Hunger for quick focus

[Doctor Andrei]

Please help me people. I own my Canon 550 for 4 months now and I'm not used to the AF yet. I have Tamron 17-50 mm 1 2.8 lens and that son of a b---h takes a fortnight every time I'm autofocusing. I've made a pack of photos of my son and none of those are in focus. The kid manages to not just move but to walk to the other room before that stupid lens reaches focus. Is there an option in Canon 550D that will make that lens work faster? I need my focus the same moment that I'm trying to take a picture, and not the next morning after it. I've read the whole 550D manual and that still don't help.

[Glenn NK]

Doctor Andrei:

I'm not familiar with your camera, but it does have have many features in common with my Canon 30D and 5DII - including the focusing setups.

Your camera has three modes of focus (AF Modes); AI focus, One shot, and AI Servo. In addition, there is also manual focus, but this isn't likely what you want.

It could be that the mode of automatic focus (AF) you are using may not be the right one for fast moving objects such as your son (do they ever sit still?). However if you have gone through all this, then ignore everything I have to say.

I would start with the manual on page 18 which shows the AF points. There are nine. The point in the centre is more accurate and faster than the outer eight points.

I'm going to recommend that you set your camera up so that the "star" (*) button on the upper right of the back of the camera is used for focusing. With a few moments practice I think you'll find it is superior to half-pressing the shutter button. Although at first this seem counter-intuitive, there are quite a few advantages which I won't go into here, but suffice it to say, both my cameras are set up this way. Once I tried it I never considered going back. This method of focusing is covered on page 97 of the manual. It's certainly worth trying.

On page 52 of the manual, "Shooting Moving Subjects", it recommends using the centre AF point (to this end, I disable the outer points).

Pages 66 and 67 of the manual are about different AF modes. The manual recommends AI Servo for moving subjects - page 67 (perhaps you have already selected this). Page 68 covers selection of the centre point.

There is one other possibility for your problems and that may be that the lens doesn't focus very accurately. The Photozone review states, "The AF accuracy was a bit so-so on our test DSLR".

http://www.photozone.de/canon-eos/48...750_28vc_canon

Another approach is to try this site:

http://www.justanswer.com/sip/canon-...FQhjhwodLHApCg

Good luck.

Glenn

[Dave Humphries]

Hi Andrei,

Two things I am wondering about;
where in the frame is your son when you say it is soft?
- because I note from reading that review that at anything less than f/8, the edges are pretty soft compared to the middle.
the second thing is what aperture, iso and shutter speed are you using?
On this last question I am wondering;
- is lack of Depth of Field the real problem?
- is it actually subject movement causing softness because shot at too low a shutter speed?
- is it soft because you're at a very high iso? (noise reduction will soften images)

Can you show us an example shot?

One last thought; AF will take longer in low light (even if you're using flash) ...
Glenn's very comprehensive answer should certainly help, but one thing not mentioned is that if you are in low light, does the 550D have a focus assist light? and is it enabled/disabled?

Welcome to the CiC forums from ...

[Doctor Andrei]

[Doctor Andrei]

[Doctor Andrei]

First half of Glenn's advices, I've already tried.
Second half might be a good help.

to Dave - softness is not an issue, I understand how to deal with that. What I cant stand is that the goddamn 550 takes a century to turn the quadrangle on the display green!!! My old Power Shot G3 does that in one eyeblink!

And I definitely hate flash for ruining the colors, esp. indoors.

[Glenn NK]

Thanks for posting images. To my eye, I can't see anything that is sharp - neither the foreground nor the background. Which leads me to ask what shutter speeds were used? Other information such as f/stop, ISO, could be useful too.

Glenn

EDIT - just looked at the third pic (it wasn't up when I replied). Your son's right forearm and sleeve look reasonably sharp, but the left sleeve is not. Seems to be little depth of field, but without knowing the f/stop it's hard to comment on this.

Just guessing a bit, but I'm starting to think the lens may be the problem, not the camera.

