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  #21    Top
Old March 8th, 2009, 09:30 PM
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RogersDA RogersDA is offline
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Re: Early Spring Blossom

Quote:
Originally Posted by SFnativeGal View Post
To make sure I understand, if I can't get an autofocus to latch onto a point of focus, that means there is too much in the frame to focus on? But, then, could I switch from the center focus to the five point focus? Or would that make it worse?
There are, in general, three reasons for not being able to autofocus:

1) The subject is too close to the lens.
All lenses have a minimum working distance - the minimum distance the object's focus point must be away from the lens to obtain focus. If this point is closer then the lens will not autofocus on that spot using whatever focus point is selected. Longer lenses will have a larger minimum working distance.

2) There is not enough contrast to autofocus.
most digital cameras use some form of horizontal and/or vertical contrast changes to determine focus. If there is not enough then autofocus will fail for whatever focus point is selected.

3) The widest aperture for the lens is greater than f/5.6.
Canon cameras need to have an aperture of f/5.6 or wider to allow autofocus. This is done to let in enough light to the sensor for enabling the contrast comparison in item 1 above. In modern lens you can set a small aperture (say f/22) for taking the picture, but the camera will open the aperture to at least f/5.6 for autofocusing purposes. You will never see this happening. If your lens can't allow the camera to open the aperture to f/5.6 then autfocus will not work. I do not know what the requirements are for other camera systems.
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Last edited by RogersDA; March 8th, 2009 at 09:41 PM.
  #22    Top
Old March 8th, 2009, 09:49 PM
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SFnativeGal SFnativeGal is offline
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Re: Early Spring Blossom

I just checked the data on one of the shots that wouldn't focus... it shows an f/20. Maybe I should submit the photo which is blurred and you can see what the subject matter was. It was a practice shot. I thought I could capture some tiny, white, wild flowers amongst some foliage.

It's totally out of focus. I couldn't bring it into focus. f/20.0 3.2 400 ISO

Is there any other data you need? If I had had a point and shoot it would have taken.... I know not the most wonderful photo, but again, I was practicing.

the second one was a bit better... not knowing why. and the last one...okay.. same time of day, same location.

Can you tell what I'm up against?
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  #23    Top
Old March 8th, 2009, 09:58 PM
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Re: Early Spring Blossom

f/20 - that's your biggest problem (or smallest since we are talking about apertures).

Set your XTi to Av (aperture priority) mode on the dial. You camera will attempt to get a proper exposure for whatever ISO and aperture you set.

For now, leave the ISO at ISO400. Set the camera for the widest aperture you can for whatever lens you have attached. If it is your 200-200 then set the focal distance to 200mm so you can get the f/5. Aim the camera at the flower and see what shutter speed you are getting. It should be about 1/80 sec. or faster.

Your setting show that you are taking a photo whose exposure is 3.2 seconds. WAAAAAAAYYY to long.
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  #24    Top
Old March 8th, 2009, 10:04 PM
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Re: Early Spring Blossom

I will say this, too: In all my life I have never, never, never used the "Pic" modes for shooting on a dSLR (except for the occasional play).

When I started shooting with the dSLR I shot 90% Av mode, and 10% manual.

Now I shoot 90% manual, and 10% Av. Occasionally I will shoot Tv (shutter priority) but not often.

Learning on Av - where the camera tries to set a good exposure based on your aperture setting is a good way to get a feel for what is happening. In Av try to keep the aperture wide (f/2.8-f/5.6) for learning. When you have a still subject, and a good tripod or other stable surface to make sure your camera does not move then f/22 can be a good experiment for learning.

For now - let's keep it simple: Av mode and wide apertures.
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  #25    Top
Old March 8th, 2009, 10:12 PM
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Re: Early Spring Blossom

You mean by Pic modes... the jpeg ones..... below the more sophisticated 'upper' ones? Like landscape, sports etc?? I think that's what you mean. I agree except when I'm in a total pinch and don't know what else to do. But, not often. I started in AV and then a friend who has a scanning back said to go totally manual, so I did that for the longest time... until yesterday when I bought the lens and the guy who sold it to me said to go back to AV.

