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  • Welcome to the new site. Here's a thread about the update where you can post your feedback, ask questions or spot those nasty bugs!

Helpful Hints/D.I.Y.: A new tool for the production of high quality output

Hi folks,

As serious photographers, we are occasionally faced with shooting scenarios that we have less experience with compared to our usual subject choices. It can be helpful if we can test several setup scenarios before doing the actual shoot.

How large can we print, which lenses do we need, how much of the subject will be in critical focus? Those are just some of the questions we may want to be able and answer in advance, and go in prepared.

Many, if not all, of those questions can be answered with the use of so-called Depth of Field calculators. Several of those calculators are available on the internet, or as a dedicated application, also for smartphones and tablets. However, one of the biggest shortcomings of those calculators is that they require to input an important calculation parameter, the so-called Circle of Confusion diameter limit, but they do not offer any guidance as to what value is best to use.

In fact, most of them offer preset values based on the selected camera model, thus totally ignoring the intended output quality requirements and viewing conditions. Producing large format output requires different settings than those required for producing images for a webpage. The one-size-fits-all approach doesn't fit at all if quality is your concern.

"It's a DoF calculator, Jim, but not as we know it."

The tool I am offering is a bit different. Of course it uses the same fundamental algorithms to calculate the physical consequences of lens settings such as focus distance and aperture, but it does so with our intended shooting goals and available equipment in mind. It also applies some automatic refinements, e.g. when diffraction is a limiting factor.

Therefore those shooting and viewing goals need to be determined as a first step, and the available equipment as the second, with a few simple selections. Only then will we be able to do meaningful calculations. The results of those calculations may occasionally surprise us because the calculated results are goal specific, instead of generic. That's particularly useful in uncommon shooting situations.

The tool will try and stay close to the input that was given earlier, if possible, therefore the order in which the input changes are made matters. Some of the choices will alter prior input, which is inevitable because everything is part of a single possible solution.

The fastest way to achieve the result we are looking for is to follow the sequential settings from top to bottom, that's why I've numbered them, unless one of the later parameters is already known to be a given.

An example is the choice of aperture / f-number, e.g. if the optimum lens performance is more important than the creative DoF consequences (e.g. in case of Reproductions), then by all means select it first, and the rest of the parameters will follow this setting, unless the tool is forced by your
subsequent input to adjust the aperture again.

Another example is with Photomacrography, where it is often more logical to set the magnification factor first, and then move the subject into the focus-range. Then by all means, set the focal length of your macro lens, and the magnification factor first.

To simplify this first setup, I've provided a number of generic shooting setups that you can choose from with a pull down menu. Those settings will get you in-the-ball-park.

Now, without much further ado, here is the link to the on-line web application:
The Depth of Field output quality planner.

As of this posting, it's a beta-testing version release, although I've tried to already eliminate as many potential issues as possible. It was tested on several web-browsers, and I've also built in some prevention for overly 'creative' input, such as negative distances. Under very rare input situations, I hope, one may run into an issue. In that case pick one of the generic scenarios to get a fresh starting situation. Refreshing the web page will ultimately solve any issue, but also requires to start all input from the beginning.

I welcome user feedback, it will help to make it an even more useful tool.

Cheers,
Bart
 

Nicolas Claris

Administrator/Moderator
Wow! Bart!
Great tool! I have abandoned for long the use of iPhone calculators for their inaccuracy…

I just had a quick glance and I saw with a great pleasure (et soulagement ;) that the 645 D is included :-D

Now 2 questions :
- What happens when one is offshore with no internet connection?
- When setting the focal length should one use the 24x36 equivalent or lens builder's definition i.e. for the Pentax 645D my wide lens for shooting interiors is a "25 mm" equivalent to 21 mm in 24x36 format… which value should I use?

Bravo, kudos et surtout, merci ! So kind of you share this neat tool!
 
Wow! Bart!
Great tool! I have abandoned for long the use of iPhone calculators for their inaccuracy…
Hi Nicolas,

I wouldn't know about the iPhone versions, but there are a few for Android that are accurate, but they usually do not offer any guidance for output referred setting of the COC parameter. The COC is viewing (distance/quality) dependent, so those tools are pretty useless without that input, or prior knowledge of what to use.

