Depth of field - is it linear?

[djaef]

Hi guys,
I'm interested in depth of field and was thinking of how to visualise the increasess and decreases of depth of field at different apertures, focal lengths and focusing distances.

For example, with each one individually, on a chart with an x/y axis, would they be linear progression, or does the effect suddenly come on?

And I know that focal length is not considered to be a technical change to depth of field, rather than an enlargement of the blur, but in the real world, it clearly affects apparent depth of field, and I was wondering if this too was linear.

So in case i haven't explained myself, I'm trying to visualise three charts, one for aperture, one for focussing distance and one for focal length and trying to imagine if the line on each chart would be a straight line, or a curved one.

Thanks. Any input is much appreciated.

Geoff

[Manfred M]

I suggest that you read the following tutorial on this site.

https://www.cambridgeincolour.com/tu...h-of-field.htm


I think you will find the write up and charts of interest.

[djaef]

I suggest that you read the following tutorial on this site.

https://www.cambridgeincolour.com/tu...h-of-field.htm

I read that first, of course. It does not answer my questions at all.

[dje]

Hi Geoff

The plots are not linear. This reference might be helpful.

How's the weather up there? Pouring rain like it is here?

Dave

[Manfred M]

I read that first, of course. It does not answer my questions at all.

The fact that the DoF in front of the subject and behind the subject changes based on the lens focal length used suggests that the phenomenon is non-linear.

[djaef]

Thanks for that Dave. Just have to interpret it now To my mind, based on my experience, dof as affected by say focusing distance happens all at one end, aperure seems also to mostly happen at one end, while the effect of focal length appears to be more linear. I'm not incredibly scientific, but I will see if I can make sense of those charts.
And yes, raining on and off all day today..

[djaef]

The fact that the DoF in front of the subject and behind the subject changes based on the lens focal length used suggests that the phenomenon is non-linear.

My experience also suggests it's not linear, but that still doens't give me any idea of what the chart would look like

[dje]

Thanks for that Dave. Just have to interpret it now To my mind, based on my experience, dof as affected by say focusing distance happens all at one end, aperure seems also to mostly happen at one end, while the effect of focal length appears to be more linear. I'm not incredibly scientific, but I will see if I can make sense of those charts.
And yes, raining on and off all day today..

Strictly speaking, you should probably look at the DOF behind the focus point and the DOF in front of the focus point separately, rather than the total of these two. This would show you where the acceptable "in-focus" points are.

There may be other plots around on the web of course. Some Googling might be necessary.

Dave

[Manfred M]

My experience also suggests it's not linear, but that still doens't give me any idea of what the chart would look like

There is a chart that shows that data for specific focal lengths in the tutorial I pointed you to.

[djaef]

The fact that the DoF in front of the subject and behind the subject changes based on the lens focal length used suggests that the phenomenon is non-linear.

And that's talking about the distribution of depth of field, not the amount. What I'm after is an understanding of how to visualise the changes made by one adjustment on depth of field. I'm not incredibly technical, but I fail to see how the change in distribution of depth of field by focal length helps me here.

[djaef]

It's a ridiculously technical subject and I'm not incredibly technical. I just wanted a better idea of how to visualise a change in dof one influence at a time.

For example if I start at 5.6 and focus as closely as possible, and measure the dof, and then increase the focus distance by 1cm for example, and again measure the dof, and keep going like that until I get to say the hyperfocal distance, what would the chart look like if I plotted it. I am pretty sure we are all in agreement that the plot would not be linear, but I'd love to see such a chart.

Anyway, thanks for the help.

[djaef]

I think I found what I was looking for in this - http://paulorenato.com/index.php/151

[dje]

I think I found what I was looking for in this - http://paulorenato.com/index.php/151

Yes Geoff, that looks like it could serve your purpose. I've downloaded a copy of the spreadsheet myself for future reference. Thanks for the link.

Dave

[george013]

That are diagrams I was looking for too. Thanks.
I wanted to build one in Javascript using the formulas of https://en.wikipedia.org/wiki/Depth_of_field.

George

edit.
I downloaded it. He is using the formulas of the link I gave. I opened it in OpenOffice but it's read-only.

George

[dje]

edit.
I downloaded it. He is using the formulas of the link I gave. I opened it in OpenOffice but it's read-only.

George

George I think when I opened it in Excel it had editing disabled but there was a button to press to enable editing. Not sure what happens with OpenOffice.

Dave

[george013]

What button? I don't see one.

George

[dje]

What button? I don't see one.

George

George

The DOF spreadsheet was in protected view mode when I downloaded it. This was shown in a small yellow banner at the top. On the right hand side of that banner was a button labelled Enable Editing. It may be that OpenOfffice can't handle this sort of thing, I don't know. Can you try it in MS Excel?

Dave

[Pippan]

Something I’ve been wondering. Given that, as I understand it, truly sharp focus is only at an infinitesimally thin plane, are the generally proffered limits of ‘sharpness’ in DOF tables and calculators really only ‘acceptable’ sharpness, and do they assume some standard image magnification (say 8” x 10”) and viewing distance (say 2 feet). Does a larger print (say 24” x 36”) or a closer viewing distance result in a thinner DOF at the same camera settings, since even slightly out of focus areas have been magnified to the viewer and would be more visibly OOF? If so, why don’t DOF tables or calculators (e.g. Paulo Renato’s) incorporate these variables?

[Manfred M]

Something I’ve been wondering. Given that, as I understand it, truly sharp focus is only at an infinitesimally thin plane, are the generally proffered limits of ‘sharpness’ in DOF tables and calculators really only ‘acceptable’ sharpness, and do they assume some standard image magnification (say 8” x 10”) and viewing distance (say 2 feet). Does a larger print (say 24” x 36”) or a closer viewing distance result in a thinner DOF at the same camera settings, since even slightly out of focus areas have been magnified to the viewer and would be more visibly OOF? If so, why don’t DOF tables or calculators (e.g. Paulo Renato’s) incorporate these variables?

Mostly because this issue is self-limiting. As the image size gets larger, you have to view if from farther away. A rule of thumb I was taught many years ago was that a good, safe approximation for minimum viewing distance is the diagonal of the print size.

[William W]

. . . do they assume some standard image magnification (say 8” x 10”) and viewing distance (say 2 feet).

Simple answer = yes.

(and that assumes a NON CROPPED image)

WW