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It’s time to force myself to document my conclusions about focusing the G9. When the G10 is announced, I’ll get caught up in all the hoopla. So here’s what I’ve learned and concluded as well as my current focusing practices for the G9.
First a summary of the G9 focus posts:
Introduction to G9 focusing
Focusing outdoors
Focusing indoors
Face detection
G9 use of hyperfocal focus
G9 hyperfocal chart
Problems focusing on low contrast subjects
Beeps when focused
After all this, I still prefer to use the small Flexizone frame, recompose and shoot when I have the time to do so. Yes, I know this can be slow and methodical, but that’s me as well. For repetitive shots, I often get small Flexizone frame focus, switch to manual and continue shooting. I focus this way for macros when the G9 is tripod mounted.
For landscape shots, I often use manual focus set to infinity. It's easy and certain but be sure to switch back to auto focus!
When wild and crazy and partying, it’s just better to set the G9 on face detection focusing – especially if the camera is passed around a bit. Usually, but not always, face detection works well.
OK, the focusing post is done, where’s the G10?
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Showing posts with label hyperfocal. Show all posts
Showing posts with label hyperfocal. Show all posts
Monday, August 11, 2008
Friday, June 27, 2008
G9: Focusing Indoors
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As previously noted, although the G9 has five automatic focusing modes, I almost always choose the small Flexizone frame centered in the LCD. I place the focus frame on the subject of interest, push the shutter button halfway, think “focus”, check for the frame to turn green, recompose the scene and finish pressing the shutter. To get additional shots from the same vantage point, I then switch to manual focus and keep the previous focus distance. This method almost always works well even if it is a bit slow and methodical.
Without recomposing, the small Flexizone frame may not detect enough contrast to obtain focus. Also, without recomposing, the small Flexizone frame may focus on the wrong object. This is particularly a problem when photographing indoors. To illustrate this problem, I set up my G9 on a tripod and tried the various focusing methods indoors.
In this scene, the G9 was set for the widest
angle, 7.4mm; the aperture was f4.5 (the “Sweet Aperture”) . The image shown was downsized from the in-camera JPEG. The focus distance, as determined by the small Flexizone frame was 15 feet but the large Flexizone frame determined the focus to be 8 feet! This discrepancy occurred because the small frame fell on a photo on the opposite wall but the large frame included a chair. The focus distance, as determined by the small AiAF matrix was 12 feet. The large AiAF matrix also determined the focus to be 12 feet. Interestingly, the large AiAF matrix did not always lock onto the same object even though the G9 was on a tripod. I had suspected that the different focus methods would lock onto different objects and I was correct.
Using manual focus, I dialed in 5 feet and took another shot. Later, to my surprise, all the pictures look essentially the same. Why? Of course, the explanation is hyperfocal distance. For the 7.4mm zoom focal length and f4.5 aperture, everything from about 4 feet to infinity is in acceptable focus. In setting up my test, I’d forgotten about the hyperfocal distance. Chalk one up for the G9.
Since this humbling experience, I’ve toyed with the various focus modes quite a bit. My basic hypothesis was correct: With any focus mode other than the small Flexizone frame, I cannot be certain of getting the exact focus point that I want. Fortunately, often it just doesn’t matter.
But sometimes it does .... (more later)
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As previously noted, although the G9 has five automatic focusing modes, I almost always choose the small Flexizone frame centered in the LCD. I place the focus frame on the subject of interest, push the shutter button halfway, think “focus”, check for the frame to turn green, recompose the scene and finish pressing the shutter. To get additional shots from the same vantage point, I then switch to manual focus and keep the previous focus distance. This method almost always works well even if it is a bit slow and methodical.
Without recomposing, the small Flexizone frame may not detect enough contrast to obtain focus. Also, without recomposing, the small Flexizone frame may focus on the wrong object. This is particularly a problem when photographing indoors. To illustrate this problem, I set up my G9 on a tripod and tried the various focusing methods indoors.
In this scene, the G9 was set for the widest
angle, 7.4mm; the aperture was f4.5 (the “Sweet Aperture”) . The image shown was downsized from the in-camera JPEG. The focus distance, as determined by the small Flexizone frame was 15 feet but the large Flexizone frame determined the focus to be 8 feet! This discrepancy occurred because the small frame fell on a photo on the opposite wall but the large frame included a chair. The focus distance, as determined by the small AiAF matrix was 12 feet. The large AiAF matrix also determined the focus to be 12 feet. Interestingly, the large AiAF matrix did not always lock onto the same object even though the G9 was on a tripod. I had suspected that the different focus methods would lock onto different objects and I was correct.Using manual focus, I dialed in 5 feet and took another shot. Later, to my surprise, all the pictures look essentially the same. Why? Of course, the explanation is hyperfocal distance. For the 7.4mm zoom focal length and f4.5 aperture, everything from about 4 feet to infinity is in acceptable focus. In setting up my test, I’d forgotten about the hyperfocal distance. Chalk one up for the G9.