I try to do all internal calculations at the highest possible accuracy, only screen output is rounded to a few decimals to avoid screen clutter.

I just had a quick glance and I saw with a great pleasure (et soulagement ;) that the 645 D is included :-D
I did that especially for you!

Now 2 questions :
- What happens when one is offshore with no internet connection?
Ah, but you should do the planning before heading for sea ;)

No, seriously, I currently have no official solution for the situation that there is no internet connection, but I may offer a stand-alone solution for that in the future.

- When setting the focal length should one use the 24x36 equivalent or lens builder's definition i.e. for the Pentax 645D my wide lens for shooting interiors is a "25 mm" equivalent to 21 mm in 24x36 format… which value should I use?
You use the actual focal length as indicated on the lens by the manufacturer. No guessing or 35mm equivalent notations, but the actual physical values.

I have not written any formal help documentation yet, so it is already helpful for me to learn how intuitive the tool is, even without further documentation. I will write documentation (also based on the questions I receive), because there is a lot to explain that is not obvious for the average user. I also intend to post a few scenarios for common questions and how to answer them with the tool.

Bravo, kudos et surtout, merci ! So kind of you share this neat tool!
You are welcome. Thanks for the compliments.

Cheers,
Bart
 

Doug Kerr

Well-known member
Hi, Bart,

A wondrous tool. Bravo.

I have not had time to play with it yet, but I do have a couple of initial editorial observations.

Your item 2.1 is, I assume, the distance at which the camera is focused. Some slightly different label might make that clearer.

I assume that your item 2.8 is the circle of confusion diameter limit, the diameter of the circle of confusion that we adopt (under one premise of another) as our criterion of the limit of acceptable (or perhaps "negligible") blurring.

The name "circle of confusion", while of course widely attached to this metric, is very inappropriate. It is as if we labeled the maximum nominal diameter of the tire that is usable on a vehicle as its "tire", or the minimum water pressure that is satisfactory on a washing machine as its "water".

You may wish to call this the circle of confusion diameter limit.

Again, a marvelous job, executed in great style!

Best regards,

Doug
 
Hi, Bart,

A wondrous tool. Bravo.

I have not had time to play with it yet, but I do have a couple of initial editorial observations.

Your item 2.1 is, I assume, the distance at which the camera is focused. Some slightly different label might make that clearer.
Hi Doug,

You are correct, focused distance or focus distance would seem to avoid such confusion.

Of course that still doesn't clarify from where it's supposed to be measured! I think that on many lenses, the distance scale is marked as the distance between focal plane (sensor or film), and often marked on the body, and subject in focus.

Most lens formulae calculate object side distance from the front principle plane, because the distance between front and rear principle plane varies with lens design and focus distance. One would then need to add the image side focal length and extension (from not focusing at infinity) and unknown distance between principle planes to get a match with the lens indicated distance.

I assume that your item 2.8 is the circle of confusion diameter limit, the diameter of the circle of confusion that we adopt (under one premise of another) as our criterion of the limit of acceptable (or perhaps "negligible") blurring.

The name "circle of confusion", while of course widely attached to this metric, is very inappropriate. It is as if we labeled the maximum nominal diameter of the tire that is usable on a vehicle as its "tire", or the minimum water pressure that is satisfactory on a washing machine as its "water"

You may wish to call this the circle of confusion diameter limit..
Strictly speaking, you are correct, but most people already understand the COC as being the limit of acceptable blur diameter that it is. They would get confused themselves if anything other was meant ;)

I would also need to reserve more screen space to display the full definition, so I'll see if I can accommodate it some way or another. But you are correct, no question about that. I can always point them to your excellent explanation here. I already used the more complete description as one hovers the mouse pointer over the input field as a tool-tip text.

Again, a marvelous job, executed in great style!
Thanks a lot.

Bart
 

Asher Kelman

OPF Owner/Editor-in-Chief
Bart,

How do you take into account the practical findings reported by Theodoros, here. If indeed the D4 with less pixels is doing far better than the D800 of an kind, then how is this considered in your software for reproduction size and viewing. Can Theodoros substantiate that with an Imatest chart picture for you, for example?

