Lenses and Optics
A Bit of A7R Sanity
A while back I wrote a post I humbly called Roger’s Law of New Product Introduction, complete with the graph shown below. The release of the Sony A7R has demonstrated the accuracy of that post as few other releases have.
A few weeks after the A7R release we seem to be following the path quite nicely.
There were a lot of unreasonable expectations prior to the camera’s release, and, as usually happens, those unreasonable expectations aren’t being met. Of course that has resulted in the usual strident Fanboy smack talk on forums everywhere. It’s also resulted in some desperate magical thinking among the group of people that wanted the A7r to fulfill all of their dreams. So let’s get some of the things the A7R is not out of the way.
- The A7R is not a 36-megapixel Canikoleica MD900 Mk IV that will shoot all lenses from every brand amazingly well.
- Little batteries do not carry as many watts as big batteries, and when they power big sensors and electronic viewfinders they don’t last very long.
- A good electronic viewfinder is still not an optical viewfinder.
- While improved, Sony’s menus do still seem to be created by someone leaving a ‘Menu Item Suggestion Box’ on the wall and letting the intern add them all in two days before production.
- Yes, they apparently tweak the raw files when they compress them.
- The shutter is loud and causes some vibration. The 1/focal length rule isn’t going to work for most people. (Truth is, it already doesn’t work for most people.)
- There are only a few native-mount lenses, and adapters are still adapters.
- It’s slow. It wakes up slow, focuses slow, and it takes 1.5 images per second.
I’m sure I left out some more reasons it’s being trashed in various forums as the worst camera ever, mostly by people who haven’t even touched it and probably never will. The last time I remember a camera being trashed this hard was the Canon 5D Mk II. You remember, that overpriced camera that did nothing well – except become the best selling full-frame DSLR that revolutionized what people do with DSLRs.
So despite everything this camera isn’t, I think it’s still a game changer. And trust me, I’m no Sony fan. I don’t like the menus. Except for the glorious 135mm f/1.8 there are few lenses in their lineup I’m even impressed with (until now). With recent improvements by Nikon and Olympus, Sony clearly has the worst factory repair service of any manufacturer (at least in the U. S., not that they actually repair anything in the U. S.). So I don’t like Sony. Despite that, I think this is a fascinating camera that is going to change the industry a bit.
I’ll carry the 5D Mk II analogy a bit further. The 5D Mk II disappointed a lot of people when it was released because of what it didn’t do. What most of those people missed was it did something really well and really inexpensively. It produced movie-quality HDMI video through excellent lenses for a small fraction of the price of the other methods available for producing movie-quality HDMI video. It didn’t do it gracefully. There were all kinds of problems and constraints, but they could largely be worked around. A whole industry sprang up to help people work around those constraints and problems.
The A7R gives us something we don’t have, too. It’s arguably the highest resolving camera (it may be slightly higher resolving than the D800e since it really has no AA filter, but maybe it’s a tie). It’s small and mirrorless, which some people really want. (Notice I don’t say YOU really wanted it, but there are definitely some people who do.) And it costs $2,300. A Nikon D800e is $600 more even on special. A Canon 5D III is $1,000 more. A Leica M is $4,600 more. Let me put the good points in a list like the one above:
- Relatively inexpensive.
- Incredible resolution.
- Easily adaptable to other lens mounts.
It’s not going to be the camera for everybody. But it is going to be a camera for a lot of people. I may even (gasp) buy one for myself. Despite all of the negatives, there are some game-changing positives. The fact that the two superb prime lenses were released with the camera makes it even more interesting. The last time Sony released awesome lenses with a camera was right after they rebadged the stuff they bought from Minolta.
Since I’m a lens guy, I think it’s worth discussing two things. First, is how good are those Sony lenses, really? They’re great on this camera but is that because the lenses are so good, because the camera is so good, or because they’re manipulating the hell out of the raw data in the camera? The second thing is what kind of performance can you reasonably expect out of an adapter, and how do you go about getting the best possible performance with adapted lenses.
How Good Are the Native Lenses
The native prime lenses have been assessed on-camera and resolution is superb. But I wanted to know why they were superb compared to adapted lenses. Are they really that good? Are they tuned for the Sony camera in a way that adapted lenses can’t be? Are the Sony lenses just OK, but the adapters make the other lenses look worse than they are? Does Sony manipulate the raw data to make them appear better than they actually are?
