DoF on digital versus film

[flyalf]

Hi,

I hope someone please can help me. I seem to remember having read a post in these fora (or other) with some thoughts on DoF differences on digital versus film on same format size. Please note that I dont need any general info on DoF, cricles of confusion and so on, just on digital versus film on same "sensor" size. Difference or not given all other factors are the same?

Anybody with a clue? Thanks!

P.S. I hope this is posted correct 🙂

 

[FrankS]

As far as I know: Same DOF effect with full frame digital sensor as with a full frame 35mm film. No difference between digital and film if the frame is the same size.

 

[Nikon Bob]

You could always got to a site such as http://www.dofmaster.com/doftable.html and plug in your info to see exactly what the difference is.

Bob

 

[Chris101]

Once folks start arguing about what happens when a circle of confusion is smaller than a single photosite, the discussion becomes one of those angels/pinhead things.

 

[user237428934]

Dofmaster uses the same circle of confusion for film and for M9. So at least in theory both are the same.

 

[jaapv]

Film has a thickness. And a milky stucture. Sensor is a clinical plane. That has an effect on DOF. A COC on film has diffuse edges by diffusion of light and turnes into an ellipsoid projection of a cone towards the corners. Think of a torch shining into a bowl of murky soup. A COC on a sensor is a defined circle. Think of a torch shining onto a sheet of paper. The ellipse towards the corners is less pronounced. That means that DOF on a sensor is more abrupt, more steep than on film. Just for the record. DOF is not a constant value between two numbers like a blockwave. It is a value that peters down from a maximum to a minimum. Imo the whole classical approach towards DOF can be tossed out of the window with present-day enlargments and sensor technology. There are far more valid views on the subject, like Harold Merklinger's ideas.

http://www.trenholm.org/hmmerk/DOFR.html

On the other hand, if you want to stick with the classical idea of DOF, this is a good basic start.

 

[Finder]

Yes, DoF field is constant with format. Merklinger's ideas are not new although a little fuzzy--DoF is subjective and people during the golden era of film were not satisfied with lens DoF scales and so they used more critical definitions.

Light focuses in the form of a cone whether the image plane is silicon or silver halide.

 

[Nikon Bob]

Once folks start arguing about what happens when a circle of confusion is smaller than a single photosite, the discussion becomes one of those angels/pinhead things.

So right. You can make it as complicated as you want or simply accept that in the real world these complications may mean nothing in practical terms.

Bob

 

[batterytypehah!]

Looks like we're right in the middle of the kind of discussion the OP explicitly did not want.

flyalf, maybe this is the thread you mean? http://www.rangefinderforum.com/forums/showthread.php?t=85149

Generally speaking, DOF depends on the lens, not on the negative/sensor size. Longer FL = Shallower DOF. Take e.g. a 105mm lens. In 35mm terms, that's a long portrait/short tele lens, but in 6x9 it's "normal." Unfortunately, the 105mm glass doesn't know what size negative it's focussed on. It just gives you the DOF of a 105.

Neg/sensor size comes into play when you're comparing lenses based on the angle of view rather than FL.

 

[Finder]

Looks like we're right in the middle of the kind of discussion the OP explicitly did not want.

flyalf, maybe this is the thread you mean? http://www.rangefinderforum.com/forums/showthread.php?t=85149Generally speaking, DOF depends on the lens, not on the negative/sensor size. Longer FL = Shallower DOF. Take e.g. a 105mm lens. In 35mm terms, that's a long portrait/short tele lens, but in 6x9 it's "normal." Unfortunately, the 105mm glass doesn't know what size negative it's focussed on. It just gives you the DOF of a 105.

And the DoF of the 6x9 with a 105mm lens is greater than the 35mm at a given aperture. Sorry, but format matters, or to be exact, magnification--the resulting 35mm image is magnifiied to a greater extent (this is why a cropped image has less DoF that the original image when printed to the same size).

 

[FrankS]

You're both right. Size of the format determines the focal length of a lens that gives a normal view. The larger the format, the longer the focal length of the normal lens (that gives an equivalent normal angle of view) is. All else being equal, the longer the focal length, the shallower the DOF.

 

[ferider]

To the OP: the model in dofmaster will give you the same good 1st order approximation of identical DOF for either film or digital for identical format and focal length.

