So let's talk about lens selection. When I was choosing lenses for a7R I did not want to adapt any of my Canon kit. One of the big reasons to move to mirrorless was to reduce size and weight of my kit. So when picking out the lenses I focused on image quality and size. Based on these attributes my options were narrowed down to native and rangefinder lenses. There are some fairly compact manual SLR primes, but adapters for these lenses are much larger than those for rangefinder lenses - so I considered legacy SLR lenses a second option only.
Don't get me wrong, if you have a large lens collection it definitely makes sense to use those lenses on a7R, but when selecting a lens to buy for a7R exclusively I would stay away from SLR and DSLR lenses unless you are trying to fill a specific gap that native or rangefinder lenses cannot. For example, if you are looking for a super-tele or a 1:1 macro there is simply no other option and that's a justified decision that makes perfect sense. Other than that my advise is to stick to Sony FE and rangefinder lenses.
Another consideration might be auto-focus - some adapted lenses offer auto-focus while rangefinder and legacy SLR lenses cannot. As far as I know, auto-focus is quite slow even with Sony DSLR lenses mounted on a native adapter. It makes them a viable option in some situations and not so good in others. For me lack of auto-focus wasn't an issue.
Leica lenses can be expensive, but you can get many of them used for reasonable price. Especially if you are going after older lenses or after the Summarit-M range. Plus Leica lenses don't depreciate if you buy used, today most of used Leica lenses cost 30-40% more than they cost in 2005. Zeiss ZM, Voigtlander VM, Leica screw mount lenses all are good options. Also Contax G, Nikon S and Canon LTM can work, if you manage to get one in good condition.
Alright, let's talk specifics!
Native options include Sony (SEL2870) FE 28-70mm F3.5-5.6 OSS and Sony (SEL2470Z) Carl Zeiss Vario-Tessar T* FE 24-70mm f/4 ZA. Both lenses support auto focus and have a similar focal range, and both are quite slow.
I bought SEL2470Z together with the camera and I sent it back a month later (many thank to guys at Panamoz for being so flexible). It's a nice lens and it got good reviews, it was also the only native 24mm option available at the time. However it costs $1500, and I don't think it's worth that price. It is very soft at f/4 across the frame. The wide end stays soft until you stop it down to f/11, and even then the corners are soft. The long end also suffers from softness, but mainly in the corners. It's also quite heavy and large by mirrorless standards.
I have only used the 28-70mm OSS once, on a test a7 body. It felt very similar to Zeiss 24-70mm. Maybe a bit softer overall.
I think both of these lenses are decent, and if you are looking for an all-around lens they fit the bill well. I wouldn't use neither on a job - they lack sharpness at the wide end, bokeh at the portrait end and they are slow.
If you are set on getting one of the two, I would go for SEL2870. It's lighter, you won't notice a difference in image quality and you will save some money.
Rangefinders don't really have a zoom range, the closest to zooms for rangefinders is the Leica Tri Elmar series. I'll cover the WATE when talking about wide angle options. Leica Tri Elmar 28-35-50 f/4 Aspherical (MATE) is the second out of the two Leica M “zooms” (detailed review at stevehuffphoto).
The MATE is a fantastic lens. It is everything you would expect from a Leica and coupled with Sony's EVF it is somewhat easier to use. My main issues with this lens are cost and speed. It is a slow lens that sets you back about $4,000. It does cover three major focal lengths and can effectively replace two prime lenses, so an argument might be made for this lens if you don't mind the small aperture. Also being a Leica you do get great performance wide open, so its actually faster than Sony native options. One last thing, at the wide end this lens does experience magenta cast and other wide angle issues in the corners and requires flat field correction. I wouldn't get this lens myself, unless I was buying into a Leica system, I rather get two-three lenses for the price of one MATE.
All the other standard zoom options are from SLR world, they are bulkier and require larger adapters. Unless you own one, I wouldn't go that route. For me this camera is about mobility. Coupled with the right lens it can produce amazingly detailed photos and prime lenses get the best out of this camera, while keeping the size and weight down.
By standard I'm mean all focal lengths that reproduce field of view similar to how the human eye sees the world, between 40mm and 55mm.
The only native option in this focal range is Sony (SEL55F18Z) Zeiss Sonnar T* FE 55mm f/1.8 ZA. I've got this lens to replace the 24-70mm ZA and it is as good as everyone says. It is a superb lens, extremely sharp and produces good bokeh (see review). One thing I noticed about this lens is that you can focus it manually closer then using auto focus. Its not an issue since I mostly focus manually now, just a bit odd... Not sure if this is true on a7 as well. Other than that I don't have anything negative to say about this lens.
