May 31, 2005

In no way shape or form am I taking credit for this information. It came from RDKirk from It explains how Canon autofocus works in mostly plain English. Very informative!

According to the major material in Canon's "Lens Work III," the description in their US patent application, and remarks by Chuck Westfall, to put it briefly:

The AF system sensors are located in the floor of the mirror box. They receive the image through the semi-silvered mirror, which is then reflected downward by a secondary mirror hinged to the back of the main mirror. This forms a virtual focusing plane that is supposed to be at the exact same plane as the sensor (a point of possible miscalibration).

Each AF sensor consists of a pair of short lines of pixels forming an array. One array comprises the outer sensors. Two crossed arrays (one vertical, one horizontal) comprise the center sensor. With lenses or f2.8 or faster, the camera activates a second vertical array in the center.

The arrays are sensitive to linear details that run perpendicular to the orientation of the array. Therefore, the horizontal arrays (identified by the horizontal rectangle marks on the viewscreen) are sensitive to vetical linear details; the vertical arrays (identified by the vertical rectangle marks on the viewscreen) are sensitive to horizontal linear details.

They are blind to linear details that run parallel to the array direction. The center array, being a crossed combination of a vertical and a horizontal array, is sensitive to linear details running both vertically and horizontally. When the second vertical array is activated, it's combined input increases the accuracy by a factor of three.

The pixel arrays are actually three times longer than indicated by the viewfinder markings. This is to cover the fact that the viewscreen has a significant amount of "slop" in its horizontal-plane positioning (what you see as left/right/up/down in the viewfinder). Therefore, the sensors actually see details that are somewhat outside the viewfinder markings, and may focus on them instead of details within the sensor markings, if those outside details are more perpendicular to the array than the details inside the markings.

When you mount a lens (whether the camera is on or off), the camera interrogates the lens for its characteristics, including maximum aperture, which one of the focusing parameters.

When you half-press the shutter release (or the * button, if you've used the custom function to move focusing control there), the activated AF sensor "looks" at the image projected by the lens from two different directions (each line of pixels in the array looks from the opposite direction of the other) and identifies the phase difference of the light from each direction. In one "look," it calculates the distance and direction the lens must be moved to cancel the phase differences. It then commands the lens to move the appropriate distance and direction and stops. It does not "hunt" for a best focus, nor does it take a second look after the lens has moved (it is an "open loop" system).

If the starting point is so far out of focus that the sensor can't identify a phase difference, the camera racks the lens once forward and once backward to find a detectable difference. If it can't find a detectable difference during that motion, it stops.

Although the camera does not take a "second look" to see if the intended focus has been achieved, the lens does take a "second look" to ensure it has moved the direction and distance commanded by the camera (it is a "closed loop" system). This second look corrects for any slippage or backlash in the lens mechanism, and can often be detected as a small "correction" movement at the end of the longer initial movements.

When the camera determines how far and in what direction the lens must move to cancel the phase difference, it does so within a tolerance of "within the depth of focus" of lenses slower than f2.8 (down to f5.6) or "within 1/3 of the depth of focus" of lenses f2.8 and faster. The depth of focus is the range at the sensor plane within which the image of a point will be reproduced as a blur smaller than the manufacturer's designated "circle of confusion" (CoC). Canon's designated circle of confusion is 0.035mm for the 24x36mm format and 0.02mm for the APS-C format. The CoC is based on maintaining the appearance of sharpness in a 6x9 inch print at about an 10 inch viewing distance (as revealed by the Euro-Canon web site). There is no guarantee that images enlarged any greater than this will appear sharp.

The depth of focus increases when the aperture of the lens decreases (like depth of field at the subject plane), but it does not change with the focused distance or the focal length of the lens (according to Canon, unlike depth of field). That is why the camera interrogates the lens for that information; it calculates the depth of focus tolerance from the maximum aperture, not the set working aperture.

As a result of this tolerance (within the depth of focus or within 1/3 of the depth of focus), the camera can place the actual plane of focus at random anywhere within the tolerance range, and not necessarily at the same place each time.

A non-exhaustive list of information about focusing:

1. The center focus square in the viewfinder represents has both horizontal and vertical sensors, so it can focus just as well on vertical and horizontal lines of detail. The outer focusing rectangles are represent sensors that are oriented either vertically or horizontally (according to the shape of the marks), and focus best on lines of detail that are perpendicular to them. You can test this easily: Line up a vertical focusing rectangle on a vertical detail (like the corner of a wall or the edge of a door) and try to focus. The camera will not be able to focus on it. But put a horizontal rectangle against that vertical line, and it will snap instantly into focus (you can turn the camera, and the same will be true). This is a valuable tool. If you are struggling with a background that competes with the foreground, look at whether either has linear detail (say, a squirrel on a tree branch). You can activate one of the rectangles and turn the camera so that the rectangle is either parallel with the linear detail that you want to ignore or perpendicular to the detail you want to focus on.

