I'm mostly shooting micro four thirds, and am looking at buying a set of primes. It occurs to me, that if I buy an MFT lens set, then those lenses can only by used with MFT cameras and those with shorter flange distances (like Sony's E-mount). But lens adapters are cheap, and if I can buy a set of Nikon F-mount primes, then I can adapt that to Canon, MFT, Sony, any number of mounts. So if I'm shooting manual everything, is there any reason not to just buy a set with the longest flange distance and rely on adapters?
... is there any reason not to ... rely on adapters?
Usually, you'll have the best experience with a camera system by sticking with native-mount lenses. However, since you specifically want to use "all-manual lenses" (which excludes electronically controlled lenses), many arguments against using adapters, such as loss of automatic control, don't apply.
- There are exceptions, such as manually-focused EF-compatible lenses with electronic apertures. If you are interested in such lenses, adapters may not be the most appropriate way to use them.
... is there any reason not to just buy a set with the longest flange distance... ?
Of the commonly used DSLR mounts, Nikon F has the longest flange focal distance. It would make sense to get lenses with the Nikon F mount if you have a Nikon DSLR or plan to adapt the lenses to other DSLR mounts, such as Canon EF. However, mirrorless cameras all have very short flange focal distances, so the particular mount doesn't matter that much. Almost any old lens can be used.
A few mounts, such as CS, D, and DL, have FFDs that are too short to be used normally with most mirrorless cameras. Unless you intend to use them for macro/close-up work, adapters would not be the most appropriate way to use such lenses.
Some mounts are not popular enough for anyone to bother mass producing adapters. Unless you intend to make your own, adapters may not be the most appropriate way to use such lenses.
Reasons to consider multiple mounts include quality, selection, and price. There are a lot of good, inexpensive lenses not available in Nikon F mount. Reasonably good lens adapters for many mounts aren't very expensive.
There are some mounts for which adapters are relatively expensive compared with those for other mounts. They are likely more complicated adapters with moving parts for lesser known mounts.
New manual lenses are produced for some modern mounts. Possibly because of low production volume, they tend to be priced fairly high. For the same price or less, you can find older lenses with excellent performance. Here are a few, there are many more:
- Canon new-FD (bayonet mount)
- Minolta Rokkor
- Pentax SMC
- Tamron BBAR MC (Broad-Band Anti-Reflective Multi-Coated)
- M42 lenses, often for "character".
It might even make sense to use adapters for the mount with the shortest FFD to which adapters from other mounts are made (EF). This would give the greatest flexibility in lens selection and use. For instance, focal reducer, smart adapter, dumb adapter, and macro helicoid adapters could be shared across multiple mounts, rather than require multiple adapters of each type for each mount.
Reasons to not use (only) Nikon F mount:
- They tend to cost more because the mount is still being used in new DSLRs.
- The longer FFD requires slightly larger adapters.
- A more expensive adapter is needed for Nikon lenses without aperture control.
- Special adapters, such as focal reducers, cannot be adapted to other mounts.
Reasons to not use (only) OEM lenses:
- Limited lens selection.
- Prices often higher.
- Lenses may lack desired "character".
- No option to use special adapters, like focal reducers or (real) anamorphic lenses.
- Miss out on joy (frustration) of using adapted lenses.
Regarding adapter selection:
- Avoid cheap, no-name adapters from China. They often have poor alignment and fit. They are often made of soft aluminum, which isn't durable. Anodized, steel, and brass adapters are available reasonably priced. Often if any specific name is associated with an adapter, it'll be fine (Pixco, Fotasy, among others).
- Avoid adapters made of hard, brushed metal (Kipon). They can grind away material from the lens.
So if I'm shooting manual everything, is there any reason not to just buy a set with the longest flange distance and rely on adapters?
As long as the set with the longest flange distance allows you to manually control the lens' function to your satisfaction there really isn't. But there are many cases where you probably won't be able to control aperture, much less anything else, to your satisfaction.
Here's the rub: most short registration cameras (i.e. newer mirrorless cameras) use electronic controls to communicate with their lenses. Micro Four-Thirds cameras have electronic only interfaces with lenses. There are no mechanical connectors for an MFT camera to control a lens that requires mechanical movements to stop down. If there is room, an adapter can include a logic circuit that can "translate" the electronic command from the camera and either a) send an electronic command to the electronic lens in the "language" the lens understands or b) use a servo to mechanically move a mechanical connection to the lens. Most of the "translation" is figured out using reverse engineering by third party adapter makers, and may or may not work as well as one would hope. Those kinds of adapters aren't the cheap ones to which you refer in the question, either.
Many other cameras with longer registration distances also use all electronic communication with lenses. Sony E-mount. Canon EOS. The lenses for those systems, and even many of the lenses made for other systems - such as Nikon's F-mount that can still use a mechanical connection between the camera and lens to control the lens' aperture do not have manual aperture control capability using the lens. Nikon "G" lenses do not have any kind of aperture control ring on the lens. The camera tells the lens what aperture to use electronically, and then the mechanical stopdown lever in the camera provides the movement to, depending on the lens, push the aperture lever to the correct position or push the aperture lever until it hits the "stop" in the lens set to the desired aperture.
So all of those lenses are potentially out, since a cheap adapter will not give you the capability to set the aperture on the lens. Depending on the mounts involved, there may not be any way to "translate" an electronic command from the camera to a mechanical movement on the other end of the adapter, regardless of the cost of the adapter. You'll be stuck using such lenses either wide open or stopped all of the way down.
Without aperture control from the body, exposure metering won't be reliable if it is even possible at all. All of those whiz-bang exposure peaking and zebras that your MFT camera can display will be totally useless.
There are also a lot of lenses for newer mounts that require communication with the camera for even manual focus adjustments. So called "focus-by-wire" lenses do not have a mechanical link between the focus ring and the lens' focusing elements. Instead the focus ring has a position sensor that tells the camera to tell the focus motor in the lens to move. All of Canon's STM lenses are focus-by-wire. There are many others in the various other mounts, and they are becoming more popular all the time. MFT lenses are almost exclusively focus-by-wire.