Does any of that make a difference? Actually it does. If all adapted lenses can’t perform well, then I have to look at this system based on the native lenses only, which makes it less interesting. If the raw data is being manipulated, then future raw upgrades or some third-party hack may help adapted lenses perform better in the near future. If third-party lenses are soft in the corners because they aren’t tuned to the camera’s sensor cover, then an optical adapter might improve adapted lenses in the future. If the adapters themselves are the problem, then people modifying adapters with optical absorbents and shims may be on the right track.
In an earlier article I compared A7R Imatest results of the Sony 35mm f/2.8 with the Zeiss 35mm f/2 and Canon 35mm f/2.8 IS lenses mounted on adapters. Since we also have an optical bench I can compare the lenses without any camera involved.
The bench we’re currently using has some serious constraints when testing E-mount lenses because of the narrow backfocus distance. We can only test them about 10 degrees off-axis, which is most unfortunate since the biggest difference we saw on the A7R was in the corners. Still, it’s worth a look.
Here are on-axis (center) optical bench and Imatest results for all 3 lenses at f/2.8. (Of course several samples of each lens were tested.)
Bench MTF Frequency Sony-Zeiss 35mm f/2.8 FE Zeiss 35mm f/2 ZE@f/2.8 Canon 35mm f/2 IS @ f/2.8
10 .95 .94 .95
30 .85 .82 .86
40 .79 .76 .83
50 .74 .73 .77
Imatest MTF50 on A7R 1320 1310 1295
Here are the results 10 degrees off-axis (about 1/3 of the way to the edge).
Bench MTF Frequency Sony-Zeiss 35mm f/2.8 FE Zeiss 35mm f/2 ZE@f/2.8 Canon 35mm f/2 IS @ f/2.8
10 .90 .94 .93
30 .77 .82 .83
40 .72 .75 .77
50 .64 .69 .73
Imatest MTF50 on A7R 1180 1095 1190
Don’t worry too much about hair-splitting the numbers. Simply remember the optical bench tests are fairly pure tests of just the lens with no camera attached, while Imatest is a test of the lens-camera combination.
Imatest results and optical bench results in the center for all three lenses are about the same. which isn’t surprising. Off-axis, though, the Sony on the optical bench is, if anything, a bit weaker than the other two lenses. On the camera as shown by Imatest, though, it’s at least as good as the Canon lens and a bit better than the Zeiss.
So why would the Zeiss 35mm f/2 fare worse on the camera, while it is better than the Sony lens when tested on the optical bench? Well, it could be the adapter, but remember I matched best adapters for the camera and lens out of a large box full of name brand adapters. Plus the Zeiss is affected a lot more than the Canon 35mm f/2 IS.
The logical answer is that the location of the exit pupil is fairly far back in the Zeiss lens. People who talk in mathematics I can’t really follow tell me that the further back the exit pupil, the more off-axis resolution (and color shift) will be affected by a thicker cover glass on the sensor. It’s the same reason so many wide-angle M-mount lenses have problems when adapted to NEX cameras.
Adapter Variation and Sanity
People are going to shoot lenses with adapters on the A7R. I’m going to shoot lenses with adapters on the A7R. But some people are driving themselves insane trying to make things perfect, and that’s not going to happen. So I thought I might save a few people a lot of hours by summarizing what we know about using adapters in general and on the A7R in specific.
Adapters aren’t perfect, but most are just fine
We all know there is variation among adapters. Even the best and most expensive adapters. You can’t add large pieces of metal between the lens and the camera without adding a little variation to tilt, centering, or backfocus distance. Here’s some things I know. You don’t have to accept them, but I’ve used hundreds of adapters of almost every brand and gotten more than a few peeks behind the curtain into places where adapters are made.
- Even big adapter manufacturers buy their parts from some factory somewhere. Most change suppliers for components pretty regularly. Which means their adapters may change pretty regularly. There is no ‘best brand of adapters’.
- There is enough variation that an adapter that is great on this camera with that lens may not be so great on this other camera or with this other lens.
- An adapter that really messes up laboratory testing results generally has very little to no effect on actual pictures.
- People often try to measure the thickness of the flat part of the adapter. That doesn’t matter as much as the thickness and alignment of the internal mounts (the part that locks into your camera or lens) for things like tilt.
