Zeiss and Cooke primes have different depth of fields? / Etiquette of using laser distance meter

[weiming]

Hi all,

 

i have a few questions which i would like to ask:

 

I downloaded the depth of field tables for both cooke(S4) and zeiss(ultra primes), and realised that at a given aperture and focused distance, the depth of field was slightly different for both brands. furthermore, when i compared both tables to the PCAM software on my palm, they were also different...

 

So should we ignore it because in the real world the difference is negligible?

 

Next,

 

what proper etiquette should we observe when using a laser distance meter, for example: leica disto, to measure a subject's distance from camera?

 

Thank You!

[Max Jacoby]

Zeiss lenses have a faster focus-fall off than Cookes, which is why their apparent depth-of-field is smaller.

[Michael Nash]

Zeiss lenses have a faster focus-fall off than Cookes, which is why their apparent depth-of-field is smaller.

 

Which, according to Joe Dunton, is really an illusion created by contrast. Zeiss lenses transmit more blue light, making them appear a little "colder" and more contrasty. When something goes out of focus you've essentially got less contrast in the "soft" area (dark and light borders get blurred together), making a greater visible difference between the sharp, contrasty areas and the soft, lower-contrast areas. Cookes on the other hand transmit comparatively more red light, making them appear not only warmer in color but also lessening the apparent contrast difference between sharp and soft areas.

 

But regardless, the visual effect is that Zeiss lenses appear to have a faster drop-off of focus, while the Cookes' depth-of-field transition appears more "graceful." Just repeating what Joe told me, and I hope I'm doing the explanation justice!

[Jon Kukla]

To answer your second question, NEVER point a laser at or near someone's eyes.

[Chien Huey]

I'd avoid pointing the laser at a person period. I don't own one but I've seen ACs who do either aim it at an object (pillar, wall) that's the same distance. Also, sometimes the 2nd will go out to the mark and aim the laser back at the camera. But in the end, the laser rarely comes out (usually only if the mark is far, far away) and mostly focus marks are taken with tape and/or eye marks through the viewfinder.

 

To answer your second question, NEVER point a laser at or near someone's eyes.

[Michael Maier]

Which, according to Joe Dunton, is really an illusion created by contrast. Zeiss lenses transmit more blue light, making them appear a little "colder" and more contrasty. When something goes out of focus you've essentially got less contrast in the "soft" area (dark and light borders get blurred together), making a greater visible difference between the sharp, contrasty areas and the soft, lower-contrast areas. Cookes on the other hand transmit comparatively more red light, making them appear not only warmer in color but also lessening the apparent contrast difference between sharp and soft areas.

 

Great assessment! Can somebody around here deliver a similar one on Lomo and Nikon glass? You don't see much detail in evaluations when it comes down to the lower end stuff.

[Chris Keth]

Are the printed DoF tables using the same circle of confusion? Visual differences in contrast shouldn't matter since DoF tables should be calculated.

[Stephen Williams]

Are the printed DoF tables using the same circle of confusion? Visual differences in contrast shouldn't matter since DoF tables should be calculated.

 

Hi Christopher,

 

When Cooke or Zeiss calculate DOF tables for their lenses they do not use the simple 'thin' lens calculation.

 

DOF is calculated from the entrance pupil of the lens, this may well be a long way from the film plane. The relationship size of entrance to exit pupil also has to be accounted for on telephoto & retro focus lenses.

 

Stephen

[Chris Keth]

Hi Christopher,

 

When Cooke or Zeiss calculate DOF tables for their lenses they do not use the simple 'thin' lens calculation.

 

DOF is calculated from the entrance pupil of the lens, this may well be a long way from the film plane. The relationship size of entrance to exit pupil also has to be accounted for on telephoto & retro focus lenses.

 

Stephen

 

I know all of that. A 50mm lens from one manufacturer should be very close to a 50mm of another make. Obviously there will be differences since you can see differences, but it really should be accurate enough 99.9% of the time to use a generic DoF chart. I get by with them, the ASC manual seems to think they are accurate enough, et cetera.

[Stephen Williams]

I know all of that. A 50mm lens from one manufacturer should be very close to a 50mm of another make. Obviously there will be differences since you can see differences, but it really should be accurate enough 99.9% of the time to use a generic DoF chart. I get by with them, the ASC manual seems to think they are accurate enough, et cetera.

 

Hi,

 

A Cooke SII 50mm is tiny compared to a modern Cooke S4. In the close focus range there will be different DOF because the image size on the negative is different! Match the 2 image sizes and the DOF at the same F stop will match.

 

Measuring from the front nodel point of both lenses DOF will be the same!

