[ratpack] Re: Shutter speed and its effect of depth of field
- From: "PAUL W WATSON" <TSWATSON78@xxxxxxx>
- To: <ratpack@xxxxxxxxxxxxx>
- Date: Thu, 26 Nov 2009 09:27:17 -0700
I said that I was just a silly ignert old man and that you and Ray are much
smarter than I will ever be. I most likely used the wrong term is Depth of
Field. Like I said I'm just an ignert ol' man. I was trying to figure out why
one part part is sharp and other parts are not, focus or depth of field, I
don't know.
Remember the more turkey you eat today the less money you'll spend on black
Friday. at least that is what somebody said on the tube the other day.
Have a great Turkey day.
p
----- Original Message -----
From: humminboid@xxxxxxxxxxx<mailto:humminboid@xxxxxxxxxxx>
To: ratpack@xxxxxxxxxxxxx<mailto:ratpack@xxxxxxxxxxxxx>
Sent: Wednesday, November 25, 2009 11:35 PM
Subject: [ratpack] Re: Shutter speed and its effect of depth of field
Good for Alexis!
A good recovery to her. I bet she won't feel much like eating Thanksgiving
goodies, though...except maybe the ice cream.
NOW! Depth of field is governed by three things only. 1. Focal length of
the lens. The longer focal length, the less dof you have to work with. 2.The
f/stop used. Bigger opening=less dof. 3. To a lesser degree, the distance
focused upon. Closer, less dof. Them's laws of physics, as close to written
stone as you are likely to get, and do not change! At least in equipment us
mere mortals can afford.
Shutter speed has no effect on dof, except as it allows a larger or smaller
aperture to be used.
Higher shutter speed also eliminates some of the miscelaneous wigglings of a
car or kid.
Dof is always at a 90 degree angle to the lens axis, unless you have a really
weird/abused lens. It starts about 1/3 in front of the subject, and ends 2/3
behind, and is not an abrupt change. If the point of focus on the Porsche is
the left fender/bumper, depending on the lens used, which I'd wager is a long
one with shorter dof, even at f/18. It is acting like depth of field always
will. If the diagram of the car is is accurate, acceptable sharpness probably
starts about 5-10 feet behind the Porsche, and extends forward past sharp focus
maybe 10-15 or so feet, resulting a dof of maybe 25 feet, not enough to cover
both cars.
Wish I'd have taken that! Anyhow, I'm going to bed, too, affter I pull Mr.
Turkey out of the water bath and stick him back in the fridge.
Good Thanksgiving!
.
----- Original Message -----
From: "PAUL W WATSON" <TSWATSON78@xxxxxxx>
To: "ratpack" <ratpack@xxxxxxxxxxxxx>
Sent: Wednesday, November 25, 2009 10:30:52 PM GMT -07:00 US/Canada Mountain
Subject: [ratpack] Shutter speed and its effect of depth of field
I haven't written much lately as I have been busy. Today Alexis went to
Primary Children's Hospital for surgery to remove her tonsil and adenoids.
Usually this is not a big deal, but because Alexis is the worlds smallest 7
year old and has some unique physical problems. Like not having her head
attached to her neck and Basilar Invasinaition [not sure of the spelling] this
is what killed Dale Earnhardt. She also had a cold with a rattle in her lungs
before the surgery. The Doctor mentioned that the surgery could cause other
complications. It was decided to go ahead with the surgery as the benefits far
out weighed the possible bad things that could happen. Anyway to make a long
story short the surgery went great and she came through with flying colors.
Now to what all this has to do with my subject line.
First of all I am not near as literate as Mr. Crosby and Mr. Buck after all I
am just an ignert ol' hillbilly, so I am just going to stumble along not
knowing where this will go.
Yesterday I received my latest issue of Road and Track and I took it to the
hospital to read in the waiting room. On page 6 and 7 is a photograph that R &
T is selling. See first photo.
This photo was taken at Laguna Seca this fall. It is a pan blur shot with
the p.o.f. [point of focus] on the rear of the Flying Lizard Porsche which is
following a Ford GTR. As you look from the rear of the Porsche forward the
subjects get more and more out of focus.
The photographer used ISO 50, and a shutter speed of 1/20 of a second at f18.
I looked and looked at this photo and tried to figure out what was going on
between the lens and the camera.
we all know that f stops affect depth of field, but I believe that under the
right circumstances shutter speed also affects depth of field. I'm not sure
why, but I'm going to give it my 2 bits worth.
This effect only works in certain angles. Doing a pan shot where the object
is roughly 90 degrees from the camera doesn't do this.
Now go to my great piece or art work, the second attachment.
Figure A: Shows the 90 degree angle shot with the p.o.f on the center of the
car. The right and axis of the object are not much greater distance from the
camera as p.o.f therefore the entire car is in focus.
Figure B.
The p.o.f. is on the very front of the first car and the left axis is within
normal focus depth of field. The problem seems to arise [in this case] on the
right axis which extends back to the rear of the second car.
Figure C.
This is sort of hard to 'splain but here goes. You are looking through the
view finder, the center is the p.o.f., the rings are .....just distance from
the center point of focus. My thinking is that the brain of the digital camera
thinks from the center [p.o.f.] out, therefore at slow shutter speed the camera
is taking its own sweet time in exposing and focusing.
Like I said I'm just a silly ol' ignert hillbilly. You guys are a whole lot
smarter than I am, you tell me what's going on. I do not see this effect on
similar angle shots at fast shutter speeds.
Check out some of the other photos of Road and Tracks web site.
www.roadandtrack.com/focalpoint<http://www.roadandtrack.com/focalpoint>.
My head hurts I'm going to bed.
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