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02/15/2006 07:35:00 PM · #1 |
| hi, this may be a stupid question, but i just can't figure it our or perhaps missed it while i was reading the manual or tutorials. i wanted to shoot a picture of a rose on a table with long shutter and small aperture using autofocus. does it matter which of the 9 af points i select? i wanted to select the petal or center of the rose, but it comes our blurry. it is not sharp and there is very little contrast between the petals. just generally, if i want a picture with everything in focus, i can select a small aperture (say f18), shouldn't that keeps everything sharp and in focus? do i need to select any of the 9 af points on the camera? it comes up when i press the shutter halfway down. i'd appreciate your response. it would definitely help me in the future if i do practice taking landscape photos. thanks! |
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02/15/2006 07:40:38 PM · #2 |
shoot it at like f/8 from a decent distance...you need a tripod when working with slower shutter speeds if the lighting isn't super bright.
To get a whole leaf in focus you only need a depth of field of like 6 inches or so (less if it's a smaller leaf, I picture a rather big leaf for some reason)...good luck.
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02/15/2006 07:41:04 PM · #3 |
It would help to know what shutter speed the camera is giving you to match that small aperture. Your problem may be as simple as too long a shutter speed if you are hand-holding this shot.
Otherwise, as a general rule-of-thumb, your DOF extends 1/3 in front of the point of focus and 2/3 behind it. If you were shooting an oblique shot of 6-inch ruler that filled the frame, you'd want to be focused on the 2-inch mark, so if you actually HAD 6 inches of DOF available, it would extend from 0 inches to 6 inches; 2 inches in front of the mark and 4 inches behind it.
So, to answer your question, choose the autofocus point that corresponds with the protion of the object that's 1/3 of the way into the image, if that makes sense. This would most likely be the bottom-center AF point for the majority of your compositions, though obviouslky that's not true if the subject is tilted away from you at a diagonal.
R.
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02/15/2006 07:48:46 PM · #4 |
I can't remember where I read this, but I believe you have diminishing returns on the f/stop-DOF versus overall sharpness.
For example, a pin-hole camera has everything in focus, but nothing is sharp.
So, as an experiment, take some shots at f/18 and then f/13, f/11, f/8, etc and see which is giving you the sharpest results. |
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02/15/2006 07:57:29 PM · #5 |
Originally posted by dwterry:
I can't remember where I read this, but I believe you have diminishing returns on the f/stop-DOF versus overall sharpness.
For example, a pin-hole camera has everything in focus, but nothing is sharp.
So, as an experiment, take some shots at f/18 and then f/13, f/11, f/8, etc and see which is giving you the sharpest results. |
This is correcxt; it's called Circle of Confusion (COF); when an aperture gets smaller than a certain physical size, light rays start refracting off the sides of the aperture itself and acuity is lost. It's not a matter of f/stop, because f/stop is a ratio between size of aperture and focallength of lens (f/22 on a 200mm lens is a larger hole than f/22 on a 15mm lens).
This is why the point-and-shoot cams, with their tiny sensors and very short focal lengths, don't even HAVE apertures smaller than f/11 usually; any smaller and things get soft.
R.
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02/15/2006 08:10:39 PM · #6 |
| Right on, Robt. And to make matters worse, the CoC for a digital camera cannot be smaller than the pixel size, regardless of lens quality (though not directly related). The pinhole analogy is a good one, typically f/250 and very soft perfectly focused images. |
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02/15/2006 08:26:46 PM · #7 |
thanks for your quick reply bear_music, dwterry, & deapee. i'll give it a shot. shooting at 8s under low light condition with a tripod. i wasn't sure that i should be selecting the rose, or the stems and so on...and what happens when i do take a landscape photo.. which focus point am i supposed to take. your responses shed some light to my questions. i'll definitely try it out. here is the picture i took. it seemed blurry to me :-). thanks again.
Message edited by author 2006-02-16 08:02:35. |
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