Magnification factors for macro lenses

[William W]

BTW: George - If you read the three links that you have provided and then re-read my repeated definition of "Working Distance" throughout this conversation you will find that your three references and my definition of "Working Distance" are, in fact, the same. . . (again in simple/lay terms) WD = distance from the front of the lens to the subject.

Thanks,

WW

[george013]

AND



Hi John

Considering your persistence that yours is the correct definition or even a definition which you state is ‘usually given’ and also considering George's passion for correct definitions: could you please cite some instances where it stated that the Distance from the Film Plane to the Subject is the "Working Distance".

Thanks.

WW

William,

I'm the one that opposes your aproach. And I've good arguments. So please tell me your arguments to me.

I'l show you where you're going wrong. Your post 13.

There is (complicated) Mathematics to arrive at the appropriate formula to use, however: if the lens actually produces x1 Magnification (i.e. 1:1), then the simplest, correct formula to find the is 1/2 of the WORKING Distance (Subject to Front Nodal Point).
I understand that the Minimum Working Distance for the EF 100 F/2.8 lens is 149mm:
Hence 149/2 = 74.5mm

Stating that the effective focal length is 1/2 of the working distance must have some corrections.
1) the working distance. That has been explained before. It even changes with or without a lenshood. It is not a optical value. But let's assume your definition, distance first lens to subject.
2) Then the "EFFECTIVE Focal Length (Subject to Front Nodal Point)". As mentioned before, the "effective focal distance" is just the image distance: distance sensor plane to optical center.
3)Your calculation of the 74.5mm is correct BUT only if the working distance is the minimal focal distance.

I understand that the Minimum Working Distance for the EF 100 F/2.8 lens is 149mm:
Hence 149/2 = 74.5mm

The same way you ask John

could you please cite some instances where it stated that the Distance from the Film Plane to the Subject is the "Working Distance".

I do the same to you for your definition of 10working distance and 2) effective focal length

I just see your last post to me. I'll answer that seperate.

George

[george013]

BTW: George - If you read the three links that you have provided and then re-read my repeated definition of "Working Distance" throughout this conversation you will find that your three references and my definition of "Working Distance" are, in fact, the same. . . (again in simple/lay terms) WD = distance from the front of the lens to the subject.

Thanks,

WW

Don't fool me! No they're not the same. You state the working distance is the distance subject first nodal point. It 's the distance between your physical camer/lens and the subject. It's the space you have to move a box between them
From the Sigma link,https://blog.sigmaphoto.com/2013/mac...robert-otoole/, camera with and without lenshood: two different working distances. It's not an optical value.
It's the space between your gear and a living object. It's the space through which light can reach the object.


And some below

When comparing macro lenses, dont forget to consider the physical length and hood depth of a lens to get a real idea of the working distance that you would see in the field. Remember that removing a hood can is an easy way to get a big increase in working distance.

About you mentioning the working distance being used in early days, I checked the Ilford Manual of 1942. You can download it in PDF. It's not mentioned.
On your recommendation I bought the last Manual of Photography, 10th edition. It doesn't have an item working distance, anyway I couldn't find it.
I also bought the second last Ilford Manual of Photography, 6th edition. The same.

All together a very difficult way to show 1/2x1/2=1/4.

George

[ajohnw]

I can't Bill. However when I bought my m 4/3 macro lens they did quote working distance as being the minimum focus distance. My main point is that no one I am aware of quotes the actual clearance between lens and subject.

Providing a lens's length doesn't change when focusing it is possible to calculate the working clearance the lens will have at 1:1 assuming that is it's max magnification and that the dimensions given are reasonably precise.

Sigma 150mm for instance. Min focus 380mm, Canon flange focal distance 44mm, lens length 150mm so 380-(150+44)=186mm - neglecting the depth of the bayonet on the lens.

Canon 100mm macro 310mm - ( 119+44 ) = 147mm

Olympus 60mm macro 190mm - ( 82+19.25) = 88.75mm

Panasonic 45mm macro 150mm - ( 62.5+19.25 ) = 68.25mm however I understand that is 2:1 not 1:1. They state 35mm equivalent.