But (not captured by the model) film and digital OOF rendering can look different; the model also doesn't capture two lenses of the same focal length appearing to have different DOF, even on identical medium - this does happen; The reasons for the difference between film and digital are as Jaap stated in post #6: film is thicker.

Roland.

 

[Finder]

You're both right. Size of the format determines the focal length of a lens that gives a normal view. The larger the format, the longer the focal length of the normal lens (that gives an equivalent normal angle of view) is. All else being equal, the longer the focal length, the shallower the DOF.

Frank, we can't be both right--the DoF is not the same with a given focal length on every format. The larger the format, the greater the DoF at a given focal length.

 

[Finder]

To the OP: the model in dofmaster will give you the same good 1st order approximation of identical DOF for either film or digital for identical format and focal length.

But (not captured by the model) film and digital OOF rendering can look different; the model also doesn't capture two lenses of the same focal length appearing to have different DOF, even on identical medium - this does happen; The reasons for the difference between film and digital are as Jaap stated in post #6: film is thicker.

Roland.

Can you show an example?

 

[ferider]

Can you show an example?

On film, Canon 50/1.2 and 50/1.4 LTM, both shot at 1.4:

Crop:

Same exposure, etc. As I said, it's a second order effect, but the 50/1.2 has slightly thinner DOF than the 50/1.4, at the same aperture.

I have seen the 35/1.4 Summilux ASPH having thinner DOF than the 35/1.4 Nokton, both at f1.4. Also, the web is full of similar observations when comparing Noctilux with 1.1 Nokton at the same aperture. Etc.

Regarding the difference digital/film, I'll have to test that quantitatively one day ... But I suggest to browse the M-mount flickr group, and compare Summilux 50/1.4 ASPH photos taken with film vs. M8/9. It's only visible in some bokeh-intensive shots. If you are a bokeh hater you won't mind the difference 🙂

Roland.

 

[Nikon Bob]

If you compare a FF digital, Nikon D700, and 35mm film you will likely find that the DOF is for all intents and purposes is the same. That is using the same focal length and same distance focused at. That is if you can believe Dofmaster, or you can complicate things by playing with all the variables. That is always fun but can be more of a case of BS baffles brains at times.

Bob

Bob

 

[batterytypehah!]

And the DoF of the 6x9 with a 105mm lens is greater than the 35mm at a given aperture. Sorry, but format matters, or to be exact, magnification--the resulting 35mm image is magnifiied to a greater extent (this is why a cropped image has less DoF that the original image when printed to the same size).

Magnification is an entirely separate issue. The OP wants to know what determines DOF at a given format. The answer is that FL decides, nothing else matters nearly as much.

 

[antiquark]

If you're adjusting your focal length to be "equivalent" to 35mm film (for example, 50mm film lens equivalent to a 25mm u4/3 lens), then smaller sensors have greater DoF.

 

[Finder]

On film, Canon 50/1.2 and 50/1.4 LTM, both shot at 1.4:

Crop:

Same exposure, etc. 50/1.2 has thinner DOF than 50/1.4.

I have seen the 35/1.4 Summilux ASPH having thinner DOF than the 35/1.4 Nokton, both at f1.4. Also, the web is full of similar observations when comparing Noctilux with 1.1 Nokton at the same aperture. Etc.

Regarding the difference digital/film, I'll have to test that quantitatively one day ... But I suggest to browse the M-mount flickr group, and compare Summilux 50/1.4 ASPH photos taken with film vs. M8/9. It's only visible in some bokeh-intensive shots. If you are a bokeh hater you won't mind the difference 🙂

Roland.

Roland:

Thanks, but I wanted an example to show the film/digital difference.

However, your example shows different renderings of the out of focus area--or Bokeh if you prefer. Also, the highlights you show really illustrate the aperture and indicate the difference in mechanical vignetting more than anything--I would bet the f/1.4 has more light fall of toward the edges than the f/1.2 @ f/1.4 simply by the size of the specular images. however, your example does not show that the DoF is actually different.

 

[FrankS]

The format determines the focal length of a normal view lens, and the focal length of the lens determines the DOF (with aperture, and focusing distance being the same.)

So, the shorter focal length of a normal view (46 degrees) lens of a smaller format, gives greater DOF than the longer focal length normal view (46 degrees) lens of a larger format.