Asher
 
Bart,

How do you take into account the practical findings reported by Theodoros, here. If indeed the D4 with less pixels is doing far better than the D800 of an kind, then how is this considered in your software for reproduction size and viewing. Can Theodoros substantiate that with an Imatest chart picture for you, for example?
Hi Asher,

I have no idea what he bases his opinion on, but it must be something else than resolution. Resolution has almost everything to do with sampling density combined with number of sensels, at which the D800 is excellent. I therefore assume he is referring to other features, such as color reproduction of certain pigments or dyes.

But it is best to keep that discussion in his thread, rather than here.

There are many aspects to image quality, but I'm focusing on measurable things like resolution in this thread, not the more subjective aspects of image quality like color (which also depends on the software profile / Rawprocessor used), or ease of handling, or Live View implementation, etc.

Cheers,
Bart
 

Doug Kerr

Well-known member
Hi, Bart,

You are correct, focused distance or focus distance would seem to avoid such confusion.

Of course that still doesn't clarify from where it's supposed to be measured! I think that on many lenses, the distance scale is marked as the distance between focal plane (sensor or film), and often marked on the body, and subject in focus.

Most lens formulae calculate object side distance from the front principle plane, because the distance between front and rear principle plane varies with lens design and focus distance. One would then need to add the image side focal length and extension (from not focusing at infinity) and unknown distance between principle planes to get a match with the lens indicated distance.
Indeed.

Strictly speaking, you are correct, but most people already understand the COC as being the limit of acceptable blur diameter that it is. They would get confused themselves if anything other was meant ;)
I understand.

The problem comes when we need to actually speak about the diameter of a particular circle of confusion (as when we calculate out-of-focus blur performance, as for example you do when you refer to infinity blur diameter).

But there's the answer: when speaking of the diameter of a certain circle of confusion, just call it the blur diameter.

It's the old story: its fine to call bison "buffalo" until the one you ordered from Exotics R Us arrives at the door.

Best regards,

Doug
 

Doug Kerr

Well-known member
Hi, Bart,

On your DoF planner, you say, for a selection of "normal quality":

The implied goal is to achieve an angular resolution of 1.0 second of arc (also known as 20/20 vision in Imperial Snellen notation)​

It is generally said that the criterion of 20/20 vision is a visual resolution of one arc minute, not one arc second.

The most common "traditional" COCDL is twice that, corresponding to a resolution of 2 arc minutes (in the context of the "traditional" assumed viewing situation).

Ah, I see that your "tooltip" on the "CoC item does give an appropriate description. Nice.

It looks as if, for a given sensor size, the COCDL does not vary with the choice of "quality" (or anything else). (And I don't immediately recognize the function of sensor dimensions!)) But sometimes it turns red (I guess to warn me of something). What am I missing here?

On a smaller point, I note that sometimes the COCDL does not automatically update when something is changed that should affect it. I have to double click on it to make it update.

Best regards,

Doug
 

Doug Kerr

Well-known member
Hi, Bart,

Oh, I see, the COCDL is based on the sensel pitch. Quality is not a factor in the COCDL I guess that comes into the picture when reckoning "permissible" output size.

It takes us old telephone engineers a while to "get it".

Best regards,

Doug
 

Doug Kerr

Well-known member
Hi, Bart,

I believe that when it is said that for "normal" human vision the eye an resolve two lines at a separation of one minute of angle, the two lines spoken of are lines in the sense of cycles, not in the sense of "TV scan lines".

The notes on your calculator suggest that, for a viewing distance of 1 m, the output resolution required to match the human eye resolution would be 1.719 cycles/mm.

That is 1.719 lines/mm in the sense used to describe human eye resolution.

At a viewing distance of 1 m, that is an angular resolution of 2 arc minutes between the lines.

Best regards,

Doug
 

Doug Kerr

Well-known member
Hi, Bart,

I may be in error that the visual acuity that corresponds to rating of 20/20 corresponds to the ability to discern lines that are 1 arc minute apart (that is, black lines 1 arc minute apart, with white spaces between.

But I see that the relationship to the characters ("optotypes") on the Snellen chart is such that the optotype used as the criterion for 20/20 vision is said to be 5 minutes of arc high, and it is 5 pixels (5 "scan lines") high.

And we would think that it could be recognized if the eye's resolution was 1 line (in the TV scan line sense) per line In the TV scan line sense) of the optotype. (As is the Kell factor was 1.)

