Thursday, August 16, 2007

Contrast beyond measurement

Part of the challenge of taking pictures outside is that the world has a lot of dynamic range, and our ability to capture that dynamic range is fundamentally limited by the flare in the lenses that we use. So, I've been working on reducing flare in my lenses for a few months.

It turns out there are some guys, Paul Boynton and Edward Kelley, at NIST who had a similar problem (here's the link). They were trying to measure the contrast of LCD displays. It turns out that customers demand higher contrast from their displays than a standard camera can directly measure, because of limitations of veiling flare in the camera. To reduce flare from air/glass interfaces, they built a camera with no air/glass interfaces by filling it with liquid. Totally cool. But also very geeky, not the kind of thing you'd expect to bump into in the day-to-day world.

This morning the DJ on the radio was reading an ad for a Pioneer LCD TV, and claimed that it had "contrast beyond measurement". The person writing that ad probably doesn't know what that means, but I wonder who he heard it from. I find it funny to think about that phrase working it's way from one of the few thousand people who actually care, through executives and ad campaigns and broadcast radio, to me, one of the other few thousand who actually know something of the back story.

Random disorganized blog thread: The high-contrast LCD TV thing raises two leading questions: how are broadcasters producing those high-contrast signals in the first place, if cameras can't capture that much dynamic range, and how is it that customers can discern contrast levels that cameras cannot?

I think the answer to the first question is that broadcasters are stretching image contrast before display, probably to make up for veiling glare on the air/glass interface at the front of the LCD.

The answer to the second is that the human eye probably has less veiling flare than a camera, because it has just one air/liquid interface. I wonder if the human eye has dichroic antireflection coatings/layers on the exterior air/solid interface? I know we've not yet evolved correction for longitudinal or lateral chromatic shift (achromatic and apochromatic lenses), which I think is odd, given the sharpness benefits.

PC sync output from Canon 1D Mark III

Recently I was faced with the problem of generating a TTL compatible pulse from the PC sync output of a Canon 1D Mark III digital SLR.

This ought to be pretty easy. The sync jack on the camera has two contacts: the center pin and the shield, normally disconnected. When the shutter fires, a switch momentarily closes between the two. My understanding is that older flash units would use this switch closing to discharge a capacitor through a xenon flash tube.

So the circuit is trivial: a 5V supply, a resistor from +5V to the TTL output, connect the grounds, and the PC sync goes between the TTL output and ground. When the shutter fires the camera pulls the TTL output low, otherwise it gets pulled high by the battery.

Except: the Mark III doesn't open the switch until the current has stopped flowing. That's not a bad thing; the camera thinks it is discharging a cap, and keeps going until the cap is drained or the arc in the xenon tube collapses. It does mean that I needed to build a one-shot instead of the single-passive circuit, but that's not really so bad.

The problem is that Canon hasn't documented this behavior anywhere. Worse still, their phone support folks told me the exact operation of the PC sync terminal is proprietary (after keeping me on the phone for over an hour). This is a standard interface! They already have a proprietary flash interface on the top of the camera -- there is hardly any need for another one.

Call me disgusted.

Sunday, August 05, 2007

Buying a house -- lessons learned

We tried to buy a house without using a buyer's agent. We got the house, but ended up with a agent. Here are our lessons learned about the transaction itself:
  1. Watch the language. The legal language is different, and more accurate, than the language used by the agents themselves. The "seller's agent" is legally called the listing agent, and the "buyer's agent" is legally called the selling agent. If you are buying a house, this is supposed to clue you in that "your" agent is really not acting in your interests.
  2. Extract more money from the mortgage broker. The mortgage broker gets a huge kickback from the bank: 1.5% in our case. We had multiple mortgage brokers find us loans, and we told the ones that were more expensive to come up with a better offer. What we did not realize is the size of their kickbacks. We could have asked, for instance, for 1% of the loan amount to be paid back to us at closing by the mortgage broker. We also talked directly to banks, and were unable to get a better loan than what we got through a broker. This seems like stupid behavior on the part of the banks.
  3. It's hard to avoid a selling agent. We found our own house, and told the listing agent that we did not want to use a selling agent. We figured we could save the 3% that the selling agent usually charges.
    1. The listing agent reacted very negatively (as did everyone else in the real estate business to whom we suggested this idea) when she heard this. She said her sellers would not give us a fair hearing unless we had an agent. She had no sensible explanation why. I finally phoned the seller at home, and left a message saying I wanted to hear directly from him that he wanted us to have an agent. What I got was a vague message back from the listing agent hinting that we needed a selling agent. We really liked the house; I caved in. I suspect but don't know that if I had used the "listing/selling agent" terminology instead of "seller's and buyer's broker" terminology, I might have broken through.
    2. We used Todd Beardsley as a selling agent. We found him in a posting at Mike's Lookout (Mike also used Todd). Todd charges 1% and rebates whatever extra the sellers are offering (typical selling agent commissions are 2.5% to 3%). He doesn't help you find the house, he just helps the negotiation. It worked, the listing agent accepted him immediately. I thought Todd was very professional, and would recommend him with one caveat: Like all selling agents, Todd is incented to (a) get you to buy the house, and (b) get you to pay as much as possible. He is a professional, but the incentive leaks through. For instance, as an opening strategy, Todd suggested that we figure out the maximum amount of money we would be willing to pay for the house, and offer that. No way!
    3. A few years ago, we bought a plot of land without a selling agent. In that case, there were no competing bids and the sellers were motivated (the land had been dropping in value and they had been trying to sell it for two years). The way it worked was that the listing agent pretended to represent both buyer and seller, and changed his fees to the seller from 6% down to 3%. The Mike's Lookout post above suggests that it's unusual for the listing agent to renegotiate his commission like this. I don't think so. Another real estate agent that we have worked with has told us that the commissions get renegotiated all the time, for instance when selling agents are trying to close the last 1% of so between the buyer and seller.
  4. Never counter-offer all of your bidders. When you counter-offer your highest bidder, you are rejecting their bid, placing the bird in hand back in the bush. In our case, I'm pretty sure we were the highest opening bidder of three. One other was a low-ball or nonserious bid. The sellers counter-offered all of us, basically trying to rachet us up. What they managed to do, instead, was tell me that I was the highest bidder. When I lowered my bid, they countered with my original bid, which told me the other bidder hadn't matched my lower bid. I should have gone lower still. Instead, I caved. Even so, the counter-offering everyone strategy resulted in us paying less.
  5. Pay the selling agent directly, instead of allowing the listing agent to do it. In our case, Todd was able to negotiate this with the listing agent during escrow. It's worth a lot to the buyers, since they pay property tax on the amount paid to the agents for as long as they own the house. But it's also worth money to the sellers: they save transfer tax, and perhaps a few other items.
  6. Try to pay the listing agent directly, instead of allowing the seller to do it. We didn't try this, because we couldn't figure out how to do it. You might phrase your offer as an amount for the house and a fixed amount for the listing agent. That way, the listing agent and seller can renegotiate their terms without involving you, and it doesn't appear that you are incenting the agent to sway his client, to whom he owes a theoretical professional obligation.