Monthly Archives: September 2007

Golden Gate from Point Bonita

From Point Bonita, the Golden Gate and the city twinkled around the bend. What was the mystery boat in the moonlight? A fishing trawler perhaps, or a coast guard ship waiting…lights of a farmhouse (actually, Golden Gate National Recreation Area employee housing) look warm and inviting, surprisingly rural so close to San Francisco.

[30mm in 35mm equivalent terms, 10 seconds at f/5 and ISO 100, tripod mounted.]

Yosemite Dreams

Here are some more redos of my Yosemite images. Here’s the original version of Yosemite Dreams (above) and the original version of Morning Glow (below).

Morning Glow

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Flight

The surf was crashing on the shore. Round the rugged coastline, I saw the keyhole above Tennessee Beach lit by the sun and pelicans in flight.

I exposed for the cliffs and pelicans in the sunshine, and let the remainder of the image go dark.

[300mm in 35mm equivalent terms, 1/80 of a second at f/5.6 and ISO 100, tripod mounted.]

Alone I Stand

Alone I Stand (above) is my second job of post-processing (the earlier version of the image is Upper and Lower Yosemite Falls). Beyond the Forest (below) is my re-do of Church Tower from El Capitan Meadow. In both cases, the point of the revision was to make the background misty, to give a feeling of solemn aloneness in a magical world, and to make only a few elements distinct.

Beyond the Forest

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Sensor Size and Depth of Field

The smaller the aperture (opening in the lens), the greater the depth of field (the distance in front and behind a subject that is apparently in focus). The aperture designated by the very small f-stop f/64 provides much greater depth of field than the far larger aperture of f/1.4. Small apertures with great depth of field are used to create photos that are entirely in focus; large apertures with low depth of field are used to isolate in-focus elements in a photo from the photo’s background.

Depth of Field and Aperture shows a high depth of field (using a small aperture opening at f/32) version and a low depth of field (a big aperture opening at f/4) photo of the same flower. If you look at the two photos in that story, it’s easy to see the impact of aperture on depth of field (and the visual implications of high or low depth of field).

Both Dahlia photos in the depth of field demonstration were taken with my Nikon D200. It may seem odd, but the macro photo below, taken with an old Canon Powershot G3 at f/8, shows about as high depth of field than the D200 photo of the Dahlia taken with a macro lens at f/32. What gives?

Flowers on Mirror 1

It’s well known that telephoto lenses have less depth of field than wide angle lenses. In other words, the wider the angle of view, the greater the depth of field. It’s perhaps less understood that the size of the sensor has a direct impact on depth of field. The smaller the sensor size, the greater the depth of field at a given effective focal length and f-stop.

Sensors are classified by their crop factor, which compares the sensor with a frame of 35mm film. My D200 (and all the Nikon dSLRs) have a sensor crop factor of 1.5, meaning that comparing width-to-width, the D200 sensor is smaller in a ratio of 1/1.5 compared to a 35mm frame. The Canon G3 used to take the photo above, like all fixed lens digital cameras, has a much smaller sensor, about 4.5 crop factor, meaning that the ratio to the 35mm film is 1/4.5, and the G3 sensor is about 1/3 the size of the Nikon sensor. (Worth noting: Canon dSLRs, as opposed to the fixed-lens Canon used here, have comparatively large sensors, many of them actually 1:1 with 35mm.)

The effective focal length of 140mm on the Canon isn’t that different in terms of depth of field from the 157.5mm used on the Nikon photo of the Dahlia (both are moderate telephotos). So the only real variables regarding depth of field between the photos is sensor size and aperture. Depth of field is directly proportionate to sensor size. So the Canon has 4.5:1.5 the depth of field (or three times the depth of field) as the Nikon at any given aperture. The f/8 aperture on the Canon gives as much depth of field as somewhere between f/11 and f/16 would on the Nikon.

Advantages and disadvantages? More depth of field at moderate apertures on the small sensor fixed-lens digital cameras means that you can take images with everything in focus (particularly in macro mode) without having to go to excruciatingly long exposures. (However, note that many of these cameras will only allow you to use macro mode at the maximum telephoto end of their zoom ranges.) Photos of general subjects taken with a camera that has a small sensor will exhibit high depth of field, often a good thing. However, even at the biggest aperture settings you still have plenty of depth of field with small sensor cameras. This means that it’s hard to take photos that isolate subjects, like flowers against a blurred background, or portraits where the background is out of focus.

