I had this dilemma a few days ago: I had taken almost 4,000 pictures during a vacation 12 months ago. The vacation was in Asia (two continents over), and the time on my camera was wrong. I was importing the pictures into Adobe’s Lightroom, and wanted them to have the correct time just in case I wanted to know when in the day certain pictures were taken. I thought of looking for pictures taken during sunset, and then using solar calendars to figure out when sunset was at a certain landmark on a certain day of the year. But then I had a better idea:

Surely in those 4,000 pictures there must be at least one picture with a wall clock or a watch in the picture.  After scanning through thumbnails of the pictures, I finally found one photo where a person seating across from me at a restaurant had his left hand by his face  and there, prominently displayed, was the face of his wristwatch.  After zooming in on the wristwatch I was able to make out the local time (8:49 p.m).  The camera thought the time was 10:28 a.m.  That made it really easy:  I was able to switch all pictures 10 hours and 21 minutes ahead, and just like that all my pictures now had the correct time.

When I travel I usually forget to reset my camera clock.  Now I know a surefire way to set the correct time on pictures: Take a snapshot of a wall clock at least once during the trip.  This way I tell the difference between the real time (the one on the wall clock) and the one in the camera.  I’m sure others have found out this trick before me, but I’m very happy that I came up with this quick and dirty hack all by myself.

Here’s one of the pictures from that trip:

A Stone Window - Taken during a recent trip to Asia

In a previous article we looked at how lenses work.  We learned about the focal length.  Today we’ll focus on camera lenses and what the term f-stop means.

The term f-stop is a ratio.  It has no dimensions.  You don’t measure an f-stop in meters, inches, kilograms or even degrees Fahrenheit.  An f-stop is the ratio of two distances.  It’s the ratio of the focal length of a lens to its diameter.  In figure 1, the f-stop is f/d where f is the focal length and d is the diameter.

The f-stop of this lens is f/d

Why do we care about a lens’s f-stop?

Before we answer this, let’s review how cameras work.  A camera uses a lens to focus light on one side of the lens (the outside) onto a film or sensor on the other side of the lens (the inside of the camera).  The more light that falls on the film or sensor, the brighter the image will be.  Most films or sensors need a certain minimum amount of light in order to take a good picture (one that’s not too dark).  If there’s too much light, though, the picture will be too bright.

Now, in photography terminology, the size of the hole that light passes through is known as the aperture.  As a simplification, you can think of this as the effective diameter of the lens.    In other words, d is the diameter of the aperture.  The bigger the aperture, the more light will pass through, and the brighter the picture will be.  So you can see why d is important.  The bigger the aperture, the less time you need to pass a sufficient amount of light for a good picture.

You can use the bucket analogy: think of the lens as a hole in the bottom of a bucket. If you want to drain the bucketful of water through that hole, the bigger the hole, the less time you need for the bucket to drain.

Another measurement of a lens that’s important is f, the focal length.  Lenses with a small focal length are called wide angle lenses — they allow light from a wider angle to pass through the lens and onto the film (or sensor).  Lenses with a large focal length are called telephoto lenses — they allow a smaller cone of light into the lens, but the benefit is that picture is bigger (you can see things far away clearly).

So now we can revisit why we should care about a lens’s f-stop. The f-stop is defined as f/d, so if you have two lenses with the same focal length, the one with the smaller f-stop will have a larger aperture – it’s diameter will be larger and it will allow more light through.

Why are advertised f-stops numbered so strangely?

Lenses are circular. The apertures through which light travels are circular. The amount of light that can pass though the lens depends on the area of the circle that defines the aperture. The area of a circle is πr² where r is the radius, or half of the diameter.

F-stops are defined so that every consecutive f-stop either doubles or halves the amount of light entering the lens. To get area to double or halve at every adjacent f-stop, the ratio of adjacent f-stops need to be the square root of 2 (1.414).  A more detailed explanation can be found here.

Why don’t we just use the diameter?

The definition of the f-stop is a way to have different lens manufacturers agree on a standard.  Two lenses with an f-stop of 1.4 means the same amount of light can enter the lens, regardless of the focal length of the lens.  This also allows for lightmeters to display their results without having to know what lens you’re using to take a picture.

