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depth of field charts of Primo


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#1 martin levent

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Posted 19 July 2005 - 04:24 AM

hi, i'm going to start a movie in august , we're shooting on panavision with primo and primo classic. i'm looking for a chart with the depth of field of primo.
i can't find anywhere these charts (from the 10mm to the 150mm).
if any one has these charts it will be great. i'm waiting for your response.

thanks a lot.
Martin
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#2 David Mullen ASC

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Posted 19 July 2005 - 10:41 AM

Why do you need a chart specific to a Primo as opposed to just the focal length?
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#3 Stephen Williams

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Posted 19 July 2005 - 11:13 AM

Why do you need a chart specific to a Primo as opposed to just the focal length?

<{POST_SNAPBACK}>


Hi,

DOF is calculated from the front nodal point of a lens. Standard DOF charts assume a thin lens, and take no account of the design of the lens. Any phisically big lens will show a slight deviation to the tables. That is why people sometimes say there is a difference in DOF between prime and zoom lenses when measuring to the film plane. The image size may also not match. When measuring to the front nodal point, the image size and dof are identical!

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#4 David Mullen ASC

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Posted 19 July 2005 - 12:22 PM

The question is from a PRACTICAL standpoint, does the deviation matter?

To what purpose will the depth of field figures be used? To shoot miniatures in which everything has to be in focus? Or just to know if an actor missed their mark whether the shot was reasonably in focus?

We had this discussion before, but ANY concept that works around an ill-defined notion of what looks "acceptably" sharp when not actually at the correct focus is never going to be precise, so the standard charts like in the ASC manual are generally good enough for all PRACTICAL uses because it's only meant to give you a ballpark range.

Otherwise, if it's going to make a big enough difference whether you put a Primo or a Super-Speed or a zoom up, with different depth of field charts for each lens type you carry, then why not also have different charts for whether the shot is going to be seen on SDTV, HDTV, or in a big theater, and based on where an audience member is going to sit relative to that image? ALL those factors affect the circles of confusion which in turn affect depth of field, so this notion that there is some definitive answer out there is nonsense. The charts can only ever be approximations.

In other words, there's a reason why there aren't charts out there specifically for Primo lenses. THEY AREN'T NECESSARY.
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#5 Max Jacoby

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Posted 19 July 2005 - 02:52 PM

then why not also have different charts for whether the shot is going to be seen on SDTV, HDTV, or in a big theater, and based on where an audience member is going to sit relative to that image?  ALL those factors affect the circles of confusion which in turn affect depth of field, so this notion that there is some definitive answer out there is nonsense.  The charts can only ever be approximations.

In other words, there's a reason why there aren't charts out there specifically for Primo lenses. THEY AREN'T NECESSARY.


Focus pullers use different values for the circles of confusion depending on whether a film is for theatre or just television.

There are depth of field charts for Ultra Primes, Master Primes, Cooke S4s, Hawks among others. Personally I'd rather use a chart provided by a lens manufacturer than one based on calculations from a formula.
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#6 Charles Haine

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Posted 20 July 2005 - 08:08 PM

There's a great book called, I believe, the Panaflex User's Manual, which has DoF charts for the Primo-L prime, as well as for three of the zooms at a variety of different focal lengths.


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#7 David Mullen ASC

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Posted 20 July 2005 - 11:19 PM

Again, no one wants to answer my question: how critical does it have to be? What are these charts being used for?

I just have a problem with people thinking so mechanically about a subject that is inherently imprecise, i.e. "does this look in focus to you?"

If this is about whether a missed focus shot is "acceptably" in focus most of us would say "well, if it's questionable, let's do another take to be sure. If we can't do another take, it's a moot discussion." No one is going to stop on the set to discuss what level of circles of confusion we want to aim for.

And again, how can there be PRECISELY one circle of confusion for television and one for theatrical? Surely different TV's and viewing distances would have an effect, as would different projectors and viewing distances in the theater. So how can it be so precise a figure? Was the TV circle of confusion figure based on a 36" Sony Trinitron with someone sitting five feet away? What row in the movie theater was used to determine the theatrical circles of confusion? And when these figures were determined, was it thirty years ago using old lens and film stock technology?

