoom to 35mm the guide number increases by 2/3-stop to 34m @ ISO 100.

zoom your speedlite

Secondly you can constrain the beam of light to create a spotlight type effect. I find that this is particularly useful with the 200mm setting on the Speedlite 600EX II-RT. By placing the Speedlite as high as my light stand allowed, I achieved this spot of light on the floor for the model to work in.


Here’s a few more festive fifty tips

Festive fifty – day #13
ISO safety shift and Image Stabilizer
Festive fifty – day #5
Festive fifty – day #23

About the author

Full-time photo tutor and photographer. I love to share my knowledge and skills to make photos, videos and teach others. I write books and articles for photo magazines and I always have at least one Speedlite flash in my camera bag