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04/19/2011 11:47:21 PM · #1 |
Ok...so I pulled up a giant picture of a center bar with numbers on either side on my computer (is this possible, lol?) and shot it at a 45 degree angle at 1.4, 2.8, and 5.6. it's the only thing I have enough light to shoot right now.
Here's a shot at 1.4:
//kevingearyphotography.com/wp-content/uploads/2011/04/MG_4394-1.jpg
Here's 2.8:
//kevingearyphotography.com/wp-content/uploads/2011/04/MG_4395-2.jpg
Here's a shot at 5.6:
//kevingearyphotography.com/wp-content/uploads/2011/04/MG_4398-3.jpg
If you can't tell, the right side of the frame is closest to the camera.
Message edited by author 2011-04-19 23:51:35. |
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04/19/2011 11:51:36 PM · #2 |
This isn't really telling us anything. Imagine a yardstick on the floor, and you standing shooting down the length of it, focusing on the 18-inch mark. We'd be able to tell if you had front or back focus by seeing if the actual sharpest focus was at 16 inches or 19 inches, see? That's the basic principle. You usually test for this wide open, DOF can mask the effects if you're only slightly off.
R. |
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04/19/2011 11:52:43 PM · #3 |
Originally posted by Bear_Music:
This isn't really telling us anything. Imagine a yardstick on the floor, and you standing shooting down the length of it, focusing on the 18-inch mark. We'd be able to tell if you had front or back focus by seeing if the actual sharpest focus was at 16 inches or 19 inches, see? That's the basic principle. You usually test for this wide open, DOF can mask the effects if you're only slightly off.
R. |
Isn't that what I did?
The 1.4 shot is wide open and the focus was on the center line Like I said, the screen was angled 45 degrees.
I can test on a book page. I don't have a ruler.
Message edited by author 2011-04-19 23:53:24. |
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04/19/2011 11:55:57 PM · #4 |
Well, the problem is we're seeing focus variation from top to bottom of the screen as well as from left to right, it's like a 3-dimensional issue here, it's hard to say where the true zero point is.
You want to do this with a tripod, and you want to align things precisely. Something on the floor is easiest for this test.
R. |
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04/20/2011 12:08:05 AM · #5 |
Flat field vs curved field lenses would make a difference in focus distance from center to edge of the frame as well if you are shooting at an angle into a flat surface.
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04/20/2011 12:12:31 AM · #6 |
This is pretty unscientific, but it's the best I can do right now:
All of these are shot wide open (1.4) using the CENTER focus point on the "24".
These are large images so I'm just posting links.
Here is a shot with zero recomposition:
//kevingeary.smugmug.com/photos/1258651260_3NGrVgV-X3.jpg
And here are various shots WITH recomposition:
//kevingeary.smugmug.com/photos/1258650145_zh9n2QG-X3.jpg
//kevingeary.smugmug.com/photos/1258652573_VC963qR-X3.jpg
//kevingeary.smugmug.com/photos/1258652062_PkHKcvq-X3.jpg
What say you? |
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04/20/2011 03:18:09 AM · #7 |
when you say "with recomposition" I assume you mean you lock focus on the 24 with the center focus point, and then move the camera--if so, all bets are off. This kind of testing needs to be with things fixed. Camera, target, focus. If you can do mirror lockup, even better. If you have a corded or wireless remote, better. On the tripod, turn image stabilization off.
Allowing for hand-held, no recomposition, I'd say the first one looks pretty good. The recomposed shots have no real value in a test of this kind. |
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04/20/2011 08:45:01 AM · #8 |
| So the bottom line is, when you recompose, you sometimes introduce some error. Otherwise, you look spot on. The other thing you want to test is performance at or beyond about 10-15 feet. It's not uncommon for a lens to misfocus only at near or far settings. |
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04/20/2011 08:57:59 AM · #9 |
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04/20/2011 09:00:35 AM · #10 |
I dont know Canon, so I don't know where the buttons are.
On my camera (D300) focus mode selector is in front bottom, easy to bump, and get it from the single to the continuous focus. Could this be a problem? |
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