There are many reasons to use primes. In the old days, primes had better image quality than zooms. These days, this is sometimes the case, but not always. Another reason to use primes is that you free yourself from having to think about the focal length and by limiting your choices, you have to think more about what you actually want within the frame and zoom with your feet. People often say that primes make you think more about your composition, and I think that is true.
A third reason to use primes is their wider apertures. This is especially important on crop sensor formats like APSC and Micro Four Thirds. The fastest MFT zooms are f/2.8 and since the crop factor of two on MFT also means that the depth of field is double for a given f-stop value than on full frame (which is good news for landscape photographers), if you want the same depth of field on MFT as on 35 mm for a given focal length (since depth of field changes with the focal length as well), you would have to use a lens twice as fast. Since zooms do not come in faster apertures than f/2.8 on MFT, that means you have to use a prime lens. Fast primes also mean that you never have to shoot at high ISOs in dim light which is nice if you don’t like noise or want to save the noise for artistic black and whites. (I usually set the ISO higher when shooting black and whites on purpose, to get a bit more texture in the frame. Some people add noise in postproduction, but why do in post what you can do there and then?)
The fourth reason to use primes is that they are often smaller than zooms. Pancake lenses like the Olympus 17 mm f/2.8, the Panasonic 20 mm f/1.7, and the Panasonic 14 mm f/2.5 are really compact and have decent or even good image quality. Some slightly larger lenses like the Panasonic Leica 15 mm f/1.7 Summilux, the Olympus 17 mm f/1.8, the Panasonic 25 mm f/1.7 and the Panasonic 42.5 f/1.7 have both really good image quality and are small and light. The slightly larger primes like the Panasonic Leica 25 mm f/1.4 Summilux, the Panasonic Leica 12 mm f/1.4 Summilux and the Panasonic Leica 42.5 f/1.2 Nocticron offer superb image quality in a package still smaller than the f/2.8 zooms from both Olympus and Panasonic, although just slightly smaller. Compared to full frame lenses, any of the MFT primes are quite small and light.
OK, so all this talk about primes is well and good, but what is the rethink on my lens setup? I have come to realise that even if I like primes, I don’t need as many of them as I thought. Some of the zooms available today are really good while also being small and with a wide enough aperture for most of what I need. I own the Panasonic 14 mm f/2.5, the Panasonic Leica 25 mm f/1.4, the Panasonic 42.5 f/1.7 and I recently bought the Olympus 17 mm f/1.8. In addition, I have the Panasonic 45-175 powerzoom because I sometimes feel the need to shoot landscapes from a distance (on the other side of a fjord, typically), want to get the background closer to the foreground on landscape shots to make majestic mountains behind buildings more dramatic or try to get a wildlife shot.
What I discovered after buying the Olympus 17 mm is that the image quality was good, but not noticeably better than with the Panasonic 12-32 f/3.5-5.6 set at 17 mm that I used to own. Since I seldom actually need low light performance beyond what I get with the 14 mm f/2.5 and since the 17 mm f/1.8 is too wide angle to give a very shallow depth of field anyway, the reason to have a faster lens at 17 mm isn’t really obvious to me. I thought this lens would be my new favourite, but in reality, I haven’t really used it much since I got it.
The 14 mm is a lens I use a lot for landscapes when my 25 is too long to fit everything I want into the frame. I don’t particularly like the wide angle look, since the background becomes so small and distant (perspective distortion), but unless I make a panorama with the 25, a wide angle lens is what I need to get all of a scene into the frame. When I use the 14, I sometimes feel that an even wider lens would be even better to get even more of a scene into the frame. I would really like to have a 12 mm sometimes, but the 12 mm Panasonic Leica prime is a bit too expensive for a “sometimes” lens.
Another realisation is that I seldom use my Panasonic 42.5 f/1.7. It is a really nice portrait lens that can also be used for faux macro since it focuses so close. However, the Panasonic Leica 25 mm f/1.4 Summilux is also a really good lens for portraits with its excellent image quality and the possibility for shallow depth of field if I want it. (Portraits do not necessarily need a very shallow depth of field.) To get a head-shot, I would have to be about a meter from the subject with the 25 mm and around one and a half meters away with the 42.5. For environmental portraits, the 25 is obviously better as it has a longer focal length that can fit more into the frame. I have also done faux macro on the 25 mm and that works quite well too. When I don’t need the shallow depth of field or the low light performance, but just need a longer focal length, I have the 45-175.
The 25 Summilux and 14 pancake combo works really well for most of the pictures I take. And sometimes I need a telephoto lens and then the small and practical 45-175 is nice to have. What I sometimes miss is not having to change lenses so much. A wide angle to standard (to short telephoto) zoom solves that problem. Kit lenses with f/3.5-5.6 now come with really good image quality for the MFT system and there is a choice between 12-60, 12-35, 12-32 (ultra compact), 12-45, 14-42 (powerzoom) and 14-140. I owned the 14-140 in the past and although it was nice to have that reach, I often felt that the long end was too short and the wide end not wide enough. Now that I have the 45-175, the long end is solved. It is of course possible to get the f/2.8 zooms as well, but the price of getting something that is good in low light compared to how little the increase in aperture wideness is seems a bit steep for me. Since the crop factor affects the depth of field as well as the focal length (or actually, it’s the other way round, since the focal length is half for an equivalent of full frame, the depth of field is also half because the physics stay the same in our universe), the f/2.8 zooms isn’t able to produce a very shallow depth of field in the wide angle or standard range anyway and since I already own the 25 Summilux which makes beautiful bokeh for the few pictures where I actually need to blur the background, the only real advantage would be low light performance. With stabilisation built into most of the zooms in addition to the sensor stabilisation in my GX8, I can get away with longer shutter times than with unstabilised lenses at the same aperture value. So even if f/3.5-5.6 isn’t fast, it is fast enough, and if I really need low light capabilities or shallow depth of field, I have the 14 mm pancake and the 25 mm Summilux.
The hard choice is which zoom to get. I was seriously considering the 12-32. It has good image quality, is quite cheap, is small and light. On second thought, what I would like to have is a weather sealed zoom that matches the GX8’s weather sealing so I can use it in any circumstance. Leaving the f/2.8 zooms since those are too expensive for me now, the 12-60 f/3.5-5.6 seems a good choice. It delivers good image quality almost on par with its f/2.8-4 Leica sibling, but cost a fraction of the price used. I first thought I would go for the 12-32 since the size and weight make it an extremely practical lens that also delivers good image quality, but the added range and weather sealing convinced me that the 12-60 is a better choice. Since its range is smaller than the 14-140, it can deliver better image quality all through the range. I also like that it gives me a 12 mm which is a nice focal length for wide landscapes (any focal length is actually good for landscapes, depending on the landscape). The relatively long zoom range makes it a good choice for a travel lens that can stay on the camera for the whole trip (unless I want to use the 25 to get shallow depth of field, low light shots or for the simplicity of using just one focal length or the 14 for a low light wide angle shot). This zoom is also still quite small and light.
(All focal lengths, unless otherwise stated, are Micro Four Thirds focal lengths. To get their equivalent in 35 mm full frame you have to multiply them by the crop factor of the MFT sensor, which is two.)