2. The actual focus sensor arrays are three times larger than the viewfinder marks. A user could put an intended subject in the mark, but if there is a strong detail just outside the mark (but within the sensor area), the camera would focus on that strong detail. This is a source of much of the complaints of the back- or front-focusing -- especially with the "ruler tests." Also, as far as the camera is concerned, a focus lock on anything within the sensor area is good, which sometimes covers more area than the photographer intended.

3. Auto focusing with the 20D only works with lenses with maximum apertures of f5.6 or greater (as determined by the information passed to the camera by the lens). This means the total maximum aperture of the lens, not the aperture you're shooting with at the momement. With a lens slower than f5.6, you have to focus manually (unless you fool the lens somehow into reporting an incorrect aperture to the camera).

4. On the 20D, the center marks have additional sensors to increase accuracy three times greater than the 10D, but these only come into play with lenses that have maximum apertures of f2.8 or greater (not the aperture set for shooting, but the maximum aperture). On a variable aperture zoom lens, if it drops below f2.8 while zooming, that information is passed to the camera, which cuts out the additional focusing sensors. The outside focus sensors of the 20D are normal accuracy.

5. The camera's AF sensors require some details in the image to determine the phase difference. It's harder for the camera to find focus when the light is dim or there is little subject detail. Contrary to recent remarks on another topic, the camera CAN distinguish contrast between equally bright hues of red and green just as the eye can--the sensors are color corrected. Although the sensors can distinguish some quite subtle detail differences, they don't see quite a sharply as the eye. If the lens starts from a very out of focus condition, it can miss very fine detail that the eye sees clearly, such as the mesh of a speaker grill from across the room. In this case, it can be helped if the photographer manually moves close to "focus" and allows the camera to find the actual focus.

6. AF controls:
Shutter release. By default, when you half-depress the shutter release, the camera will focus with the active sensors on the strongest contrasts within those sensor areas. Whether or not it will hold that focused distance depends on what AF mode you're shooting in.

AE/AF Lock Button. The asterisk button on the back near your right thumb. You can set this button to be the focus button in the Custom Function menu (CF4--choose option 1). When this is set, you focus by putting the active AF mark in the viewfinder on your subject and press the asterisk button. The camera focuses on that spot and does not change focus until you press the button again. In AI Servo mode, the camera continuously evaluates focus only as long as you have the button pressed.

Multicontroller (joy button) and AF Selection button. These controls, plus the control wheels, allow you to select which focus marks are active--they provide multiple ways to do the same thing, so take your choice. You can either select one point or you can set the camera to choose its own points as you focus. If the camera chooses the points, it will usually focus on any number of points that are closest to the camera. About the only time this is better is when you're focusing on fast-moving activity that you can't keep under a single mark (say, a soccer player). Otherwise, it's usually better to select your own point. The diagonal points on the 20D are very close to the "Rule of Thirds" intersections, so sometimes it's convenient (if you use that composition rule to place your subject in the frame) to select one of those points.

7. AF Modes:
One Shot: When you set the camera to "One Shot," you set the condition "The subject is definitely not moving." The camera is in a "focus priority" mode. The shutter release is locked until the camera achieves what it thinks is the proper focus. This is best if your subject and the camera will be motionless, because it allows you to focus and change the framing without the camera refocusing automatically.

AI Servo: When you put the camera into AI Servo mode, you have set the condition "The subject is definitely moving." The camera is in a "shutter priority" mode. Therefore, the camera goes into a routine that continually collects data to predict the subject movement and move the lens to intercept the subject at its new position. You can shoot even if out of focus (however, the camera cannot release the shutter if the lens is actually in motion). If you know your subject will be in constant motion, this is the best mode. If the subject is actually not moving, the chance of a misfocused shot increases as the camera goes through its data-collection routine. However, often a handheld camera does move (as the photographer sways naturally) for AI Focus to detect and correct for the sway. AI Servo will use whichever focus point you have activated. However, if you activate all the focus points, you must put the center point on the subject and half-press the shutter release for about half a second for the camera to "acquire" the right subject. After that, while you hold the shutter release, the camera can intelligently "hand off" the subject focus from point to point as the subject "wanders" over the viewscreen.