If that is the case, then in your calculator, for viewing at a distance of 1 meter, the resolution of the human eye would indeed be 1.719 cycles/mm.

I'll sniff around this a bit more.

This ambiguity in terminology is maddening!

Best regards,

Doug
 

Doug Kerr

Well-known member
Hi Bart,

One reference says:

For a human eye with excellent acuity, the maximum theoretical resolution is 50 CPD (cycles per degree) (1.2 arcminute per line pair, or a 0.35 mm line pair, at 1 m)

If "excellent acuity" corresponds to "20/20" (and I'm not sure that is the right correspondence), then that would be 2.86 cycles/mm at 1 m.

I'm still trying to relate this to the matter of the height of the optotype on the Snellen chart.

Of course, I saw that in a Wikipedia article that may be "suspect" (it had a big "punch list".

More as it comes.

Best regards,

Doug
 

Doug Kerr

Well-known member
Hi, Bart,

Here we go:

A resolution of 2 arcminutes per line pair, equivalent to a 1 arcminute gap in an optotype, corresponds to 20/20 (normal vision) in humans.​

So, to match "normal human vision" with the output resolution of our image, at 1 meter viewing distance, we would need a resolution of about 1.718 cycles/mm.

So you are right on!

But I had to go through that!

You may wish to reflect on this description at the outset:

The implied goal is to achieve an angular resolution of 1.0 second of arc (also known as 20/20 vision in Imperial Snellen notation).​

Because of the "line" ambiguity, it is much safer to explicitly speak in terms of cycles, perhaps thus:

The implied goal is to achieve an angular resolution of 60 cycles per degree (generally corresponding to "20/20" vision as measured with the Snellen eye chart in US customary measure, "6/6" in SI units).​

Best regards,

Doug
 
The problem comes when we need to actually speak about the diameter of a particular circle of confusion (as when we calculate out-of-focus blur performance, as for example you do when you refer to infinity blur diameter).

But there's the answer: when speaking of the diameter of a certain circle of confusion, just call it the blur diameter.
Hi Doug,

I agree that 'blur diameter' is what we're after when seeking for the resolution limit of our capture device. After all, the COCDL input cannot become smaller than the sensel when we seek the limiting resolution.

I did however want to maintain the (almost phsychological) reference to the COCDL, because the input field is named COC in other applications and this value could be copied to those applications one-on-one, should one like to produce certain types of output that those applications might offer. Without the reference to COC(DL) I would generate a lot of (un-asked) questions what value to use in those other applications.

Thanks for the feedback, I'll try and figure out how to implement it.

Cheers,
Bart
 
It looks as if, for a given sensor size, the COCDL does not vary with the choice of "quality" (or anything else). (And I don't immediately recognize the function of sensor dimensions!)) But sometimes it turns red (I guess to warn me of something). What am I missing here?
Hi Doug,

It depends on other inputs. One reason might be that a combination of settings produces a COCDL that is smaller than the sensel dimensions. That is the physical limit on how small the COCDL can be and still make a difference to resolution. That's why the sensor dimensions are factored in, to determine the smallest practical COCDL limit. One could still debate on a circular blur diameter versus a (somewhat) rectangular sensel aperture, but I chose the horizontal/vertical sensel pitch versus the COCDL diameter as the cut-off point.

Another reason might be that the choice of Aperture, causes an absolute diffraction limitation (based on a Luminance weighted average of wavelengths of 564 nm) on the specific sensor that was selected, at the sensel level. Also the focus distance may influence the size of the diffraction pattern, and additionally trigger an 'MTF at Nyquist' comment/warning.

Going in the other direction, e.g. by reducing the output size requirements, will increase the COCDL size, because the output is smaller than the sensor can theoretically resolve.

On a smaller point, I note that sometimes the COCDL does not automatically update when something is changed that should affect it. I have to double click on it to make it update.
Ah, the 'double click' is an undocumented feature (actually everything is undocumented for the moment ;)), but you discovered it. Very clever. Yes, I implemented that very recently as a means to reset the COCDL, but it actually violates the inputs that caused it to differ. I have yet to decide how to handle some of the situations that could cause a need to double click.

