using auto focus

lisarhinehart · May 17, 2009

I'm just learning how to use my slr and wanting to learn more about autofocus. My rebel allows me to choose one-shot, AI focus and AI Servo.

I like to use natural light indoors and have trouble with images being out of focus. I have bumped up my ISO, but that cna look grainy and maybe I just have to use a flash with diffuser, but I'm wondering if ajusting these settings would help me at all.

Sometimes one person is in focus and the other isn't, even though they are right next to eachother-- I chose a focal point for one-- figured that they were at the same dof and shut the app a little to get more depth, hoping that woudl help both people to bein focus, but I think my understanding is flawed or my subject moved b/c the person with the focus light on them is in focus and the other is blurred.

Qarik · May 18, 2009

lisarhinehart wrote:

I'm just learning how to use my slr and wanting to learn more about autofocus. My rebel allows me to choose one-shot, AI focus and AI Servo.

I like to use natural light indoors and have trouble with images being out of focus. I have bumped up my ISO, but that cna look grainy and maybe I just have to use a flash with diffuser, but I'm wondering if ajusting these settings would help me at all.

Sometimes one person is in focus and the other isn't, even though they are right next to eachother-- I chose a focal point for one-- figured that they were at the same dof and shut the app a little to get more depth, hoping that woudl help both people to bein focus, but I think my understanding is flawed or my subject moved b/c the person with the focus light on them is in focus and the other is blurred.

Can you post an example and exif data? You understanding is in general correct..if they appear to be in the same plane..closing the aperture should help to keep them both in focus. But it really depends on what your aperture, distance, zoom was.

Dig that shot up and then enter you settings in this DOF calculator:

http://www.dofmaster.com/dofjs.html

lisarhinehart · May 19, 2009

Here are the shots

These

2.

were

3.

all taken at f4, 1/15, and 800 ISO.

Zooming away from the couple slightly was the only adjustment-- yet one of them is always blurred-- maybe they are moving?

Whoever I didn't have the focus dot on was generally out of focus, but I can only choose one point, no?

She is a little bit behind him but that shoudn't have an effect as the people way in the distance are pretty clear.

I'm also surprised at how clear the people are in the background, even with f4-- I tried to go lower, but I'd need to bump it up to 1600 and was worried about picture quality

There is proably somthign obvious that I'm missing... use a flash maybe?

T. Bombadil · May 19, 2009

lisarhinehart wrote:

i suspect she moved. 1/15 is pretty slow to hand-hold, especially if you have zoomed in a bit. it is conceivable (to me, anyway) that there is some camera motion at work here and that the male subject also moved - but in a way that off-set the camera movement (hey, it COULD happen :-)

lisarhinehart wrote:

2.

i think she moved again. notice that her hair could easily move around a lot more with small movements of her head, but his hair won't do that. from what little i can see of the back of her chair, it seems in focus - so i would blame subject movement for this one.

lisarhinehart wrote:

3.
[IMG]http://[/img]

i would say subject movement was the issue here also. this time he moved.

lisarhinehart wrote:

all taken at f4, 1/15, and 800 ISO.

in my opinion, 1/15 of a second is a long time. i wouldn't expect sharp photos of people at that speed.

lisarhinehart wrote:

Whoever I didn't have the focus dot on was generally out of focus, but I can only choose one point, no?

you can only choose one plane, though your camera can likely use more than one point (not sure what that would mean exactly, either that all the selected points are in the same plane, or that the average distance of the chosen points was used. my camera is a nikon, but probably functions in a similar way to yours - anyway, it sometimes chooses multiple focus points)

lisarhinehart wrote:

I'm also surprised at how clear the people are in the background, even with f4-- I tried to go lower, but I'd need to bump it up to 1600 and was worried about picture quality
... use a flash maybe?

most of the "depth" in depth of field is behind the focus point.

a flash would effectively shorten the exposure to the very small fraction of a second that the flash fires. even just a small amount of "fill flash" can help with image sharpness.

Scott McLeod Photo · May 19, 2009

The general rule for handholding shots is to have a minimum of 1/lens focal length. So if you are using a 35-70mm lens and its at 50mm then you should not let you shutter speed go slower than 1/50 of a second or the resulting image will have blur from the slight movement of the camera because you are handholding it. The longer the focal length (say 200mm) the faster shutter needed because the more likely a very slight movement changes whats in the viewfinder. Then with the possibility of people moving you probably want at least 1/90 for that.

Those are pretty good for 1/15 some stuff is sharp.

lisarhinehart · May 19, 2009

shut too slow, focal points, settings
Thanks! Someone at another form actually just told me the 1/lens focal length before I took those shots. My problem was that I was on AV and that is the shut speed the camera chose for me. I'm not really sure how to use manual, if I was, could I choose the same ap and just put the shut speed where I wanted?

