newbie needs help...focusing problems

Hi all,

I hope you can bear with me here, but I am going a bit crazy trying to work out this focus problem on my Canon 20d (not trying to imply it is not user error!) Please advise me if I have come to the wrong place.

I find the images very soft, but blurry, out of focus, not even able to be sharpened. Last week I did a shoot of a family in a room where there was loads of natural light streaming in, using my 50mm f1.4 lens. I would have thought this would be ample to enalbe me fast shutter speeds, but when i had the lens wide open, or close to, I got a lot of blur around the edges. The centre person would be in focus, but not the people either side. Should depth of field be consistent across the horizontal plane??? Or am I getting dof all wrong?

Either way, in case this was the issue, I decreased the aperture to f4, but was now stuck with a shutter speed of 1/30th (and that was pushing the ISO to 400), just nowhere near fast enough to prevent motion blur or camera shake. What am I doing wrong?? In the end, I had to choose between only having my focal point sharp (I set the camera to the centre focal point to try to make it easier), or risking motion blur. If the 50mm 1.4 can't cut it, then what will?

Any help or advice would be really appreciated, because I have just about given up on finding a solution..I am only keeping around 25 of every 200 shots because of this soft focus problem...even shooting outdoors in shade the other day, the fastest shutter I could get on the 50 mm was 100 at 400 ISO. Does this sound wrong to others?

Thanks heaps for any feedback you can offer,

From the way you describe the issue, I would say that the problem is the performance of your 50mm f/1.4 wide open. You lens sounds like it performs similarly to mine - wide open it has significant edge softness which extends quite a way into the middle of the frame. Stop it down to f/4 and the softness is gone.

Of course, most lenses are softer wide open and benefit from being stoped down, but with the 50 f/1.4 this issue can be particularly significant.

Of course, I should clarify that there does seem to be sample variation. Many 50mm f/1.4 owners don't encounter this issue.

Try doing proper tests at various apertures using a tripod. This should reveal if what I've described is what's happening. Oh, and post some samples if possible...

Simon C
http://www.eyematter.com

I'd like to see you post an example of the problem.

But at f/1.4, the depth of field will be terribly shallow. It'll make focusing very critical, and anything not exactly in the "plane of focus" will be soft.

So stopping the lens down is the way to go to fight that problem. But that means slower shutter speeds and/or higher ISOs.

For one thing, with a 20D, don't be afraid of ISO 800 or even 1600. At times it's better than the alternatives, and as long as you do not underexpose things, the noise is quite acceptable and even fixable with certain noise-reduction programs. Give it a try and see what you think.

So you're just running up against the same problems everyone has. It's all a set of tradeoffs for exposure.

ISO/Shutter Speed/aperture.

Those are the three things you can generally control. The fourth thing is the amount of light available. Sometimes you can control that and other times you cannot. A flash, used properly, can be very handy in situations where you just don't have enough light.

But there is another tool available in the arsenal.

Many people insist on using wide aperture lenses, claiming that a huge aperture is the answer. But as you've found, in situations where there is some depth to the scene, large apertures give you such shallow DOF that they may not be acceptable.

So if you've got to stop the lens down to get the DOF you want anyhow, then why not get a lens with image stabilization built in? I know that's not a fix for your current situation, but I find that in a lot of cases, the EF-S 17-85mm IS lens is awesome because I can use decent apertures (f/5.6 to f/8) indoors and shoot at longer shutter speeds to make up for the smaller apertures. Thus, I get decent DOF and no blur due to shake. Of course, the tradeoff here is that the subjects need to hold still for you too! (It's always something!!!)

I guess for the situation you were in, with no flash and no IS, the only thing you could do is bump the ISO up higher. Give ISO 1600 a try and see what you think. Just play with it a bit and see if you think it would have been useful.

But be darn sure not to underexpose any high ISO shots. That's where you get the noise. In fact, don't underexpose any shots at all. You can have nasty noise in an ISO 100 shot if you underexpose it.

As for whether or not the field of focus is supposed to be a flat plane with the 50mm f/1.4 lens, I would have thought the answer would be yes. But I don't know for sure. Perhaps someone who has that lens or knows for sure can answer that.

Some lenses have more of a spherical field of focus, and some fall somewhere in-between. But I think many modern lens designs shoot for a flat plane of focus. It's a good question.

--
Jim H.

Thanks Jim,

Great, informative post! I actually have the 17-85 IS, and in that particular shoot, I stuck it on, but there was nowhere near enough light, and the ss was waaaay to slow...I was shooting an infant, and he didn't understand 'stay still, say cheeze'!

I am reassured to know it is a common problem...so are you saying that with such a wide aperture, it is quite possible that the father was positioned slightly further back, and this would show as blur because of the dof? I thought I had a little more play than that...does subject distance come into it? I was about 3ft away...I am new to this board, so will figure out how it all works, and try to post a sample.

Thanks again

OK, think I have worked out how to post a sample of what I mean. Its a low res copy, but to me, there is detail near the child's hand and across the father's t-shirt, and that is about it.