Cheers,
Bart
 
Here we go:

A resolution of 2 arcminutes per line pair, equivalent to a 1 arcminute gap in an optotype, corresponds to 20/20 (normal vision) in humans.​

So, to match "normal human vision" with the output resolution of our image, at 1 meter viewing distance, we would need a resolution of about 1.718 cycles/mm.

So you are right on!

But I had to go through that!
Hi Doug,

I'm glad we arrived at the same conclusion. I agree that there can be some confusion caused by the use of lines and line-pairs, versus angular cycles/mm. That's why I chose to do the calculations for the users by simply selecting a resolution quality goal, and translate that to sensel dimensions and PPI output references.

You may wish to reflect on this description at the outset:

The implied goal is to achieve an angular resolution of 1.0 second of arc (also known as 20/20 vision in Imperial Snellen notation).​

Because of the "line" ambiguity, it is much safer to explicitly speak in terms of cycles, perhaps thus:

The implied goal is to achieve an angular resolution of 60 cycles per degree (generally corresponding to "20/20" vision as measured with the Snellen eye chart in US customary measure, "6/6" in SI units).​
Very good suggestion. Very useful.

Cheers,
Bart
 

Cem_Usakligil

Active member
Hi Bart,

This is a great tool and I'm sure I'll use it from now. It seems that many input fields end up effecting others. I'm impressed that you were able to create a solution which would not just throw up error messages but provides a meaningful answer by adjusting some other parameters such as increasing the COCDL when output size decreases: bravo! Additional points for taking care to make it multi browser compatible. I've tested the site in: Firefox, explorer, safari, opera, dolphin, Web-kit based browsers, iPad, and Android; it is consistent in all those. I'm also impressed by the focus stacking section, very valuable in demonstrating how shallow the dof can get, especially in close quarters and macro. For landscape photographers who demand a huge dof (from the foreground to the horizon) it is clear to see that it is not easy to achieve unless one uses the Scheimpflug principles (tilt/shift lenses or a camera with movements) or does focus stacking or perhaps uses the Merklinger technique.

Doug's testing and input are invaluable and it was very interesting to follow his progress in determining the cycles/mm wrt the "normal human vision".
 
Hi Bart,

This is a great tool and I'm sure I'll use it from now. It seems that many input fields end up effecting others. I'm impressed that you were able to create a solution which would not just throw up error messages but provides a meaningful answer by adjusting some other parameters such as increasing the COCDL when output size decreases: bravo!
Hi Cem,

Thanks for the kind words. Although inspired by Doug's other thread(s) on the subject of DOF and COCDL, it also originated from my own need for a tool that would answer some frequently recurring questions, but would be easier to provide an output quality referred solution than possible with most of the previously available tools.

Additional points for taking care to make it multi browser compatible. I've tested the site in: Firefox, explorer, safari, opera, dolphin, Web-kit based browsers, iPad, and Android; it is consistent in all those.
I knew you would appreciate that kind of attention to detail. It was quite an interesting endeavor so far, because there is still a lot of incompatibility between the rendering of HTML content by the various engines used by even the most common web-browsers.

I have reserved some space in the top right of the section 2 input area, to be filled with some useful graphical representation of the calculation results. But there again, one needs to be careful with older browser versions and future HTML5 compatibility. So that may take a while to materialize.

I'm also impressed by the focus stacking section, very valuable in demonstrating how shallow the dof can get, especially in close quarters and macro.
Neat, isn't it? It also was added due to a general lack of available tools to solve those issues where we cannot stop down the aperture enough without getting hit by diffraction losses, macro being an obvious application. I made a spreadsheet version to do the number crunching myself, but that wasn't too helpful when shooting on location without a computer. Now we can calculate our options in the field as long as there is an internet connection to start the webpage (once started and not refreshed it should keep working, it doesn't 'call home' after loading).

The Focus Stacking section will be improved a bit more, to make it more robust against silly input. We photographers sometimes want to bend the rules of physics, e.g. by choosing a very close near focus distance, which can lead to very long calculation times because of the number of slices that need to be calculated.

For landscape photographers who demand a huge dof (from the foreground to the horizon) it is clear to see that it is not easy to achieve unless one uses the Scheimpflug principles (tilt/shift lenses or a camera with movements) or does focus stacking or perhaps uses the Merklinger technique.
Exactly, and that educational aspect (reality check) was also intended. Of course, a lot of DOF restrictions are also reduced if one only produces small output.