As far as focal points, it seems that I have a few to choose form when I'm manually selectingit and it will only let me choose one-- if the camera selected the point it didn't choose his eyes, which was the one I chose.

As a side note, is there a way to clear all your settings when you go from one location to another?

T. Bombadil · May 19, 2009

lisarhinehart wrote:

I'm not really sure how to use manual, if I was, could I choose the same ap and just put the shut speed where I wanted?

you could, but in this case you would have under-exposed :-)
try putting your camera on manual and see what happens. there will be an indicator in the viewfinder telling you what the camera thinks of your exposure setting (over/under/ or good), but the nice thing about manual settings is you can make your own decision about what is the right exposure instead of accepting what the camera's algorithms worked out.

after all is said and done, you still are going to capture one image by exposing the camera sensor to a certain lens opening (aperture) for a certain amount of time (shutter speed). but not everything in the photo is of the same importance - there might be a lot of shadows that you don't care about, so you could choose to ignore them (while the camera's auto modes might take them into consideration), for example.

lisarhinehart wrote:

As far as focal points, it seems that I have a few to choose form when I'm manually selectingit and it will only let me choose one-- if the camera selected the point it didn't choose his eyes, which was the one I chose.

yes, you can only choose one at a time. your camera may have a dynamic focus mode that lets the camera choose more than one (in which case you aren't choosing anything). i honestly don't know what my nikon is doing when multiple focus points light up. it may only mean "i focused on the subject, and these points happened to be exactly in the focus plane."

lisarhinehart wrote:

As a side note, is there a way to clear all your settings when you go from one location to another?

somebody with a canon, or access to the owners manual will have to answer that. there almost certainly is a way to do this.

ziggy53 · May 19, 2009

lisarhinehart wrote:

Thanks! Someone at another form actually just told me the 1/lens focal length before I took those shots. My problem was that I was on AV and that is the shut speed the camera chose for me. I'm not really sure how to use manual, if I was, could I choose the same ap and just put the shut speed where I wanted?

As far as focal points, it seems that I have a few to choose form when I'm manually selectingit and it will only let me choose one-- if the camera selected the point it didn't choose his eyes, which was the one I chose.

As a side note, is there a way to clear all your settings when you go from one location to another?

Lisa,

Use a higher ISO to increase shutter speed at a given aperture. An aperture of f4 is normally where I shoot events as well, so bumping up the ISO until you achieve a shutter speed of around 1/100th is generally a very good idea for people stuff.

I will often shoot events in manual mode with a flash and flash modifier and set the camera at f4 and 125th and then adjust the ISO and FEC to get the perticular combination of ambient light and flash that I want.

Sometimes I use aperture priority mode as well, but I generally only use that in brighter settings when I can use a custom setting to force the camera to x-sync at highest shutter speed to subdue ambient light.

Selecting a particular AF point is something that I do regularly and it does take some practice to work and change quickly between landscape and portrait mode. If you have enough distance to subject(s) then the center focus dot and focus-and-recompose can work fine.

Some cameras do have the ability to rapidly reset all settings but I tend to use my own presets for aperture priority in well-lit places and then my own presets for manual mode in lesser lit locations, and then switch back and forth between those modes as needed.

Qarik · May 19, 2009

The 1st shot was at f/4. Do you know what the zoom and approximate distance was? I will take guess and say 55mm and 6 feet. This translates to a depth of field of around 6 inches using an online DOF calculator. That is cutting it close. Notice she is actually behind him and not in the same plane. So for instance if you hit exact focus on the guys eye for example...you get 3 inches of focus in front and 3 inches of focus behind. That is enough to get the guy himself focus but perhaps not the lady.

Compund this with high iso noise and slow shutter speed.

Again this is the danger of shooting in Av mode and with out a flash. Av mode screwed up you shutter speed. Lack of flash forced you to shoot hi iso and open aperture.

jeffreaux2 · May 19, 2009

ziggy53 wrote:

Lisa,

Use a higher ISO to increase shutter speed at a given aperture. An aperture of f4 is normally where I shoot events as well, so bumping up the ISO until you achieve a shutter speed of around 1/100th is generally a very good idea for people stuff.

I will often shoot events in manual mode with a flash and flash modifier and set the camera at f4 and 125th and then adjust the ISO and FEC to get the perticular combination of ambient light and flash that I want.

Sometimes I use aperture priority mode as well, but I generally only use that in brighter settings when I can use a custom setting to force the camera to x-sync at highest shutter speed to subdue ambient light.

Selecting a particular AF point is something that I do regularly and it does take some practice to work and change quickly between landscape and portrait mode. If you have enough distance to subject(s) then the center focus dot and focus-and-recompose can work fine.

Some cameras do have the ability to rapidly reset all settings but I tend to use my own presets for aperture priority in well-lit places and then my own presets for manual mode in lesser lit locations, and then switch back and forth between those modes as needed.

This is solid...sound advice.

