Help with focus issue with new lens

Hello everyone!

 

Recently purchased a Canon EF 70-200mm f/2.8L Is II USM that I'm using on a Canon 7D. This is a learning curve for me. In the image that I have posted my question is, why are his rear legs in focus but not his head. I use the center focus point and my settings were as followed.... f4 shutter 1/1600 ISO 500 at 123mm in AI SERVO. I was told that f4 would be the sharpest f stop for this lens. Any help would be greatly appreciated!

We focus on a specific distance and objects at this distance are tack sharp. Theoretically, only objects at this specific distance are sharp and all other objects nearer and further will be blurred. However, we know from experience that a zone of acceptable sharpness outspreads both back towards the camera and away from the point focused upon. This span, in the jargon of photography is depth-of-field.

 

 

Before getting tongue tied -- the answer to your question is: The span of Depth-of-field is not split down the middle; it extends approximately 1/3 back towards the camera and 2/3 further back from the point of focus. Had you focused on the forequarters of the animal, depth-of-field would have carried.

 

Depth-of-field is a vast subject and you are not going to learn it in a few paragraphs. This is a subject that you should Google to learn more. In a nutshell:

 

Short focus lenses (wide-angle) deliver expanded depth-of-field. Large lens openings (apertures) like f/2 or f/4 deliver shallow depth-of-field. Tiny lens opening like f/22 or f/16 deliver abundant depth-of-field.

 

Greater subject distances yield increased depth-of-field.

 

Short subject distance yield shallow depth-of-field.

 

 

 

When you do your research, you will find the web is rich with information plus tables and carts. This like other fine points of photography separate the outstanding photographer from the snapshotter. Do invest study time!

According to my HyperFocal Pro app, assuming a focus distance of about 15 feet, with your combination of lens, camera, and aperture, the DoF is only about 7.5 inches, or 187 mm. At 10 feet the DoF is only just over 3 inches. At 20 feet the DoF is just over 13 inches. The dog's body is considerably longer than that, so only a small portion of the dog could possibly be in focus. In this case, the focus point is clearly well behind the dog's shoulder. For a DoF sufficient to encompass even 1/2 of the animal's body length, given the exposure data, you would need an aperture of f:16-22, which would put you into the range of softening due to diffraction, not to mention the much slower shutter speed and/or much higher ISO required to make the exposure. Better to go with the shallower DoF and carefully select your focus point. Typically for animals the preferred focus point is the near eye, and let DoF control the rest. For a shepherd with a long snout, you might want to go for a deeper DoF so as to keep the nose in focus, or as close to focus as possible. (Most people, with some few exceptions, don't have the same DoF problem with their noses as do dogs. :))

We focus on a specific distance and objects at this distance are tack sharp. Theoretically, only objects at this specific distance are sharp and all other objects nearer and further will be blurred. However, we know from experience that a zone of acceptable sharpness outspreads both back towards the camera and away from the point focused upon. This span, in the jargon of photography is depth-of-field.

 

 

Before getting tongue tied -- the answer to your question is: The span of Depth-of-field is not split down the middle; it extends approximately 1/3 back towards the camera and 2/3 further back from the point of focus. Had you focused on the forequarters of the animal, depth-of-field would have carried.

 

Depth-of-field is a vast subject and you are not going to learn it in a few paragraphs. This is a subject that you should Google to learn more. In a nutshell:

 

Short focus lenses (wide-angle) deliver expanded depth-of-field. Large lens openings (apertures) like f/2 or f/4 deliver shallow depth-of-field. Tiny lens opening like f/22 or f/16 deliver abundant depth-of-field.

 

Greater subject distances yield increased depth-of-field.

 

Short subject distance yield shallow depth-of-field.

 

 

 

When you do your research, you will find the web is rich with information plus tables and carts. This like other fine points of photography separate the outstanding photographer from the snapshotter. Do invest study time!