Doug's testing and input are invaluable and it was very interesting to follow his progress in determining the cycles/mm wrt the "normal human vision".
Yes, very recognizable indeed, but all feedback from others is also useful in some way or another. I've also subtly implemented the support for (non-metric) distance units that can vary a lot in magnitude (e.g. in the Hyperfocal distance feedback), although I still need to add the non-metric selections to section 2 (partially based on earlier feedback on the common use of non-metric units in another thread). I just didn't want to wait for that to be finished before publishing the tool for a wider audience.

Cheers,
Bart
 
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Doug Kerr

Well-known member
Hi, Bart,

Thanks for all your observations on my observations.

A benefit to me of the path I went through to reconcile the various matters relating to human visual resolution is that I am now in a position to better explain, in my paper, "Depth of Field in Film and Digital Cameras", the premise behind the "traditional" values of COCDL (as, for example, 1/1400 of the image diagonal dimension).

I will present that updated explanation in another note shortly.

Recall that the overall premise of the "traditional" adoption of a COCDL value is that "acceptable blurring" is blurring on the photographic print that does not degrade the sharpness of object on the print from that available via the resolution of the human eye, based on an assumed viewing situation.

That assumed viewing situation, by the way, is the one that, if the camera had used a 50 mm lens, would give "life-size" viewing of objects on the print; that is, objects on the print would be seen as having the same angular dimensions as if they had been seen directly from the camera position.

You of course in the main hold to a wholly different outlook on the establishment of a COCDL: except in cases certain other other factors suggest overriding this, the COCDL used for depth of field calculations should be that one that defines acceptable blurring as blurring that is comparable to the resolution of the imaging system, as inferred from its pixel pitch.

Said another way, "negligible" blurring is blurring that does not (noticeably) degrade the image resolution from the inferred resolution capability of the sensor system.

All interesting stuff.

Best regards,

Doug
 
Hi, Bart,

Thanks for all your observations on my observations.

A benefit to me of the path I went through to reconcile the various matters relating to human visual resolution is that I am now in a position to better explain, in my paper, "Depth of Field in Film and Digital Cameras", the premise behind the "traditional" values of COCDL (as, for example, 1/1400 of the image diagonal dimension).

I will present that updated explanation in another note shortly.
Hi Doug,

Looking forward to that!

Recall that the overall premise of the "traditional" adoption of a COCDL value is that "acceptable blurring" is blurring on the photographic print that does not degrade the sharpness of object on the print from that available via the resolution of the human eye, based on an assumed viewing situation.

That assumed viewing situation, by the way, is the one that, if the camera had used a 50 mm lens, would give "life-size" viewing of objects on the print; that is, objects on the print would be seen as having the same angular dimensions as if they had been seen directly from the camera position.
I'm sure there are other considerations (e.g. viewing distance versus linear projection perspective) involved as well, but we'll get to that in detail when you present your updated explanation.

As an additional tidbit, when the sensor array dimensions in section 1.3) of my tool are updated, or selected from the Camera brand/model selections database, a default focal length is calculated and filled in at section 2.2). It is based on, and rounded up a bit from, the sensor's diagonal dimensions. Viewing images from roughly the same distance as the diagonal image dimension seems to convey a somewhat 'normal' viewing sensation/perspective. It also saved me from maintaining a complete database of 'normal' focal lengths for the various cameras that will be added to the database ... Specific requests for camera models to add are welcome, it helps me to prioritize.

You of course in the main hold to a wholly different outlook on the establishment of a COCDL: except in cases certain other other factors suggest overriding this, the COCDL used for depth of field calculations should be that one that defines acceptable blurring as blurring that is comparable to the resolution of the imaging system, as inferred from its pixel pitch.

Said another way, "negligible" blurring is blurring that does not (noticeably) degrade the image resolution from the inferred resolution capability of the sensor system.
Well, our outlooks are maybe not wholly different, after all we should arrive at the same COCDL values for the same viewing distance, but I also have to consider that we nowadays can produce much larger output much easier, and may want to exploit all the resolution that modern optics and software enhancements have to offer.

