G12: Focal Lengths

The G12 has a 5 to 1 zoom lens with focal lengths ranging from 6.1 mm on the “wide angle” end to 30.5 mm on the “telephoto” end.  The lens is not infinitely adjustable; there are 14 different focal lengths.  The available focal lengths are:

6.1 mm	12.1 mm
6.8	13.8
7.4	15.7
8.1	18.1
8.9	21.5
9.8	25
10.8	30.5

These are the focal lengths needed to do depth of field calculations using programs like DOFMaster.  There is also a DOFMaster App for the iPhone that is very handy and accessible in the field. The iPhone App does not always have the precise G12 focal length as part of its database.  For those focal lengths, I just use the closest available value.

7D Hannah

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Having previous posted a series on portraits and depth of field based on my G9, I decided to repeat one shot using the 7D. Fortunately, Hannah was still available. The 7D was fitted with a Canon 85mm f1.8 and set in Av mode for f1.8 at ISO 100. The setup and distances were roughly the same as previously posted with the G9.



It was a nice clear day outside and even at ISO 100, the shutter speed was 1/8000 second! Incredible as this seems, it actually is almost exactly the “Sunny Sixteen” exposure albeit shifted quite a bit. The combination of sunlight and concrete made for very harsh lighting and I give full credit to Hannah for not squinting. But, getting back to the point, notice the blurred background. In fact, notice the slight blur of the front tire!

With the setup and a patience model, I just had to try a few shots using the 7D as a trigger for a 580EX flash outdoors. The 7D flash system is very intriguing and I’ll be learning more about it. In fact, I learned something today.

I first attempted to place the 580EX slightly behind Hannah to provide a bit of back lighting and separation from the background. The 580EX simply would not flash. Hand-holding the 7D, I was about 20 feet away. It turns out that you have to remember to turn it on! But even then it would not fire until the 7D was about 4 feet away. I could see the red light blinking on the 580EX but finally realized that the 580EX was seeing a tiny little pop-up flash and a huge bright sun. With the 580EX facing away from the sun, the 7D will easily trigger it from 20 feet away. Lesson learned.

Taking another approach to lighting Hannah, I decided to underexpose the background and use the 580EX to light Hannah from camera right. Accomplishing this was made complicated because the sync speed of the 7D is limited to 1/250 second and at 1/250 second, the ambient exposure was f11. Giving it a try, I switched to manual mode and set 1/250 second and f22 – about two stops underexposed for the background. The 7D flash system was set to an 8:1 ratio for the external flash. The result – first attempt! – is below.

Not too bad for a first try and definitely better than most of my first guesses with fully manual exposure and manual flash.

I like the ability to blur the background and the opportunity to use my 85mm lens with the 7D. As a flash trigger, the 7D seems OK outdoors with a range of 20 to 25 feet provided the auxiliary flash can see the 7D without also seeing the sun.

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G9: Blurring the background

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A blurred background is useful for isolating and emphasizing the main subject. Extremely blurred backgrounds add a particularly nice effect to portraits. Unfortunately, extreme background blur is not easily obtained using short focal length lenses such as are used with the Canon G series and most other small sensor digital cameras.

The concept for producing a blurred background is simple: use a combination of focal length, aperture and distance such that the background is outside the depth of field. In practice, this means selecting a telephoto lens with a large aperture, placing the camera near the subject and placing the subject away from the background. With the G9, this means zooming the lens to near maximum, forcing the largest possible aperture and placing the subject far from the background.

A previous posting showed how the depth of field varied with the focal length of the G9 at “portrait” distances. Another post showed the maximum aperture for those focal lengths. These two posts illustrate the relationships between zoom (focal length), shooting distance and aperture for the G9.

For this picture of Hannah, I used the G9 at maximum zoom, f4.8 and was about 12 feet from her. The shrubbery was another 12 feet away; the fence (barely discernable) was about 30 feet behind Hannah. These are fairly generous distances; in fact, more separation than is often available. Even so, the background behind Hannah is not particularly blurred (click for a larger image).

Depth-of-field calculations are based on small but noticeable blurs at certain enlargements and viewing distances. For more information, visit and study at DOFMaster. In contrast, the background blur that many photographers want for portraiture is extreme. My own personal favorite is of Wallace; however, it was not made with the G9.

