My Photo


  • Jen-Luc Piquant sez: "They like us! They really like us!"

    "Explains physics to the layperson and specialist alike with abundant historical and cultural references."
    -- Exploratorium ("10 Cool Sites")

    "... polished and humorous..."
    -- Physics World

    "Takes 1 part pop culture, 1 part science, and mixes vigorously with a shakerful of passion."
    -- Typepad (Featured Blog)

    "In this elegantly written blog, stories about science and technology come to life as effortlessly as everyday chatter about politics, celebrities, and vacations."
    -- Fast Company ("The Top 10 Websites You've Never Heard Of")
Blog powered by Typepad
Bookmark and Share

« liar, liar | Main | help make michael a hottie »


(activate chemist pedant mode)
1. The color dyes that form during development of photographic film are azine dyes, not cyanines. Cyanine dyes are the "molecules sensitive to other wavelengths of light" that are attached to the silver halide grains during manufacturing.

2. "The finer the crystal the 'faster' the film." Backwards, as your next few sentences imply. Indeed, fast film (big grains) is "grainer" than slow film. The reason has to do with the critical number of photons that have to hit a grain to activate it, as you mention. Size matters here - with a given number of photons available in the image, more of them will hit a big grain than a small one. Similarly, that's why flat grains are more sensitive than cubic ones - more surface area to collect photons. The atoms of silver (created by the reactions you show) act as hyper-efficient catalysts for the subsequent development of the grain.

3. "Kodak says you need four silver atoms to nucleate the developing process" and "Color films take about 20-60 photons per grain to produce a latent image" You seem to be mixing up two different processes here. In the developing bath, it takes four Ag+ ions to drive the most common coupler + developer image dye forming reaction, although there are some souped-up couplers than need only two. For the latent image on the film in the camera, tens of photons per grain are typically required, although the theoretical minimum is less than 10.

4. "If you overexpose a piece of film, you've started reducing silver halide grains that weren't part of the original image." Not strictly correct. If you overexpose your film, you've left the shutter open too long, and those few photons coming from the darker regions of your image have added up and activated grains that should not have been. So you lose contrast between the light and dark regions, and your photo looks washed out.
(deactivate chemist pedant mode)

It's cool that you described chemical photography in this context, because very few people (even among chemists) know much about how it actually works.

PS. Speaking of "'should so-and-so have been included," Boyd & Smith owe a big debt of graditude to Steve Sasson, who took their CCD chip and a bunch of scrap parts and fashioned the first digital camera in 1975. See for an interview with Steve that shows the actual (8 pound!) camera. gives more of the story.

I suppose it's some consolation that Steve has received a bunch of other awards.

Great summary of film chemistry, a little short on the digital end. But never mind that. Here's my question. Standard color print film seems to have an infinitely higher resolution than even the best digital images, or it used to anyway. Nowadays I'm not so sure. My Uncle Ed had a tiny imported film camera that fit in his pocket, and for a while we had 110 film, but the photos from these were never quite as good. So how much resolution do you need to make a perfect picture?

Well, of course there's no such thing as a "perfect picture." But here's some pertinent information:

A typical 35mm negative is estimated to have the equivalent of tens of megapixels of information. 110 film is much smaller.

As discussed in Diandra's post, each pixel in your digital camera is only sensitive to one color of light (red, green or blue), so divide your megapixels by three to approximate its true resolution. (The "missing" color in each pixel is filled in by software after the picture is taken, by extrapolating the data from neighboring pixels.)

If you don't enlarge the photo too much, a digital camera with about 5 megapixels will give a satisfactory image for the average person's eyesight. Higher resolution is better, but the quality of your optics becomes increasingly the limiting factor. There’s an analogous situation with film - a cheap point-and-shoot camera will give an inferior photo compared to a professional SRL with superb lenses, even though both may use the same film.

So, as usual, it depends on what you pay. An amateur photographer taking family snapshots and viewing them on a computer screen will be perfectly satisfied with an inexpensive 8 megapixel digital camera, while a photographic aficionado would sneer at such a setup.

One important advantage to high pixel count is the ability to crop unwanted peripheral parts of the image afterwards without sacrificing much quality. For example, if you’re a birder and want to prove to the world that you’ve seen an authentic Ivory-Billed Woodpecker, you will need expand that little white and red spot in your photo with plenty of remaining pixels.

The comments to this entry are closed.

Twitter Updates

    follow me on Twitter

    Physics Cocktails

    • Heavy G
      The perfect pick-me-up when gravity gets you down.
      2 oz Tequila
      2 oz Triple sec
      2 oz Rose's sweetened lime juice
      7-Up or Sprite
      Mix tequila, triple sec and lime juice in a shaker and pour into a margarita glass. (Salted rim and ice are optional.) Top off with 7-Up/Sprite and let the weight of the world lift off your shoulders.
    • Listening to the Drums of Feynman
      The perfect nightcap after a long day struggling with QED equations.
      1 oz dark rum
      1/2 oz light rum
      1 oz Tia Maria
      2 oz light cream
      Crushed ice
      1/8 tsp ground nutmeg
      In a shaker half-filled with ice, combine the dark and light rum, Tia Maria, and cream. Shake well. Strain into an old fashioned glass almost filled with crushed ice. Dust with the nutmeg, and serve. Bongos optional.
    • Combustible Edison
      Electrify your friends with amazing pyrotechnics!
      2 oz brandy
      1 oz Campari
      1 oz fresh lemon juice
      Combine Campari and lemon juice in shaker filled with cracked ice. Shake and strain into chilled cocktail glass. Heat brandy in chafing dish, then ignite and pour into glass. Cocktail Go BOOM! Plus, Fire = Pretty!
    • Hiroshima Bomber
      Dr. Strangelove's drink of choice.
      3/4 Triple sec
      1/4 oz Bailey's Irish Cream
      2-3 drops Grenadine
      Fill shot glass 3/4 with Triple Sec. Layer Bailey's on top. Drop Grenadine in center of shot; it should billow up like a mushroom cloud. Remember to "duck and cover."
    • Mad Scientist
      Any mad scientist will tell you that flames make drinking more fun. What good is science if no one gets hurt?
      1 oz Midori melon liqueur
      1-1/2 oz sour mix
      1 splash soda water
      151 proof rum
      Mix melon liqueur, sour mix and soda water with ice in shaker. Shake and strain into martini glass. Top with rum and ignite. Try to take over the world.
    • Laser Beam
      Warning: may result in amplified stimulated emission.
      1 oz Southern Comfort
      1/2 oz Amaretto
      1/2 oz sloe gin
      1/2 oz vodka
      1/2 oz Triple sec
      7 oz orange juice
      Combine all liquor in a full glass of ice. Shake well. Garnish with orange and cherry. Serve to attractive target of choice.
    • Quantum Theory
      Guaranteed to collapse your wave function:
      3/4 oz Rum
      1/2 oz Strega
      1/4 oz Grand Marnier
      2 oz Pineapple juice
      Fill with Sweet and sour
      Pour rum, strega and Grand Marnier into a collins glass. Add pineapple and fill with sweet and sour. Sip until all the day's super-positioned states disappear.
    • The Black Hole
      So called because after one of these, you have already passed the event horizon of inebriation.
      1 oz. Kahlua
      1 oz. vodka
      .5 oz. Cointreau or Triple Sec
      .5 oz. dark rum
      .5 oz. Amaretto
      Pour into an old-fashioned glass over (scant) ice. Stir gently. Watch time slow.