Update as of July 1st 2019: Panasonic in collaboration with Leica has released a new 10-25 mm f/1.7 zoom that solves the shallow depth of field issue with the hitherto minimum f/2.8 zooms for the micro four thirds system. It is of course also better in extreme low light than f/2.8 zooms. Gordon Laing has a “review this far” on cameralabs.com as of now, and other reviewers like mirrorlessons’ Heather Broster and Mathieu Gasquet, David Thorpe of youtube, DP review and more are probably soon going to release their take on the lens.
I recently watched a youtube video from 2016 where Gordon Laing and Doug Kaye discussed the best lenses for Micro Four Thirds available at the time. In it, Mr. Laing says he feels that on the Micro Four Thirds system, zoom lenses do not make sense and that he prefers to shoot with primes for his own personal work. I shoot MFT and often use primes. However, I think that even on MFT there are both pros and cons to zooms, so I thought I would write a post discussing this in further detail.
If you come from the full frame world into the Micro Four Thirds system, you might be surprised to learn how many zooms are available, their quality, low weight, small size, different price points and different compromises. There are f/2.8 Pro zooms from both Olympus and Panasonic, there are lots of high optical quality kit zooms in different sizes and focal lengths, and there are superzooms with large ranges at different speeds.
So far, so good. Then you start to think about the crop factor. If you want an equivalent to full frame 24-70, you have to half the focal length on MFT and go for a 12-35. Since you half the focal length, you also double the depth of field, just as you would when going from 24 to 12 mm on full frame.
The doubled depth of field on equivalent angles of view lenses with the same maximum aperture might be an advantage when you want to shoot with a larger depth of field with a wider aperture to not have to increase your ISO. This cancels out the often cited problem of higher noise on smaller sensors at high ISOs since you would usually shoot at half the ISO for an equivalent depth for field if you are aware of this. If you would shoot a landscape with a 50 mm lens at f/11 and ISO 400 on full frame, you could shoot the same landscape with an equivalent field of view with a 25 mm lens at f/5.6 to get the same depth of field and at ISO 200 because you have doubled the aperture size. This means you would shoot the same landscape with a lower ISO on MFT than on full frame with the same angle of view and the same depth of field.
For landscapes and macro where you want as large a depth of field as possible while using as low an ISO as possible, MFT is actually a good choice even before considering the other advantages like cheaper, lighter, smaller lenses and cameras with EVFs that are also smaller, lighter and sometimes cheaper. If you want the versatility of focal lengths and seldom shoot in low light, zooms make a lot of sense for these genres. Since macro needs close focusing and extreme sharpness, you would probably use a specialized macro prime for it, but for landscapes, one of the sharper zooms make a lot of sense.
On the other hand, when you want a picture with shallow depth of field, you would have to double the size of the aperture, ie half the f-stop to get the equivalent at an equivalent focal length, so if you use a 70-200 f/2.8 pro zoom wide open on full frame to shoot weddings and you would like to get the same look on MFT, you would have to use a 35-100 f/1.4 zoom. Those do not actually exist, and that is where we get into trouble with zooms on Micro Four Thirds.
People often say “it is harder to control the depth of field on micro four thirds”. This is not true. You just have to know that when the crop factor halves the focal length to get an equivalent angle of view as on full frame, you also get double the depth of field, and you have to choose your lenses accordingly. If you think you will get the same look on f/2.8 on all crop factors at equivalent focal lengths, then you would have trouble controlling depth of field on any system, but if you know what you are doing, you are of in full control even on MFT.
In comparison with APSC, on MFT this is 0.5 or 0.4 times more of an issue since APSC cameras’ crop factors are either 1.5 or 1.6, so full frame shooters taking up any crop size camera will have to think about this. People seem ignorant of APSC having exactly the same issue. And if you go the other way into medium format, you get the same issue in reverse and might get too shallow depth of field if you are unaware of this issue. The issue isn’t that it is harder to control depth of field on any size sensor than on any other, but if you are unaware of what changing the focal length of the lens does to the depth of field (even if you use different focal lengths on the same system), you will have trouble controlling depth of field on any system.
If you like really shallow depth of field at equivalent angles of view as you would get with f/2.8 zooms on full frame, you would have to use primes on micro four thirds. The good news is that there are lots of good primes for Micro Four Thirds since the lens mount is an open standard with both the two major camera manufacturers and many third parties making primes ranging from the mediocre to the superb and from manual focus only with no electronic data transfer to fast autofocusing lenses with built in stabilization and weather sealing. Prices also vary a lot.
In addition, you can adapt lenses from almost any system to MFT and make them even faster with speed booster, but usually the native lenses have better optical quality, smaller size, lower weight and sometimes cheaper cost, so why you would want to adapt lenses is a bit beyond me. I think most people adapt lenses to get a certain vintage look or because they have used another camera system before coming to MFT. The bad news is that if you really want the flexibility of a zoom and at the same time as shallow depth of field as on the equivalent focal lengths on full frame with f/2.8, you are out of luck. (See the update above that changes this somewhat.)
Of course, you can get shallow depth of field also by using longer focal lengths, having the subject closer to the lens (and the background further away) and using the largest possible aperture. Maybe you would have taken a portrait with f/2.8 on full frame with 90 mm focal length and have the couple two meters away. On MFT, you could get more or less the same depth of field by using a f/2.8 zoom not at 45 mm (= 90 full frame), but at 56 mm (= 112 FF) and having the couple at 1.5 meters away approximately, but that would of course change the compression and the composition of the image even if you would get the same DOF and it might not be what you want. So even if primes are the obvious way to get shallow depth of field on MFT, it is not impossible to get it with zooms either as this example shows. It is just not possible to get the same DOF with the same f-stop at an equivalent focal length as on full frame.