AI Focus: The camera is normally in One Shot mode and the shutter will lock until it achieves focus. However, if it detects the subject moving (that is, the subject goes out of focus), it will automatically switch into AI Servo mode and try to maintain focus. If you are focusing on something that frequently stays still but could move suddenly (like a toddler) this mode comes in handy. The important point wiht AI Focus is that it does not lock the shutter. However, the camera will usually interpret "focus and recompose" as movement of the subject, and will refocus.

May 30, 2005

Rob Galbraith DPI: Firmware updates to fix lock-ups, image corruption with Canon cameras and Lexar CF:

Great, I'm off for my first and probably last trip to Ireland on Friday and I have two 1 GB CF cards that are subject to a recall. Great! There is no time to get these cards fixed before I leave in FOUR DAYS. Oh well, I may lose a few pictures but I doubt I will lose anything amazing. I'm not that good of a photographer.

May 25, 2005

Woohoo! My blog is back! My ISP has had some serious problems with their FTP service and I haven't been able to upload in about two weeks. Let's see, what have I missed?

May 16, 2005

Lenses for Canon EOS cameras - Canon, Promaster, Sigma, Tamron, Tokina and Vivitar: There is very little information about lenses available for the Canon EOS system that isn't captured on this page. My god, what would it be like to have all of these lenses?

May 15, 2005

God damnit. I just upgraded my Gallery to version 1.5 and I still cannot get the "Photo Properties" function to work. I'd love to be able to access the EXIF data quickly but I've probably spent 10 hours on this over the years and it just isn't going to work. Argh.

May 13, 2005

The natural progression of aperture settings (f stops) goes 1.4, 2.0, 2.8, 4, 5.6, 8, 11, 16, 22. With each progression, the light let in is halved. Good to know!

May 5, 2005

My parents are going to love this one! Brought about by this thread on the Car Lounge, I just had to tell my "top speed" story

The first summer working for Yazaki, I also worked at the Michigan Daily on Sunday nights. That meant I got to drive home from Ann Arbor to Livonia at 12:30 AM on Sunday night / Monday morning. The highway between, M-14, was always completely dead so I routinely drove 85-90 MPH. One night, I picked a stretch of highway where I had never ever seen a cop nor were there any exits for one to hide out behind me on. I just opened up and decided to go as fast as I could. I got up to 112 before I freaked and coasted back to 85. Now that I think about it, I probably should have hit the brakes immediately when I freaked out. If I was going to get pulled over, I was still well over the speed limit as I coasted from 112 to 85, though I'm not sure how much the not-too-bad aerodynamics (.33 Cd) of a '96 Probe GT played a part.

May 2, 2005

Mark my words: at 6 PM PST on 02May2005 while listening to Liz Phair's Shitloads of Money, Something Very Bad just happened to the life of Michael Paul Bibik Junior. I'm not sure what, but I felt it and boy did it feel weird. I can best describe it as "Well, shucks, that's horrible, but there is abso-f'ing-lutely nothing I can do about it so I might as well finish this Diet Coke and end my work day."

May 1, 2005

Puerto Rico! Kat won an all-expenses-paid trip to the Wyndham El Conquistador Resort in Fajardo, Puerto Rico and we just got back. Other than a handful of dinners and events planned by the company, we were on our own to do what we wanted!

Saturday, 23Apr2005

As we were packing and just a few hours away from our flight, I noticed that some of Kat's clothes smelled a bit funny. I immediately realized that she had put most of her clothes on the futon in the den a few days prior and that Sebastian had a habit of "claiming" the futon. Yes, the cat pissed all over her clothes. Luckily, it was only one pile and those items were quickly tossed into the wash and dried just enough to pack them. Travelling took us from 5 PM on Saturday in Seattle to 9:45 AM on Sunday in Puerto Rico. Kat slept for all but an hour on the seven hour leg from LA to Puerto Rico; I hadn't slept more than an hour. I was a bit slap happy all day, but recovered quickly.

Sunday, 24Apr2005
Check-in was smooth without incident, eventhough their system had shown that we should have checked-in the day before. They simply changed it to Sunday and didn't charge us for Saturday at all. Over the next few days, we heard horror stories of people not being able to check-in for hours, some coming in around 4 PM and not being able to get to their rooms until 9:30 PM! Most people showed up for the trip on Monday and the computer systems were down for a few hours, probably causing most of the problems.

Given that this was a free day (no planned activities), Kat and I decided to check out the island that the resort owned, Palomino. On the water taxi ride over, we bumped into one of the only people that Kat knew was going to be on this trip, Michelle. We ended up sun bathing with them for awhile, Kat talking with them and me fighting falling asleep in the sun. The beach was attractive, the view was amazing and the sun was hot.