Small sensor cameras like the G9 are great when the goal is to have nearly everything in focus but such cameras are just not the right tool for producing extreme background blur for ‘portrait’ photography.
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G9: Portrait Distance

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It seems to me that actual height for a tightly composed head shot is about two feet. How far away from the subject should the camera be to capture this two foot high subject? I suppose the distance can be calculated but frankly it is just easier to tape a yardstick to the wall and take a few shots.

For my G9, these are the camera-to-subject distances for various focal lengths.





The focal lengths in the chart are the same as the focal lengths from the previous posting which gave the maximum aperture for various focal lengths.

The depth of field can be calculated from distance, focal length and aperture. Taking some liberties in rounding off, depth of field for a portrait setting with the G9 is about one foot – give or take a few inches.

This little experiment would seem to indicate that a blurred background would be easily obtained with the Canon G9; however, the opposite is true. In fact, blurred backgrounds are difficult to obtain and extreme blur for portraits and larger scenes is nearly impossible to achieve with the G9. The apparent discrepancy is because the depth of field calculation is intended to predict the onset of blur and not the extreme.

Next: an example of typical G9 background blur for portrait setting
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G9: Variations in Focusing Outdoor Scenes

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The first posting in this series on focusing showed the five auto focus modes possible with the G9. The second posting explained how the hyperfocal and depth-of-field concepts benefit and limit focusing. Now let’s examine and compare the results when using the various auto focus modes. For this posting, a landscape scene was photographed using each auto focus mode. The G9 was mounted on a tripod and the composition was not changed from shot to shot. The focal length was near the middle of the zoom range. Exposure was set at 1/60 sec and f4.5 in manual exposure mode for ISO80 sensitivity for all shots. The G9 was set for Raw+jpg mode but all images here are from the in-camera jpg for consistency. The image shown here is the first one taken; the auto focus was set for Flexizone using the small frame because this is the way I normally focus. The small focus frame was placed on the front of the canoe.

The G9 has a nice feature for checking focus that I’d forgotten about. Here’s the display showing the focus point for the above image. This feature is available in both shooting (page 86) or playback modes (page 162). (But if your practice is to focus, recompose and shoot, as is mine, then the focus check does not remember that first focus point.) I paced off the distance from the G9 to the canoe; it was about 115 feet. My workhorse software, BreezeBrowser, says that the focus distance was set at 82 feet. Strangely, neither Canon’s ZoomBrowser nor Adobe’s Photoshop include focus distance in the image properties.

From the G9 Hyperfocal Chart, the hyperfocal distance for 25mm focal length and f4.5 is 76 feet. With the focus distance actually set at 82 feet, everything from 39 feet to infinity should be in focus. (OK, I didn’t think ahead on this one but used DofMaster directly.) Although the basis of depth-of-field is not pixel peeking, when examining the full image file, it seems to me that the in-focus distances are from about halfway to the canoe to infinity – as predicted in the DofMaster calculation. So even though the G9 selected the focus point I wanted, it set a slightly different actual distance; however, the final result was essentially the same as if the G9 had set the exact distance.

What about the other focus modes? Results varied.

The large Flexizone frame also fixed on the front of the canoe but the focus distance was actually set at 66 feet. This is probably because the large focus frame includes more of the foreground than does the small frame. Results were good with, by computation, everything from 35 feet to 493 feet in focus.

Surprisingly, the small AiAF frames did not do very well and I don’t understand why. The focus distance was set for only 43 feet so everything from 28 to 99 feet was in focus but the distant background was blurred. The large AiAF frame actually was more accurate than the small frame with respect to the distance to the canoe. Using large frame AiAF, the focus distance was set at 72 feet.

Using face detection focusing but without faces in the scene, the G9 logic switches to large frame AiAF and, again, the focus distance was set at 72 feet.

Lastly, I switched to manual focus and dialed in infinity. BreezeBrowser interpreted this setting as 216 feet. In that case, everything from 56 feet to infinity should be in focus. Pixel peeking the manually focused image, I see the relative differences but differences are small except in comparison to the small AiAF closer focused image.

Based on this experience, I’ll be continuing my current practice: small frame Flexizone, focus, recompose, shoot. But indoor photography, usually without the benefits of hyperfocal focusing, can be more challenging. Next I’ll take a closer look at face detection.

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