Longtime readers of this column have met Timothy, Gulliver, Marilyn and Dave -- the dogs that have been companions and test subjects since we first started photographing.

Dave's short, tan Weimaraner coat made him the ideal low-contrast, high-spatial frequency test target. Note the Leitz Digilux II tests.

He arrived from Friends for Pets. The pound had called them and asked Friends to take Dave before the pound had to put him down. But Dave was almost six years old and 110 pounds - not what folks looking for a puppy had in mind. He had been there six months when we showed up looking for a dog.

A number of puppies, wriggling and jumping, applied for the job. When Dave finally appeared, he took one look at the open front door and ran for freedom. Three handlers chased him down the street and eventually brought him back. Dave was big enough that when he lay down he could rest his head on my lap. He did - and then he fell asleep. My kind of dog.

And so - Dave came to live with us.

The California half of our bicoastal existence is in an area that has streams, wooded trails and trees filled with squirrels. And the house has two sofas and two double beds. Just what a dog needs.

It's also in an area that puts you in contact with considerably less people than midtown Manhattan; so, a big dog that hangs out with you is just what a man needs.

Dave and I became friends after both of us had passed middle age. As a rule, the bigger the dog, the shorter the life span. Dave's country life, long walks and chasing squirrels in the garden kept him in good health. He had the occasional sports injury. And when he began to have trouble walking we thought he had hurt himself trying to climb up the banks of a dry stream bed before he could be rescued.

A number of X-rays and exams later, we found out that Dave had cancer. The tumor was pressing against his spine. Fortunately, medication shrank the tumor, and Dave was soon his old self.

The dosage would have to be increased over time. That would lead to side effects. It was decided to operate.

Dave trotted off to the back room of the animal hospital with his new friends. The surgeon called that night to report Dave would not be dying of cancer and had some good times ahead of him.

The next time I saw Dave, two days later, he was crying and in great pain.

Three days later, Kenny, who cares for the animals staying at the center, called us to say she thought Dave would die before the night was over. We had spent part of the day with Dave, but Kenny let us into the hospital after hours. To a small degree, Dave's suffering was lessened when we crawled into his cage, gave him snout massage and chest tookies and sang his favorite song, the "Silly Old Dog". My wife and I spent a long time holding him and comforting him.

We spent a fair amount of time talking to Kenny and Alex, his all-night equivalent. Dave's painkiller dosage had been upped, and he eventually fell asleep. We left rather than interrupt his sleep.

A few minutes before midnight, Alex called to tell us that Dave had gotten up a few times, in true dog style, to reposition himself. She had repositioned his intravenous tubes. When she came to give him his next round of medication, she saw that he wasn't breathing.

The day after he died, one of the doctors said to my wife that the cancer would have killed Dave anyway in a few weeks, that the biopsy report indicated generalized cancer. Whether that estimate of how long he had to live was optimistic or pessimistic, it indicates that Dave did not die of cancer. The actual cause of Dave's death was avoided by the doctor in that last conversation.

More important is whether Dave suffered needlessly.

"Master, pity Thy Servant! He is deaf and three parts blind.
He cannot catch Thy Commandments. He cannot read Thy Mind.
Oh, leave him not to his loneliness; nor make him that kitten's scorn.
He hath had no other God than Thee since the year that he was born.

"Lord, look down on Thy Servant! Bad things have come to pass.
There is no heat in the midday sun, nor health in the wayside grass.
His bones are full of an old disease - his torments run and increase.
Lord, make haste with Thy Lightnings and grant him a quick release!"

By Rudyard Kipling