References

• Focal length and F-Stop Explanation
• A Tedious Explanation of the F/Stop
• Plural Posessive of Lens – TheFreeDictionary.com

Licenses

• Figure 1was adapted from
  http://en.wikipedia.org/wiki/File:Focal-length.svg and is licensed under
  the Creative Commons Attribution ShareAlike 3.0 License.

One of my favorite activities in spring, summer and even early autumn is sitting outdoors by a campfire.  For safety reasons, outside my home I can’t make a campfire on the ground, so I use a standalone fire pit.  The older children, as well as my nephews and nieces like learning how to start a campfire without matches.  I usually use metal and flint.

To start a nice, controlled, roaring fire, I can’t just use the flint to throw some sparks at firewood.  I have to use something really airy and flammable.  This is called tinder.  I get enough tinder to burn for about 20 to 30 seconds, and slowly start feeding larger and larger pieces of wood (fuel) to the fire.  Once the tinder is burning I start adding little twigs the size of my ‘pinky’ finger, and slowly get enough heat to burn larger pieces of firewood.  In a later post we’ll look at different ways to start a safe campfire.   Today, though, I want to address a cheap and easy source of tinder.

When I first started dabbling in woodworking at the age of 15, the only tool I used to cut wood was an old, rusted woodsaw.  Every cut would start straight and true, but as I’d push the saw deeper into the wood, it would buckle and warp, my arms would get tired, and the cut would stray from the line.  A few years ago I learned about pull saws and once I started using them I have stuck with pull saws for all my manual wood-cutting tasks.

Pull saws have been said to have originated in Japan more than 2,000 years ago.  The main difference between pull saws and ‘Western’ saws is that pull saws cut on the backstroke.  That is, they cut when you pull the saw against the wood, not when you push the saw against the wood (as in the case of Western saws).  Whereas a Western saw is being compressed when it’s cutting, a pull saw is put under tension (a pulling force).  This means that the pull saw can be a lot thinner than a ‘push’ saw, because it doesn’t need to be as rigid to overcome the compression forces.  This thinness in turn means that its kerf, the thickness of the cut, is a lot smaller than that of the Western saw.  And because it’s thinner, it requires less force to cut through the wood, and cuts faster.

A Japanese Pull Saw

You don’t have to buy an expensive hand-crafted Japanese pull saw to start using this tool.  Popular home improvement stores like Menard’s and Home Depot sell low priced pull saws that work very well.  I’ve bought a couple over the past two or three years and they have served me well as the only saws I use.

References:

• Larry Eisinger’s Home Repair Workshop
• Japanese Saw – Wikipedia

Licenses:

• The image of the pull saw is from the Japanese Saw page on Wikipedia and is licensed under the under the Creative Commons Attribution ShareAlike 3.0 License.

As of this past weekend it’s been fifteen years since I started my career as a software developer.  With the exception of a few months here and there, I’ve spent all these years working on Linux or Unix-like operating systems.  I’ve noticed that despite the wide variety of tools and applications I have used and continue to use, some key skills are always in demand in this field. One of these is mastery of a text editor.

I’m interested in tinkering with High Dynamic Range photography, but before I get Photomatix, the software that’s recommended most often, I thought I’d try out a technique that’s a very crude approximation of HDR.  It involves taking one image that’s underexposed, and one that’s overexposed, and merging them in Photoshop.  The technique is described in this article at luminous-landscape.com.  Essentially, you put the underexposed image in a layer above the overexposed one.  Create a layer mask on the darker layer, and copy the brighter image to the layer mask.  Apply a Gaussian blur to the layer mask, and you have your blended image.

I took 3 shots, one underexposed, one overexposed and one correctly exposed (the Programed Auto setting on the camera).  Then I blended the first two images and compared the resulting image with the correctly exposed one.  I like how the blending brought out the dark areas, and lessened the washed out highlights.  I can’t wait to try this outdoors, when the weather gets a little warmer.  It’s a very quick and simple technique, and might work out well for some kinds of landscape photography.