Simon, I think what you have described is what I am experiencing...so the scene doesn't necessarily have to have much depth to be out of focus...the focus can actually get lost around the edges of subjects all at roughly equal distance?

Hi there.

Yes, you're absolutely right about camera to subject distance playing into all of this too. Think of the DOF as representing a percentage of the distance between the camera and the subject. Longer camera to subject distances will have deeper DOF (in absolute terms) but the percentage or proportion will be the same.

I don't have the exact math right here, but you get the idea. So at such close distances, your DOF will be very tiny. I deal with this on an even more critical scale when shooting macro photos where the subject is very close to the camera and there is almost no DOF. I've recently been taking photos of snowflakes and it's darn near impossible to get the whole flake's depth in sharp focus even at the smallest apertures allowed by the lens!

At f/1.4, and three feet away, you'll find that the depth of field is so shallow that you might get their eye in focus and nothing else on their face will even be in focus. Shallow DOF is just the price you pay for wide apertures like that.

Many people like to use shallow DOF to isolate a subject from its background and so they like to use large apertures to accentuate this effect. But, like everything else in photography, it is a tradeoff.

For portraits, you will often see shots made with very shallow DOF like this, but when you've got two people in the shot, it is very difficult to arrange things so that they'll both be focused the way you want. From three feet away and at f/1.4, you're probably getting a DOF of 1/2 inch or so!

Now to really make for a striking image, if you want the shallow DOF look, you could either get the father to move back and forth until you get one of his his eyes (only one!) and one of the the child's eyes both in sharp focus at the same time.

Or you could alter your position so that the angle between you and the subjects allows you to get one of each of their eyes to be sharp. In effect, if the lens has a flat plane of focus, you'd be playing with your position to achieve a setup where the plane of the image sensor in the camera was exactly parallel to the line that passes through their two eyes.

It'd take a little moving back and forth to get it right but might be worth it for the effect.

So don't feel bad about what you're getting. It sounds pretty normal for such a large lens aperture and at the distance involved.

But if the infant is moving, then this complicates things even more because you won't be able to just take your time to get it right. Thus, you may very well need a smaller aperture to give you some range for the child to move within and still have him in good focus. Yet you need a higher shutter speed to freeze his movement.

That leaves you with ISO and ambient light to work with. Here is where a flash might be required.

Many people hate to use flash because of the unnatural look it can give to a photo. But if things are done properly, using bounce or diffusion, or both, or even multiple flash units, reflectors, and other tricks - then great effects can be achieved.

But now you're talking about even more equipment and more good things to learn about, I guess

If you can post an example, I think it'll show exactly what we're talking about.

In any case, have fun with all of this. It's a challenge but also very interesting and entertaining.

--
Jim H.

That will be helpful.

And I don't think you're suffering from lens problems as much as just shallow DOF here. I don't dispute that the lens may be imperfect, but I believe that what you are seeing is simply shallow DOF due to the large aperture.

No 50mm lens in the world wold solve what you're seeing. It's just the way things go when shooting at such a large aperture.

--
Jim H.

Hi again Jim,

Thanks again for your detailed previous post. I have attached another pic, but labour under no illusions the lens is to blame! I had no idea depth of field would be that shallow at that distance. I use the 50mm to shoot babies and love the blurred effect up close, but certainly didn't expect it to be a problem further back.

You have explained yourself perfectly (certainly better than my tutor does!) and I can see I either have to push the ISO or use the flash. I have the 580ex, but haven't yet mastered it in any way that gives pleasing results. I am interested that you can use the 17-85 indoors...I have real problems with that, and was considering getting the 24-70 f2.8 IS to overcome the light problem, but thankfully (because it aint cheap!) I might reconsider now since I might have to stop down anyway....it can wait until I feel my skills justify the expense. And the flash might just be the answer for the time being.

I am taking some photos of my family tomorrow at a 97th birthday party and really didn't want to get it wrong! Thanks so much for your help, I would have made the same mistakes all over again.

sandyoh said:

Thanks again for your detailed previous post. I have attached
another pic, but labour under no illusions the lens is to blame! I
had no idea depth of field would be that shallow at that distance.

Click to expand...

Yep, at f1.4 and 3 feet from the subject, your DOF is about 1cm - and when you look at the shot, that's exactly what you have - the right sleeve of his white T-shirt and the lady's left shoulder are in focus - the rest isn't. It's really that simple. That's down to the geometry of photography, not a lens or camera problem, just mathematics. Unfortunately it's something we need to nderstand to get the best from shots.

I've written two tutorials that might help you - one on DOF and one on using the 50mm f1.8 - which is very similar for this issue to the f1.4.

http://www.zenadsl5251.zen.co.uk/photos/50mm.html
http://www.zenadsl5251.zen.co.uk/photos/doftut.html

Two very simple rules to keep in mind:

[1] To increase DOF; "stop down, step back or zoom out".

The closer to the subject, the longer the focal length and the wider the aperture, the shallower the DOF - you'll improvbe your lot if you can make any adjustments to either/all of those factors, so without changing much - had you moved back 2 feet and gone to f2.8 - you would have increased the DOF to about 10cm.

