I'm going to use lenses that we optically adjusted back into proper alignment as examples. I'm doing this because it's a great opportunity to show you the difference between an optically misaligned and a properly aligned lens.
I'm not giving a tutorial on optically adjusting your lenses. Optical adjustment is very different for every lens, very time consuming and requires at least partial lens disassembly. Most people who try optical adjustment at home convert a below average lens into a totally useless lens.
For a couple of the examples, I'll show some Imatest MTF charts of the lenses so you can see some correlation with how our home test looks compared to the MTF numbers of the lens.
One last point. I'm using mostly Canon lenses for these demonstrations. The main reason is very simple; we stock more Canon lenses than all other lenses combined. So we see more Canon lenses with optical problems, and we're more practiced at fixing those. I can show you decentered pictures of some other lenses, but not 'after' pictures of them all better. Because we can't make them better.
Finally, if you haven't read the last article, there's not too much reason to read this. You probably won't understand what you're seeing.
There are a lot of right ways to do optical testing. The gold standard is to put the lens on a $150,000 optical bench or run it through a well-equipped Imatest lab. But unless you have an optical bench or Imatest lab handy, that's not practical.
We have to optically test around 400 lenses a day, which is more than our Imatest lab can possibly handle. So over the years we've learned a lot about practical ways to test lenses. We've constantly double-checked our methods using Imatest and an optical bench, refining our optical testing.
We've developed a simple set up that is about 98% accurate in identifying lenses that are decentered or optically misaligned. A lot of people could do this at home themselves. Certainly any camera club could make an identical setup.
Judging from the emails I get, a lot of people want to be able to test their lenses optically and few know how to do it, so this should be useful for them.
By far the most common email and PM I get basically says, "I think my lens is optically out of sorts. What do you think?" The second most common is, "So what's the best way to optically test my lens without a ton of equipment." Years ago I wrote an overly long post about testing lenses, but it was not specifically about optically testing. Plus, I've learned a bit since then and have been trying different things that anyone could do without a lot of equipment.
So I thought I'd write a series of posts about optically testing a lens. Not 'determine MTF and write lab-test reviews' kind of testing. But enough to tell if your lens is optically centered and a good copy.
We all know simply taking a few hundred images will tell you if you like the lens or not. But sometimes people don't have that kind of time. They need to know if their lens is OK while they still have the opportunity to return it.
Other times they know they don't like the lens, but they do want to know if that's because they have a bad copy (especially if they've bought a used copy), or if that's just how the lens is. There's no sense trying 5 more copies of the lens if the one you tried at first is a good representation of how the other copies are going to be. But there's also no sense giving up on a lens that everyone raves about just because you tried a bad copy. (For those who want to know, overall our experience is about 2% of lenses we buy are out of spec right out of the box.)
I'll get into the setup I recommend for optical testing over the next couple of posts. But first, let's talk about why I tell 90% of the people who ask me if their lens is decentered that I can't tell anything from that image because it's taken with autofocus.
This is a long article, meant to be read at your leisure.
You better start swimmin' or you'll sink like a stone
For the times they are a-changin'. Bob Dylan
Technology changes tend to be of two types: incremental improvements or disruptive innovations. Incremental improvements allow one manufacturer to take market share from another and give fanboys fuel for internet forums. Disruptive innovations may create a million new customers. Or make a million potential customers leave for some new hobby or way of doing things.
People love incremental improvements but often dislike disruptive innovations at first. Disruption causes major changes and can be threatening. It may be several generations before the new technology is clearly superior to what already exists. But eventually the disruptive innovation has a huge effect on the market. It causes some existing manufacturers to fail, others to flourish, and creates brand new manufacturers nearly overnight.
A decade ago, some of these manufacturers were imaging mainstream, some were just about like they are today, and some didn't even make cameras.
By my definitions, the D800 is a good example of a strong incremental innovation. Some photographers changed (or added) brands to shoot the D800. Nikon increased their high-end SLR sales for a while. But the SLR market as a whole didn't change because of it. Nikon did a little better for a while, other manufacturers did a little worse, but there weren't any massive changes.
Cell phone cameras and social media were certainly a disruptive innovation. Depending upon your point of view, they've either cut the photography market severely or increased it amazingly. If you are a point-and-shoot manufacturer, the photography market is disappearing. If you own Instagram or Facebook, it's growing phenomenally.