I just have never understood this obsession some people have with "perfect" depth of field charts. They are trying to make something precise which can never be precise. It's like the Uncertainty Principle at work. Just get used to the idea that the concept of "not at the focus point but looks acceptably sharp anyway" is inherently subjective.
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#8 Stephen Williams

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Posted 21 July 2005 - 02:59 AM

I just have never understood this obsession some people have with "perfect" depth of field charts.  They are trying to make something precise which can never be precise. It's like the Uncertainty Principle at work.  Just get used to the idea that the concept of "not at the focus point but looks acceptably sharp anyway" is inherently subjective.

<{POST_SNAPBACK}>



Hi,

At close distances it can be a big issue. For example with a Cooke 20-100 zoom at 20mm the front nodal point is 10.5 inches infront of the film plane. So if you measure 30.5 inches , you will be way off as the front nodal point is only 20 inches away. The image size and DOF is as if you are 20 inches away. At the 100mm end the error is 5 inches. A 100mm lens F4 at 10 feet has only 7 inches DOF. IMHO accurate charts are quite important!

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#9 David Mullen ASC

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Posted 21 July 2005 - 12:47 PM

Hi,

At close distances it can be a big issue. For example with a Cooke 20-100 zoom at 20mm the front nodal point is 10.5 inches infront of the film plane. So if you measure 30.5 inches , you will be way off as the front nodal point is only 20 inches away. The image size and DOF is as if you are 20 inches away. At the 100mm end the error is 5 inches. A 100mm lens F4 at 10 feet has only 7 inches DOF. IMHO accurate charts are quite important!

Stephem

<{POST_SNAPBACK}>


Again, what is the PRACTICAL application? Are you honestly going to accept a shot that is 7" off from the correct focus and say "well, I guess since we're using a 100mm prime instead of 100mm on the zoom, we're OK! Let's move on!"

And how do you know that you really have 7" of DOF? How do you really know what parameters were used to determine that? How do you know that the circles of confusion figure being used is actually accurate to the viewing conditions of the final product? What if in reality, you only had 6" DOF? Or 7.5" Or 6.5"? How do YOU know that it is EXACTLY 7" and not a quarter inch more or less?

Again, we're talking about a subjective, vague concept of something not at the focus point that looks acceptably in focus -- key word is "acceptably". It's obviously not a situation where something at the far end of the DOF range is razor sharp but is then visibly soft if another 1/8" off. Focus obviously rolls off into unsharpness, so how can there be a firm dividing line between sharp and soft, except when there is absolutely no depth of field to cover you?

So I'm back to the question: what are you guys using these depth of field charts for on the set? Are you really playing the focus to the edges of what these charts tell you is acceptable? You trust a chart that much?

I mean, I've only shot thirty features, but I can count the number of times a depth of field chart made any practical difference on the set on one hand. But I also don't believe in the concept of "holding a split" either because I think with modern lenses, you can tell where the point of focus is set, so the notion of setting it in mid-space between two people doesn't fly with me unless I've first stopped down the lens to a "Citizen Kane" type degree.
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#10 Max Jacoby

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Posted 21 July 2005 - 02:04 PM

'For modern, high-quality wide-angle cine zoom lenses that are typically about 6-12 inches long, the lens lenght cannot be ignored when calculating depth of field.'

page 184 of Iain A. Neil's article on 'Lenses' in the 8th edition of the American Cinematographers Manual.