I can't find enough info to do the same with the Canon 5x lens but would bet that the working distance will be much more than would be obtained from a typical bellows lens of the same focal length at the same magnification. Shame on Canon if not. From memory the old massive Nikon macro lens beloved by pathologists etc had longer than would be expected working clearances. It all depends on what magnifying elements the manufacturer choose to put in the lens itself. There are likely to be some in any lens as that is how abberations are usually balanced out.

Me - well I'll stick to working clearance.


John
-

[Stagecoach]

George,

Your copied quote ..........................

""When comparing macro lenses, dont forget to consider the physical length and hood depth of a lens to get a real idea of the working distance that you would see in the field. Remember that removing a hood can is an easy way to get a big increase in working distance.""


I think you are simply using a text you have read somewhere on the web that uses the term 'working distance' very loosely as a description specific to what the author is describing, which is available space.

And we all understand that this space varies considerably with such things as hoods, flashes, diffusers and sticking out branches.

I suspect the author had absolutely no intention to use it, or for it to be taken as, scientific, optical or photographic correct terminology.

[george013]

George,

Your copied quote ..........................

""When comparing macro lenses, dont forget to consider the physical length and hood depth of a lens to get a real idea of the working distance that you would see in the field. Remember that removing a hood can is an easy way to get a big increase in working distance.""


I think you are simply using a text you have read somewhere on the web that uses the term 'working distance' very loosely as a description specific to what the author is describing, which is available space.

And we all understand that this space varies considerably with such things as hoods, flashes, diffusers and sticking out branches.

I suspect the author had absolutely no intention to use it, or for it to be taken as, scientific, optical or photographic correct terminology.

Graham,

Tell William. It's not more and not less as that.

William is trying to calculate the subject distance being the distance subject-lens, the optical center. And than it is with an magnification of 1 subject distance = image distance = "effective focal length" = 2xfocal length.
And subject distance + image distance = focal distance.
But one can never measure the subject distance since the optical center is somewhere in the lens. And with a macro lens it changes.
You can focus on infinity and find a place on the lens on a distance from the sensor sine equal as the focal length. But only at infinity.



From http://www.school-of-digital-photogr...-distance.html

The importance of Working Distance in Macro Photography

Working distance of a lens dictates how close you need to get to the subject to capture it at the lens's maximum magnification. This is important for many reasons.

If you are photographing insects or other live subjects the closer you try to get to them, the more the chances of you scaring them away. So longer the focal length / working distance the greater the chances of you getting the shot.

Sometimes when the subject is placed in not very accessible places it is impossible to get close (like when an insect is resting on grass or other foliage) in such cases having a longer working distance is critical.

Another important factor is lighting; with very short working distance you will actually be blocking the light from reaching the subject and it gets very hard to get the light to hit the subject without being blocked by the lens. Even specialist macro lighting equipment like twin flashes and ring flashes find it had to light subjects that are just millimeters away from the lens.

George

[William W]

Working distance is usually given as distance from sensor/film plane to subject George. This goes way back on macro lenses from a time when manufacturers actually produced tables particularly for bellows lenses.
...
all I have ever seen quoted on modern macro lenses is the distance from the focal plain to the subject. Old ones too but also in the form of tables for different levels of magnification.
John

Hi John
Considering your persistence that yours is the correct definition or even a definition which you state is ‘usually given’ and also considering George's passion for correct definitions: could you please cite some instances where it stated that the Distance from the Film Plane to the Subject is the "Working Distance".
Thanks.
WW

I can't Bill.
John
-

Thank you.

WW

[William W]

. . . I checked the Ilford Manual of 1942. You can download it in PDF. It's not mentioned.
On your recommendation I bought the last Manual of Photography, 10th edition.

I do not recall ever recommending that you should purchase that book. If I did not recommend the purchase, then please do not say I did.

***

. . . William is trying to calculate the subject distance being the distance subject-lens, subject distance.

