Aperture & Sharpness

Death Valley. Even for extreme cases such as this three image stitch, f/9.0 was all that was required for full depth of field.
Death Valley. Even for extreme cases such as this three image stitch, f/9.0 was all that was required for full depth of field using th e Panasonic GX1.

At one time I didn’t understand the relationship between aperture & image sharpness. I read many magazine articles and books where Landscape Photographers would commonly say they stopped the lens down to the smallest aperture to ensure the image was sharp from front to back. What I hadn’t realised is that they weren’t discussing image sharpness but depth of field. I also hadn’t realised that many of these photographers were using medium format cameras where depth of field could be a real issue. Fortunately, I now understand this relationship but there continues to be misinformation published on the subject.

Here then are the key points you need to be aware of in relation to depth of field:

  • Depth of field is how much of your image appears to be in focus from the nearest point to the most distant.
  • Depth of field is determined by the aperture you use. If all other variables remain the same, as you make the aperture smaller (larger f/ stop number), you will increase the depth of field.
  • Other factors affecting the depth of field include:
    • Where you place the point of focus – the nearer the camera the shallower the depth of field. It’s also worth remembering that the depth of field will extend twice as far beyond the point of focus as in front of it.
    • The size of the film or the image sensor – the smaller this is, the greater the depth of field at the same aperture.
    • The focal length of the lens can also make the depth of field appear greater – a wide angle lens makes the depth of field appear greater than a long telephoto lens.

When I first started in photography, what I failed to grasp is that the factors determining how sharp an image is are different to depth of field. Let’s take an example where you shoot three images using a typical lens; the first image with the aperture as wide as it will go, the second with the aperture as small as possible and the third with the aperture between the two extremes. If you then review the images looking at the point of focus, you would find that the third image with the aperture at mid-value is the sharpest image. This is because lenses are design to perform at their best when aperture is closed down by a couple of stops. Once you go to the smallest aperture though, the performance and sharpness is compromised by something called diffraction, which makes the image appear soft.

One benefit of using a Micro 43 camera for Landscape work is that you can typically achieve front to back sharpness (depth of field) without needing to stop the lens down to the smallest apertures. In my own work I tend to shoot Landscapes with the lens set to 12mm (24mm equivalent on a full frame camera). The aperture I tend to use is f/7.1 or sometimes f/8.0. Providing you place the point of focus correctly you will have all the depth of field you typically need and the lens will be near to its optimum performance.

Where I use the Sony RX10 which has a smaller 1-inch sensor, I tend to shoot with an aperture of around f/5.6 for full depth of field at 24mm. And when I was shooting with the LX5 compact camera I was using f/3.5 to f/5.0 for full depth of field at 24mm.

I hope this helps all you small sensor Landscaper photographers.

9 thoughts on “Aperture & Sharpness

  1. Thanks for clearing that up. I have wondered about that. I do a lot of Macro work, and was wondering if you could say something about the macro lens for the Olympus? I don’t want a large depth of field for that, but often do need enough to keep much of the object sharp. I often bracket the aperture to be sure I get the sharpness I want along with a nice blurred background. I understand the ratio of my full framed Canon a little better than I do 43, so I’m still trying to get a better handle on that.

    1. I will try to do something in the future but it’s quite tricky to judge. The Olympus 60mm Macro is a superb lens but often hard to work with. I often struggle to handhold mine. When you are working at close range the depth of field becomes minimal even at small apertures. What you might need to do is consider focus stacking where you take multiple shots but move the focus point between shots. You then use a programme such as Helicon Focus to blend them together and achieve a great depth of field that would be impossible with a single shot.

      The downside to this can be that your background is more in focus than you want. What people often don’t realise is that with Helicon you can select the best background and then paint that in around the object that’s now in focus. Well worth experimenting with and there used to be a good example on their website.

  2. Thank you, I’ve been confused as well I guess. This is mighty helpful. I’ll experiment a bit with my camera and find my “sharp” spot for landscapes. I tend to shoot macro or landscape very little in-between. A lot to learn still.

    1. Pleased to hear this has helped you. As a rough rule of thumb, the sweet spot with most lenses is once they the aperture is closed down by around 2 stops. This is then good for a couple of stops before diffraction tends to kick in. Outside of this range is also where Chromatic Aberration becomes more obvious.

      1. I shoot with a Sony RX100 and I am slowly learning where that sweet spot is. I think it is at 3.5 or 5.6 depending on what I am shooting. I tend to forget this though and just close the aperture down fully when trying to get the most in a landscape. A poor habit I will more than likely break after reading this! Thank you.

      2. Having owned the RX100 myself, I agree the sweet spot is around 3.5 to 5.6. I tended to shoot mainly at 5.6 as I do now with the RX10. Great little camera but hard to handle when your fingers are cold.

      3. Very good explanation of an issue that many newer photographers who lack the experience of shooting fully manual fail to grasp. Most people grasp optics only in practice because they are intimidated by geometry and math.

        It’s a rough rule of thumb. The upside to m43 is increased depth of field at moderate apertures like 5.6 and 7, where autofocus is not yet compromised, and high ISOs often not necessary,but diffraction is a function of the ABSOLUTE size of the lens opening, so it becomes a serious problem much sooner (at f/11 or 13) than with larger sensors. And of course, it’s less an issue with larger, faster glass, where center sharpness is not as great an issue as softness at the corners where there is always CA.That’s why Oly and Panasonic correct it in camera and embed the data in the raw files in order to assure crisp output for jpgs and for when people do not do a thorough job of correcting aberrations in post.

  3. Beautifully explained. Coming to M43 as I was from APSC, it took me time to figure out that I didn’t need to use the same apertures as before. I’ve also stumbled on to the fact that f7.1 is the sweet spot with my GX1 and its Lumix G Vario 14-42mm f3.5~5.6 ASPH Mega O.I.S (Phew!) kit lens, for landscapes (such as they are, in urban New Delh)i. And BTW, Robin, I think Panasonic have tweaked this lens to close to the same sharpness as the much touted Lumix 14-45mm, possibly irked by the disappointed comments from users / reviewers. Or maybe I was just lucky to have got a good copy with my trusty GX1… it’s sharpness at times rivals / outdoes my 20mm f1.7, leaving me stunned and disbelieving, and the IS is amazing (I don’t use a tripod down to a half-a-second (hand supported – and me running 68 :).

    1. Thank you. I have never tried the 14-42 Lumix lens but I did try an Olympus equivallent and wasn’t impressed. I used to use the 14-45 which was excellent for the money. It sounds that you have a very good example of the lens and I can imagine it producing excellent results with the GX1. I loved my GX1 but in the end couldn’t justify keeping it.

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