I have the 16x Manual Servo Lens, so this should be easier to accomplish (I hope) from what you have mentioned. So by using rack focus, I could go from my foreground being in focus to the foreground and background being in focus. This would of course be achieved by the correct aperature setting.

Is my above statement on target or am I missing something?

I think with some experimentation this effect could be achieved. You may have to combine the split field technique with the rack focus technique. Use a square split field (Cokin, Singh-Ray etc.) and a square soft focus filter. When mated this would give approximatly 1/2 in focus (near subject) and half soft focus. Remove both filters (someone would need to pull focus also). This would leave perhaps several frames to touch up in post. Going from limited near focus to infinite focus is not easily accomplished. However, respectable results could be obtained with some experimentation and practice. Of course if your George Lucas, just do it in your computer.

Jeff

Well my results have been horrible. I guess I just need more practice. I appreciate your comments and will continue to work on this technique.

Maybe I will hit the Texas Lottery and be able to buy a "George Lucas" style mini studio!

Hi
I'm a masochist and would love to hear somebody to explain me the "circle of confusion". It popped up from time to time in this threat, but everybody avoided it somehow.

I learn from the DoF-charts of the American Cinematographer Manual 8-th edition (The bible) that this is one of the main factors in determinating the DoF, BUT I don't understand what it is and why it does effect the DoF.

I found it also interesting that the charts are given for ALL formats the same value, so there are no differences for 16,35 or 65 mm lenses.

Thanks
Istvan

Hi,

I pretty much defined it in my post above, but I'll give it the complete treatment this time.

Circle of Confusion - The diameter of a circle formed by a lens imaging a true point. The largest circle which will appear as a point to the eye (without producing perceptable unsharpness). A primary factor in determining sharpness to the viewer.

As the diaphragm is closed (stopped down), the circle of confusion is reduced in diameter. However, the presence of spherical aberration, causes the plane of sharpest focus to shift along the optical axis, toward the film plane.

The smallest area of crossing for incoming rays produces not a point, but a circle, hence the term circle of confusion. If the circle has a diameter of 1/3000 of the viewing distance or less, it is considerd by the eye to be a point. Therefore, as the viewing distance increases, a physically larger diameter circle is still considered to be a point by the eye.

This post will explain sperical aberration http://www.dvinfo.net/conf/showthread.php?s=&threadid=2847&highlight=defects

Jeff

Hi Jeff,
and thank you very much!!!
I think I start to understand at least a part.

But I still have a little question: in the Cinem. Manual they calculated the DoF charts with a Cc of 0.001' and suggest to consider for the 16mm a Cc 0.0005', which would mean to consider as reference much more open lens, actually like 2 F stops more open.
If I understand this well then this would mean less DoF for 16mm then for 35mm at the same distance and same focal length????

Or did I miss something?
Thanks
Istvan

Viewing distance also has to be considered. Does the manual state any viewing distances? If not, then their data is incomplete. Viewing distance is usually stated in a distance so many times the diagonal of the screen. My data is in inches, not mm or cm. As an example, a billboard (larger than your typical 35mm screen) looks sharp when viewed from the road. Yet when viewed at a close distance the dots (circles of confusion) are very large and the image is not recognizable.

Jeff

Paul:

I've been thinking about your wanting to transition from a frame where the foreground alone is in focus, to one in which both the foreground and background are in focus.

With a film camera, you would achieve this by doing a combination aperture/shutter ramp. As the aperture (T-stop) is dialed from wide (short DOF) to narrow (greater DOF), the shutter speed is correspondingly decreased. The effect is controlled by an external device that calculates the rate at which both parameters are changed so the effect is invisible.

On the XL1, I have not found a way to do this as elegantly--I would think that in aperture priority mode, the shutter should follow the aperture and as you dial it up and down, the shutter compensates. I think that it doesn't do this smoothly enough to manage the effect without seeing changes in exposure, unfortunately. Perhaps someone will be able to figure out how to pull this off?

I've been doing some tests in my short vacation and have achieved
some beautiful DOF shots (as I like to call em). Where my
foreground was in sharp focus and the background was all
blurry. Very very nice. I followed the tips and opened up
the lens too its max. I added two ND filters (I was shooting
outside in the sun). Gain was at -3 dB (where it always is).
Shutter was 1/25 th I think but I can check that if anyone wants
to know for sure.

The trick is to zoom in as much as possible (which is a lot
easier outdoors than indoors). This creates a very nice shallow
DOF.... Now I need to run some indoor tests!