It’s also a fact of life that the smaller the sensor, the smaller the pixel. Smaller pixels mean more noise. Therefore, for a given size capture, small sensor images will always have inherently more noise than larger sensor images.

Breaking Wave

Walking along the Marin Headlands cliffs between Rodeo Beach and Tennessee Beach, I was struck by the brightness of the breaking waves in the sunset light against the darkness of the shore in shadow.

Depth of field was not an issue. I spot metered for the brightness of the waves, made sure that a shutter speed fast enough to stop the motion of the wave was selected, and allowed the camera to choose the aperture.

[300mm in 35mm equivalent terms, 1/250 of a second at f/6.3 and ISO 100.]

Worlds Within

This is a photo from about a year ago. I stood in my garden and saw these water drops clinging to a web. The rain had stopped and the sun was shining. The water drops were against a dark background, but reflected the colors of the garden.

I exposed at an intermediate aperture (f/18) so that a horizontal cross section of water drops were fully in focus.

[200mm f/4 Nikon macro lens, 300mm 35mm equivalent, 1/60 of a second at f/18 and ISO 100, tripod mounted.]

View North from Muir Beach Overlook

The sun had just set and the wind was blowing in on the Muir Beach overlook. You can see the wind whistling over the ocean straight towards the camera, and the lights of a few cars along coastal Highway California 1.

[27mm in 35mm equivalent terms, 1.3 seconds at f/5.6 and ISO 100.]

Woodland Pond

Like Wood between the Worlds, the background of this photocomposite combines Big Sticks (from New Mexico above Santa Fe) and Water Meditation (from Blake Garden in Kensington, California).

I thought the compostion needed some detail for the eye to rest on, differentiated from the background. So I added the lotus flowers on a layer, and “painted” them in.

Incoming Storm

Yesterday at dusk I watched the setting sun race an incoming storm over the Golden Gate.

[300mm in 35mm equivalent terms, 30 seconds at f/25 and ISO 100, tripod mounted.]

Tracking the Sun

Landscape photographers know that there is nothing more important than light. Learning to pay attention to light is a major job requirement. Tracking the sun is part of this job. That’s easy you say, the sun rises in the east and sets in the west. Well, no.

To quote the loquacious cob in E.B. White’s The Trumpet of the Swan:

There are all those in-between directions: north-northeast, east southest, west-southwest. There’s north by east, and east by north. There’s south-southeast a half east and there’s west by north a half north.

Taking sunset, the point at which the sun hits the western horizon varies from north to south, from summer solstice (north) to winter solstice (south). I suppose this is probably reversed if you are on the opposite hemisphere of the earth (I’d like to hear from someone who can confirm this). At the equinoxes, the sun would be about smack dab in the middle of its setting range north to south along the western horizon. The extent of the north to south range, and the daily difference between setting points, is determined by latitude (how far north or south you are).

Photographs of sunset behind the Golden Gate are usually better when the sun is behind (or not that far from either side) of the bridge. This happens twice a year during the annual migration of sunset points, roughly speaking in November and February. Since I enjoy photographing the Golden Gate over time, it’s important to me to keep track of the sun in relation to the bridge. (A book of my photos of the Golden Gate, 100 Views of the Golden Gate , will be appearing in 2008.)

The photo above was taken in early February of 2006. The sun was setting just to the right of the bridge, as you can see in this photo earlier in the same set of captures.

San Francisco from Muir Beach Overlook

We parked Mark’s truck near the Pelican Inn behind Muir Beach and drove in my car over to the Tennessee Beach trailhead parking lot. There was a stiff wind blowing, with some roiling clouds to the north. The parking lot was full of high school kids running a race.

In our hiking boots, backpacks and tripods on our backs, we headed down the easy trail, and then up, to the north, towards the ridgeline and away from the crowds come for the race. A fairly short, but very steep, climb got us to the top of the line of hills marching down to the sea. We took a shortcut down to the Coastline Trail, and joined it just to the north of Pirate’s Cove.

By the time we’d hiked along the trail to the point above the south end of Muir Beach, the wind had picked up to over forty miles an hour. I took a handheld grabshot back at the spectacular coast, and was almost blown over the edge.