For example - my 30D is several generations older than your camera, but with my Canon 17-55, I don't have this problem at all. This lens focuses quickly.

G

[Doctor Andrei]

Someone tell me what general purpose lens should I buy to make excellent everyday-life photos with excellent focus that is obtained immediately after I press the button, not centuries after.

[Goldcoastgolfer]

I need to ask what might seem like a stupid question and I'm also a Nikon user so I'm not sure if this applies to Canons. However, when a friend of mine got her new camera she was having a lot of focussing issues. It turns out the autofocus switch on her lens had been switched to manual instead of AF which was why her photos were all out of focus.

Is there a focus switch on the lens and what position is it it? Apologies if it's a stupid question.

[Doctor Andrei]

Thanks for posting images. To my eye, I can't see anything that is sharp - neither the foreground nor the background. Which leads me to ask what shutter speeds were used? Other information such as f/stop, ISO, could be useful too.

Glenn

EDIT - just looked at the third pic (it wasn't up when I replied). Your son's right forearm and sleeve look reasonably sharp, but the left sleeve is not. Seems to be little depth of field, but without knowing the f/stop it's hard to comment on this.

Just guessing a bit, but I'm starting to think the lens may be the problem, not the camera.

For example - my 30D is several generations older than your camera, but with my Canon 17-55, I don't have this problem at all. This lens focuses quickly.

G

ISO 100 f 4 1\99s

[Dave Humphries]

Hi again Andrei,

Thanks for posting nice big images to look at, it makes life easier.
I will assume these are full frame and not cropped, for composition, after the event.

The first shot does look to be mis-focused, the foreground twig is sharper, although not that sharp.

The second shot's shutter speed was just 1/100s, iso 100 and aperture f/4 and this has led to a combination of things;
there is significant camera shake, are you using it with the VC (vibration compensation) on?
there is also too much subject movement for that shutter speed
I also believe there is insufficient DoF for all those people at f/4 at 33mm

I would suggest a higher iso; 400, or even 800, on a dull day to give more shutter speed and say f/5.6 or f/8.

However, for these shots, my thoughts about AF assist light are clearly irrelevant, as possibly, is the bit about edge softness, especially in the first. Again; maybe there is camera shake and subject movement issues since the EXIF is almost identical; 1/100s, f/4, iso100, 32mm.

Hope that helps,

[Doctor Andrei]

I need to ask what might seem like a stupid question and I'm also a Nikon user so I'm not sure if this applies to Canons. However, when a friend of mine got her new camera she was having a lot of focussing issues. It turns out the autofocus switch on her lens had been switched to manual instead of AF which was why her photos were all out of focus.

Is there a focus switch on the lens and what position is it it? Apologies if it's a stupid question.

It's with AF on , definitely.

[Glenn NK]

Andrei:

I'm very reluctant to recommend what you buy because there are so many variables (cost, focal length, etc), but even though it was quite expensive, I've never regretted buying my Canon EFS f/2.8 17-55. Many people decry it's build quality, but I've had mine for four years and it hasn't fallen apart. However even those than complain about the cost and seemingly not so great build quality, no one denies that it is:

1) fast focusing,

2) has excellent optics.

I very often use this lens indoors for family occasions, and rarely use flash with it. In fact the only flash I have it the built-in one on the 30D.

Glenn

PS: there is also the Tokina 17-50, but the Photozone review also notes that using Live View it is rather slow focusing. Not exactly what you're looking for.

http://www.photozone.de/canon-eos/531-sigma1750f28os

[Doctor Andrei]

Hi again Andrei,

Thanks for posting nice big images to look at, it makes life easier.
I will assume these are full frame and not cropped, for composition, after the event.

The first shot does look to be mis-focused, the foreground twig is sharper, although not that sharp.

The second shot's shutter speed was just 1/100s, iso 100 and aperture f/4 and this has led to a combination of things;
there is significant camera shake, are you using it with the VC (vibration compensation) on?
there is also too much subject movement for that shutter speed
I also believe there is insufficient DoF for all those people at f/4 at 33mm

I would suggest a higher iso; 400, or even 800, on a dull day to give more shutter speed and say f/5.6 or f/8.

