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Old Jul 13, 2005, 7:30 AM   #1
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Hi,

Probably a really dumb question or a very complicated answer!

I take a lot of sports shots, mainly using Tv and going from 1/250 to 1/1000 or even faster, but themain setting is 1/500.

Iget quite a lot of shots okay. But I fancy going fully manual and was wondering how to calculate depth of field. If I set my manual focus for 30ft away (middle of the track where the racing line is) and I'm doing a panning shot I'd set that up with probably 1/250, ISO100 (assuming sunny day) but what should I be setting my Apperture to? Or should I just shoot and work on getting the exposure right by altering the Apperture.

Also, do I need to use just the centre spot for exposure or the centre spot with the brackets round it????

Or RTFM more :lol:Hate reading but love putting advise to the test. Going to N.I. this weekend for a bike race and want to improve my photos!

Many Thanks,
Carl.
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Old Jul 13, 2005, 3:06 PM   #2
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Put "circle of confusion" into Google and you will get many hits that will range from very simple and superficial to fairly mathematical and complete.

Since the answer depends on how large you are going to print, viewing distance, subject, eyesight, lens quality, ... you will do well to do some experiments to figure out what works for you. Since your subject distance is about 30 feet, find a 100 ft or longer picket fence, brick wall, concrete block wall, or any other linear feature with regularly spaced "markers". Focus at 30 ft, try various aperatures, and look at the results. (Best to shoot off a tripod to avoid any hint of shake confusing the issue.)

Be sure to look at some of the key results printed at whatever size you figure your final prints will be. Looking on your computer screen is OK, but you really do want to look in the same way your real prints will be made to really figure it out.
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Old Jul 13, 2005, 4:35 PM   #3
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If you want maximum depth of field you want the smallest lens opening or highest aperture number you can work with. If you want less DOF to blur the background open the lens all the way. If you can't generate enough shutter speed to compensate a neutral density or polarizing filter will help.

This might help. There are several online: http://www.dofmaster.com/dofjs.html

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Old Jul 15, 2005, 4:26 AM   #4
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When manual focussing with my camera, a distance indicator pops up on the right of the screen. The smaller the distance, the smaller the increments it display, and the larger the distance, the larger the increments.

Right after the 5m mark, there is the infinity mark. That cant be right, can it? Everything after 5 meters cant be considdered infinity for focussing purposes, can it?

That would mean the DOF would range from say 10m to 100km.

Its a Canon S2.

Sorry for thread jacking.
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Old Jul 17, 2005, 4:45 PM   #5
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Carrots wrote:
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When manual focussing with my camera, a distance indicator pops up on the right of the screen. The smaller the distance, the smaller the increments it display, and the larger the distance, the larger the increments.

Right after the 5m mark, there is the infinity mark. That cant be right, can it? Everything after 5 meters cant be considdered infinity for focussing purposes, can it?

That would mean the DOF would range from say 10m to 100km.

Its a Canon S2.

Sorry for thread jacking.
With the small sensor on your camera the DOF is very large. It seems the difference between 5m and infinity should increase some at full zoom compared to wide though. The only long zoom I have for comparison is my FZ10, and Panasonic doesn't seem to feel you need any sort of distance information in the viewfinder.

My little Z750 jumps from 1M to infinity in a very short distance.

I think it is a proper indication for cameras with small sensors.

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Old Jul 17, 2005, 7:38 PM   #6
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Slipe is right, but if you want to look up the mathematics of DOF you will find it explained in terms of the focal length of you lens. The actual focal length, not the 35mm equiv.

A short lenses has a large depth of field.
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Old Jul 18, 2005, 1:08 AM   #7
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Actually the DOF has nothing to do with the sensor. It is all taken care of in the lens.For example( HD = FL^2/(A*CofC)/1000) This is before the image gets to the sensor.All the sensor does is too crop the shot. If anyone has MS EXCEL on their PC I can send them a full DOF chart for meters and feet. Just send me your email address.
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Old Jul 18, 2005, 4:19 PM   #8
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geriatric wrote:
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Actually the DOF has nothing to do with the sensor. It is all taken care of in the lens.For example ( HD = FL^2/(A*CofC)/1000) This is before the image gets to the sensor.All the sensor does is too crop the shot. If anyone has MS EXCEL on their PC I can send them a full DOF chart for meters and feet. Just send me your email address.
Not true.

COC is closely bound up with format and is not determined "in the lens". Assuming a constant print size the crop DOES change the DOF.

Consider for example:
APS-C format COC = 0.019 mm
35mm format COC = 0.03 mm
645 format COC = 0.045 mm

There is no difference between a piece of film and a sensor of the same size however.

For a more complete set of DOF equations see:
http://www.dofmaster.com/equations.html

For a COC calculator:
http://www.dofmaster.com/digital_coc.html#coccalculator

And as a simple test try the DOF calculator:
http://www.dofmaster.com/dofjs.html

e.g. 50mm lens, f2.8, 10m from subject, 5x7 print, 35mm film => DOF = 7.62 m
e.g. 50mm lens, f2.8, 10m from subject, 5x7 print, APS-C sensor => DOF = 4.48 m






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Old Jul 18, 2005, 4:47 PM   #9
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The circle of confusionin my little formula covers any sensor whether it be .03mm fullsize or .03/1.6 for the 1.6 crop = .019. So naturally it will affect the final DOF. There is a good write up on different cameras with their different size sensors giving different C of C.
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Old Jul 18, 2005, 11:53 PM   #10
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Taking this further however . If you have a medium format camera , Take a film shot ,the C of C as you say need only be .045 because less enlargment is required. Put a 35mm film back on this camera and you will have to revert to the 35mm C of C. As you know this is all based on the Zeiss formula FILM DIAGONOL/ 1730.
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