For over a decade, now, the photography market has had one incremental improvement after another: increased pixel density, better high ISO performance, improved autofocus, and sharper lenses. But I think there's more disruption going on right now than simply cell phone cameras.
Most people, though, don't realize what a disruptive innovation first looks like. They expect a burning bush of technological triumph that is instantly recognized as the next great thing. Historically, that's not what a new disruptive innovation looks like at all.
Do not try this at home. This post was made by semi-trained, semi-professional repair technicians who sort of know what they're doing.
The following blog post contains graphic images of the inside of a very nice camera. If such things make you squeamish, don't read further.
No cameras were harmed in the making of this blog post. The camera has been fully reassembled and is functioning normally.
Yeah, We Had to Do It
Ever since we first tested a Sony A7R, we were dying to take a look under the hood. Say what you will about Sony as a company, but they create some of the most elegantly-engineered camera bodies we've seen. Plus, the A7R is something of a groundbreaking camera, and we wanted to see how they crammed all that stuff into its little body. Oh, and finally, we've wanted a closer look at how thick the cover glass over the A7R's sensor is, since there is some evidence that it may affect the edge performance of certain adapted lenses.
But we were a bit afraid of what we were getting ourselves into. Because Sony engineers its cameras so efficiently, they tend to be difficult to disassemble, let alone reassemble. And Tyler, knowing us like he does, had probably set computerized alarms on the inventory control system, notifying him the instant an A7R got sent to the repair department for any reason. But Tyler was out sick for half a day -- and there were actually some A7R bodies in stock. So we did what we had to do. Continue reading →
There's been a lot of interest in the newly released Tamron 150-600mm f/5-6.3 SP Di VC USD lens. (For those wondering what the initials mean, VC means vibration compensation, the others all read 'marketing drivel'.) But meaningless initials or not, with a price under $1,100, a superior range, and vibration compensation, this lens has created a lot of excitement.
Recently, the good people at Imatest have developed an ultra-high resolution, backlit chart printed on photographic film that is perfect for testing long telephoto lenses in the lab. The combination of a new, cool Imatest setup and a new, cool lens proved irresistible, so we decided to compare the new Tamron with the older Tamron 200-500mm, Sigma 50-500mm OS, and Canon 100-400mm IS lenses.
Photography companies love catchword marketing. They like catchwords because photographers make assumptions about what those words mean, even though the words really don't mean anything. So basically, they say nothing, but it makes you believe something.
Two of my favorite examples are "professional quality construction" and "weather resistance". When I read those terms, my brain translates them to "Blah, blah, blah. Blah, blah." They are subjective terms, just like 'elegant design' and 'innovative styling'.
Most photographers, though, make all kinds of assumptions about what those catchwords mean, and have all kinds of expectations about the equipment that is described by these largely meaningless bits of marketing. We all know what Oscar Wilde said the word assume really means. Expectations, of course, are simply a down payment on future disappointment.
I have watched several world-class internet meltdowns with great amusement recently. All were started when photographers found out that their assumptions and expectations about what catchwords meant were wrong. They became a firestorm when people added a lot of 'facts' that weren't really facts.
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.
I have to admit I didn't get too worked up when the Sony A7 and A7R were released. The last time I wrote about Sony it was how there were so few lenses for the NEX system years after introduction. So now we're going to a system requiring a whole new lens mount. Sure the camera's specs were interesting. But the idea of yet another camera body good mostly for shooting lenses on adapters wasn't very exciting. So I planned to ignore it.
But my friends over at Imaging-Resource / SLRGear.com were waxing poetic when they talked about their testing of the A7. Then they started claiming that the lenses were really good, too, and sent me some rather shocking test results. Plus, I will admit when it arrived I kind of liked the look and feel of the camera. It's a very small camera for a full-frame, but with a nice deep grip that felt good in my overly large hands. Sort of a retro appearance. So even though we were a bit backed up, Aaron and I decided to at least run some some preliminary testing in our Imatest lab with the A7R.
Let me be clear - this isn't an A7R review. Think of it more as a screening test to see if I was even interested in looking at it more seriously. For me, the lack of lenses with a newly released camera means going through several adapters and numerous lenses to see if I could make a reasonably useful kit. There are other options out there that would be a lot less trouble. So unless there was something about it to really impress me, I'd just skip it for now. If things were merely good, I wouldn't be interested in looking further.