An often posed question is; "How large can I print my images with a still decent enough quality?" That is now a lot easier to answer. Smaller output is easy, plenty of DOF, lot of opportunities for shorter exposure times. There is also no need to focus beyond the 'Hyperfocal distance', unless you want to blur the foreground.

I full well remember the times when I had to project my negatives on a wall of the darkroom with my enlarger head tilted sideways to expose the paper that was stuck to that wall, if the column of the enlarger was not tall enough and I had no shorter focal length enlarger lens available. I'm glad things are so much easier now.

Cheers,
Bart
 

Doug Kerr

Well-known member
Hi, Bart,

Well, our outlooks are maybe not wholly different, after all we should arrive at the same COCDL values for the same viewing distance, . . .
Oh, not at all. One approach does not take at all into account the visual acuity of the eye, and the other does not at all take into account the resolution potential of the sensor system. There is no reason to expect they would lead to comparable recommendations as to COCDL.

For example, in the absence of various overriding conditions, for a sensor with a sensel pitch of 10 um, your planner adopts a COCDL of 0.01 mm (10 um).

The traditional COCDL value, for a 36 mm × 24 mm sensor, is 0.031 mm (31 um).​

.. but I also have to consider that we nowadays can produce much larger output much easier, and may want to exploit all the resolution that modern optics and software enhancements have to offer.
Indeed a very appropriate outlook. I have no problem with that.

Best regards,

Doug
 
Oh, not at all. One approach does not take at all into account the visual acuity of the eye, and the other does not at all take into account the resolution potential of the sensor system. There is no reason to expect they would lead to comparable recommendations as to COCDL.

For example, in the absence of various overriding conditions, for a sensor with a sensel pitch of 10 um, your planner adopts a COCDL of 0.01 mm (10 um).​

Hi Doug,

The emphasis added is mine.

Yes, and 0.010mm is pretty close to an 8x12in output size (my calculator gives 0.01031 mm for that).

However, that is not the basis on which the DOF assumption of 0.030mm was founded, as far as I know. That was more related to common output sizes at that time, closer to 4x6 inches (0.020mm) or even a bit smaller.

The traditional COCDL value, for a 36 mm × 24 mm sensor, is 0.031 mm (31 um).​
Yes, but do remember that the 35mm still camera format as we now know it originated in Europe (soon followed by US models). Oscar Barnack's Leica used also 35mm Cine film as its fundamental film stock, and made the larger 24x36mm frame size (instead of the more 'common' 24mm 'half-frame' size) popular, and in Europe a print size of 6x9cm (0.035 mm according to my calculator) was common (also because that was the same size as a contact print from roll film, later 120 spool film).

So maybe, not that different after all ...? It just depends on who one supposes set that traditional value of 0.031mm, not on the calculator ;).

Cheers,
Bart
 
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Hi folks,

For those interested, I've added a bit more control to the choices in focus stacking.

Before this update, there were more automatic assumptions being made under-the-hood. Now you can specify whether the tool needs to search for a solution at the front or the back of the stacking range, when the total (goal) range is changed.

It is even possible to allow the tool to determine an Aperture setting for a single frame that would achieve a similar Depth of Field as a stack of images (which may not be possible, or could lead to significant diffraction blur being introduced). Be careful with using that, because it could negatively impact the resulting image quality (which was why it was not an option before).

Cheers,
Bart
 

Doug Kerr

Well-known member
In a complex dialog that unfortunately arose in a separate (but related) thread, Bart has helped me to understand the very sophisticated concepts behind this calculator.

For example, the establishment of the COCDL that is then used as a premise to calculate depth of field, various concepts are taken into account as appropriate to the situation. The process begins revolving around the concept of not substantially compromising (for objects at the DoF limits) the theoretical resolution of the sensor itself (based on its sensel pitch).

But, when such matters as diffraction, or the impact of finite human eye resolution, "come into the arena" because of the particulars of the shooting and viewing context, they are taken into account in ways that draw upon the observations of Bart's considerable experience.

Congratulations, Bart, on a really fine treatment of an extremely complicated situation.

Best regards,

Doug
 
In a complex dialog that unfortunately arose in a separate (but related) thread, Bart has helped me to understand the very sophisticated concepts behind this calculator.