 

"Thank you" for your time! I will invest in study time :)

 

 

According to my HyperFocal Pro app, assuming a focus distance of about 15 feet, with your combination of lens, camera, and aperture, the DoF is only about 7.5 inches, or 187 mm. At 10 feet the DoF is only just over 3 inches. At 20 feet the DoF is just over 13 inches. The dog's body is considerably longer than that, so only a small portion of the dog could possibly be in focus. In this case, the focus point is clearly well behind the dog's shoulder. For a DoF sufficient to encompass even 1/2 of the animal's body length, given the exposure data, you would need an aperture of f:16-22, which would put you into the range of softening due to diffraction, not to mention the much slower shutter speed and/or much higher ISO required to make the exposure. Better to go with the shallower DoF and carefully select your focus point. Typically for animals the preferred focus point is the near eye, and let DoF control the rest. For a shepherd with a long snout, you might want to go for a deeper DoF so as to keep the nose in focus, or as close to focus as possible. (Most people, with some few exceptions, don't have the same DoF problem with their noses as do dogs. :))

 

"Thank you" for your time! DOF has always been confusing to me.

[ATTACH=full]1279112[/ATTACH]

(snip)

I was told that f4 would be the sharpest f stop for this lens. Any help would be greatly appreciated!

 

Others have mentioned depth-of-field, which is the important part of the answer, so I

will answer this one.

 

If you are shooting a flat object, so no depth-of-field to worry about, and if you have the

focus perfectly, which you get close to with most AF systems, then how sharp is the image?

 

There are two things that make the image less than perfect. One is lens aberration, as lenses

aren't perfect for a variety of reasons. Most of those reasons, such as spherical aberration,

get worse at larger apertures.

 

One that isn't dependent of lensmaking ability is diffraction. Diffraction comes from the

wave nature of light, and gets worse at small apertures.

 

The combination of the two, means that there is some aperture where the lens is sharpest.

But you should almost never consider that ... unless you are shooting completely flat

objects that aren't moving with the camera on a tripod, and with the mirror locked up.

 

Lenses are plenty sharp at f/8, f/11, and even f/16. For ordinary situations, don't worry

about those, especially when you can use full depth of field. If you need maximal

depth of field: people in front of a scenic sight in the distance, go for f/22 without worry.

(And manually focus the lens half way between, in focus ring rotation, between the

near and far focus points.)

 

But lenses are tested on flat targets with the camera on a tripod, using resolution

test targets, and so in tests can find the aperture that the lens is sharpest. Try not

to think about this test, though.

 

For actual shooting, you need to choose an appropriate shutter speed to stop motion

(of both subject and camera), and aperture for enough depth of field. Outdoors in

daylight, that should not be f/4. I suspect dogs jump slower in snow, so you could

use a shutter speed of 1/250 or 1/125. The electronic noise level on the 7D should

be plenty low at ISO 1600, but for outdoors the 500 that you used should be fine.

 

It takes some practice to get used to the compromise between shutter speed and

aperture, for subject motion and depth-of-field. And with digital cameras, you also

get to choose the ISO value.

Holly - just a thought. I've always shot my animal shots with the point of focus being their eyes. The results have fully met my expectations for many years. It can be hard to do when the animal is in motion, but a little practice can produce significant results. Also, especially with animals, I've found, no matter what the lens,shooting at f/5.6-8, especially with animals, gives a lot more keepers because of the wider DOF than when using wider apertures, which I reserve for when the animal is at rest,

+1 for the eyes - and that goes for animals that walk on two legs, too.

here are some useful files from Zeiss to download and study:

 

Lenspire

 

https://lenspire.zeiss.com/photo/app/uploads/2018/04/Article-Bokeh-2010-EN.pdf

A beginner doesn't need to know any of that technical garbage. They need to know how to set the AF up on the camera properly.

 

Holly, I presume you're just letting the camera choose a focus point automatically? If so, there's your issue.

 

Have a read of the camera manual and find out how to take charge of the focus point yourself. So that you can control where the camera focusses.