So do zooms make any sense on the Micro Four Thirds system? Yes and no. If you use zooms for flexibility of focal ranges, then yes. If you come from full frame and usually shoot f/5.6 and above and only go lower f-stops for low light, then zooms would work perfectly for you on MFT.
If your type of photography do not require a very shallow depth of field, then zooms make a lot of sense if you do not want to change lenses a lot. For travel, landscapes and even for studio portraits, you do not necessarily need a very shallow depth of field, and the versatility of zooms might be more valuable for you than the shallower depth of field you would get with primes. Take into consideration that even if you double the depth of field at equivalent focal lengths with the same f-stop, f/2.8 gathers the same amount of light on MFT as on full frame per square millimetre on the sensor, so you get the same low light capabilities with a f/2.8 zoom no matter what system you use, but you get different depths of field.
If you want zooms to deliver the same shallow depth of field as f/2.8 zooms on full frame when you shoot MFT, then no. The solution is dead simple. You get a few primes for shallow depth of field and extreme low light at the focal lengths you use the most, and you use your zooms when flexibility is more important or when you want to fill in the gaps between your primes. The catalogue of MFT primes is vast and covers a lot of different focal lengths with excellent lenses, and primes can also force you to think a bit more about your choice of focal length and where you stand in relation to the subject which might improve your photography.
When it comes to stabilization, which might be important in low light or windy conditions, most Panasonic zooms have it (including kit zooms) and most Olympus zooms don’t. Most of the other manufacturers only make primes for MFT. Most MFT primes do not have stabilisation, but there are some exceptions. In addition, most Olympus cameras have sensor shift stabilization and most newer Panasonics (since the GX7) also have this, so even if f/3.5-5.6 might not sound that impressive for low light, the combination of lens stabilization and camera stabilization (Panasonic lens + newer Panasonic body) or either or (Panasonic lens + Olympus body, or Olympus lens with any body) will give you a few more stops of shutter speed without loosing sharpness unless you shoot fast moving subjects where longer shutter speeds do not really work. This also means hand holding photos you would not be able to hand hold with a full frame camera both because the camera and especially the double focal length lenses are heavier on full frame and because you would usually have less stabilization in the lens and/or camera on full frame than on MFT. I almost never use a tripod. There really is no need for it except for long exposures or when using really long focal lengths, which I seldom do.
With telephoto zooms, you may get shallow enough depth of field for portraits even with an f/2.8 zoom, depending on your style of shooting. Even when taking portraits, shallower depth of field is not always better. Often it is better to have more of a person’s face in focus than to make the background completely blurred. I know there are some wedding and portrait photographers that use MFT and telephoto zooms at f/2.8, so it’s not undoable, but I think if I were a wedding photographer, I would probably use two bodies with a f/1.4 or f/1.2 standard lens on one for groups and environmental shots and a longer portrait lens like the Panasonic Leica 42.5 f/1.2 Nocticron, the Sigma 56 mm f/1.4 DN Contemporary or Olympus M.Zuiko 75 f/1.8 on the other. Even with two bodies and two primes, an MFT setup is probably lighter and smaller than a full frame one with a 70 – 200 mm f/2.8 zoom.
All this also means that unless you use your zooms often in extreme low light or really want as shallow a depth of field as possible with a zoom on MFT, there is little point in investing extra cash in the f/2.8 pro zooms on MFT. The f/3.5 – 5.6 (kit) zooms will deliver the flexibility you need, and since neither these nor the f/2.8s can give you a very shallow DOF at equivalent focal lengths, there is no point in investing in slightly faster zooms for a lot more money unless you really need the low light performance at f/2.8, the slightly shallower depth of field or feel that the image quality of your kit lens is not up to scratch (which you probably won’t feel as most newer MFT kit zooms are quite good). Some of the f/2.8 zooms are also weather sealed unlike most of the f/3.5-5.6 zooms, so that might be an additional benefit if you need the low light performance.
Personally, I own the Panasonic Lumix 12-60 f/3.5-5.6 which I use for maximum flexibility situations where I think I might want to use short telephoto as well as standard and wide angles and not just stick to one focal length for a period of time, where the weather would prevent me from switching between primes or when I need the splash and dust-proofing because of rain, wind or snow. I also own the Panasonic Lumix 12-32 f/3.5-5.6 which is extremely light and small. I use it to fill in the gaps between my 14 mm and 25 mm primes, as a 12 mm wide angle and for general walkabout photography, especially when travelling. It makes the GX8 look more like a point and shoot which might be useful for street photography where you would like to look more touristy and less like a serious photographer. Both of these lenses have built in stabilisation that together with the sensor shift stabilisation in my GX8 means I can hand hold shutter speeds up to about half a second easily even though I live in a very windy place. I have read reviewers hand holding the 12-60 for up to a second indoors.
All in all, I would say that both zooms and primes have their strengths and weaknesses on MFT as well as on other systems, but that you have to be aware of the doubled depth of field compared to equivalent focal length full frame lenses with the same aperture as on any system that has a crop factor. This means sometimes zooms aren’t fast enough and you need primes. Therefore, you are probably more inclined to use primes on the Micro Four Thirds system than on full frame systems. I exemplify this by having two zooms and three primes in my camera bag and two more primes on its way from japanphoto.no. Gordon Laing is definitely right that primes are important for many MFT shooters, but zooms also have their uses. What equipment to use ultimately depends on what you shoot and what results you are after.