Yet another camera problem...

[I meant to finish this post up in Korea, but I neglected to do it. So here it is. I have a follow-up to it which I'll get up in a few days.]

When I was going through some of my pictures on Tuesday, I noticed that about 10 of the images from the end of the session have vertical lines through them like you see in the 100% crop above.

The whole trip I was shooting JPEG, so it is unlikely it is a CF problem or file problem. Most likely, I believe it is a sensor problem. I expect it would be relatively easy to fix the images using PSP XI, but the bigger question is whether I'll need to get the camera fixed (thank goodness for the SquareTrade warranty). It hasn't happened again though, so it could have just been a random malfunction in the Jeju humidity.

I did a quick Google search on the issue and turned up a few good links. Consensus seems to be that this sort of problem indicates a sensor connection issue although most links weren't exactly the same problem I'm having. Apparently these types of issues are relatively common on the 20D.

Did I mention I was glad for the SquareTrade warranty? More and more, I think it is well-worth it to warranty cameras because of their inherent complexity and chances of breaking in a very expensive way. Especially used/refurbished cameras. Lenses aren't as important to warranty, in my opinion, since they are much simpler pieces of equipment and don't break as easily.

Helpful Hints From Jeju, South Korea...

Wow, over two weeks has elapsed since my last post. Luckily, I'm in Jeju, South Korea for a conference and I've had lots to point my camera at. Expect a bunch of pictures in the near future.

For now, some helpful hints for the next time you are on the Hawaii of Korea:

Helpful Hint #1: In a warm and humid climate, your lens will fog up when you leave an air-conditioned room and go outside. This morning it took half an hour for my camera lens to defog when I went to the beach, and I missed a bunch of photos.

Helpful Hint #2: Sometimes it is just better to go to the hotel restaurant and point to what you want when ordering room service instead of getting nowhere on the phone. Edit: The ox-tail soup I ordered is pictured at left.

Helpful Hint #3: Bring an umbrella. And lots of clean underwear and shirts. Coming from the desert that is the Bay Area, I was shocked how quickly I could soak a shirt with sweat, even when it wasn't raining.

Back to the Future

Here's a memory for you:

I'm cruising to school in my decade-old stickshift, blasting Pearl Jam on the radio with the windows down, wind whipping around me... Sure, the car was a piece of crap, but I could still get that thrill of speed as I moved through the gears, rev'd it up a bit, and enjoyed that special freedom which came with MY OWN CAR.

Of course, I'm actually talking about last Wednesday.

You know, most guys with a mid-life crisis get to sleep with younger women, drive a fast sports car, or start doing all the daring stuff they wanted to do when they were younger but didn't have the resources. Me, I have a mid-life regression. I'm still in school, I'm around high school kids constantly, I'm still married, and now I'm driving a car with so many problems I can remember them all. But I'm enjoying life :)

Although the fantasy burst when I realized I couldn't get the piece of %&*# radio to eject the CD. I swear, the dealer must of sent in a few UPC symbols from a cereal box to get the thing; I didn't technology this bad was still out there. Reliving my youth is cool (and I still like Pearl Jam), but always driving around in a '98 Honda listening to Pearl Jam?

Definitely uncool.


Speaking of cool, since my Honda isn't much to look at, the images in this post are all of cars that... aren't mine. I took them at the Palo Alto Concours D'Elegance in late June. In order of appearance:

1. A DeLorean, the only production car with stainless steel body panels. Apparently the DMC isn't dead though.
2. A 2001 Lamborghini Diablo 6.0 from the last year of the Diablo. Yeah, a $250,000+ car. Really.
3. A 2007 Tesla Roadster Roadster, the first electric supercar. A woman in my lab is doing an internship with them, I'm pretty jealous. For the low, low price of $98,000, you too can pre-order a car that can go toe-to-toe with a Lamborghini Murcielago in acceleration (0-60 in 4 seconds), hit 130+ mph, go 200 miles on a single charge, yet get an equivalent of 135 mpg. I'm not a car guy, but I love what the Tesla stands for: more efficient, yet better performance. I really hope electric/hybrid cars go in this direction.
   
4. No idea what this is, but it looks really cool.

How to Test Autofocus

This post ended up so large, I split it between entries. The follow up entry (much delayed) is here.