What do you think?  Is the blended image decent?

The Underexposed Image

The Overexposed Image

The Blended Image

The Correctly Exposed Image

This is the first in a series of blog entries on photography.  Today we look at one of the most critical parts of any camera – the lens.

Have you ever noticed that people can run faster on flat ground than on sand or water?  It’s the same way with light.  Light travels faster in air than in glass.

When light travels through air it moves at roughly the ’speed of light.’ When light hits a glass surface, it can’t move as fast, and slows down. If the light hits the glass at an angle, something very strange happens. It bends a bit.

Imagine a car driving off an asphalt surface onto a sandy pit at an angle. As shown in Figure 1 below, the right wheel gets onto the sand first, and slows down a little bit.  Meanwhile, the left wheel is still moving at the original speed.  This causes the car to turn slightly towards the right.

Figure 1

Light behaves the same way – depending on the angle at which it hits the glass, it bends a little bit or a lot when it starts moving in the glass. Similarly, light also bends when it comes out of glass into the air.

Figure 2

Now, a lens is just a specially shaped piece of glass.  A convex lens is one that bulges outward.  When a beam of light hits a convex lens ‘head on’ (parallel to the principal axis), the shape of the lens will cause the light to bend so that it passes through a point known as the focal point.  For every lens there is only one focal point, and the distance between the focal point and the lens is known as the focal length.  This is shown in Figure 2.

Objects reflect rays of light in all directions.  When rays of light reflected off a nearby object hit a convex lens the features of the lens cause the rays of light to converge on the other side of the lens in such a way that the object appears upside down, as in Figure 3.  The image will appear sharp (focused) at a distance that depends on the focal length of the lens and how far away the object is from the lens.  This is essentially how cameras work.  They bend the light so that it appears focused on a film or, in the case of digital cameras, a sensor.

Figure 3

Now that we know the basics of how lenses work, we can look at commercial camera lenses and see what f-stops are.

References

• Focal Length and F-Stop Explanation
• How Cameras Work from HowStuffWorks
• Focal Length from Wikipedia
• Lens (Optics) from Wikipedia

Licenses

• Figure 2 was adapted from
  http://en.wikipedia.org/wiki/File:Focal-length.svg and is licensed under
  the Creative Commons Attribution ShareAlike 3.0 License.
• Figure 3 was taken from
  http://upload.wikimedia.org/wikipedia/en/thumb/7/71/Lens3.svg/550px-Lens3.svg.png and is licensed under
  the Creative Commons Attribution ShareAlike 3.0 License.

This man had brought a bagful of bread to feed the birds

As I walked along the Corniche, I saw a huge flock of gulls in one spot in the lagoon.  On the shore was this man, throwing bread into the water.  I approached him and asked if I could take a picture of the bread.  “Are you with a newspaper?” he asked. “No.”  “Then it’s fine.  No newspapers.”  He turned back to a bench and I saw the huge bag full of bread.  Today the birds would eat well.

Feeding Frenzy

I liked the composition of the picture from this side (below).  The juxtaposition of the masjid to the man seemed to be more appropriate here.

Bread in the air

Tethered to the shore, this boat is used to pick up garbage floating in the lagoon by the Sharjah Corniche

This boat looked out of place on the Khalid Lagoon by the Al Buhaira Corniche in Sharjah. It was too small to be a water taxi, and too drab to be for tourists.  As I approached it, I realized that its purpose was to pick up all the garbage floating in the lagoon.  It was full of soggy plastic bags and other detritus.  I’m glad I wasn’t close enough to smell it.

A cyclist makes his way into my shot of the masjid

This picture was taken on my walk along the Sharjah Corniche on January 6th 2010, shortly after dawn.  I framed my shot carefully, right in front of the minbar, to exploit the symmetry of the building.  As I clicked, I noticed a blur as a cyclist strayed into my shot.  I had just enough time for one more shot before he left, and this second shot is what you see here.  I think the lucky addition of this man into the frame makes this a better shot than the one I was planning.

1/50 sec at f/4.5 :: 22mm focal length :: ISO 400