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Old Oct 29, 2008, 1:30 AM   #1
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I'm new to DSLR. I'm using the default lens (Canon EFS 18-55 mm) which came along with Canon XTi.

I would like to know what setting I should use when I want my picture to be full frame focus i.e. focus everything in the snapshot, not just a single 9-AF points.

Thanks,
Rama.
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Old Oct 29, 2008, 5:56 AM   #2
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Getting EVERYTHING in the frame in focus may be difficult depending on how far away EVERYTHING is from your position. Do a google on depth of field (DOF) and read up a little. If the frame has subjects of greatly varying distance from you it may be tough to get them all in focus. If everything is the same distance it's not an issue.

It might help to understand what it is your trying to take a picture of.
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Old Oct 29, 2008, 9:18 AM   #3
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Thanks for the response.

If I've 3 people in my frame and they are around 5m in distance what best setting should I go with so that I get a clear picture.

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Old Oct 29, 2008, 9:27 AM   #4
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ramkip wrote:
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Thanks for the response.

If I've 3 people in my frame and they are around 5m in distance what best setting should I go with so that I get a clear picture.
OK, first the long answer - the 'teach the person to fish' part:

depth of field refers to how much in front of and behind the point of focus will actually be in focus.

Depth of field for your camera is controlled by several factors:

1. Physical focal length of lens (not 35mm equivelant)

2. Aperture value used

3. Distance to subject

You've got the answer to question 3 - > 5 meters. What you're likely wanting to know is what value to use for #2. But, there is still a variable at play - #1 - what focal length. The focal length used will depend on the type of shot - just the heads of the 3 people, torsos or full body. If your distance remains the same you would use 3 different focal lengths to achieve those 3 different types of shots. Consequently the aperture value needed to get all 3 in focus may be different. It would probably range between f4 and f8 depending on the type of shot.

here is a dof calculator you can play around with:

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

Now the short answer - assuming the 3 people are standing together and not half a meter behind one another, if you use an aperture of f8 and focus on the person in the middle you should have all 3 in focus for full body or even half body.


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Old Oct 29, 2008, 11:20 AM   #5
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Thanks John, I'm pretty much a newb and your answer taught me something... its a good way to start the day
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Old Oct 29, 2008, 11:45 AM   #6
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BTW, your Canon XTi has a mode known as A-DEP (Automatic Depth of Field). Check your manual for more details. This mode is designed to compute the needed aperture to maximize depth of field by computing it based on the subjects closer and further away from the camera that you want to be in focus.

When changing apertures for more depth of field, just keep in mind that smaller apertures (higher f/stop numbers) require slower shutter speeds for proper exposure. So, you may end up with more blur from camera shake or blur from subject movement if you're not careful with aperture settings, depending on lighting and ISO speed.


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Old Oct 29, 2008, 12:43 PM   #7
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Thank you very much for the Long and Short Answers. Will certainly work on the points which you have suggested.

As 'JimC' pointed out, when taking snaps on Aperture Priority some of the images are blurred when the fstop number is high since the shutter speed is pretty low. For ex : F-Number : F/6.3 , Exposure Time : 1/6 sec , Focal Length : 18 mm : resulting image is bit blurred.

I've not yet explored on A-Dept, will look into the manual.
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Old Oct 29, 2008, 12:49 PM   #8
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ramkip wrote:
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For ex : F-Number : F/6.3 , Exposure Time : 1/6 sec , Focal Length : 18 mm : resulting image is bit blurred.
Those settings tell me you're either using too low of an ISO value (i.e. using iso 100 when you should be using 800) OR you should be using a flash. And, truth be told even upping the ISO probably isn't enough for those light levels (assuming you were at ISO 100, going up to 800 would only increase shutter to 1/50 - borderline shutter speed for non-flash photos of people who have a tendancy to move). At those light levels you should be using a flash.
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Old Oct 29, 2008, 2:04 PM   #9
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ISO used for that snap was 400, but not 800 as you mentioned with pop up flash (not external).

Thanks for your inputs, it will certainly help me alot.
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Old Oct 29, 2008, 2:10 PM   #10
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ramkip wrote:
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ISO used for that snap was 400, but not 800 as you mentioned with pop up flash (not external).

Thanks for your inputs, it will certainly help me alot.
A couple additional remarks then. First of all, 5 meters is probably the limit of the built in flash. BUT, I would also find it odd the camera would select 1/6 shutter in either P or Auto mode. I would only expect a shutter speed that low if you were using AV mode. In which case the solution is to use manual exposure - set for 1/60 f8 ISO 400. Any further away though and the built in flash isn't going to be of much use.
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