If depth-of field-charts specifically calculated for these kind of lenses are not available, he suggests to sutract the physical lenght of the lens from the object distance:

'It goes without saying that a lens at a close-focus distance of 4 feet (object to film), after the subtraction of, say, one foot, will produce a significant difference in the depth of field from that expected-just look at any contemporary depth of field table to compare 4 feet and 3 feet at T2 for a lens of any focal lenght.'
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#11 David Mullen ASC

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Posted 21 July 2005 - 04:38 PM

I ask again, what are you guys using these depth of field charts for?
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#12 Max Jacoby

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Posted 22 July 2005 - 12:00 AM

To know what your depth of field is (obviously). Not necessarily to calculate splits, but in case of a tricky shot (long lens wide-open and handheld for insatance) you know what you are playing with. How big the margin of error is. So that at the end of the take you can make an accurate guess as to whether the take is all sharp or not and can give the script supervisor this information to make a note to the editor.
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#13 David Mullen ASC

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Posted 22 July 2005 - 12:23 AM

To know what your depth of field is (obviously). Not necessarily to calculate splits,  but in case of a tricky shot (long lens wide-open and handheld for insatance) you know what you are playing with. How big the margin of error is. So that at the end of the take you can make an accurate guess as to whether the take is all sharp or not and can give the script supervisor this information to make a note to the editor.

<{POST_SNAPBACK}>


So you're dealing with appromixations anyway. In the course of a handheld shot, you can't know exactly what the distance the subject is to the lens because it keeps changing. You use the chart to give you a general area of focus within you can work, which is fine, but that's what I mean about practical use of DOF charts. You generally won't look at a range in the chart and put two objects EXACTLY at each end of the range and then assume they will look sharp because the chart tells you.

I mean, if the subject ends up exactly on the farthest limit of the DOF range that the chart tells you is acceptable, you don't live with that and move on if you could get another chance at getting it closer to the correct the focus?

These charts were only created to be helpful guides, not the final word on whether a shot is sharp or not.
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#14 Stephen Williams

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Posted 22 July 2005 - 03:28 AM

I ask again, what are you guys using these depth of field charts for?

<{POST_SNAPBACK}>


Hi,

I look at the DOF charts in the planning stage. I can then decide film stock and lighting and lense for a shot. Its a bit late when the 1st says 'but thats less than 1 inch DOF, your handholding the camera and the model is moving too!'

Stephen
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#15 Max Jacoby

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Posted 22 July 2005 - 01:53 PM

On the shoot I'm currently on, the depth of field chart came out last week. We were doing a shot with the main character in the foreground and where the background was going to be changed in CGI. Since both needed to be in focus, we needed to adjust the stop accordingly.

This is quite common on CGI heavy shoots.
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#16 David Mullen ASC

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Posted 22 July 2005 - 07:34 PM

On the shoot I'm currently on, the depth of field chart came out last week. We were doing a shot with the main character in the foreground and where the background was going to be changed in CGI. Since both needed to be in focus, we needed to adjust the stop accordingly.

This is quite common on CGI heavy shoots.

<{POST_SNAPBACK}>


I think this is where the charts are most critical, for efx shots -- like shooting a miniature that has to be in deep focus. However, even in these cases, the truth is that you basically light for as deep as stop as you can get away with practically if you want everything to be in focus. But the charts can tell you what hyperfocal distance to use, etc. But the charts don't negate the need for eyeballing things too, which is why focus is as much an art as it is a science.
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#17 oarad

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Posted 15 August 2005 - 12:53 PM

David, Please...

This is esoteric knowledge we pocus pullers keep secret for years while you irresponsibly share it with DoP?s. Focus is not calculated based on formulas and we care very little about physical length of lenses (except of-course when we haul cases back and forth). Focus is organic and has to be decided based of things other then focal length, f-stop and object distance, things like motion, mood, color, contrast and generally the type of scene we?re looking at.

I know my working limits for a shot but I?m aware they?re mostly virtual. I also aware most people think they?re absolute. Believe it or not, but this fact helps me do my job. At the end of the shot if something?s out of focus then we?ll know thanks to modern lenses and viewing systems on cameras.

So let cameraman (and many ac?s I?m afraid) stay oblivious and believe lookup tables will save the day while we focus pullers just keeping it in relative focus, nothing more.

Take care,

Oren Arad
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