That night was one of the only free nights for dinner so we made reservations at the "nice" Italian restaurant in the resort. The food was mediocre, the ambiance was worse than an Olive Garden considering the harsh lighting and noisy children, and the cost was simply far too great for what was offered. We sat next to a couple on their honeymoon and they were definitely not happy with the resort. They complained about their dinner as well, spoke of check-in troubles and were pretty annoyed with the class-level and rampant children of the other resort-goers. I tended to agree, but at least our trip was free!

Monday, 25Apr2005 : Pictures

On Monday, we went back to Palomino, but we decided to do more than just sit around the beach. After deciding that $120 (plus tip) was too much for the two of us to go horseback riding for 30 minutes, we decided to hike the island. Getting to the top wasn't too strenuous but the heat was vicious. The air was so hot and humid it was difficult to breathe. Hiking to the backside (pun intended) of the island offered a small reward, a nude beach! When we got there, we didn't see anyone until we had walked most of the sand. In a little alcove was a fully naked older man bathing stomach down, thankfully, with a skin color that showed just how often he did just that. We grabbed a few of the chairs and laid out, clothed. As time went on, we saw two more fully naked guys, one fully naked woman and one topless woman. Nothing exciting.

Instead of hiking back the way we came, we circled the island. Again, we laid out for a bit and then headed back to the main resort. The work festivities started off with a welcome dinner, buffet style. After a few announcements from the VP of sales, we were left to finish dinner and have the rest of the night to ourselves. We met up with Michelle and her friends and went to the only "club" in the resort. It was basically 12 people from her company in the club with at most half of them dancing at any one time. I danced for a bit, but I was still pretty tired overall so Kat and I bailed at 12:30 AM.

Tuesday, 26Apr2005 : Pictures

Tuesday started a string of three days of tours. First stop, old San Juan and the San Cristobal fort. The fort was fairly interesting, mostly because of the few engineering marvells, such as the gutter system, the thickness of the walls, the sand filling of the walls to diperse impact damage and the segmentation of the ceiling so that if one part of the fort falls, it won't take down the rest.

Old San Juan had a modernized old-world feel: narrow streets, lots of shops and various types of people milling about (along with a large number of tourists for a Tuesday) but with numerous cars zipping about and other present-day conveniences. We ate lunch at a local fast food restaurant, El Meson. It was mostly sandwiches, but we were so hungry everything tasted great. Old San Juan is also known for high-end outlet shops, so we hit Dooney&Burke, Coach, Polo, etc. Nothing caught my eye and same went for Kat. We saved our money for a couple of bottles of Ron del Barrelito, a rum you can only buy in Puerto Rico. We haven't tried it yet, but I'm sure it's great. We ended up walking around mostly with a couple from McAllen, TX, Lupe and Sandra. They were great people and I wouldn't be surprised if Kat keeps up a relationship with them.

Tuesday night was the "dine around" dinner, mostly meant to allow winning teams to have a meal together without managers to celebrate. Kat won without her team so we were able to have a romantic dinner alone. We picked up a bottle of Phelps Le Mistral 2002 and it was the best blend I have had to date. It was characterized by a very soft strawberry/blackberry (and a hint of vanilla) start with a strongly contrasted peppery finish. The dinner was as good as the wine but the dessert had nuts and so I had to finish it myself.

Wednesday, 27Apr2005 : Day, Pirate Party

A trip to El Yunque (officially known as the Caribbean National Forest) was the tour of the day. For my first trip to a rainforest, I was actually pretty disappointed. We saw a handful of slugs, a billion walking sticks, an anole, some hummingbird-like birds and a few coquis. Kat has been to the rainforests of Costa Rica so she was disappointed as well. It was a nice walk and I think I got a few good pictures so it was still worth going. We primarily hung out with Lupe and Sandra all day again.

The company rented out the entire island I spoke of before to hold an evening pirate party. Kat and I had brought pirate costumes (not full costumes, just small bits of pirate clothing) and a few others had done so as well, but the company had purchased hats, eye patches, an earring and a sword for everyone. At least our costumes stood out! Dinner was Caribbean in nature, including a pig on a spit. We met some fairly cool people from Memphis and sat with part of their team. Discussion didn't have a chance to veer from the basics of college, work and life before it started to rain a bit and we scampered back on the water taxi.