- The best way I know to check if an adapter is good is take some careful pictures with it, using the lens and camera you plan to use. If the four corners look the same, it’s a good adapter.
So, taken to an extreme you might try a few copies of an adapter and find the best one. If you’re really, really OCD, you might even match the best adapter for each lens. What doesn’t work, though, is trying 16 copies of an adapter hoping the lens just gets sharper, or the corners all get better.
Blacking Out Adapters
There have been some well thought out posts and blogs from Marc Aurel and others who are concerned that light glare within an adapter might be causing increased softness in the outer areas of the image. Marc has even posted templates for cutting out black felt to line the Metabones III adapters that most people are using.
A number of reports have indicated this definitely is helpful for tilt-shift lenses, but it’s unclear if it’s of benefit for non-tilting lenses. I tested lenses on a Metabones III adapter, then blacked the adapter with some optically black ink and retested, then lined it with black gaffer tape (in case the roughened surface might be of further help).
I won’t bore you with tables of numbers, but none of the 35mm or 50mm lenses we tested showed the slightest improvement in the edges and corners. So this is probably worthwhile for tilt-shifts. It might (although I doubt it) be worthwhile for very wide-angle lenses. It’s certainly not effective for standard range lenses.
So What’s Left?
Whenever I don’t know for certain what an issue is, I go talk to lots of people I know who are smarter than me and know optics better than I do. They were about 100% in agreement that the off-axis softening seen with the A7R and third-party adapted lenses (or, if you’d rather, the lack of softening with the native mount lenses) has to do with the thickness and composition of the sensor’s cover glass.
Different manufacturers use different glass and the refraction of this material off-center causes smearing and color shifts to some degree. The effect is worsened with lenses that have an exit pupil near the back of the lens, it’s less severe with exit pupils further forward.
Unfortunately, I don’t have a list of exit pupil positions in all the lenses, and don’t know if anyone does. In general, M mount lenses and wide-angle lenses will have a rear exit pupil, telephoto and tilt-shift lenses tend to be more forward. Hopefully as more people report their experimentation with alternative lenses someone will start a database for those who are interested.
I’m also told it’s not too difficult to make an adapter with an optical element to correct for sensor glass differences. Assuming there’s enough demand I expect someone will be releasing something like that in a few months. Sony lenses designed for FE mount certainly already take this into effect, which is why they seem better in the corners and edges. It probably also explains why some NEX lenses, despite vignetting, also do well. Whether Alpha cameras had a similar sensor cover I do not know, but maybe someone out there can tell us.
Conclusion (for now)
There’s no question the A7R has some issues. Some of them we can expect to be improved with a firmware update or two. Some are the nature of the camera and won’t clear up until the A7X or whatever comes next. Given the limitations the options are to either trash it on forums or to learn how to work around those limitations.
The camera does some things very well at an excellent price. That will be enough to assure some people will learn how to work around those limitations. In another month or two the screaming will die down and some people will be using the camera regularly and making superb images with it. Because it’s fully capable of making superb images.
It’s never going to work for action photography. It may (or may not) be a great walk around camera. But it will do certain things better than any camera out there at a price that’s going to attract a lot of attention.
And lets not forget what may be the biggest change Sony seems to have made: it already has at least two excellent lenses, maybe more. And more are coming. I expect when Sigma and the other third party manufacturers release FE mount full-frame lenses they will have corrected for sensor glass effects and we’ll see good performance from those, too.
That doesn’t help those who want to shoot native mount lenses on the A7R right now, though. Right now it seems that most people buying the camera are planning to use lenses on adapters. Despite spending a lot of time discussing the problems off-axis, lets remember that most lenses perform every bit as well adapted to the A7R in the corners as they do on their native mount cameras. They perform much better in the center on the A7R, which makes the edges seem problematic. For people shooting landscapes it’s something of an issue, but for many other types of photography it’s insignificant.
Sony did some things very wrong with this camera. They did some things very right. Mostly they did things very different. I applaud the differences. They may not all work, but at least they’re shaking things up a bit. And I do predict when all the dust settles in a couple of years, we’ll look back on this camera as one that created some changes.
Author: Roger Cicala
I’m Roger and I am the founder of Lensrentals.com. Hailed as one of the optic nerds here, I enjoy shooting collimated light through 30X microscope objectives in my spare time. When I do take real pictures I like using something different: a Medium format, or Pentax K1, or a Sony RX1R.