For example, the establishment of the COCDL that is then used as a premise to calculate depth of field, various concepts are taken into account as appropriate to the situation. The process begins revolving around the concept of not substantially compromising (for objects at the DoF limits) the theoretical resolution of the sensor itself (based on its sensel pitch).

But, when such matters as diffraction, or the impact of finite human eye resolution, "come into the arena" because of the particulars of the shooting and viewing context, they are taken into account in ways that draw upon the observations of Bart's considerable experience.

Congratulations, Bart, on a really fine treatment of an extremely complicated situation.
Hi Doug,

Thanks for the kind words, and for a very nice summary of the other exchange indeed.

As I said in the first post of the thread, it's a DOF calculator, but not as we know it. There are other bits of logic built in as well, but human reasoning can be complex, so I sometimes had to choose how to tackle an issue where more than one possible solution exists.

One such example is when inputting the dimensions of our object/subject as a parameter at 2.5) to find a solution for. Well, there are two possible avenues one could follow. One is by changing the distance to the subject, thus making it bigger or smaller by changing the magnification and focus distance. Another way to solve it is by choosing a different focal length and shoot from the given distance. Hence the optional user control over the path to follow next to the input boxes. Both are 2 sides of the same coin for the focus plane, but not for the background blur.

Another example is the way the tool reacts to changing the Front or Rear DOF distance. Since the choice of aperture will dictate the amount of DOF, one cannot solve both Front and Rear distance by entering only a distance. One therefore needs to increase the Aperture first to get enough DOF to begin with, and then select either Front or Rear DOF distance as being more important. Alternatively one can approach the Front/Rear DOF range issue as a Focus stacking issue, and even let the tool figure out which aperture would be required.

Cheers,
Bart
 
As requested, I've just added some initial support for Non-SI units of distance to the Camera-lens settings, sections 2.1) - 2.1.2).

A number of associated fields (e.g. 2.1.3) and the Hyperfocal distance) are updated as well, depending on the distance unit choices. The Hyperfocal distance is reported in the same type of units as selected for the Focus distance, because one might want to take that clue as a new focus distance. The type of units for the Front and/or Rear DOF distance will determine the scaled units for the total DOF range at 2.1.3). That Total DOF range will be scaled to relatively meaningful numbers and units, to allow an accurate value in a few digits without too many zeros before or after the decimal point.

There are more distance fields that need to be enabled for Non-SI units, but I wanted to already share this for those who can't intuitively relate to metric units for the most important distances. I also added the relatively unpopular yards, for those who want to try their skills at shooting sports.

I need to do some more testing, but it looks like I didn't break anything vital by adding this.

Later I may add a simple choice to switch all units with a single click, but there may be specific requirements for more detailed unit choices, hence the current high level of control (I also added some larger distance units - km and mi - to the Rear DOF selection, to allow input with fewer digits in some cases).

Cheers,
Bart
 
Since it's appreciated, thanks Doug for letting me know, I've further expanded the support for non-SI units to include the Object dimension settings.

Additionally I've changed the handling of the (optionally chosen) resulting optimized Focal length value. It formerly defaulted to nice rounded (to 5mm) focal lengths, but that also introduced slightly less accurate results for the depending parameter values. Now, one can double-click on the Focal Length field, and it will do the rounding to the nearest 5mm, and additionally recalculate the entire model where it depends on the focal length.

The Object dimension settings allow to automatically set all other related parameters, and can be used if the object dimensions are already known in advance. This can be used with reproduction of e.g. paintings/drawings, or when the main subject has a known size in the plane of optimal focus.

Do note that it only applies to the subject dimensions in the focus plane (that's why that is usually set first, or is optimized for), and that the use of a different focal length will produce a different rendering (size and blur) of the foreground and the background features. The photographer must still make creative choices, but won't have to worry about fitting the main subject in the frame.

This still leaves the 2.7) Total Depth of Field (and it's dependents) to be enabled for non-SI unit input, but that's a tricky parameter to change anyway, because it impacts the original quality goal for the required image size. It is generally not advised to change it there, but e.g. change the Aperture if more or less DOF is needed.

The value of the total DOF is reported at 2.1.3) anyway, and there it uses the distance units that were set for the Front or Rear DOF distance.

Cheers,
Bart
 
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