It was nearly 6PM, with sunset a little before 7:30. We decided that the best way to go was to get some dinner at the Pelican Inn, and then find a good place to photograph sunset. After crab cakes and apple crisp with ice cream (me) and fish and chips with beer (Mark) we headed out for the Muir Beach Overlook to the north of Muir Beach.

The wind had gone down a bit, but there was still plenty of windchill. We fumbled out in the dusk on the walkway, and I took some exposures in the 20-30 second zone in both directions. The clouds we had seen earlier had blown up from the north, and were now in position, reflecting both city lights and the last of the sunset. If you look closely, you can see the Coastline Trail to the south of Muir Beach where we had hiked earlier in the day.

By now, it was dark and a ranger came out to say they were shutting the parking lot, and we chatted a bit. Mark drove me back around to my car, and I headed home across the Bay.

A mild but fun adventure, and a good antidote for the “sitting at the computer too long” blues.

[150mm in 35mm equivalent terms, 25 seconds at f/6.3 and ISO 100.]

Zulu Prince

Here’s another unblogged image from my files. The photo shows a Zulu Prince flower (the botannical name is Venidium Fastuosum). This story about a sunflower has another Zulu Prince (scroll to the bottom).

[200mm f/4 macro, 300mm in 35mm equivalent terms, 4 seconds at f/36 and ISO 100.]

Depth of Field and Aperture

I shot these two photos of a dahlia to illustrate the impact of aperture on depth of field. The photo above, with a large aperture of f/4, has minimal depth of field, while the photo below with a small aperture of f/32 has much more depth of field.

The flower is in focus in both photos. In the low depth-of-field image (above) the background is out of focus, and therefore visually separated from the foreground.

In this situation, the low depth-of-field image is preferrable. An important point with low depth-of-field photos: since most of the photo will be out-of-focus, try to maximize the focus you do have by placing the camera as parallel as possible to the primary subject of the photo.

[Both photos: 105mm f/2.8 macro lens, 157.5mm in 35mm terms, ISO 100, tripod mounted. Above 1/1250 of a second at f/4, below 1/20 of a second at f/32.]

Dahlia at f/4

Apparent Sharpness Versus Optical Sharpness

A reader of my Photoblog 2.0 writes: “I notice that in more than one of your photos you use high f-stop values. Your results look great, despite what I’ve read about diffraction problems occurring at such small apertures.”

The reader is perfactly correct on both counts. I do often use small apertures in my macro photos. For example, the photo of the iris shown below was taken with my 200mm f/4 macro lens (300mm in 35mm equivalent terms) at the smallest possible aperture, f/40. It is also in fact the case that most telephoto lens (and the lens I used for the iris photo is a macro telephoto) exhibit the most optical sharpness within the range of 1-3 f-stops from the maximum aperture (in the case of the 200mm f/4 that would imply the range between f/5.6 and f/11).

Why this discrepancy between the best the lens can offer optically and my choice of aperture?

Iris (No Passing Zone)

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Before answering the question, first a word about optical sharpness. Optical sharpness is an abstract (rather than practical) concept. In the real world, sharpness varies from lens sample to lens sample. There’s certainly no guarantee that your particular lens will deliver the same optical results as the lens tested by the manufacturer (or by a third party). In case you are interested, this page has links to good resources that explain lens testing, and shows you how to test your own lenses.

The only real way to get a good handle on the characteristics of your particular lens is to use it again and again, and check the results carefully at a high magnification.

In any case, the optical sharpness of a lens is only one of the factors that determines total sharpness (you also need to consider the qualities of the sensor that will be recording the image, and software that is applied to sharpen the image).

Now we get to the meat of the matter. Photographic technique is far and away more important to the ultimate apparent sharpness of a photo than optical sharpness (or the other hardware and software considerations I’ve mentioned). Of course, you could contradict me by taking things to the limit: a plastic lens coated with vaseline will never produce an apparently sharp image. But given a halfway reasonable lens, the incremental difference in sharpness between the sharpest and least sharp apertures is close to irrelevant.

To give you an example, intentionally creating intermittent sharpness (some parts of a photo are sharp and some are not) makes the sharp parts of the photo look sharper than they would if the photo were at one overall level of sharpness.

With both telephoto images and macro images, and doubly so with macro telephoto shots like the iris, depth-of-field (the range from front to back of in-focus elements) is shallow. My most important concern in this photo is to maximize depth-of-field, to get as much of the image as possible in focus: hence my choice of a small aperture.

Here’s an excellent article about sharpness from a practical viewpoint.