Depth of field on Canon 18-200 IS

Newbie question here. I have a 40D with a Canon 18-200 IS. I want to be able to zoom in at 200MM, while setting the F stop that gives me the greatest amount of detail in case I want to crop the photo. I'm talking about outdoor shots, with plenty of sunlight. Would I need to set my f stop closer to 5.6, or go higher to around f16? Or is there a "sweet spot" with this lens for accomplishing this?

If what you want is MORE in Focus you use a smaller Aperture ( Bigger Number ) i.e. f 16 VS f5.6 .


I also suggest that you browse the stickies on here .


David

f 16 is a bit extreme. Maybe try f8 and see how i goes =)

themadman wrote in post #9483736
f 16 is a bit extreme. Maybe try f8 and see how i goes =)

Sorry I just used f16 as an example .

That's kind of what worries me then. I tried taking some test shots of the same subject at 200MM, started out at f5.6, then another at f10, then f16. After zooming in on the shots, I noticed that the subject got blurrier as the aperture got smaller. The shot at f5.6 was much sharper than the one at f10.
Does this mean that I have a bad copy of this lens, or there's a problem with my 40D?

In theory most lenses are sharpest 1-2 stops down until about f10 or 11 where diffraction starts softening the image again. Since this is an f5.6 lens, 2 stops down is f11, so you are probably going to want to stick to somewhere around f8. Although if you need f5.6 to maintain the proper shutter speed, that will help sharpness more than anything else.

looking at this review, f8 @ 200mm is the sharpest aperture.
http://www.slrgear.com …t.php/product/1​219/cat/11

eaglefan wrote in post #9483774
That's kind of what worries me then. I tried taking some test shots of the same subject at 200MM, started out at f5.6, then another at f10, then f16. After zooming in on the shots, I noticed that the subject got blurrier as the aperture got smaller. The shot at f5.6 was much sharper than the one at f10.
Does this mean that I have a bad copy of this lens, or there's a problem with my 40D?

What mode / Shutter Speeds were you shooting at ?


David

I was shooting in AV mode, and had ISO set to 100.

eaglefan wrote in post #9483774
That's kind of what worries me then. I tried taking some test shots of the same subject at 200MM, started out at f5.6, then another at f10, then f16. After zooming in on the shots, I noticed that the subject got blurrier as the aperture got smaller. The shot at f5.6 was much sharper than the one at f10.
Does this mean that I have a bad copy of this lens, or there's a problem with my 40D?

As the aperture gets smaller, the shutter speed will almost invariably decrease to compensate for the change in exposure, meaning that any subject or camera motion during exposure becomes more visible in the image, blurring it. IS is great, but it is not magic. At 200 mm, on an APS-C body, with IS, you probably need to have a shutter speed of 1/40 s or faster to avoid camera shake being a problem, but that may not be quick enough to freeze subject movement.

eaglefan wrote in post #9483916
I was shooting in AV mode, and had ISO set to 100.

Therefore the Camera chose the Shutter speeds , it may have dropped below hand holding capabilities .


David

eaglefan wrote in post #9483774
That's kind of what worries me then. I tried taking some test shots of the same subject at 200MM, started out at f5.6, then another at f10, then f16. After zooming in on the shots, I noticed that the subject got blurrier as the aperture got smaller. The shot at f5.6 was much sharper than the one at f10.
Does this mean that I have a bad copy of this lens, or there's a problem with my 40D?

You see f5.6 lets in over twice as much light as f8 and f8 lets in close to twice as much light as f10 (it lets in twice as much as f11). So each time you make the aperture smaller, the camera (trying to give you a well exposed image) lowers the shutter speed. When the shutter speed gets sufficiently slow, small hand movements will cause the photo to look unclear or blurry.

Thanks for everyone's help. I think that the shutter speed did drop below hand holding capabilities. I'm still learning the in's and out's of photography

We all did at some point... we still are learning

eaglefan wrote in post #9483973
Thanks for everyone's help. I think that the shutter speed did drop below hand holding capabilities. I'm still learning the in's and out's of photography

Not a problem , Keep shooting .

David

The distance from your subject is also important when working out how much dof you will have in a shot. If your shooting a landscape, mountains in the distance sort of thing, the 5.6 will give plenty of dof, but shoot a toy on a coffee table 3 feet away and 5.6 will give a very narrow depth of field.

So think about what your shooting to determine what f stop you need to achieve what you want in the shot, then consider you have the right shutter speed to stop camera shake spoiling the shot for static subjects.

For moving subjects think about what shutter speed is needed to freeze the action to get a sharp shot and choose f stop and/or iso to help get whatever background effect you want.