NO

EMPHATICALY NO!.

William is not trying to calculate any such thing..

William has never mentioned: “subject distance” or “subject-lens, subject distance”

HOWEVER what William has consistently stated using various different words to aid people’s understanding of these two simple concepts is:

1 The Working Distance is the distance from the Front of the Lens to the Subject

And

2. The Focus Distance is the distance from the Film Plane (not “plain”) to the Subject

Also William has provided two images to illustrate those distances.

WW

[ajohnw]

It looks like one useful thing has come out of the posts. Going on the lenses I selected the working distance is likely to be around 1 1/2 times the focal length. That seems to be true of the Panasonic lens too even though I think it's max mag is 2:1.

John
-

[george013]

I do not recall ever recommending that you should purchase that book. If I did not recommend the purchase, then please do not say I did.

***



NO

EMPHATICALY NO!.

William is not trying to calculate any such thing..

William has never mentioned: “subject distance” or “subject-lens, subject distance”

I think that's the problem.

HOWEVER what William has consistently stated using various different words to aid people’s understanding of these two simple concepts is:

1 The Working Distance is the distance from the Front of the Lens to the Subject

No, you said something else.
"There is (complicated) Mathematics to arrive at the appropriate formula to use, however: if the lens actually produces x1 Magnification (i.e. 1:1), then the simplest, correct formula to find the EFFECTIVE Focal Length is 1/2 of the WORKING Distance (Subject to Front Nodal Point).".
If you said minimal focus distance everything would be ok. It's mentioned in the specs of the lens: 31cm. I divide that by 4, and you do 1/2*1/2. But you said: "The “4 times” formula is only correct for a Single Element Lens.". We would say the same if you didn't stick to the working distance.Post 13.

If you state that the effective focal length is half of something, than that can only be the subject distance.

Leaves me one more question you don't want to react on.
Post 23.

3. a simple way of determining the EFFECTIVE FOCAL LENGTH of the lens (to put into the CiC calculator) is to find out or measure the Minimum WORKING Distance of the Lens when it is at the Minimum Focus Distance.

Again the working distance when you should mean minimal focal distance. I reacted before on this. Note under the calculator.

Notes: the "focusing distance" is measured as the distance between camera sensor and subject, and the "lens focal length" is the actual lens focal length (without multipliers).

You just don't react on the posts.

About the Manual of Photography, you mentioned it as authoritative. I just bought 2 of them. It was more informative. I thought you would like it to hear.

I stop quoting over and over. Unless there're some real arguments I quit.

George

[Saorsa]

[William W]

George, I shall try one last time to explain.

I ask you to read very carefully and do not rephrase or use words that I do NOT write.

I shall go through my commentaries, step by step and define the key words, as I proceed.

If your goal is to seek the understanding of the concepts, then it is my advice that it will serve you little purpose to continue any arguments about inconsequential matters such as: the type of tape measure that I use; or to misquote me or imply words and phrases that I stated when I did not.

***

1. The Initial Question posted on the thread.

The initial question was about using the CiC Calculator to assess if a Lens actually could achieve 1:1 or x1.0 Magnification.

Rob asked the question because when he put in the MINIMUM FOCUS DISTANCE and the FOCAL LENGTH of his lens he got an answer which was not x1.0.

The reason he got that WRONG answer was because he used the NOMINAL FOCAL LENGTH of the Lens.

What he needed to put into the CiC calculator to get the correct answer was the EFFECTIVE FOCAL LENGTH of the Lens.

