OLAF's Lens Art

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This is a Geek Article, with very little practical information. But there are pretty pictures that non-Geeks might like. (Not the construction pictures, the ones further down.)

First, I should explain why I haven't posted much lately. Lensrentals was able to expand into some adjacent space, which was desperately needed. But the testing and repair departments were moved and expanded into the new space. Over the last 10 days the second testing area went from this . . .

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I Sing of OLAF . . .

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I have a couple of things to talk about today. First, is to announce the winner of our name the new machine contest. Second is to answer about 1,000 people's questions regarding optical testing and adjustment.

The New Machine's New Name

First, if you don't known what we are naming then you can find out about it here. Second, as so often happens, I was unprepared for the number of responses. We received nearly 700 suggestions here, not to mention dozens more via Petapixel, DPReview, and the Imaging Resource.


We quickly realized that, once again, we'd started a contest without establishing any criteria for winning.

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Roger's New Toy Needs a Name

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First and foremost, if you aren't at least a little Geeky, this post is not for you. Unless you're one of those people who thinks 'just take some pictures, dammit' when I write some article about resolution testing.  In that case, you might like this article because we're taking pictures to test lenses. Sort of.

For the last 18 months or so I've been on a Holy Quest, trying to find better ways to optically analyze and adjust bad lenses. Why? Partly because we need to. Factory service just can't seem to return some lenses to proper optical adjustment. Partly because some smug people told me I could never learn how to do that, which, of course, made me really, really want to.

I can use any of several tools we have to generate MTF charts that tell me the lens is decentered. But those don't tell me in what way the lens is decentered. More importantly, when we optically adjust a lens, those MTF charts tell me it's better or worse, but not exactly how it's better or worse.

We discussed things with some very high-power optical consultants who said exactly what many photographers have been saying all along. The numbers don't tell you everything; you need a picture. That led to some meetings with the fine engineers at Optikos, who manufactured a machine to do what we wanted. Continue reading

The Heights and Depths of Nadar: TL;DR Version

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Nadar Rotating Portrait. Circa 1865, Bibliothèque Nationale de France


"He is a man of wit without a shadow of rationality . . . His life has been, still is, and always will be incoherent."  Charles Philipon, describing Felix Tournachon.

Photographers are the most fascinating people. I'm sure there are some that simply spent their life just taking great photographs, but I tend not to notice those. There are too many more who were great photographers and a whole lot more. I write about the 'whole lot more' photographers. It can be the photographer who invented strobes and took pictures of atom bombs. Or the photographers that made the fastest automobile of their day. Or the photographer who invented the telegraph, or the drunken geologist that invented the telephoto lens.

It just seems that the most interesting photographers had a lot of other things going on. Today's subject had more going on than most.

He was at least the first great photography marketer, if not the greatest self-promoter ever. He also was arguably the best portrait photographer of his day, the first to routinely use electric lights, and the first aerial photographer. In his spare time he filed dozens of patents, was the model for the main character in a Jules Verne novel, wrote over a dozen books and hundreds of articles, was the top editorial cartoonist in Europe, and sort of established the first airmail service.

That stuff is pretty great, of course, but my boy Felix was way more interesting than even those things would suggest. He hung out with people like Jules Verne, Sarah Bernhardt, and Victor Hugo. He openly despised Napoleon III when that was politically incorrect in a much more dangerous way than we use the term today. He gave the Impressionist guys (Monet, Renoir, Cezanne and others) their first exhibition largely because he knew it would upset all of the Paris art critics. He sued his brother. He made several fortunes, but was always out of money. 

Unfortunately, while there is an out of print biography of him, there are only snippets of information here and there online. I'm a blogger, I know the drill: 1,000 words is all people will read these days. But 1,000 words just can't tell the story sometimes. So I wanted to gather all that information together in one place.

I'll warn you, though, it's a long story. But it's a good story. Nadar was so awesome that I already look forward to reading this post in a few years when I've forgotten that I wrote it. (My wife says it won't take a few years. A month or two is sufficient for me to forget almost anything.)

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The Sky is Falling and the Light is Leaking: the A7r Anti-Massacree

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Anti-Massacree - A humorous anti-war movement from the 1960s, suggested in the Arlo Guthrie song Alice's Restaurant. The song, like many of my posts, was criticized for being overly long.

Believe it or not, I'm mostly a lurker in online forums. I read the hysteria of the day mostly for my own amusement. Sometimes I type a response but I almost always delete it. Interjecting facts into one of the daily hysterical rants would be about as welcome as a cat at a dog show. Usually I don't even go that far. I just think there's a lot of people online without much to do and go back to work. Continue reading

A 24-105 Comparison

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Sigma has been releasing one great lens after another for a while now. Some, like the 35mm f/1.4 and 18-35mm f/1.8 zoom, have created feeding frenzies soon after (or even before) their release. Others, like the 24-105 f/4 OS, haven't created a whole lot of fuss. So I thought we would do a little optical testing and make the logical comparison between the classic Canon 24-105mm f/4 IS and the new Sigma 24-105 f/4 OS.

As usual, this is not a complete lens review, just a simple resolution test on several copies of each lens. One thing we'll do with this test that we haven't been doing a lot -- we'll test the lenses both with Imatest and also on an optical bench so we can compare performance both at infinity and at closer focusing distances. Continue reading

Examples Using an Optical Testing Station

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OK, I've done a couple of posts about critical focus for testing, and setting up an optical testing station.  This post will provide some demonstrations about actually using it.

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.

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Setting Up an Optical Testing Station

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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. 


Post-rental testing bays at Lensrentals

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Why You Can't Optically Test Your Lens with Autofocus

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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.

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Disruption and Innovation

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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.