Cheers.

<<<-- Originally posted by Charles Papert : Paul:

I've been thinking about your wanting to transition from a frame where the foreground alone is in focus, to one in which both the foreground and background are in focus.

With a film camera, you would achieve this by doing a combination aperture/shutter ramp. As the aperture (T-stop) is dialed from wide (short DOF) to narrow (greater DOF), the shutter speed is correspondingly decreased. The effect is controlled by an external device that calculates the rate at which both parameters are changed so the effect is invisible.

On the XL1, I have not found a way to do this as elegantly--I would think that in aperture priority mode, the shutter should follow the aperture and as you dial it up and down, the shutter compensates. I think that it doesn't do this smoothly enough to manage the effect without seeing changes in exposure, unfortunately. Perhaps someone will be able to figure out how to pull this off? -->>>

Charles,

Have you had a chance to read the latest issue of American Cinematographer? There is an article in there that talks about the filming of Road to Perdition. Conard L. Hall (DP) talks about how "constently shot at the bottom of the aperture." His goal was to cut down on the depth of field. He shot a lot at "T1.9 to T2.5, which cut down on depth of field, made the focal plane more specific and softened the backlight."

Hall goes on to say, "I like to shoot wide open, with only one point in the depth of field sharply focused." He "feels" this technique gives the imagery an emotional dimension.

I thought that this article described some of the things that I am trying to achieve. Now of course I am not shooting with a Panavision Platinum and Primo lenses, but I still think this look can be pulled off. My thought that being wide open with the correct lighting, you should get a pretty nice look/feel.

I haven't read that issue at length yet, it's kicking around on my desk somewhere. Most DP's like to shoot fairly open, but it does depend on the project. I was fortunate enough to do some Steadicam work for Roger Deakins last month, and was a bit surprised that we were working at an 8/11 stop for a day exterior walk-and-talk...but then figured that it was a definite choice, and came to understand why he would want a deep focus for that particular shot. I like to work that way also, considering what is appropriate for a given shot or mood.

That's for film though. There is no question that video looks better with shallow depth of field, I think it probably has something to do with the rather harsh edges in a video image. The less of them in the shot, while there is still something in sharp focus, the more attractive the image. But unless you are using something like the Mini-35, it's really hard to get DV to fall off in focus at a wide to medium focal length, regardless of how wide open the lens is (and the supplied lenses, while good, are not sharpest at their widest opening).

Hi Jeff,

<...Viewing distance also has to be considered. Does the manual state any viewing distances? If not, then their data is incomplete. Viewing distance is usually stated in a distance so many times the diagonal of the screen. My data is in inches, not mm or cm. As an example, a billboard (larger than your typical 35mm screen) looks sharp when viewed from the road. Yet when viewed at a close distance the dots (circles of confusion) are very large and the image is not recognizable....>

The manual calolats first the Hyperfocal Distance for every F.stops and then the "NEAR" AND "FAR" limits for different "Distances from camera to object"

You want me to put the formulas here?
Istvan

Depth of field is the distance between the nearest and farthest objects that appear to be in acceptably sharp focus in the image plane. Depth of field involves one image plane and the area between two target planes (in front of the lens).

Depth of Focus is the distance range through which the image of an abject, in a single plane, can be shifted axially and still have the image appear to be sharply defined. This is the area behind the lens, at or near the CCD (film plane).

So, depth of field is a distance, in front of the lens. Approxomately 2/3 of the distance is behind the image plane (subject) and 1/3 the distance is in front of the plane.

I've moved recently and many of my books are still in storeage. I'm sure many would like to see the formulas. Thanks!

Jeff

OK, so here is the formula, taken from the "American Cinematographer Manual" 8-th edition, pag:698,699

First the Hyperfocal Distance (definition from the manual: Hyperf.Dist of a lens is that focus setting where objects at infinity and half the focus distance are of an acceptable sharpness)

H= F^2 / (f)(Cc)
F=focal length of lens
f=f-stop number
Cc=circle of confusion

Depth of Field
Near limit
(H)(S) / H+(S-F)

Far limit
(H)(S) / H-(S-F)

Where:
H=HYperfocal distance
S=Distance from camera to object
F=Focal length of lens

Istvan

This forum is addictive!

I have learnt so much from this thread it is hard to beleive. I meant to go out and shoot some gritty night time shots an hour ago and I'm still in my way-too-comfortable desk chair!

thats it! I'm leaving!

Hehe, i can imagine and know what you mean.... Thanks for
the compliment though.