The 1/focal length rule cannot be applied to photography when the subject(s) are living breathing beings that may or may noy move. Instead, you HAVE to anticipate that they might and use a shutter speed fast enough to keep them sharp. Also, I have successfully taken shots...of people...handheld....with a 70-200mm stabilized lens as low as 1/30.....but....THAT is luck my friend.....and my general rule of thumb is to try to get a 1/125 or so shutter speed. Try that and watch how sharp your subject's eyes appear!

For general shots and portraits of people(not sports) I stay in the single shot focus mode and utilize single focus points. I select which focus point to use(enable) according to where my subject falls in my composed frame.

lisarhinehart · May 20, 2009

f4 1/125, dof, focus points
Thanks everyone for your excellent advice. It will take me a while to digest all of it, but I feel like my understanding is really coming together thanks to all of your help.

As far as the f4 and 1/125th ish-- I love knowing that and having some type of starting point. If my understanding is correct, and it is likely that it isn't, those settings working would be completely dependant on the place you are shooting-- indoors outdoors, time of day, etc. no? Was that a suggestion for this photo-- early evening, indoors, dark or in general?

Q- I think you are right about the 6 inches. So would the shutter need to be faster for her not to be blurry? But woudln't she still be blurred as "backgroud" in f4? Should I have adjusted the ap to say f6 or so just so that the dof woudl be correct? The calculator is cool, but I think I don't understand the general concept behind it, so it's not as useful to me as it could be.

I am getting better with the focus points. A lot of this is practice and now that I am doing better with the language and getting all this advice, my manual is starting to make a little more sense to me and I am actualy using more of the features on my camera.

Qarik · May 20, 2009

lisarhinehart wrote:

Thanks everyone for your excellent advice. It will take me a while to digest all of it, but I feel like my understanding is really coming together thanks to all of your help.

As far as the f4 and 1/125th ish-- I love knowing that and having some type of starting point. If my understanding is correct, and it is likely that it isn't, those settings working would be completely dependant on the place you are shooting-- indoors outdoors, time of day, etc. no? Was that a suggestion for this photo-- early evening, indoors, dark or in general?

Q- I think you are right about the 6 inches. So would the shutter need to be faster for her not to be blurry? But woudln't she still be blurred as "backgroud" in f4? Should I have adjusted the ap to say f6 or so just so that the dof woudl be correct? The calculator is cool, but I think I don't understand the general concept behind it, so it's not as useful to me as it could be.

I am getting better with the focus points. A lot of this is practice and now that I am doing better with the language and getting all this advice, my manual is starting to make a little more sense to me and I am actualy using more of the features on my camera.

f/6 would have probably been enough along with 1/50s shutter and iso 200 or so if you had a flash!

T. Bombadil · May 21, 2009

lisarhinehart wrote:

As far as the f4 and 1/125th ish . . . those settings working would be completely dependant on the place you are shooting-- indoors outdoors, time of day, etc. no? Was that a suggestion for this photo-- early evening, indoors, dark or in general?

i won't try to speak for the other advice givers, but i suspect the settings of f/4 at 1/125 were not meant as specific suggestions for that photo. anyway, you are absolutely correct, for f/4 at 1/125 to be the correct exposure depends on the situation.

if you need at least as fast as 1/125 to stop motion (and i agree with that advice), and you need f/4 or smaller (bigger number) aperture for sufficient depth of field (in your situation, yes) then you need enough light (or high enough ISO) to make it work. adding a flash can help.

i think most of us wish for higher ISO (without noise) more often than we wish for lower ISO.

lisarhinehart wrote:

Q- I think you are right about the 6 inches. So would the shutter need to be faster for her not to be blurry? But woudln't she still be blurred as "backgroud" in f4? Should I have adjusted the ap to say f6 or so just so that the dof woudl be correct? . . .

there are a couple different possible causes for her being blurry. sometimes more than one can be happening.
1) Movement. could be subject, camera, or both.
2) Focus. insufficient depth of field or just plain missed the focus (that didn't happen here because you got him in focus).
3) Poor quality (or dirty) lens/filter. (but again, that didn't happen here because you got some of the photo sharp.

Your shutter speed must be fast enough to stop motion from causing lack of sharpness. How fast is fast enough? Depends on what you are shooting (people - 1/125, race cars - 1/16,000?) and it depends on focal length (the more zoomed in you are, the more slight camera movement is a problem. that's why the minimum rule of 1/focal length). Shutter speed does not change depth of field.

The depth of field depends on the aperture you select, and the distance from camera sensor to your subject (what you focused on). Aperture can not stop motion blur.

These things are all tied together by your need for correct exposure (the right amount of light). If you decide that you need a fast shutter speed, then you will have to use a wider aperture (and/or higher ISO, and/or a flash). Alternatively, if you decide that you need a narrower aperture, then you will have to use a slower shutter speed.

Part of the art is making these trade-offs.

using auto focus

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