Focus and re-compose advice

[ajax_andy]

I'm looking to inprove the sharpness in the eyes of my pics and have always shot using the multi matrix thing where it selects loads of different points of focus.

I'm looking at single point focussing and understand the centre spot is the strongest in terms of focussing. I came across a tutorial on "Focus & Re-compose" and am I right in thinking that if I set the focus to the single centre spot point, point this at the eyes, focus on them with it, then keep the shutter half depressed, then re-compose the image that it'll keep the focus on the eyes even though the centre spot is now pointing somewhere completely different?

[RichardTaylor]

That's correct, providing your subject distance doesn't change.

[ajax_andy]

Originally Posted by RichardTaylor

That's correct, providing your subject distance doesn't change.

Great thanks for confirming that... I've finally upgrade from my kit lens to a 50mm prime, so hopefully with that and the focussing technique I should be getting some excellent sharp results

[Doug Sundseth]

Richard Taylor's statement is correct as far as it goes. But understand that when you turn your camera, you're quite likely to change the camera-to-subject distance, even if only slightly. When using a very small depth of field like that afforded by a fast 50 wide open, this distance change can be enough to unsharpen the eyes.

Try it, but also try moving your single focus point to one that allows you to focus on the subject while the photo is framed as you want to shoot it and see which gives you better results.

HTH

[ajax_andy]

Originally Posted by Doug Sundseth

Richard Taylor's statement is correct as far as it goes. But understand that when you turn your camera, you're quite likely to change the camera-to-subject distance, even if only slightly. When using a very small depth of field like that afforded by a fast 50 wide open, this distance change can be enough to unsharpen the eyes.

Try it, but also try moving your single focus point to one that allows you to focus on the subject while the photo is framed as you want to shoot it and see which gives you better results.

HTH

Thanks for the info Doug

I'll bare what you said in mind, and if it's more than just an ever so slight re-compose (maybe moving more than a millimeter or two) i'll use the closest focus spot instead of the centre one.

[ajax_andy]

I had a quick go with the 50mm prime last night and took a couple of snaps of the dog with the aperture wide open. I just used auto focus as was just messing around and the pic looked amazingly sharp in the viewfinder.

However when I put it on the PC I noticed that I'd focussed on the end of the dogs nose, and the eyes weren't sharp at all. It would seem that using a lens like this you have to be very accurate due to the very shallow depth of field... so I think I'll need to practice lots on getting the focus just right as it's much less forgiving that the kit zoom lens.

It's going to make things harder but will make me a much better photographer using this lens so i'm very excitied about using it properly for portraiture shots

[RichardTaylor]

You may find this thread of interest.

DOF Notes:1 - Head shots using a 50mm lens.

[ajax_andy]

Hi Richard,

Thank you for the link... I was just about to search for tips on shooting with a wide aperture for portraiture

So it would look to me that when shooting head shots that anything below f2.8 will be too soft on the rest of the face, and anything above f/4 will be lovely and sharp, but also start to incorporate a little too much detail in the background? So shooting between f/2.8 & f/4 would be the ideal aperture for shooting head shots?

What about full body shots? I usually work on the principle that if you are including most or all of the body then it's usually to work with an interesting backdrop or location anyway, so shooting between f/7 and f/11 would be enough to get the whole body in sharp focus?

Sorry if these seem like basic questions but this is my first venture in to prime lenses.

[ajax_andy]

Looking at that DOF calculator it would also suggest that the wider the aperture the closer you need to be to your subject I believe too. Is that correct?

If so I'm shooting with a Canon 450d which isn't a full frame camera, so i'd image i'd need to take a step back from the composition I see in the viewfinder to make up for the crop that will happen once the photo is taken. So would it be best to also take a step back on the aperture too to make up for the slightly further distance between myself and the subject?

[RichardTaylor]

It all depends on what you are trying to achieve.

Have you seen this thread?
DOF Notes:2 - Blurring backgrounds with shots of multiple people


and this one.
Exposure (3): Aperture

Re the Canon 50mm F1.8 - keep in mind it is not real sharp, let alone having a super shallow DOF, when used wider than F2.8.

It really isn't much difference, photographically, in using primes or zooms except that the prime may be faster. I use both.

The DOF is controlled by the focal length and the shooting distance (as well as the viewing distance and final image size).
The appearance of the background will depend on the distance the background is away from the subject.
Changing the sensor size, if the subject distance is the same, doesn't change the DOF
However if you change the shooting distance, with a different sized sensor body, so that the subject size is the same then the DOF will change.

If I am using a good lens I have no problems using it wide open, even at F2, to kill the background.

(1) In a city street

Camera Canon EOS 40D + CVanon 135mm F2 L lens
Exposure 0.001 sec (1/1600)
Aperture f/2.0
Focal Length 135 mm
ISO Speed 100
Exposure Bias -2/3 EV
Flash Off, Did not fire

(2) Same lens & body again at F2


Re including the backgrounds. F8-11 makes for a good starting point (focal length dependant)
Have a look at some of the examples in this post where I was using wide angle lenses at smaller apertures..

Lenses #4 - Wide angle.

(3) This is F7.1 and 73mm


Camera Canon EOS 5D
Exposure 0.003 sec (1/320)
Aperture f/7.1
Focal Length 73 mm
ISO Speed 800
Exposure Bias -2/3 EV
Flash Off, Did not fire

Sometimes you may want to give a feel of a background.

(4) Here I was just sitting on the other side of the relatively small table

Camera Canon EOS 5D
Exposure 0.025 sec (1/40)
Aperture f/4
Focal Length 24 mm
ISO Speed 1600
Exposure Bias -2/3 EV
Flash Flash did not fire

Keep in mind the shooting conditions, especially lighting, may determine the aperture you can use. It just means you take a different style of photograph.

I sometimes shoot wide open at longer distances, especially in low light, if need be.