[Blue]

Guys. You are all missing a point

DOF is a function of lens aperture and the ratio of image size including the enlargement of the print related to subject size

If you take a picture of something with a 200 mm lens for example and shoot with both formats ( film and ASP-C) and print the subject to the same size the depth of field will be the same

Where people vet crossed up is they use shorter lenses and move closer to get the same image size on the two different sensors and then enlarge them with different print ratios from the sensor to print

The net result is comparing apples and oranges

Actually, given the question regarding sensor size and DOF, the question was answered.

[Lowell Goudge]

Actually, given the question regarding sensor size and DOF, the question was answered.

Not unless you read in detail the linked explanation of Circle of Confusion

The fact is, that it is all a function of enlargement of the final image. No one in the text of their posts EVER made that point clear

The present "standard" for DOF is all based upon an 8" x 10" enlargement of the full frame of the respective format.

But that now almost becomes meaningless because we all have bigger computer screens than that, and zoom in to incredible ultimate magnifications.

I stand by my position, you cannot have a discussion of DOF without addressing the final print/viewing magnification as well as the focal length image distance and aperture. (as they relate to the overall reproduction ratio between subject to image as viewed.

[Blue]

Not unless you read in detail the linked explanation of Circle of Confusion

The fact is, that it is all a function of enlargement of the final image. No one in the text of their posts EVER made that point clear

. . .

Really?

True, but the Circle of Confusion is used in the calculation and the C of C changes depending on format.

Circles of Confusion for Digital Cameras

[Lowell Goudge]

Really?

yes really,

the link to the calculator states specifically a CofC for 35mm film at 0.030mm but does not, in that link explain the reason WHY 35mm film is based upon 0.030mm. The link to Wikipedia does explain it all.

It goes back to the fact I stated above, that the depth of field is ultimately a function of how BIG you print something.

This is similar to the issue for shutter speed and 1/FL as a minimum for hand holding. It is again based upon an 8 x 10 enlargement. If you blow something up bigger it requires a different shutter speed to eliminate shake, the same as a bigger enlargement has less depth of field.

[RioRico]

We're doing this again? Let's not forget that DOF is partly in the camera and partly in the presentation. Yes, aperture and focal length and focal distance and frame (film/sensor) size are critical; but so are enlargement, and how an image is displayed, and the placement and quality of a viewer's eyeballs.

I can adjust distance and aperture when I shoot. I can factor frame size into the equation by allowing for 1+ f-stops when I read a lens' DOF chart -- so I'll set the aperture to f/11, but hyperfocus as if it were f/7. Or I can just print the image at 9x12cm / 3.25 x 4.25 inches, and nobody will notice the crappy DOF. Big deal.

[Lowell Goudge]

We're doing this again? Let's not forget that DOF is partly in the camera and partly in the presentation. Yes, aperture and focal length and focal distance and frame (film/sensor) size are critical; but so are enlargement, and how an image is displayed, and the placement and quality of a viewer's eyeballs.

I can adjust distance and aperture when I shoot. I can factor frame size into the equation by allowing for 1+ f-stops when I read a lens' DOF chart -- so I'll set the aperture to f/11, but hyperfocus as if it were f/7. Or I can just print the image at 9x12cm / 3.25 x 4.25 inches, and nobody will notice the crappy DOF. Big deal.

+1 (or is it two since I am singing the same tune?)

[Blue]

yes really,

the link to the calculator states specifically a CofC for 35mm film at 0.030mm but does not, in that link explain the reason WHY 35mm film is based upon 0.030mm. The link to Wikipedia does explain it all.

It goes back to the fact I stated above, that the depth of field is ultimately a function of how BIG you print something.

This is similar to the issue for shutter speed and 1/FL as a minimum for hand holding. It is again based upon an 8 x 10 enlargement. If you blow something up bigger it requires a different shutter speed to eliminate shake, the same as a bigger enlargement has less depth of field.

Lowell, I like how you conveniently left out all the C of C for the other sensor/film formats. Your problem is you want to change and evaluate every variable but the one asked about. Show me where I was debating enlargement with you?

[Blue]

We're doing this again? Let's not forget that DOF is partly in the camera and partly in the presentation. Yes, aperture and focal length and focal distance and frame (film/sensor) size are critical; but so are enlargement, and how an image is displayed, and the placement and quality of a viewer's eyeballs.

I can adjust distance and aperture when I shoot. I can factor frame size into the equation by allowing for 1+ f-stops when I read a lens' DOF chart -- so I'll set the aperture to f/11, but hyperfocus as if it were f/7. Or I can just print the image at 9x12cm / 3.25 x 4.25 inches, and nobody will notice the crappy DOF. Big deal.

Except Lowell is doing everything but answering this question which is dealing with the format aspect of it.

Sensor size vs. DOF
I know that a larger sensor means less depth of felid, but why is that exactly?

[Lowell Goudge]

Except Lowell is doing everything but answering this question which is dealing with the format aspect of it.

Because the sensor format is only a middle point between the lens and the final image.

It all comes down to the two parts of magnification, that from subject to sensor, and that from sensor to final image size.

Unless you bring both into the equation, it is only a part answer.

Go back to my origonal post, where I pointed out that you cannot discuss this without discussing the final image size.

You rejected it, yet it MUST be considered, because all the other discussions around the CoC are all pre-determined on a supposed final image size that no one actually prints to any more.

[Blue]

Because the sensor format is only a middle point between the lens and the final image.

It all comes down to the two parts of magnification, that from subject to sensor, and that from sensor to final image size.

Unless you bring both into the equation, it is only a part answer.

Go back to my origonal post, where I pointed out that you cannot discuss this without discussing the final image size.

You rejected it, yet it MUST be considered, because all the other discussions around the CoC are all pre-determined on a supposed final image size that no one actually prints to any more.

I didn't reject a thing. I was answering the question about format size and its effect on the question. There is generally a standard enlargement and viewing distance taken into account. The viewing distance of a print is generally ~ the diagonal of the print for the resolving power of the human eye (5 lp/mm on the average). The print sizes are typically 4X6 and 8x10 with about 7 inches and 13 inches viewing distance respectively.