Since this humbling experience, I’ve toyed with the various focus modes quite a bit. My basic hypothesis was correct: With any focus mode other than the small Flexizone frame, I cannot be certain of getting the exact focus point that I want. Fortunately, often it just doesn’t matter.
But sometimes it does .... (more later)
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Saturday, May 31, 2008
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.
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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Sunday, May 25, 2008
G9 Hyperfocal Chart
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Continuing the series on focusing the G9, knowledge of the hyperfocal distance is extremely useful when focusing any camera. Previous postings have included observations about the G9’s use of hyperfocal focusing and depth of field for closeups.
Somewhat loosely speaking, but easy to remember, is that if a camera is set for the hyperfocal distance then everything from that distance to infinity is acceptably in focus. In fact, everything from half that distance to infinity is in focus. For more details, check Wikipedia .
A most useful reference for both hyperfocal distance and depth of field is DOFMaster . Since both hyperfocal distance and depth of field vary with digital sensor size and focal length, here’s a chart of hyperfocal focusing distance specifically for the Canon G9 that was made by using the DOFMaster online calculations.
In addition to the hyperfocal distance, the table includes the near/far distance that is in focus when the G9 is focused at 10 feet. Why 10 feet? When the G9 is first turned on and switched to manual focus, it is set for (roughly) 10 feet.
Here’s an example of how the chart can be used. With your G9 turned off, set the Av mode at f5.6. Now turn the G9 on. The default focal length is the wide angle (7.4mm focal length) when the G9 comes on in Av mode. Immediately, switch to manual focus. You’ll see that the default focus distance is about 10 feet. Referring to the chart above for the 7.4mm lens, the hyperfocal length at an aperture of f5.6 is 5.3 feet. This means that, if the focus distance had been set for 5.3 feet then every distance from 2.65 feet (=5.3/2) to infinity would have been in focus. However, the default distance is 10 feet so everything from 3.5 feet (near focus) to infinity is in focus.
The G9 almost does not require focusing at the wide angle setting! But this happy situation changes dramatically at the longer focal lengths as shown in the chart.
Since aperture, focal length and manual focus distance can be saved as a custom setting (page 109 in the manual), the G9 can be preset for special situations -- including hyperfocal focusing.
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Continuing the series on focusing the G9, knowledge of the hyperfocal distance is extremely useful when focusing any camera. Previous postings have included observations about the G9’s use of hyperfocal focusing and depth of field for closeups.
Somewhat loosely speaking, but easy to remember, is that if a camera is set for the hyperfocal distance then everything from that distance to infinity is acceptably in focus. In fact, everything from half that distance to infinity is in focus. For more details, check Wikipedia .
A most useful reference for both hyperfocal distance and depth of field is DOFMaster . Since both hyperfocal distance and depth of field vary with digital sensor size and focal length, here’s a chart of hyperfocal focusing distance specifically for the Canon G9 that was made by using the DOFMaster online calculations.
In addition to the hyperfocal distance, the table includes the near/far distance that is in focus when the G9 is focused at 10 feet. Why 10 feet? When the G9 is first turned on and switched to manual focus, it is set for (roughly) 10 feet.
Here’s an example of how the chart can be used. With your G9 turned off, set the Av mode at f5.6. Now turn the G9 on. The default focal length is the wide angle (7.4mm focal length) when the G9 comes on in Av mode. Immediately, switch to manual focus. You’ll see that the default focus distance is about 10 feet. Referring to the chart above for the 7.4mm lens, the hyperfocal length at an aperture of f5.6 is 5.3 feet. This means that, if the focus distance had been set for 5.3 feet then every distance from 2.65 feet (=5.3/2) to infinity would have been in focus. However, the default distance is 10 feet so everything from 3.5 feet (near focus) to infinity is in focus.
The G9 almost does not require focusing at the wide angle setting! But this happy situation changes dramatically at the longer focal lengths as shown in the chart.
Since aperture, focal length and manual focus distance can be saved as a custom setting (page 109 in the manual), the G9 can be preset for special situations -- including hyperfocal focusing.
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Friday, May 23, 2008
G9: Focus on Focusing
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The G9 automatic focus methods are:
Flexizone – a single rectangular frame normally in the center of the display but which can be moved as desired. The frame can be large or small. The G9 focusing logic sets the focus distance so that the object in this frame is in focus.