As I mentioned in my 20D review, I am concerned that the auto-focus in my 20D is out of calibration. So I decided to test it... at least somewhat scientifically. If you are one of those people that likes to read the last page of the book before the first, I'll give you the end before the beginning:

My 20D's autofocus is fine, or at least not worth sending to Canon to 'fix'.

But, you may be asking, how do I figure out if my autofocus is working correctly?


How Autofocus Works:

This discussion only really relates to SLRs, specifically Canon digital SLRs. Most fixed-lens point and shoots use an active autofocus system (for more information, see here).

Canon dSLRs use a passive, TTL (through the lens), optical system. In other words, your autofocus judges focus much like you do: it looks through the lens and determines when the image looks the sharpest. But unlike a person, who will keep rotating the focus wheel until it looks sharp, Canon's system can calculate where focus should be after one reading, then commands the lens to move to a position which should give the correct focus. The gory details are in Gordon McKinney's autofocus post. There's also an interesting discussion about the 30D autofocus in this DPC thread. And here are two more threads with lots of good info.

To compute focus, Canon has placed special sensors on the bottom of the mirror box (using a secondary mirror underneath the half-silvered main mirror). These sensors can measure the focus as long as there are high contrast regions in the image projected onto the sensor. In other words, if you point your camera at a blank wall, the sky, or a polar bear in a blizzard, there will be no contrast and the system will be unable to find focus (instead, it will hunt through the full range of focus hoping to find something it can use). Also, the focus regions are small strips of the viewfinder area, so it is possible to 'miss' the object you are trying to focus on (resulting in a confused camera).

There are three take-home messages about the 20D (and 30D) autofocus:

• Autofocus is not perfect. In fact, much of the time you'll be lucky to get the object used to focus within the range necessary for a good image. Because Canon cameras measure the 'focus' and then command the lens to move open-loop, it isn't hard to be off in focus, especially since there is some inaccuracy built in. A feedback loop around focus would be great, but for some reason Canon didn't do that (probably too hard given the range of lenses and focusing systems).
• The 20D and 30D autofocus system isn't really a step up from the 350D. For some reason, autofocus is an area where these cameras seem to have poor quality control. This means you need to be tolerant (almost expect) a bit of autofocus slop in a 20D.
• There are techniques which can help you compensate for poor focus performance of the 20D.
  

So, what can you do?

Test your camera, of course! In my opinion, anyone who gets a 20D or 30D should run some simple tests on their camera to verify it doesn't have a (major) focus problem and identify any specific focusing issues.


Testing Procedure:

The testing procedure I used is modeled after Francis Poon's test (and uses his target). Go to his site for the details. An alternate test and target are here and the idea is the same (but the target construction is advanced origami).

The basic procedure is:

1. Print a test pattern and assembled the 45 degree target. I taped mine to a clipboard.
   
2. Set the target on a 45 degree slant which will face the focusing target directly at the camera. I leaned mine on a box and secured it with scotch tape.
3. Make sure you have plenty of light on the central focusing target. I used a lamp for the full area, then a flashlight on the focusing target. In all honesty, I should have gotten more light on it. See the image that opened this post for the full setup.
4. Set your autofocus to use your center sensor. You could run the test on the other sensors too, but start with the center one.
   
5. Focus, using manual or autofocus depending on the test, and then take a picture. Better yet, take a bunch of pictures, with different lenses, different focusing techniques, and keep track of what you did.
6. Look at the images on the computer (usually 100% crops) and use the scale to the left and right of the primary focusing target to determine where the depth of field is. The letters ('a') are the best guide to seeing the region of focus. The scale is designed to give millimeter depth measurements if the image is tilted at a 45 degree angle (I didn't do anything special when I printed mine, so it could be a little off).
   
7. Compare your measurements to the expected degree of field for your focal length and aperture measurement. I used the DOF calculator here for my computations.
   

It may seem complicated, but it really isn't. The hardest part is determining what you will test and keeping to the scientific method. Generally, you should try to keep everything as similar as possible between test photos except the variable you are testing. This includes controlling your lighting, camera to target distance, viewing angles, etc.

If the focus is good, you'll get an image like this (click to see the unedited 100% crop of the JPEG):


Note the 'blurriness' of the 'a' line. That was my main guide for finding the degree of field.

If the focus is bad (for reasons listed below) you'll get a crop like this:


The image above shows a front-focus of about 12 mm. Depending on the lens and aperture, that may not even be out of the depth of field.

Seriously, this test isn't that hard. Just takes a little organization and a few hours.