Thursday, 28Apr2005 : Pictures

The final paid tour was snorkeling. We had to get up at 6:45 AM in order to get down to the catamaran at the marina at 7:45 AM. After about 45 minutes of sailing, we anchored near a small island of the Fajardo coast. I had never been snorkeling, so the concept of being able to dunk my head underwater and still be able to breathe was a bit odd. I was definitely breathing heavy for the first five minutes and I did suck in water at least five times. There wasn't anything amazing that we saw, but we did see hundreds of fish and lots of coral, though most of it was a boring brown. We were served sandwiches and fruit after being in the water and I will admit, there is little better than a nice lunch after being in the water. We all beached ourselves on the catamaran and relaxed as we sailed back to the resort. Kat and I did not reapply sunscreen stupidly enough, and thus we both got a bit burnt.

That night was the award dinner. We sat with Lupe and Sandra and endured a decent dinner while listening to every single winner get announced (all 110+). The night actually wasn't as bad as we had expected, especially knowing that it was scheduled from 5:30 PM to 10 PM! Videographers had been around the resort since we got there so of course there was a highlight video. With limited time, they actually put together an entertaining bit with high production values. A few people were highlighted more than others so I think one of the camera guys had a crush. The only bits with me in it were with me behind the dSLR, no surprise. We had planned on hitting the casino afterward, but we were all a bit too tired and many people were leaving early in the morning.

Friday, 29Apr2005 : Pictures
Considering how much time we had spent at the resort, Kat and I decided to escape for the day so we rented a car. We initially had wanted to go to Ponce, the second largest city on the island, but decided that the estimated travel time of two hours each way without traffic was simply too great. Instead, we decided to go back to San Juan and see the other major for, El Morro, and then take the Bacardi Distillery tour.

When renting the car, I decided that I wanted something non-luxury and small but new and with A/C. They gave us a Suzuki Aerio and my frist reaction was a bit of dread. In all actuallity, the Aerio is a darn good little car! The interior is pleasing to the eye and well laid out, the seats were more comfortable than Kat's Impala, the engine had more than enough punch even with the A/C blowing, the handling was perfectly reasonable for that type of car and it was fairly spacious overall. The only two negatives were the looks (not an issue with a rental car) and the transmission. It had a habit of kicking down if you cut the throttle when the engine was near but not at full boil. Basically, if I needed to accelerate quickly but for just a short burst, the trans would downshift, I would accelerate as needed and if the engine was in the 3500-5500 RPM range, the following upshift would be a bit jarring. Oh well, not a bad deal for being able to rent a car directly from the resort for a day for only $60!

First was the Bacardi tour. Getting from Fajardo to Catano was only 36 miles but took about 80 minutes. The tour started out in a building off to the side of the distillery. It started with a brief video about the history of the company and the drink and then moved on to a recreation of the first distillery process. There were two rooms connected, one that had the barrels and machinery for distilling and the other as a recreated office of the founder of the company. The guide said that photography was not permitted in the office so I asked if flashless photography was okay. She told me it was not. After investigating the office, I started to take pictures in the recreated distillery. After a few pictures, the guide came up to me and said "If you do not stop taking pitures, I will have to call security." Pictures were allowed everywhere else I had been and she specifically said only the office was off-limits. Whatever, bitch. Power trip, much? I put the camera away but I was fairly disinterested with the rest of the tour after that. The next room was a series of booths that explained more about the current distilling process including a few small buckets that contained rums and rum precursors so you could smell the difference. The last room was a tour of Bacardi facilities and advertising through the last 50 years.

Kat and I both figured this was just the start of the tour and the actual distillery was to follow. We hopped back on the little shuttle and it drove right past the distillery and dropped us off at the gift shop! The tour had mentioned a bottle of 12 year aged rum that was only available at this location so we dropped the required $50 to pick up a bottle. Once again, latin sense of hurry came into affect as the seven people in front of us in line resulted in waiting almost an hour to buy a single bottle of hooch. It better be worth it.

El Morro was similar to San Cristobol in construction, but primarily only the external portions of the fort were available. I'm a bit fort'ed out at this point, but I'm still glad I went. The drive back was a complete pain though, as traffic was quite bad on a Friday in the late afternoon of San Juan. It took us two hours of complete stop and go traffic to get back to Fajardo.

Saturday, 30Apr2005

The flight back was a set of two four-plus-hour flights, never enjoyable. On the flight from Dallas to Seattle, I noticed a weird event. The flight attendant (the only one for first class) put a cart between the flight deck and first class as she had done before so one of the pilots could use the bathroom. Instead of having a pilot come out and go directly to the bathroom, one pilot came out and the flight attendant went in! The door was closed and the pilot just leaned against the wall with his arms crossed. The lasted for about ten minutes when the flight attendant came out and the pilot went back in. Two minutes later, the same thing happened with the other pilot! I'm pretty sure this was a mid-flight stress release exercise.