 

Not familiar with the Canon 7D, but maybe it has face-detect focussing. Sometimes this works with animal faces too. You'll have to experiment.

 

There will also be quite a few other choices for AF setting - single or continuous for example. For moving subjects the continuous setting is usually the best choice. Again, you need to experiment to see what works for you.

 

My own choice is usually to set a single central focussing point, so that I know exactly where the camera is going to focus. Half-press the shutter to lock the focus, and then re-compose.

 

This focus-and-recompose method only works if the subject stays relatively still, and it may not work for you and your dog. But it's worth trying. Sometimes keeping it simple is better than all the fancy technology in the world. Certainly better than filling your head with depth-of-field formulae, that don't actually work in practise anyway!

 

Just try things out. The beauty of digital is that it costs nothing to experiment, and the more you practise, the better your pictures will become.

Others have mentioned depth-of-field, which is the important part of the answer, so I

will answer this one.

 

If you are shooting a flat object, so no depth-of-field to worry about, and if you have the

focus perfectly, which you get close to with most AF systems, then how sharp is the image?

 

There are two things that make the image less than perfect. One is lens aberration, as lenses

aren't perfect for a variety of reasons. Most of those reasons, such as spherical aberration,

get worse at larger apertures.

 

One that isn't dependent of lensmaking ability is diffraction. Diffraction comes from the

wave nature of light, and gets worse at small apertures.

 

The combination of the two, means that there is some aperture where the lens is sharpest.

But you should almost never consider that ... unless you are shooting completely flat

objects that aren't moving with the camera on a tripod, and with the mirror locked up.

 

Lenses are plenty sharp at f/8, f/11, and even f/16. For ordinary situations, don't worry

about those, especially when you can use full depth of field. If you need maximal

depth of field: people in front of a scenic sight in the distance, go for f/22 without worry.

(And manually focus the lens half way between, in focus ring rotation, between the

near and far focus points.)

 

But lenses are tested on flat targets with the camera on a tripod, using resolution

test targets, and so in tests can find the aperture that the lens is sharpest. Try not

to think about this test, though.

 

For actual shooting, you need to choose an appropriate shutter speed to stop motion

(of both subject and camera), and aperture for enough depth of field. Outdoors in

daylight, that should not be f/4. I suspect dogs jump slower in snow, so you could

use a shutter speed of 1/250 or 1/125. The electronic noise level on the 7D should

be plenty low at ISO 1600, but for outdoors the 500 that you used should be fine.

 

It takes some practice to get used to the compromise between shutter speed and

aperture, for subject motion and depth-of-field. And with digital cameras, you also

get to choose the ISO value.

 

"Thank you" so very much!!

Edited January 15, 2019 by holly_goyea

Holly - just a thought. I've always shot my animal shots with the point of focus being their eyes. The results have fully met my expectations for many years. It can be hard to do when the animal is in motion, but a little practice can produce significant results. Also, especially with animals, I've found, no matter what the lens,shooting at f/5.6-8, especially with animals, gives a lot more keepers because of the wider DOF than when using wider apertures, which I reserve for when the animal is at rest,

 

"Thank you" so very much!

here are some useful files from Zeiss to download and study:

 

Lenspire

 

https://lenspire.zeiss.com/photo/app/uploads/2018/04/Article-Bokeh-2010-EN.pdf

 

"Thank you" so very much!

A beginner doesn't need to know any of that technical garbage. They need to know how to set the AF up on the camera properly.

 

Holly, I presume you're just letting the camera choose a focus point automatically? If so, there's your issue.

 

Have a read of the camera manual and find out how to take charge of the focus point yourself. So that you can control where the camera focusses.

 

Not familiar with the Canon 7D, but maybe it has face-detect focussing. Sometimes this works with animal faces too. You'll have to experiment.

 

There will also be quite a few other choices for AF setting - single or continuous for example. For moving subjects the continuous setting is usually the best choice. Again, you need to experiment to see what works for you.