Possible Areas of Failure:

There are a number of areas in a camera which can be miscalibrated. Luckily, pretty much everything can be tested with the target set-up above. Just come up with your own sequence of images and procedure (I'll list mine in my next post). Make sure you check the following:

1. Viewfinder plane calibration. This isn't often a problem, but you'll want to know if the sensor plane is at a different distance than your viewfinder plane. Just manually focus on the target and shoot a few shots (clearing your focus each time). This ends up being an eyesight test too, but if you take your time and have decent eyes, you'll definitely get within the depth of field.
   
2. Test the autofocus calibration. Test your best lens, the longer the focal length the better, since longer focal lengths have a narrower depth of field and the autofocus will be more accurate. Autofocus from both focus extremes (close and far) and see how well it does. If there is a consistent focus offset that is significantly larger than the DOF for that focal length and aperture, you may have a problem. Apparently, this is more common than problem #1, since the floating mirror has some play in it. A little offset, especially on a 20D or 30D (of about 1 DOF) is probably to be expected, any more than that and you probably ought to have Canon calibrate it if it is under warranty.
   
3. Test each of your lenses. Since the camera works with the lens, there can be significant variation between lenses. If one lens is much worse than the others, it needs to be calibrated.
   
4. Test each focus sensor. I drew horizontal and vertical lines of different thicknesses, and tested to see how well the different focus sensors picked them up. If one of your sensors is faulty, this is the way to find the problem.
   
5. Test for viewfinder screen offset. While the plane of the viewfinder screen is usually well constrained, there is a decent amount of play in the horizontal direction for the sensor boxes. So see if you can focus with the sensor indicator slightly above or below a feature -- with some experimentation, you can determine how your viewfinder indicators are offset from the actual sensors. Unless it is a huge amount, just keep that in mind when you are using your camera. Also, keep in mind that each sensor is usually three times the length as the indicator, but relatively narrow in the other direction.
   

That covers it, stay tuned for my next post about my results.

Excuses, Excuses...

This is going to be one of those posts where I just make excuses about the lack of updates on my blog. But, the genius is I can hammer out a quick post and feel all... productive.

Anyway, if you care more about photography than my life, you may want to skip this one. There's nothing photography related in this post.

So, with that out of the way, I want to give my readers (Hi Mom! Just kidding, even my mom doesn't read this blog) a heads-up that I'll be dropping down to about a post or two a week for a few months. The reason is best explained with a list of my activities lately:

• Found and signed a contract on a rental house. That may not seem like a big deal, but when you need to deal with commutes, school districts, open houses, craigslists ads, ten families showing up to each open house ("Bid up" the agent says), and finally the fact that on paper (and in real life) most rental houses have a monthly rent of 90% of our pre-tax income, it is a time consuming task. But, all that is simplified now that we've signed a contract for a house that ONLY costs $2,495 a month. And doesn't have a refrigerator. Which brings me to...
• ... we need to move our family of four (and about twice as much stuff as most families have) in two weeks. Assuming we can even move in on August 1st, which is not guaranteed.
• Right after we move, I present at a conference in Korea (South Korea of course, hold your jokes, please), my wife starts her full-time school program, my son starts at a new school, and my daughter learns to babysit herself starts at a preschool. Which brings me to...
• We need to find my daughter a preschool.
• This whole time, I've been putting in about thirty billable hours a week for my SAT prep job. Which is the equivalent of forty hours a week when you consider travel and prep time. Luckily that will drop off a bit after this week, which is good, because we'll be moving. Either way though, I've been spending a lot of time on the road, which brings me to...
• ... we just bought a new (used) car. After realizing that my wife would need to be able to drive to school each day and it isn't going to be practical to swap the minivan back and forth (plus its gas mileage is less than ideal) we started a quick search for a second car, mostly for commuting. We ended up getting a '98 Honda Civic EX for $4,000 pictured at right from Harry at Auto Best Buy (click picture to see the details). As far as used car dealers go, Harry is as honest as they come and he has a good selection of lower-priced Japanese cars. We still spent about four hours in his lot...
  
• ... and now I have a sun burn. Ok, I guess I'm whining at this point. I'll cut myself off.

My point is, I've been busy and will be busy until I get back from Korea. Actually, I'll probably remain busy after my trip since fall is prime SAT season and I'm considering submitting a paper for a September deadline.

On the positive side, I'm aiming to bang out the autofocus post tonight, so hopefully that will get posted early this week.