Focus on the eyes?!?!

[SandeeWig]

I have a new Canon XSi and am need of some good focusing techniques. So far - in the six days I've owned it - I'm not particularly pleased with the 9-point autofocus. I've played with using the center autofocus point, focusing on my subject, then recomposing and that seems to work okay. I've played with manually focusing also, and that's ok too. Primarily I've been in Tv or Av mode due to dim lighting/indoor shots.

But what do you use?!

What methods or tricks are there if, for example, I'm taking a portrait of someone and I want her eyes nice and sharp? Is auto or manual focus better?

And if there's two people in the picture, how can I be sure to get both of their eyes sharply focused?

Also, is there a way to "zoom" in to your focal point w/o actually zooming? That probably makes no sense, but I thought I read in my manual somewhere that you could zoom in to focus and then recompose your shot before taking it...how does that work?!

Sorry to sound like a dufus but would appreciate any and all input. I do have my manual and plan to look it over again tonite, but figured it would also be to my advantage to have it explained by those who actually do it.

Thanks so much!!

[lputman]

I do use auto focus but I manually select my focus point that I want to use, this way, especially for the eyes, I pick the focus point that is over the eye. I have an XTi, and I think it the same for the XSi, but you can't choose multiple focus points in manual.

I don't know about the zooming thing.

[daft_biker]

Originally Posted by lputman

I do use auto focus but I manually select my focus point that I want to use, this way, especially for the eyes, I pick the focus point that is over the eye. I have an XTi, and I think it the same for the XSi, but you can't choose multiple focus points in manual.

I don't know about the zooming thing.

I think that's good advice....and have not long finished typing the same sort of thing in another thread:

Clicky

Great minds and all that

[SandeeWig]

Thank you lputman and daft_biker for your replies; also thanks for the link to the other thread, it was quite helpful.

Actually, daft_biker, I posed a question to you based on your response there.

I guess focusing at center point and recomposing the shot is one of my problems. Another is most likely trying to use a wide aperture when it's not necessary or where it creates too narrow dof for the shot.

Still workin out the kinks...

[jdepould]

If I'm doing portraits or studio work, I usually use live view with manual focus. I zoom way in to whatever I want sharp (on the live view, not the lens), focus, then shoot.

[SandeeWig]

Originally Posted by jdepould

If I'm doing portraits or studio work, I usually use live view with manual focus. I zoom way in to whatever I want sharp (on the live view, not the lens), focus, then shoot.

Ah-HA! That's what it is!!!

OK. So I haven't played much w/ the live view yet, but this has to be what I was reading about but did not get at the time (mind you, I was reading my manual in the car via crappy flashlight ).

I just now got my camera out and tried it and this works great. I had stayed out of live view over the holiday cuz it eats battery life so much, but this will be great for portraits and narrow dof.

THANK YOU SO MUCH!

[Mr Guy]

Originally Posted by SandeeWig

Thank you lputman and daft_biker for your replies; also thanks for the link to the other thread, it was quite helpful.

Actually, daft_biker, I posed a question to you based on your response there.

I guess focusing at center point and recomposing the shot is one of my problems. Another is most likely trying to use a wide aperture when it's not necessary or where it creates too narrow dof for the shot.

Still workin out the kinks...

It is important to remember that focusing and recomposing is only going to cause problems with a very narrow depth of field. It's just basic maths at work. Think of it as a right triangle. If you compose your shot 5 feet from your subject, then move your point of focus 2 feet away, you've potentially changed your distance by a little under six inches. At 5 feet, 1.8 aperture that matters, because that six inch difference is greater than your depth of field. However, at 8 feet, it matters much less, because moving the focal point two feet changes your focal distance by only 3 inches while your depth of field is much larger than that.

It's all a game of numbers, but I'd still love tips on how people focus on the eyes perfectly without using the focus indicators. It's just against my nature to let absolute statements like that go without pointing out they really need to be qualified.

[Mr Guy]

And actually, after thinking about it more, I'm not sure it's possible for that to be the case. Granted, it's late, and I've taken some cold medicine and a sleeping pill because I've been sick.

However, think of it this way. You set your focus to be a certain distance to the subject's eyes. Pivoting the camera creates an arc of focal range exactly that distance. Assuming the pivot point remains the same (ie, you don't actually MOVE the camera's sensor, at all), the eyes will ALWAYS remain on that arc while you pivot the camera, because they will always be that exact distance away. I was wrong before thinking of the two distances as a right triangle, when you will in fact always be creating an equilateral one as you traverse the arc.

If you actually could rotate the camera perfectly around the sensor, the depth of field would actually be a three dimensional perfect sphere. As long as you don't move the sensor and merely pivot it, the eyes will remain perfectly in focus. Therefore, the real answer, I believe, is that the eyes will remain perfectly in focus as long as the ERROR in your rotation of the sensor remains within the depth of field.

[SandeeWig]

Originally Posted by Mr Guy

...Therefore, the real answer, I believe, is that the eyes will remain perfectly in focus as long as the ERROR in your rotation of the sensor remains within the depth of field.

Mr. Guy, thanks so much for taking the time to respond and provide so much information. I really need to read and wrap my brain around how depth of field is calculated so I know how to adjust for different apertures and focal lengths.

That said, I did understand the quote above, and in the end, maybe that was the most significant piece, given the cold medicine and sleeping pills!

Hope you feel better.

[dhart]

Don't have a Canon, but what I do on my Nikon is choose a specific autofocus point in the viewfinder. If I am taking a photo of a landscape or a moving target, I will choose the one in the center. If I am taking a portrait I will choose a focus point on the right or left. I choose the one on the right more often so when I turn the camera sideways, the focus point is just about where I want their eyes to be anyways. And when I am in landscape orientation, an offcenter focus point gives me the option of keeping my subject out of dead center and has actually helped my framing a lot! I just made this change (from center focus point to off-center) and it's been really amazing.