 

My own choice is usually to set a single central focussing point, so that I know exactly where the camera is going to focus. Half-press the shutter to lock the focus, and then re-compose.

 

This focus-and-recompose method only works if the subject stays relatively still, and it may not work for you and your dog. But it's worth trying. Sometimes keeping it simple is better than all the fancy technology in the world. Certainly better than filling your head with depth-of-field formulae, that don't actually work in practise anyway!

 

Just try things out. The beauty of digital is that it costs nothing to experiment, and the more you practise, the better your pictures will become.

 

"Thank you", new to the lens but not my camera :) I use the single central focusing point and back button for focusing. Still have so much to learn!

Certainly better than filling your head with depth-of-field formulae, that don't actually work in practise anyway!

Holly, I both agree and disagree with RJ's statement. Except in the case of very static subjects (think still life and landscape), rarely does a photographer have time to evaluate DoF in detail. So, RJ is correct in that point. However, it is essential that the photographer have an effective and useful understanding of the principles which govern DoF in order to avoid problems such as you experienced in your dog image. Aperture, and its relationship to DoF, is likely the most difficult concept, from among the three which make up the "exposure triangle", for new or beginning photographers to fully grasp. You likely understand that a "correct" (meaning it achieves the photographer's desired effect) exposure is dependent upon how much light reaches and is absorbed by the image sensor, whether digital or film. The components which are controlled by the photographer are the duration of the shutter opening (shutter speed), and the size of the opening in the lens through which the light can pass, called aperture. The third leg of this triangle is the sensitivity to light, or ISO, of the sensor on which the light impinges, which can also be selected. We all play with various balances within this triangle to get the images we want. A very fast shutter speed used to freeze apparent motion means either or both a larger aperture and/or a more sensitive (higher ISO) sensor. Depth of Field (DoF) is a secondary effect of these choices, tied directly to the size of the aperture. In practice, we generally just know that larger apertures (designated by smaller f numbers, such as 1.8, 2.8, 3.5, and 4) have a very shallow DoF, and so, without making laborious calculations, we compose our images to incorporate or accommodate the shallow DoF. Hence the "focus on the near eye" advice. Medium to small apertures (designated by larger f numbers, such as 5.6, 8, 11, 16, 22, etc.) provide progressively "deeper" DoF. So, in a landscape image where nothing is moving at over glacial speeds, I might choose a very small aperture, such as f/11-f/16 such that the entire image is in focus, from the nearest elements out to infinity. Since I also will want the best resolution for printing and dynamic response, I'll choose ISO 64. This combination will then require a very slow (long duration) shutter speed in order to get sufficient light onto the sensor to make the image. If there is a foreground subject that is critical be in focus, then I'll either experiment with various settings and focus points to get the outcome I want, or I'll use a technical aid (such as the app on my phone) to help me get a starting point for my focus and exposure settings.

 

As RJ suggests, the goal in this is not that you carefully calculate DoF for every image. That is neither feasible nor practical. Rather, understanding the relationships of the choices you make in your focus and exposure settings, and then automatically adapting to those conditions, is the goal. Definitely use the low-cost opportunity of digital to experiment with these and other issues to improve your knowledge and ability. The experiments will be much more meaningful and informative if you fully comprehend what it is you are playing with and adjusting for.

 

Just FYI: I use back button focus on all of my cameras, so good for you on that choice. It allows you to separate the focus completely from the exposure, allowing more control over the image. I'm a Nikon guy, but in reading up on your Canon 7D, it looks like your focus settings are part of the problem. The AI Servo setting, when combined with 65 point AF, means the camera may not choose the focus point you want, but will track the moving subject using all of the focus points. Given a shallow DoF and a subject that fills much of the frame, it's just luck if the camera selects and follows the particular focus point you want. On my Nikon gear, for moving subjects (like my 3 YO grandaughter), I typically choose either single point or small group (9 point) autofocus, with my BBF set to "continuous". Then I do my best to keep her eyes in the focus point or group. This usually works pretty well, with the facial recognition and tracking making up for many of my mistakes. You'll need a Canon guru to suggest the best AF settings for your kit. Good luck and have fun!