AiAF – A 3x3 matrix of rectangular frames in the center of the display. These frames can be large or small. Only the small frame matrix can be moved off center. The G9 focusing logic somehow selects one or more of these frames and sets the focus distance accordingly. (“AiAF” apparently means “Artificial Intelligence Auto Focus” but I can’t find that definition in the manual.)
Face Detection – Magically, the G9 detects faces (or objects resembling faces) and sets the focus accordingly.
The autofocus mode is a menu setting (page 116 of the manual) as
shown above but can also be set with a few button presses on the back of the G9 as shown here. First, with the G9 in shooting mode, press the AF frame button (numbered 19 on page 42 of the manual) shown circled here. The display will change as shown (but with the current AF frame selection). The AF frame selection is then toggled between Flexizone, AiAF and Face Detection by pressing the Menu button, examples are shown below.
For Flexizone and AiAF, the size of the frame can be changed by pressing the Display button, the smaller frames are shown below. Both Flexizone and the small AiAF frames can be moved with the Control Dial.
When in Face Detection mode, pressing the Display button indicates how many faces are detected.
When using the G9, I always recommend pressing the shutter button halfway to achieve focus. Once focus is achieved, the G9 gives two quick beeps and the focus frame turns green.
My normal practice is to use the small Flexizone frame in the center position to obtain focus on the subject of interest. I press the shutter button halfway to achieve focus, hold the button at the halfway position, recompose and shoot. To get a second or similar shot, I might switch to manual focus because the manual focus position is retained until the next autofocus.
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The G9 is an extremely versatile camera. Among its many options 
are (at least) five different choices for automatic focusing methods plus manual focus. I’ve always used the same method in the past but it is past time to learn the others so the next several posting will be about focusing the G9.
are (at least) five different choices for automatic focusing methods plus manual focus. I’ve always used the same method in the past but it is past time to learn the others so the next several posting will be about focusing the G9. The G9 automatic focus methods are:
Flexizone – a single rectangular frame normally in the center of the display but which can be moved as desired. The frame can be large or small. The G9 focusing logic sets the focus distance so that the object in this frame is in focus.
AiAF – A 3x3 matrix of rectangular frames in the center of the display. These frames can be large or small. Only the small frame matrix can be moved off center. The G9 focusing logic somehow selects one or more of these frames and sets the focus distance accordingly. (“AiAF” apparently means “Artificial Intelligence Auto Focus” but I can’t find that definition in the manual.)
Face Detection – Magically, the G9 detects faces (or objects resembling faces) and sets the focus accordingly.
The autofocus mode is a menu setting (page 116 of the manual) as
shown above but can also be set with a few button presses on the back of the G9 as shown here. First, with the G9 in shooting mode, press the AF frame button (numbered 19 on page 42 of the manual) shown circled here. The display will change as shown (but with the current AF frame selection). The AF frame selection is then toggled between Flexizone, AiAF and Face Detection by pressing the Menu button, examples are shown below.For Flexizone and AiAF, the size of the frame can be changed by pressing the Display button, the smaller frames are shown below. Both Flexizone and the small AiAF frames can be moved with the Control Dial.
When in Face Detection mode, pressing the Display button indicates how many faces are detected.
When using the G9, I always recommend pressing the shutter button halfway to achieve focus. Once focus is achieved, the G9 gives two quick beeps and the focus frame turns green.
My normal practice is to use the small Flexizone frame in the center position to obtain focus on the subject of interest. I press the shutter button halfway to achieve focus, hold the button at the halfway position, recompose and shoot. To get a second or similar shot, I might switch to manual focus because the manual focus position is retained until the next autofocus.
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Wednesday, November 21, 2007
G9 and Closeups
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A telephoto lens set at the minimum focus distance is the opposite extreme from the wide angle hyperfocal settings discussed previously. To get this picture, the G9 was set at full telephoto: 44mm (usually referred to as 210mm equivalent in terms of 35mm film). The aperture was f8 and the matching shutter speed was 1/160 sec for ISO 80 in sunlight. The G9 was about two feet away from the ring – almost, but not quite the minimum focus distance at full telephoto. In fact, I used the “macro” setting to focus on the ring.
Under these conditions, the theoretical depth of field is about ¾ inch. That is, only a distance of about ¾ inch into the picture appears to be sharply focused. The horizontal ring in the picture is about 4 inches in diameter and all of it is not in focus. Therefore, regardless of how the calculation is done, it is very obvious that the depth of field is on the order of one inch.
The G9 and similar small sensor cameras are sometimes said to be diffraction limited and those disparaging it as such will disapprove of using the f8 aperture. Don’t be afraid to use f8 – it’s OK.
Besides, at f5.6 the depth of field would only have been about ½ inch!