 

Stephen

[Chris Keth]

I found what the difference is likely from. Depth of field of any lens of any design, at a given stop, focal length, circle of confusion, and object distance will be identical. So, the most likely cause of the difference is a difference in the distance of the front nodal point from the film plane.

 

In an exaggerated example, say the camera is focused 4 feet from the film plane. Lens A has a front nodal point 1 foot from the film plane and lens B has a front nodal point 2 feet from the film plane. This makes lens A's object distance 3 feet and lens B's object distance 2 feet. We can use the formula:

 

D1^2/D2^2=U1/U2

 

where the Ds are object distance and Us are corresponding proportional (not actual) depths of field. This formula only applies if the object distances do not exceed the hyperfocal distance of the lens.

 

 

So in the above situation:

 

3^2/2^2=9/4

 

Lens A has just over twice the depth of field of lens B in the same situation, just because its front nodal point is closer to the film plane. ;)

 

If anyone wants to read a bit more, this formula comes from "Basic Photographic Materials and Processes, 2nd edition" (focal press, written by Leslie Stroebel, John Compton, ira Current, and Richard Zakia)

 

Hi,

 

A Cooke SII 50mm is tiny compared to a modern Cooke S4. In the close focus range there will be different DOF because the image size on the negative is different! Match the 2 image sizes and the DOF at the same F stop will match.

 

Measuring from the front nodel point of both lenses DOF will be the same!

 

Stephen

 

Heh, see above. It clicked to me exactly why while you were posting your explanation. Thanks! :D

Edited December 11, 2006 by Christopher D. Keth

[Stephen Williams]

I found what the difference is likely from. Depth of field of any lens of any design, at a given stop, focal length, circle of confusion, and object distance will be identical. So, the most likely cause of the difference is a difference in the distance of the front nodal point from the film plane.

 

In an exaggerated example, say the camera is focused 4 feet from the film plane. Lens A has a front nodal point 1 foot from the film plane and lens B has a front nodal point 2 feet from the film plane. This makes lens A's object distance 3 feet and lens B's object distance 2 feet. We can use the formula:

 

D1^2/D2^2=U1/U2

 

where the Ds are object distance and Us are corresponding proportional (not actual) depths of field. This formula only applies if the object distances do not exceed the hyperfocal distance of the lens.

So in the above situation:

 

3^2/2^2=9/4

 

Lens A has just over twice the depth of field of lens B in the same situation, just because its front nodal point is closer to the film plane. ;)

 

If anyone wants to read a bit more, this formula comes from "Basic Photographic Materials and Processes, 2nd edition" (focal press, written by Leslie Stroebel, John Compton, ira Current, and Richard Zakia)

Heh, see above. It clicked to me exactly why while you were posting your explanation. Thanks! :D

 

Hi Christopher,

 

I only worked it out one day when I swopped a Cooke S4 100mm lens for my Cooke 20-100 zoom set to 100mm. The DOF of the Zoom lens was way less than the prime. However the object in frame was much bigger too!

 

Make the image size on the negative & F stop match, the DOF will also match regrdless of lens focal length!

 

Stephen

[Chris Keth]

Hi Christopher,

 

I only worked it out one day when I swopped a Cooke S4 100mm lens for my Cooke 20-100 zoom set to 100mm. The DOF of the Zoom lens was way less than the prime. However the object in frame was much bigger too!

 

Make the image size on the negative & F stop match, the DOF will also match regrdless of lens focal length!

 

Stephen

 

That would do it. The zoom would have a much differently located front nodal point than the prime.

[Hal Smith]

When comparing zoom to prime lenses don't compare T stops, compare F stops. Comparing T stops overlooks the difference in light efficiency between zooms and primes. T4 on a zoom could be F2.8 while T4 on a prime might be F2.8-2/3.

[Stephen Williams]

When comparing zoom to prime lenses don't compare T stops, compare F stops. Comparing T stops overlooks the difference in light efficiency between zooms and primes. T4 on a zoom could be F2.8 while T4 on a prime might be F2.8-2/3.

 

Hi Hal,

 

Probably not that bad, the 30 year old Cooke 20-100 is F2.8, T3.1 Thats nearly a 1/3 stop, a prime will be less.

 

Stephen

[Hal Smith]

Probably not that bad, the 30 year old Cooke 20-100 is F2.8, T3.1 Thats nearly a 1/3 stop, a prime will be less.

Agreed for better lenses. But my old Angenieux L2 35-140mm has both T and F stops on it, F3.5 equals T4.4. Which is one of the reasons why people drool over old Cookes and spit at old Angenieux's!