Before someone beats me up, yes, I still am in the dark ages (manual) of photography, but I am amazed how something once so simple has become so overly complicated.

I am amazed how something once so simple has become so overly complicated.

Chuck, the only complication I see is the addition of autofocus and its various iterations and options. Pretty much everything else is the same as it was, for me, at least, when I learned on a hand-me-down Nikkormat EL 45 years ago. I still shoot aperture priority, and nothing has changed about how I apply DoF and shutter speed. I remember with clarity how much of a challenge it was to fully understand the relationships between DoF, aperture, and choosing a focus point. It wasn't until I attended a Nikon School event in 1980 that it all came together for me. I had all the individual bits of knowledge, but the synergy just wasn't there, until I saw it demonstrated and explained in real time. Then, suddenly, those little, colored stripes on my push-pull zoom made sense! I have to say that, properly applied, the technology of autofocus sure makes easier what was once very hard, like simultaneously tracking, zooming, and focusing on a moving subject, but only if the settings are correct. So, I'll grant you the complexity, but offer it makes attainable what was previously the near-impossible.

I shake my head when I see 30 pages in an instruction manual devoted to 'how to focus'. Those Nikon schools were very good. Being I sold Nikons at the time, we - (myself and other managers from the same company) went to several and used some of their teaching techniques to put on our own seminars. These days I still make a lot of use of the DOF scales on my lenses.

 

Back when I was doing photography for a living, for a moving subject one of my methods was to pre-focus to a spot where I anticipated the action. When the subject got there, I took the photo.

 

FYI - the company was Brown Photo out of Minneapolis, MN, USA which has been long gone for a long time.

Edited January 15, 2019 by chuck909

Hi @holly_goyea, I think you've already got more than enough tips on focusing (eyes), DOF, etc. I have the same lens and it's wonderful! Once a year I shoot some 'action photos' at a local running event (often at f2.8 or 5.6) and I'm guessing the speed of movement is about the same as your dog. Your settings look fine to me and if your spot focus really was sharply on the dog's eyes (with the body slightly less sharp), you wouldn't have asked this question.

 

Most of my 'action close-ups' with this lens are good enough, occasionally really good but - even after doing this for a vcouple of years - I still get some blurry/out of focus shots too. The main thing I learned from the blurry/out of focus shots was to give the lens enough time to focus when half-depressing the 'click'button. It's very tempting (especially in action shots) to see the action and 'press click'. I have no idea whether this is useful to you. But 'slowing down' and letting the lens focus (1/2 second) helped me.

 

Two other points to consider: AI Servo tracks movement and refocuses. It's just possible that your dog's head (eyes) moved more quickly that the lens could track.

Aperture, and its relationship to DoF, is likely the most difficult concept

 

- Not really. It can be summed up very quickly.

 

'The bigger the aperture number, the bigger the depth of field.'

 

We might want to supplement that with 'The longer the lens, the shallower the depth of field', or 'The wider the lens the deeper the depth of field', but that's about all anyone needs to know.

 

The trouble with getting bogged down putting actual numbers to DoF, is that it totally depends on final viewing magnification, which is rarely known. And to an extent, the lens aberrations and optical construction, which is also anyone's guess.

 

As anyone who's pixel-peeped at 100% knows, depth-of-field is an illusion. There is none. Just a depth of acceptable blur when we zoom out to a normal viewing distance - whatever 'normal' is these days.

Not really.

I'm glad for you. It was the most difficult for me, and it remains the biggest challenge for beginners that I know. Once understood it is clear and makes sense, and can be readily applied. It's just that initial leap of understanding that so many find a challenge.

It was the most difficult for me, and it remains the biggest challenge for beginners that I know.

