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Old May 1, 2009, 2:32 PM   #1
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:?:? I have a 5d canon camera and a 50mm lens . I find that when I take pics of a person and keep the camera on auto it throws areas out of focus which is pretty annoying. It's fine to have the background thrown out of focus ,but not the subjects hair. Does anyone have any tips?
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Old May 1, 2009, 2:39 PM   #2
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:? I have a canon 5d slr with a 50 mm lens. When I keep my camera on auto I find that it may throw the subjects hair out of focus. It is pretty annoying. Anyone has any tips?
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Old May 1, 2009, 3:39 PM   #3
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Welcome to the forums.

Your post touches on more than one subject, since it involves issues like Depth of Field for a given aperture, focal length and focus distance; as well as camera specific issues like how the Autofocus settings impact the focus points a camera is going to use by default.

Most 50mm lenses have relatively wide apertures available (for example, f/1.8 or f/1.4).

Aperture works similar to the pupils in your eyes, where you can open up the aperture iris wider to let in more light, or close it down to let in less light. If you let in more light with a wider aperture, you can expose the film or sensor faster. If you let in less light with a smaller opening, it takes longer to expose the film or sensor. Note that aperture is normally expressed as f/stop, which is a ratio between the focal length of the lens and the diameter of the aperture iris. So, smaller values represent a larger iris diameter.

So that the camera can use faster shutter speeds to help reduce blur from camera shake or subject movement, the Autoexposure algorithms are going to lean towards using wider apertures (represented by smaller f/stop numbers) in lower light conditions. In bright light, you may see the exposure algorithms selecting a smaller aperture (represented by a higher f/stop number).

The aperture scale in one stop increments (with larger than f/1 apertures possible but very rare in lenses) goes f/1.0, f/1.4, f/2.0, f/2.8, f/4.0, f/5.6, f/8.0, f/11, f/16, f/22... With each one stop move to a smaller aperture (represented by higher f/stop numbers), you will need shutter speeds twice as long for proper exposure for the same lighting and ISO speed (only half the light gets through compared to a one stop larger aperture).

When you use a wider aperture (smaller f/stop number), you will have a narrower depth of field (the part of the image that is in focus as you get further away from your focus point). That's what you are seeing with your 50mm lens if you let the camera make the decisions, since it's algorithms are going to be weighted towards trying to reduce the amount of blur you'd see, leaning towards using faster shutter speeds if light is low, and if you use smaller apertures (higher f/stop numbers) for greater depth of field, slower shutter speeds would be required for proper exposure, increasing the potential for motion blur or blur from camera shake.

These links may help you understand how aperture (represented as f/stop), ISO Speed (how sensitive the film or sensor is to light) and lighting levels work together to insure proper exposure.

http://www.robert-barrett.com/photo/...alculator.html

http://www.photonhead.com/simcam/shutteraperture.php

You're also touching on Depth of Field. When you use a wider aperture (represented by a smaller f/stop number) or allow the Camera's Autoexposure Algorithms to use a wider aperture, you'll have a shallower depth of field for a given focus distance and focal length.

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

Note that the same concepts apply to both film and digital cameras. So, any good book you can find at your local library about basic photography would probably help you to understand these subjects a bit better.

As for the focus points a camera is using, most of the time, a camera's Auto modes are going to use the closest subject a focus point can lock on. This varies by camera model.

The best way to approach it when Depth of Field is very shallow is to use a mode that allows you to select the focus point (versus letting the camera decide the focus point to use).

So, Auto modes are going to have limitations, especially if you are using brighter lenses with wider available apertures. The camera needs more input from you on how you want it to behave (and you'll see the same types of issues with virtually any dSLR using a brighter lens if you keep the camera on Auto).

My preferred way of using a camera with a brighter lens is to go with Aperture Priority (so that I'm deciding how wide of an aperture to use in a given lighting, keeping shutter speeds in mind to reduce the potential for blur from subject movement if shooting non-stationary subjects). I usually prefer to select my own Focus Point, too (versus letting the camera decide on focus point, which could be something closer or further away than my intended subject).