See this calculator and crunch some numbers to see what effect practical changes might have, so you get a feel for the implications of exposure choices you make: http://www.dofmaster.com/dofjs.html

[2] Some of your DOF extends in front of the point of focus as well as behind - so choose your point of focus carefully.

It doesn't appear to be the case in this instance, but a common problem is that new users generally focus on the foremost point of their subject without realising they're squandering DOF in front of the subject at the expense of not enough within the scene.

In very broad, generalised terms, you have about 40% of the DOF in front of the point of focus and 60% behind, when you're close to the subject - more of it goes behind as you move further away - so for a landscape, 1/3 and 2/3 is perhaps more like it.

In that scene, had you focused on the baby's eyes, you'd have the same problem with not enough DOF, but it would have worked better. Always focus on the main subject's eyes - that's the place your eye goes to and expects to be right. The shot will be percieved as at least sharp if the main subjects eyes are. You've got good sharpness on this otherwise lovely shot, just in the wrong place.

And don't be afraid to up the ISO, on the 20D it's incredibly clean - and any problems you potentially have using higher ISO are far easier to correct than movement blur of lack of DOF. I use 800 and 1600 routinely - I've written another tutorial on that too:

http://www.zenadsl5251.zen.co.uk/photos/highiso.html

Make sure that you don't underexpose, as you've already been advised and If you're shooting JPEG, set some custom Parameters for -2 sharpening - it will help the potential noise enormously - you can sharpen later - preferably just where needed, which is what I do, but you'll start with a cleaner shot. Better still if you work in RAW.

Just to give you an idea of how good the high ISOs are - these are all either 800, 1600 or 3200 ISO. They've not had any noise reduction on them, just handled with care.











--
So many photos, so little time . . .
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Please do not amend and re-post my images unless specifically requested or given permission to do so.

Wow, great information, thanks for taking so much time to help me out.

It is slowly dawning...and the problem is more as I originally suspected, one of blurring due to lack of depth, not a blurring from the outsides inwards (sorry for the completely untechnical attempt at explanation!)

I was just about to ask a pile of questions about the implications of using a wide aperture when a good distance from the subject, but have reconsidered...I'm going to grab my camera tomorrow morning and get out and get some practice! And, re-read those tutorials you sent me. (and the 20d manual for sharpening in camera!)

I really appreciate the help you have all offered, thanks again.

Boo
these r very good examples!
i like ur work very much! as well as the article!

Great explanations ! I've been taking pictures for 30+ years, and totally unuderstand DOF, but somehow never realized that wide open, the margin of error was so small !

carolyn
--
Ranger a.k.a chammett
http://www.pbase.com/chammett

'elegance is simplicity'

sandyoh said:

It is slowly dawning...and the problem is more as I originally
suspected, one of blurring due to lack of depth, not a blurring
from the outsides inwards (sorry for the completely untechnical
attempt at explanation!)

Click to expand...

The area of the image that was sharpest just happened to be pretty much in the centre of the scene, leading you to think it was a circular focus issue. But I think it's really nothing more than insufficient DOF due to the wide aperture and close proximity. Don't forget, a 50mm lens on a 20D sensor is equivalent to 80mm on 35mm, so even less DOF than you might have been used to if you've used film.

sandyoh said:

I was just about to ask a pile of questions about the implications
of using a wide aperture when a good distance from the subject, but
have reconsidered...I'm going to grab my camera tomorrow morning
and get out and get some practice!

Click to expand...

There's no substitue for trying things for yourself and learning that way - but feel free to ask questions here too. Have fun tomorrow.

--
So many photos, so little time . . .
http://www.peekaboo.me.uk - general portfolio & tutorials
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Please do not amend and re-post my images unless specifically requested or given permission to do so.

c.hammett said:

Great explanations ! I've been taking pictures for 30+ years, and
totally unuderstand DOF, but somehow never realized that wide open,
the margin of error was so small !

Click to expand...

It's not usually obvious until it bites you and you find out the hard way. The firgures I quoted were for a very wider aperture and close to the subject.

I often show this example to illustrate the point. Taken wide open with the 50mm, I focused on his eyes and in the time I re-framed and took the shot - as he was laughing, he'd moved from ideal focus - see how the front-most areas of the towel are sharper than his face - just those few mm of movement was enough to prevent it from being properly focused. The geometry was about the same as the OP's, I had about 10-12mm of available DOF.

The same can happen with the photographer if they move while taking the shot, focus can end up somewhere other than the intended place if you wobble a little while framing the shot.



--
So many photos, so little time . . .
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Please do not amend and re-post my images unless specifically requested or given permission to do so.

lionking said:

Boo
these r very good examples!
i like ur work very much! as well as the article!

Click to expand...

--
So many photos, so little time . . .
http://www.peekaboo.me.uk - general portfolio & tutorials
http://www.boo-photos.co.uk - live music portfolio
http://imageevent.com/boophotos/ - most recent images

Please do not amend and re-post my images unless specifically requested or given permission to do so.