Saturday, November 17, 2007
G9 and Hyperfocal Focusing
The small point-and-shoot “digicams” so popular today have a significant depth of field. That is, for a given scene, the distance from the camera that is acceptably in focus is much more than might be expected with, say, a 35mm film camera. In fact, sometimes it seems that everything is in focus. The G9 is no exception to this rule.
At first thought, having everything in focus seems preferable although there can be good reasons for intentionally producing out-of-focus areas. In particular, in landscape photography the camera is often set to produce pictures having deep depth of field. Typically, this is done by setting a small aperture (large f-stop number) such as f22.
The G9 does not have apertures of f22; in fact, the smallest aperture is f8. The G9 has been criticized by some for this apparent lack of smaller apertures but f8 is more than adequate for depth of field. If smaller apertures are needed for exposure then the G9’s internal 3x neutral density filter should be turned on.
In some of my early tests, I noticed that the G9 automatically selected focus distances of about 25 feet whereas the main subject was easily 300 feet away. When I manually changed to infinity focus, there was no obvious change in the picture. How could this be?
The key phrase to understanding this phenomena is hyperfocal distance. Briefly, when the focus is set to the hyperfocal distance then everything from half that distance to infinity will be in acceptable focus. Remember that old camera that did not require (or allow for) focusing? It was built with the lens set at the hyperfocal distance. The focusing instructions for my old Kodak Brownie camera were simply to be certain that the subject was at least six feet away (as I recall).
Some love to debate the exact nature and mathematics of depth-of-field, focusing, focal lengths, enlargements, circle of confusion, etc. An excellent source of information, including computer programs, is http://www.dofmaster.com/. For now, let’s just consider that the depth of field depends on the focal length of the lens, the distance that the lens is actually focused at and the aperture.
For the G9 widest angle zoom setting, the focal length is 7.4mm. At 7.4mm with f4 aperture, the hyperfocal distance is about 8 feet. This means that with the camera set for 8 feet everything from about 4 feet to infinity is in focus! No wonder I was confused! For my scene, automatic focusing was selecting about 25 feet – which was actually OK even though the main subject was much farther away.
At the other extreme, the G9 telephoto zoom is 44.4mm. At 44.4mm and f5.6, the hyperfocal distance is nearly 200 feet; everything from 100 feet to infinity is in focus. Therefore, as is known from experience, focusing is much more critical when using telephoto lenses.
So when using the automatic focusing modes of the G9, be aware that automatic focus settings rely on the principle of depth-of-field and make use of hyperfocal distance.
At first thought, having everything in focus seems preferable although there can be good reasons for intentionally producing out-of-focus areas. In particular, in landscape photography the camera is often set to produce pictures having deep depth of field. Typically, this is done by setting a small aperture (large f-stop number) such as f22.
The G9 does not have apertures of f22; in fact, the smallest aperture is f8. The G9 has been criticized by some for this apparent lack of smaller apertures but f8 is more than adequate for depth of field. If smaller apertures are needed for exposure then the G9’s internal 3x neutral density filter should be turned on.
In some of my early tests, I noticed that the G9 automatically selected focus distances of about 25 feet whereas the main subject was easily 300 feet away. When I manually changed to infinity focus, there was no obvious change in the picture. How could this be?
The key phrase to understanding this phenomena is hyperfocal distance. Briefly, when the focus is set to the hyperfocal distance then everything from half that distance to infinity will be in acceptable focus. Remember that old camera that did not require (or allow for) focusing? It was built with the lens set at the hyperfocal distance. The focusing instructions for my old Kodak Brownie camera were simply to be certain that the subject was at least six feet away (as I recall).
Some love to debate the exact nature and mathematics of depth-of-field, focusing, focal lengths, enlargements, circle of confusion, etc. An excellent source of information, including computer programs, is http://www.dofmaster.com/. For now, let’s just consider that the depth of field depends on the focal length of the lens, the distance that the lens is actually focused at and the aperture.
For the G9 widest angle zoom setting, the focal length is 7.4mm. At 7.4mm with f4 aperture, the hyperfocal distance is about 8 feet. This means that with the camera set for 8 feet everything from about 4 feet to infinity is in focus! No wonder I was confused! For my scene, automatic focusing was selecting about 25 feet – which was actually OK even though the main subject was much farther away.
At the other extreme, the G9 telephoto zoom is 44.4mm. At 44.4mm and f5.6, the hyperfocal distance is nearly 200 feet; everything from 100 feet to infinity is in focus. Therefore, as is known from experience, focusing is much more critical when using telephoto lenses.
So when using the automatic focusing modes of the G9, be aware that automatic focus settings rely on the principle of depth-of-field and make use of hyperfocal distance.
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