TriX Loc: Raleigh, NC

Four. Two green, one red and one blue.

khildy Loc: Brownsburg, IN

DocDav Loc: IN

Hey. Didnt you leave out the ,'z; axis. How about a parabolic formula.?

CHG_CANON Loc: the Windy City

I did assume the relationship is linear. Maybe not and that is why it's so hard to express how many dots fit in a pixel?

DocDav Loc: IN

Lol

User ID

Your third post since you got here only a week ago. In accordance with the safety regulations for public places, the exit is very prominently marked. So, if you’re feeling uncomfortable, there’s certainly no reason to feel trapped.

WILLARD98407 Loc: TACOMA, WA.

Can't I just zoom or crop to the image composition I want and then print any size at somewhere between 300 and 1400 dots per inch, depending on what is most visually pleasing?

selmslie Loc: Fernandina Beach, FL, USA

You example is flawed.

By changing the subject distance you are changing the perspective. The only part of the image that has the same magnification is the object at the focus distance. Everything else is magnified more or less in the two images.

To keep the same perspective you need to keep the same focus distance. To keep the same field of view you need to change the focal length. And when comparing two formats you need to adjust the aperture.

Both formats must have the same aspect ratio or the two images will not be the same. You would need to crop one or the other (or both) to get to the same height and width in the final image on your screen or print.

Another problem with comparing a full frame sensor to a 1.5x crop sensor is that the apertures change by a factor of 1.4, not 1.5, so you aren't going to get an exact match.

Here is an example with the same perspective and field of view:
-

Difference is because the crop factor does not match the aperture ratio

(Download)

Ysarex Loc: St. Louis

No it is not. The claim about DOF that I responded to is flawed. My example illustrates that.

I responded to this claim by another poster: "Depth of field depends on the magnification of the image on the sensor and the selected f number. Assuming that the f number is constant the depth of field for a head shot of a person will be less on 8 x10" film than it is when using micro 4/3. This is because the size (magnification) of the head on the micro 4/3 sensor is smaller when compared to the actual size of the head."

There is no mention of perspective in that claim nor any mention of subject distance. The illustration provided by the claimant makes it clear that magnification means magnification of the subject in focus (head shot).

My illustration meets the specifics of that claim -- same magnification of the subject in focus and f/stop.

selmslie Loc: Fernandina Beach, FL, USA

As soon as you mention that it's a head shot you introduce the need to maintain the perspective. If you change the subject distance you are going to change the relationship between the size of the nose and the size of the ears. So you must do the comparison from the same distance to maintain the same perspective. That will also maintain the relationship between the subject and the background and foreground.

But the what most photographers overlook is that DOF is based on the magnification of the subject in the print or display. If a 10 foot tall subject is printed or displayed at 10 inches in height the final magnification is 1:12, regardless of the size of the sensor or film format.

In fact, if you capture an image on a full frame sensor and later crop it in post processing before printing and displaying it, you will be changing the DOF. And if you view the image on your monitor and change the magnification you will be changing the apparent DOF. That's what happens when we look at an apparently sharp image that fills the screen (maybe at 50%) and the change it to see it at 100%.

My example makes that clear and yours does not. And since you changed the subject distance it's not a valid comparison.

To learn about the reason you need to change the aperture see Equivalence theory for cross-format photographic image quality comparisons. It's a a lot to go through but the bottom line is that you need to change the aperture in proportion to the change in the size of the circle of confusion.

Ysarex Loc: St. Louis

No you don't. You're just throwing off-topic nonsense around. The poster I responded to never made a claim about trying to take the "same photo". The post I responded to was clear: "Depth of field depends on the magnification of the image on the sensor and the selected f number." That's incorrect. There is no mention of same perspective or subject distance or equivalent f/stops or a need to take the same photo. My example makes it clear that statement is incorrect.

Do you want to make a different claim?

selmslie Loc: Fernandina Beach, FL, USA

It's not off-topic since it addresses "equivalent focal length", the topic of this thread.

If you think it's nonsense you don't really understand the meaning of DOF which is, "... the distance between the nearest and the farthest objects that are in acceptably sharp focus in an image."

But you can't see the image on the sensor. You have to print it or display it. To do that you have to decide how big to print or display he captured image.

DOF is not a property of the image or the sensor. It's a property of the final image, the one you can see. And since you are going to display or print it at a particular magnification in relation to the original subject it's the final magnification that really matters, not the magnification at the sensor.

That's why no DOF calculator tells the whole story. The one from Cambridge in Colour comes closest and it would be complete if it mentioned cropping of the original image in the generation of the final print.

Since there are many film and sensor formats you can use (4:3, 1:1, 3:2, 4:5, 5:7, 11:14) to make an 8x10 print, all formats need some cropping.

If you really understood DOF you would know that it's always an approximation. It's subjective based on the meaning of "acceptably sharp".

Ysarex Loc: St. Louis

I didn't respond to the topic of the thread I responded to a specific claim by another poster. He said; "Depth of field depends on the magnification of the image on the sensor and the selected f number." I pointed out that is incorrect. I provided an illustration that demonstrates that.

I've no interest in your ramblings otherwise. Are you claiming that the poster I responded to is correct? Are you making some other claim?

selmslie Loc: Fernandina Beach, FL, USA

So your response was also off topic. Two wrongs don’t make a right.

But your response was still flawed because you don’t really understand DOF completely.

And you are apparently unwilling to learn from someone who does. That’s your loss.

Ysarex Loc: St. Louis

My response was on topic to the poster to whom I responded.

The poster I responded to said: "Depth of field depends on the magnification of the image on the sensor and the selected f number." I demonstrated that is incorrect.

Are you claiming that the poster I responded to is correct? Are you making some other claim?