I have noticed that when shooting with the Olympus EM5 I have become very lazy about setting the aperture. I have fallen into the habit of shooting at f/7.1 when using the 12-40mm lens. Unless there is something that’s very close to the camera I find that I can get away with using this aperture almost all the time. With this lens and aperture combination I find that it gives me an excellent depth of field for Landscapes but also produces sharp images that are well focussed from corner to corner.
But this isn’t to say that it’s the best aperture for the lens.
I have actually found that my lens tends to perform at its best when stopped down to around f/5.6. There is less depth of field at this aperture but you can still achieve a hell of a lot when used with the 12mm wide angle end of the lens. You just have to take care where you place the focus point – but more on that in another blog post.
You might also find a similar setting are also good with other Micro 43 lenses in this focal range. I also used to use a Panasonic 14-45 and this seem to match the performance characteristics of the 12-40.
The image above was taken inside an old kiln in the Royal Mint in Bolivia. It was shot at f/3.5 so that I could keep the ISO low (in this case ISO400) together with reasonably fast shutter speed as I was shooting hand held. Actually the shutter speed was 1/15” but it was sufficiently fast. I had the camera in burst mode and fired of a few shots one after the other to ensure one of these was sharp.
This lens seems to perform very well across most of the aperture range. Take a look at the enlargement of the top left of the image, shown below. This has minimal capture sharpening applied as part of the RAW conversion in Lightroom.
So whilst I am always keen to use my lenses at the optimum aperture, I don’t mind deviating if it means that I can capture the image.
The Lightweight Photographer 
Great post. I’ve been wondering about using a prime 12mn on my EM5 as agree that although a brilliant lens, when I’m out hill walking, even the 12-40 Oly pro zoom feels heavy and strangely vulnerable. I currently swap between my iPhone SE and the pocket sizedCanon S110 in raw mode. Great blog by the way, cheers.
Thanks for the positive feedback.
Intereesting that you say you have been considering a 12mm prime. I have also been considering one of these. The only thing that puts me off (besides the high cost) is a friend who has owned a couple of these now. He keeps selling them as the corner/edge performance isn’t gret. He says there is a lot of colour fringing. Although the 12-40 is heavy the performance is excellent.
Dear Robin
I have been reflecting upon your comments and for travel photography I am often shooting at f2.8 with the Oly 12-40, simply because I do not like taking the ISO above 1000 ISO (1600 max), unlike 6400 on my old Nikon D800.I understand how f7.1 is fine for landscape, when using a tripod. I have got around the low light problems by using a Voigtlander 17.5mm Nokton 0.95, which seems works well.
Regards
Martin
If you like shooting wide open then the Voigtlander is an excellent choice. I have the Olympus 17mm f/1.8 which is also a lovely lens (even wide open) but its obviously not as fast is the Voigtlander.
Sorry for this late entry. Just a comment that there’s no way to search your blog. After reading this very interesting post, I’m now looking for the blog post you mentioned “You just have to take care where you place the focus point – but more on that in another blog post.” Thanks
Thanks for the feedback. I have added the search tool now.