However, for these shots, my thoughts about AF assist light are clearly irrelevant, as possibly, is the bit about edge softness, especially in the first. Again; maybe there is camera shake and subject movement issues since the EXIF is almost identical; 1/100s, f/4, iso100, 32mm.

Hope that helps,

Im only startin to learn that ISO aperture shutter speed stuff. If I would go on with using that old camera I would never start becuz I didnt have to, Power Shot would make nice pics on Auto mode, always. This one riht here kills any nice pic in Auto mode, P mode also, and trying to play games with shutter speed only makes everything black. Im tired of all photographic science stufff, I just wanna take pictures.

[Dave Humphries]

Hi again, again, Andrei

The third shot is sharp in one or two places, but behind the subject.

I would be looking at using the single central point only and not have the AF in any 'clever' modes the 500D might have turned on which might be using an alternate focus point causing the arm and wall on left to be sharp.

Hope we can get this sorted for you, one way or another.

[Dave Humphries]

Im only startin to learn that ISO aperture shutter speed stuff. If I would go on with using that old camera I would never start becuz I didnt have to, Power Shot would make nice pics on Auto mode, always. This one riht here kills any nice pic in Auto mode, P mode also, and trying to play games with shutter speed only makes everything black. Im tired of all photographic science stufff, I just wanna take pictures.

Hi again, ag ... no, that's been done to death

Does the 550D have scene modes?
If so, for a shot like the third, try one.

Scene modes may automate more stuff to avoid the issues you're having with Auto and P modes - which will still leave a lot of the 'sciency things' to spoil a picture.

Cheers,

[Glenn NK]

Hi again, again, Andrei

I would be looking at using the single central point only and not have the AF in any 'clever' modes the 500D might have turned on which might be using an alternate focus point causing the arm and wall on left to be sharp.

Yes.

Glenn

[Andrew1]

From what I can see maybe review of your techniques before buying new equipment. The three you've posted are attributable to how you took the them. Number 1 is just blurry and with all that white it's hard to tell if it was movement on your part or focus someplace else. Number 2 is camera shake. Number 3 is a wrong focus area. Looks to me like just some practice and attention may fix your concerns. It could still be a focus speed issue but it would have to be awful slow not to be able to get these shots as nothing looks like it's moving very fast. If you're focusing then recomposing check you're not on continuous focus.

[Steaphany]

If the auto-focus is too slow, don't use it !

Here is a simple way to have your camera always ready for that shot.

First, you need to determine a minimum close "working" distance that you'll use for your camera to subject distance. From this you need to do a bit of math, the goal is to determine the camera settings to keep everything from this minimum working distance to infinity in an acceptable focus.

If you are wondering how a camera could be set to keep everything in focus with auto-focus turned off, check out the concept of Hyperfocal Distance. The trick is quite simple: set the auto-focus off, set the camera to aperture priority, select an aperture that yields a Hyperfocal distance which is twice as far as your minimum working distance, Set the lens to focus at the Hyperfocal Distance, and adjust the ISO to bring your shutter speed where you want it. ( if the camera meters a long shutter, raise the ISO to shorten it ) Now, every time you snap a photo, everything, from your minimum working distance to infinity, will all be equally focused.

Normally, the Hyperfocal Distance is calculated from the focal length of the lens ( The Real Focal length, not factored by the imager size ), aperture, and a parameter called the "Circle of Confusion".