 

- If demonstrated using a digital camera, I really don't see why it's so difficult to grasp. Couple a suitable camera to a digital projector; point the camera at a line of pencils or somesuch, and then open and close the aperture. The DoF can easily be seen to change by the entire class at once.

 

A couple of follow up handouts with liberal illustrations, and all but the most obtuse students are enlightened.

 

Using film it's not so easy.

Using film it's not so easy.

My point, exactly. Digital tools do make it much easier than in days of yore (which is when I learned). Still, it is the one concept I observe as the most challenging for beginners, even though it has become so much simpler to illustrate/demonstrate/experience, as you correctly point out. Perhaps this is because we want them to apply the concept intuitively, without a firm metric they can read on their camera settings (unless, of course, they are using an old lens with an inscribed DoF scale=unlikely). As you said, so eloquently and accurately, "A beginner doesn't need to know any of that technical garbage. They need to know how to set the AF up on the camera properly." I agree emphatically. I also agree that getting out and experimenting at the low cost of digital is the best way, by far, to get understanding of all the various techniques and issues. Not sure why we're arguing. Seems like we agree more often than we disagree...:)

Holly, I both agree and disagree with RJ's statement. Except in the case of very static subjects (think still life and landscape), rarely does a photographer have time to evaluate DoF in detail. So, RJ is correct in that point. However, it is essential that the photographer have an effective and useful understanding of the principles which govern DoF in order to avoid problems such as you experienced in your dog image. Aperture, and its relationship to DoF, is likely the most difficult concept, from among the three which make up the "exposure triangle", for new or beginning photographers to fully grasp.

 

Well ... it used to be that lenses had a depth-of-field scale on next to the focus ring, that gave, for each aperture setting, the limits on depth of field.

 

I think most non-zoom manual focus lenses, for interchangeable lens cameras, have this scale.

 

With AF, it tended to go away. For zoom lenses, it has to change with zoom focal length. I know some push-pull zooms

have such a scale, with lines that show the changes with zoom. Not so easy for rotating zoom rings.

 

Without this scale, it is difficult to have a good idea of the depth-of-field.

 

No-one gets out DOF tables to look up the values, while focusing and setting the aperture.

For any who might be too young to remember, here's one example of a DoF scale on a (now antique) Nikkor lens:

Note that the f numbers on the aperture ring are color coded to the DoF scale lines. f/3.5 is the largest aperture, and so has the narrowest/shallowest DoF on the scale (in green). f/22, in white, is the smallest, and has the broadest/deepest DoF. This is a push-pull zoom, extended to its maximum focal length. Also note how the DoF narrows in at all aperture settings as the focal length of the lens increases. You can read the anticipated DoF directly off the range scale on the focus ring. In this case, at the current f/8 setting, the DoF would extend approximately from 7 feet to 8 feet from the focal plane. You can see that switching to f/22 would increase the DoF to cover an area from just over six feet to just beyond nine feet from the focal plane, but would require an additional three stops of shutter speed for the same exposure (assuming you don't change film speed /sensor ISO). For any who are curious, this is, perhaps, Nikon's worst-ever lens, the infamous 43-86mm/3.5, mounted on an even more antique Nikkormat EL. Can you say "Nikon shuffle", anyone? Condition on both would be listed as "heavy brassing and other signs of extensive use and wear." They both still work...;)

Edited January 17, 2019 by DavidTriplett

at the current f/8 setting, the DoF would extend approximately from 7 feet to 8 feet

Just FYI: My HyperFocal Pro app says that the DoF for this setting would be from 7.019 feet to 8.052 feet, so the old tech and the new tech appear to agree. Who woulda' thunk it?

Just FYI: My HyperFocal Pro app says that the DoF for this setting would be from 7.019 feet to 8.052 feet, so the old tech and the new tech appear to agree. Who woulda' thunk it?

 

My TA would have marked that off for excessive significant digits. Maybe round to 7.0 to 8.1 feet