The reason I picked this lens over other options below is because its sharpness and how well it renders the scene. It doesn't quite have the same warm character of Leica lenses, but it does not feel like a soulless precision instrument either. It has pleasant color rendering with a bit of a 3D pop and it is sharp from wide open. Plus you get the auto focus, which comes handy, as well as manual focus assist that turns on automatically whenever you touch the focus ring. There are some great alternatives to this lens, but I think this lens is so good that you don't really need to consider others, unless you are looking for a lens to use on other camera as well.
Since I've wrote this section, another native option joined the lineup - Zeiss Loxia 50mm f/2 Planar T*. I have yet had the chance to try it out, but based on reviews it seems to be a good contender for SEL55F18Z. I think the main deciding factor here is auto-focus and aesthetics. Read a review at DearSusan
Out of all the rangefinder lenses, Leica M mount ones are the only real contenders to challenge the Sony's 55mm quality. I had a hard time deciding which way is the best... I still wonder sometimes if I should've gotten the Summilux 50mm f1.4 or Zeiss 50mm f/1.5 Sonnar ZM, but being objective it would be silly to exchange the benefits of the native lens for half a stop of light. I don't believe that Zeiss Sonnar is better than the Sony. The Summilux is a winner by a small margin and its more about the character than sharpness or detail. The Summilux is also expensive and heavy compared to Sony 55, so unless you own a Leica body I wouldn't get it.
Leica 50mm f/2 Summicron-M, 50mm f/2.5 Summarit-M, and Zeiss 50mm f/2 Planar ZM are also great options, albeit slightly slower than the Sony. All of these lenses are fantastic and you won't be disappointed if you get one - especially the Cron. If you can find those cheaper than the Sony or if you are contemplating getting a Leica body down the line - don't think twice and get them. I would go for the Leicas over Zeiss, mainly because they hold their price better. The Summicron is renowned for its sharpness, while the Summarit might be getting some bad publicity from Leica diehard fans, but in my experience it is also extremely good. The only negative thing about the Summarit is the focus, the focus ring is not well dampened and easy to move accidentally.
See this page by KenRockwell.com for more info and reviews of all aforementioned 50mm M-mount lenses.
One thing has to be said about Leica M lenses and rangefinder lenses in general. Due to their design they focus pretty far from the subject. For me it was another reason to chose Sony 55mm over them. But that problem can be overcome with a close focus adapter - an adapter that employs a helicoid extension tube (Voigtlander VM-E Close Focus Adapter).
Voigtlander 50mm f/1.5 Nokton is another great rangefinder lens that works well on a7R. Although not small and quite heavy (especially when mounted on VM-E close focus adapter) this lens is beautiful, but today it's unfortunately not easy to get. Image quality rivals that of the Summicron, and has similar mood to it. Bokeh is beautiful as well (here is a report on this lens). Its not cheap, but just like with the Summilux and other Leica options an argument can be made to use this lens if you don't mind being limited to manual focus.
If you are looking for a cheaper option than Sony 55mm and the lenses I have mentioned already, you might want to check out other rangefinder lenses below. All of which are good options, but I don't think saving couple of hundred dollars is worth compromising on image or build quality, nor on the resale value. I would still get either the Sony 55mm or one of the fast rangefinder lenses.
There are few other rangefinder lenses I have skipped. The ultra-fast Noctilux and a few others (here is a quick report by SteveHuffPhoto). These lense are too expensive and large for my liking. But I doubt you will be disappointed if you get one. It is a matter of priorities, if you think you need a f/1.1 lens - who am I to tell you otherwise.
Last to mention is the Voigtlander 50mm f1.1 Nokton (review by SteveHuffPhoto here). For the price, it is a great lens. But it will not match some of the best 50mm lenses mentioned above until you step it down to f/5.6. If you are looking for ultra-fast 50mm that won't break the bank - I think this is it. For me, f/1.8 is plenty fast.
This sums up the standard focal lengths. Considering the available selection, I would not venture into SLR territory unless you have a camera body to use them on.
As much as we all would like to believe that we make decisions based on logic, most of us mix ironclad rational with some irrational arguments. The most common of which is the aesthetics... We love our cameras, we care how they look, we care how our lenses look on our cameras. Some care less, others more, but it is universal that we are looking for something to please the eye. We are photographers after all... When it comes to lens selection, I like the look of rangefinder lenses. I prefer the look of Leica and Voigtlander lenses on my a7R to any other lens out there. I know many like the Zeiss ZM range for their simple classic looks.
It wasn't easy to go with Sony FE 55mm, because I don't dig the looks. It is very clean and boring. It has no character. However the combination of quality, price and features forced this decision for me. I dont have any other Sony FE lenses (not that there are many out there). What I'm trying to say is that if rangefinder lenses appeal to you and you don't care about the native lens-to-camera coupling, then don't overthink it - just get what looks good. Many of the rangefinder lenses are some of the best out there, you won't go wrong. And the good thing about those lenses, is that if you get one used you probably will be able to sell it for just as much.
In Part 3 I will discuss telephoto, wide and ultra-wide options. Thanks for reading folks.