I've learned more in manual.... but maybe missed some stuff too. And, with a new lens... it's back to square one. BUT! I love it! Just as long as I learn.

the last shot, which came out pretty good... not one I'd keep, though, was in AV. I don't know why it was better than the other one. It was set at. f/20.0 1/13 (what is the '1/13'? Maybe because I had more light, it came out better?

if I don't ask dumb questions I won't learn.
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  #26    Top
Old March 8th, 2009, 10:28 PM
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squirl033 squirl033 is offline
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Re: Early Spring Blossom

David beat me to it, Kathy... you should never need to shoot at f/20. stopping down that far doesn't gain you anything, unless you're really trying to slow the shutter for some reason (and there are valid reasons, but that's another story). actually, the best range for clarity and sharpness with most lenses is between f/8 and f/16. in shade, like you were shooting here, opening up to a wider aperture would be necessary to get a decent shutter speed. you might also have to increase the ISO to 640 or even 800 to help things along.

like David suggested, i would set the camera to Av mode, back the lens off to 200mm, and see what exposure you get. your lens is not stabilized, so at 200mm, unless you're on a tripod, you'll need a minimum of 1/250 or faster to avoid blurring due to camera shake. as you zoom in more, the shutter speed needs to go up as well, to compensate. there's an old rule of thumb from before stabilized lenses that says your shutter speed should always be at least the reciprocal of your focal length to avoid blur when shooting freehand. that means at 200mm, you need at least 1/200 second; at 500mm, you need at least 1/500 second, and so on. of course, if you're shooting from a tripod, especially with a remote release, those rules don't apply, but they're good to keep in mind anyway.

also remember, as i mentioned, that lens has a minimum focus distance of 8 feet. any closer, and it won't give you a clear shot, and might not focus at all.
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  #27    Top
Old March 8th, 2009, 10:34 PM
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Re: Early Spring Blossom

Quote:
what is the '1/13'?
That's the shutter speed for the image taken - One Thirteenth of a second in this case.
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  #28    Top
Old March 8th, 2009, 10:34 PM
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Re: Early Spring Blossom

Quote:
Originally Posted by SFnativeGal View Post
You mean by Pic modes... the jpeg ones..... below the more sophisticated 'upper' ones? Like landscape, sports etc?? I think that's what you mean. I agree except when I'm in a total pinch and don't know what else to do. But, not often. I started in AV and then a friend who has a scanning back said to go totally manual, so I did that for the longest time... until yesterday when I bought the lens and the guy who sold it to me said to go back to AV.

I've learned more in manual.... but maybe missed some stuff too. And, with a new lens... it's back to square one. BUT! I love it! Just as long as I learn.

the last shot, which came out pretty good... not one I'd keep, though, was in AV. I don't know why it was better than the other one. It was set at. f/20.0 1/13 (what is the '1/13'? Maybe because I had more light, it came out better?

if I don't ask dumb questions I won't learn.
Kathy, 1/13 was the shutter speed. still way too slow unless you're on a tripod, but a lot better than 3.2 seconds! if you got 1/13 at f/20, back off to maximum aperture and see what you get. i would guess at f/8, you'd be somewhere around 1/80 to 1/100. still a bit slow for that lens, but from a tripod, it'd be okay. try a few shots at the widest aperture setting, then stop the lens down one stop at a time and take some shots, and note the results. but there's no need to ever go smaller than f/16 or maybe f/18 for most purposes - all that does is slow down your shutter unnecessarily.
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  #29    Top
Old March 8th, 2009, 10:35 PM
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Re: Early Spring Blossom

David, you're too quick for me!
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  #30    Top
Old March 8th, 2009, 10:39 PM
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Re: Early Spring Blossom

Sorry. I'll go slower next time.

Darn - that was a good pun.
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