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Old May 1, 2009, 3:43 PM   #4
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The Canon "nifty-fifty" is an f1.8 lens. Great little lens at sensational price.

IDEA #1

You should use a higher fstop and shoot from a bit farther away.

The blurring is caused by the depth of field is to narrow. My guess is you're not a seasoned veteran of photography. So you should wait on others to comment. But here's what I think I know, and I'll put it in non-photo speak.

Depth of Field means: At what distance are objects in focus. For example, your camera, when set at an fstop of 1.8 and you're 10 feet away from the object you're photographing, then everything 10 feet away plus or minus 8 inches is in focus. Eveything else gets blurry.


However, if you keep that same lens on your camera, and manually change the cameras settings to an fstop of 4.0, then everything 10 feet away plus or minus 18 inches is now in focus. By changing the fstop, you picked 20 additional inches of focus (10 in front of the object and ten in back of the object).


It's the combination of the low fstop (numerically low) and the distance between you and the object. I think if you change your fstop to 4.0 or 5.6, you're problem will be resolved.

Also, it might help if you could tell us the exif information on the photo. Exif is all the data you find if you load the photo on to your computer and then right click on the photo and click on Properties. If you're using a Mac, these instructions are worthless. You'll need someone who speaks Mac-ese.

IDEA #2

out of focus hair may be because either the hair was moving and you need to shoot at a much faster speed .

IDEA #3

Your hands were a bit shaky and you need a tripod with a time delayed shutter.

(hey, if this is bad advice, speak up quick before Photo Flyer screws this thing up. This is my first attemt at helping someone else!!)



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Old May 1, 2009, 3:53 PM   #5
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I noticed that you started more than one thread with the same questions.

The best place for your thread is probably our Canon EOS dSLR Forum, where members can answer questions about specific focus mode behavior if I'm not being clear enough about the limitations you may see letting the camera decide focus point in it's Auto modes. So, I'll move this thread there for you.

If this is your first dSLR, it will take time for you to be accustomed to it's behavior, especially if you're coming from a digital point and shoot model that has dramatically greater depth of field for the same subject framing and aperture settings. The larger the film or sensor size, the shallower your depth of field is going to be for a given subject framing and aperture setting, and a dSLR model has a much larger sensor compared to a point and shoot model.
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Old May 1, 2009, 3:57 PM   #6
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Note that I've merged the two threads you started into one thread in our Canon EOS dSLR Forum. That way, any responses to your questions will be in the same place.


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Old May 1, 2009, 4:03 PM   #7
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To change the depth of field, you have to take the camera off full auto.

(It scared me to death the first time I did this. It was like the day your dad takes the training wheels off your bike)

Turn the dial on the top of your camera to AV

Turn your camera on and look at the video display on the camera. Turn the big disk on the back of your camera until you see AV 4.0 or 5.6.

Welcome to photography.

A friend of mine said going off full auto is more like the difference between driving an autocatic transmission vs. a stick. If you don't know how to drive a stick, then all you learned in driver's education was how to steer. If you know how to handle a stick, then you can do more than steer, you can drive....


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Old May 1, 2009, 4:06 PM   #8
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Jim, your lessons on me appear to not be a total waste.

I tried to help Photo Flyer and I appear to have given him the same advice you gave him. However, I wrote my advice BEFORE I saw what you had written.

It seems you're getting thru to me!

If a photo is worth a million words, then thank you 1 million times.
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Old May 1, 2009, 4:18 PM   #9
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Thanks. But, I don't know about all that. I think I'm a probably bit too "wordy" with my responses.

Your response is easier for someone new to a dSLR to grasp (i.e., learning to set the aperture to something else without needing to know as many tiny details about why they'd want to do it that way). :-)

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Old May 2, 2009, 11:25 PM   #10
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Thank you for taking the time to answer me. I read up on photography , but never understood the concept of depth of field. How do I know exactly the distance between me and the subject each time and how do I know the exact depth of field that will stay in focus at a given aperture? Sounds complicating. Is there some sort of depth of field guide?
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