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Digiprime DOF tables


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#1 renfield sonia

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Posted 22 November 2010 - 05:20 AM

I would like to have the DOF charts for the digiprime lenses in decimal system, as I can't find them on the internet, anyone can help me?
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#2 Randy Wedick

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Posted 22 November 2010 - 08:02 PM

Hi,

Depth of field for any lens will be the same, for the most part, regardless of the size of the imager. A 28mm Ultra Prime on a super35 camera will have the same depth of field as a 28mm digiprime on a 2/3" 3-chip camera.

The difference between the 2 will be the resulting field of view. On a Super35 camera, the 28mm lens will have a more or less wide field of view. On the 2/3" camera it will be quite telephoto (similar to 65mm lens on S35). Both lenses are compressing/expanding the image in nearly the same way, but the digiprime is projecting a smaller slice of that onto a smaller sensor, effectively cropping the field of view by a factor of about 2.2.

The 28mm digiprime will give you the field of view of a 65mm lens, with the depth of field of a 28mm lens.

Here are how they stack up. Digiprimes on left, equivalent field of view S35 lens on the right. Nearest equivalent in Zeiss Ultra Prime is in parenthesis.

3.9mm = 9mm (close to UP 10mm)
5mm = 11mm (UP 12mm)
7mm = 16mm (UP 16mm)
10mm = 23mm (UP 24mm)
14mm = 31mm (UP 32mm)
20mm = 45mm (UP 50mm)
28mm = 64mm (UP 70mm)
40mm = 90mm (UP 100mm)
70mm = 159mm (UP 180mm)

6-24 zoom = 14-48mm zoom
17-112 zoom = 39-254mm zoom

You can use depth of field charts for identical focal length lenses to determine DOF, and use this info above to determine which equivalent DOF chart to use.

Many phone apps like pCam, etc have all of this information at the ready.

Please let me know if you have more digiprime questions, or if I didn't quite get to the answer you were looking for.

Thanks,

Randy Wedick
Technical Consultant
Band Pro Film & Digital
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#3 renfield sonia

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Posted 23 November 2010 - 06:29 AM

Thanks a lot for such a clear answer, here we have the eternal argument among a camera crew, about the question of DOF depending on a different lens.
It's quite extended the believe that a telephoto lens has less DOF than an angular one (that would be right if we avoid the fact that we're using a lens to achieve a precise type of shot), while the DOF is related to the type of shot we have (that forces us to move back or forth the camera in relationship with the objet that's been photographed, depending on the lens we're using). Following that principal, to achieve the same shot using a 2/3 inch camera with a precise lens (let's say a 28mm) we'll have to move back the camera to the same distance than if we were using a 65mm in s35 format, thus, achieving the same DOF. Well, it's sounds a bit complicated but I think that would be the reason, am I wrong?
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#4 renfield sonia

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Posted 23 November 2010 - 06:30 AM

Anyway, doesn't different lenses have different resolution power, and so a different CoC, thus a slight different DoF?
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#5 Chris Keth

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Posted 23 November 2010 - 10:48 AM

Anyway, doesn't different lenses have different resolution power, and so a different CoC, thus a slight different DoF?


Resolving power only comes into play where the lens is focused. Everywhere else it is just plain out of focus and resolving power can't possibly even be measured.
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#6 Stuart Brereton

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Posted 23 November 2010 - 11:11 AM

Anyway, doesn't different lenses have different resolution power, and so a different CoC, thus a slight different DoF?


Lens manufacturers do produce DoF tables for their own lenses, but they rarely differ from generic tables by a significant amount.
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#7 Chris Keth

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Posted 23 November 2010 - 11:13 AM

Depth of field is a strange thing to teach because it is mathematical yet sometimes things on screen can look much more out of focus than they are because of issues of greater enlargement. With a given circle of confusion determined by the format, depth of field is affected by three things: focal length of the lens, distance of the subject from the focal plane, and the f-stop of the lens.

Lets use a 50mm lens set to f4 on super 35 focused at 6' as our starting point and I'll explain how these three factors change depth of field.

Our starting point has a total depth of field of 8".

If you double the stop number (change from f4 to f8) the total depth of field will double. If you only change by one stop (f4 to f5.6) the depth of field will multiply by the square root of 2. The same relationship goes for opening up. Opening to an f2 would halve depth of field to 4", and opening one stop would divide total depth of field by the square root of two.

The other two factors are related in that together they determine the total enlargement of the subject. You will get the same length shot on a person with a 100mm lens at 10", a 50mm lens at 5", or a 25mm lens at 2.5". The difference will be the background, which will be enlarged to different degrees. If we start again at the starting shot we established and halved the distance OR doubled the focal length of the lens, the depth of field would halve. If we were to double the distance or halve the focal length of the lens, depth of field would double.



The rogue element that everybody thinks affects depth of field actually doesn't. Circle of confusion is meant to be the sliding rule for depth of field calculations that helps us tailor things to the intended end format. Everybody knows that a focus puller needs to be more "on" when they're shooting for big theater projection than if they were shooting for TV. The circle of confusion is what defines that numerically. It has no bearing on what the lens does, it only defines what "sharp" is.


There is another rogue element that is not mathematical. There is an element of perception that affects how sharp your eyes think something is. This is seen the most when you compare the same closeup at the same stop and one was on a wide lens and one was on a long lens. Mathematically they have the exact same depth of field. Perceptually, the long lens closeup has a much softer background. This is because the enlargement factor of the background is much greater, so you see the softness better.
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