The best way to think of the Circle of Confusion is the diameter projected by a point in the scene onto the imager that is considered acceptably focused. Often, the Circle of Confusion uses standard values based on the size of the imager or film, but I have done the calculations for digital by the photosite spacing. If the largest acceptable blur a point in a scene makes on an imager is no greater than the spacing between photosites, then the image focal clarity is only limited by the photosite pitch of the imager. ( You can't get a better focus )

For this example I looked up the specifications of the Canon 550D which states that the Max resolution is 5184 x 3456 across a Sensor size being APS-C ( 22.3 x 14.9 mm )

* DANGER * Formulas to follow *

So, to calculate a Circle of Confusion yielding an optimal focus:

22.3 mm / 5184 = 0.0043 mm

Since we have already determined the minimum working distance, we need to calculate the necessary aperture by:

Aperture = Focal Length ^ 2 / ( Hyperfocal Distance * Circle of Confusion )

or, in terms of the Minimum Working distance:

Aperture = Focal Length ^ 2 / ( 2 * Minimum Working Distance * Circle of Confusion )

For example, you are using a 24 mm lens and you want the minimum working distance to be 12 feet, 3.7 m. Well, if you are one of the few in the world who measures in feet, you first need to turn feet into mm by:

mm = feet * 304.8

and in this example:

12 * 304.8 = 3657 mm

The rest of us know to multiply meters by 1000 to get mm. Now on to calculating aperture:

Aperture = Focal Length ^ 2 / ( 2 * Minimum Working Distance * Circle of Confusion )

Aperture = 24 ^ 2 / ( 2 * 3657 * 0.0043 )

Aperture = 576 / ( 31.467 )

Aperture = 18.3

So, if you set the aperture to f/18 on a 24mm lens with the focus to a distance of 24 feet, 7 m, everything within 12 feet, 3.6 m, and infinity will be focused with the maximum blur not exceeding one pixel. A trade off here is the small circle of confusion means that you need to use a small aperture and long shutter times ( even at high ISO settings )

A more traditional Circle of Confusion for Canon cameras is 0.019 mm ( 4.4 times greater than the photosite pitch ), lets do the calculation again:

Aperture = Focal Length ^ 2 / ( 2 * Minimum Working Distance * Circle of Confusion )

Aperture = 24 ^ 2 / ( 2 * 3657 * 0.019 )

Aperture = 576 / ( 139 )

Aperture = 4.1

Obviously, now having a f/4 is a lot easier to manage at the expense of image clarity, but play with the numbers and see how you go with your lens, a minimum working distance that you need, and post your results. Keep in mind that if you are using a Zoom lens, the calculation needs to be with the focal length that your lens is set to.

[Glenn NK]

Andrei:

Further to Dave's comments, my first additional comment is that I can't recall when I used an ISO setting as low as 100. Now this may shock some purists, but on my ancient 30D, I commonly use a value of 640, and although noise can be seen by peeping, 11" x 14" prints don't show any noise.

Looking at the individual images:

1) two boys in the snow: ISO 100, 1/100th second @ f/4. At f/4 there isn't much depth of field to work with, but still I can't find anything that is in focus - even the leaf Dave mentioned is not great. At ISO 400, the f/stop would have been f/8 which may have salvaged something.

2) Group of people: ISO 100, 1/100th second @ f/4. Again, nothing much in focus - this is strange.

3) Your son in blue T-shirt: ISO 100, 1/30th second @ f/2.8. Because your son's right arm and the background on the left look reasonably sharp, the slow shutter speed can't be to blame. This must be partially due to missed focus. The wide open f/stop (at f/2.8) gives so little depth of field that the focus must be accurate (and preferably on the eyes). It looks as though focus was somewhere between his right arm and the wall. As above, ISO 400 would have used f/5.6 which might have pulled his face into focus.

I am certain that this camera will produce very good images (it's a better camera than my 30D which I still use with great results). But - it may be that the lens is letting you down.

I don't know if you have access to a camera shop where you live, but if so, I would suggest trying one of their better Canon lenses on your 550D body, taking a few shots - take your son along - he will probably move around enough.

But first set the camera up as I suggested. One central focus point. Use the "star" button the back for focus, and use AI Servo (which is for moving subjects).

I didn't mention it earlier, but the advantage of this focusing method is that you can keep the "start" button pressed while you follow your subject, then press the shutter with your finger when you're ready to take the image.

Waiting to hear how things are going.

Glenn