DEFINITIONS:

LENS = unless otherwise stated, “Lens” means a typical lens that we use on a typical camera

MINIMUM FOCUS DISTANCE = the distance from the Film Plane to the Plane of Sharp Focus when the Lens’s Focus Turret is set at the minimum focussing distance

NOMINAL FOCAL LENGTH = the “nominated” Focal Length of the Lens, what is written in the nomenclature. The NOMINAL Focal Length of a Lens is approximately the EFFECTIVE FOCAL LENGTH of the Lens when the Lens is focused at Infinity

EFFECTIVE FOCAL LENGTH = is the ACTUAL FOCAL LENGTH of a Lens for the purposes of calculations, such as Field of View (just as one example). If the Optics of the lens are known, then the EFFECTIVE FOCAL LENGTH can be computed mathematically for any specific FOCUS DISTANCE. However a key point to note is mostly all Lenses exhibit a feature referred to as FOCUS BREATHING

FOCUS BREATHING = is the change in the ACTUAL FOCAL LENGTH of a Lens as the lens is focused at different FOCUS DISTANCES.

(BTW - FOCUS BREATHING is NOT the correct term to be applied to the common phenomenon of many ZOOM LENSES which will change the Plane of Sharp Focus when the Lens is being zoomed. The correct term to use for that phenomenon is to designate the Lens as a “Non-parfocal Lens”, a more recent term “Varifocal Lens” is also often used)

PLANE OF SHARP FOCUS = is the PLANE at the SUBJECT which is in SHARP FOCUS

***

2. My initial response:

To answer Rob’s question I responded with Post #13, the four key points made in that post are:

a) The formula “x4” is only good for a single element lens – (I.E. for a lens that has ONE bit of glass)

b) The CiC Calculator requires that the EFFECTIVE FOCAL LENGTH of the Lens put into the box “Focal Length”

c) There is complicated mathematics involved in attaining the value of the EFFECTIVE FOCAL LENGTH of a Lens

d) Notwithstanding the complexity of the mathematics mentioned in point c) above, there is a really simple method of calculating the EFFECTIVE FOCAL LENGTH of the lens by using the WORKING DISTANCE

DEFINITIONS:

WORKING DISTANCE = is the distance from the FRONT NODAL POINT of the FRONT ELEMENT of a LENS to the PLANE OF SHARP FOCUS. WORKING DISTANCE is often abbreviated to “the distance from the front of the Lens to the Subject".

3. Points for GEORGE to NOTE CAREFULLY –

This concept seems to be confusing you.

WORKING DISTANCE indeed is a mathematically useful distance.

WORKING DISTANCE when it is used as a technical term it is not affected by lens hoods, filters, flash heads or any other physical element.

It seems that another area of confusion for you is my use of this phase in post #13 “(Subject to Front Nodal Point)”.

That phrase was used because I assumed that most Photographers would know what the WORKING DISTANCE was.

The reason I used the phrase “(Subject to Front Nodal Point)” was to emphasize that for the purposes of using the CiC Calculator it would be necessary to measure WORKING DISTANCE very accurately – not just from the Plane of Sharp Focus to the "front" of the Lens – BUT to the ‘front nodal point’ referring specifically to the ‘front nodal point’ of the FIRST ELEMENT in the LENS’S ASSEMBLY.

If there was any confusion using the terminology ‘front nodal point’ in Post #13, then surely it was clarified by –

a) the Image #4 in Post 21:

IMAGE #4


b) also the text in Post #32:

Working Distance in Macro Photography is the distance from the front of the LENS (specifically the front nodal point of that first bit of glass of the Lens) to the Plane of Sharp Focus, just as I measured it.

***

4. SUMMATION of my commentaries:

One of the key purposes of my commentaries in this conversation was to inform the readership that there is a very simple method of calculating the EFFECTIVE FOCAL LENGTH of the lens, so that number can then be used as the “focal length” in the CiC Calculator.

To attain the EFFECTIVE FOCAL LENGTH of the macro lens, all you need to do is accurately measure the MINIMUM WORKING DISTANCE and then divide that number by two.

This will give you the EFFECTIVE FOCAL LENGTH of the Lens at the MIMNIMUM FOCUS DISTANCE and this is the number which can then be used in the CiC Calculator in the “Lens Focal Length” field.

DEFINITIONS:

MINIMUM WORKING DISTANCE = is the WORKING DISTANCE when the lens is at the MINMUM FOCUS DISTANCE.

***

5. The CiC Calculator and what number is really need to be put into it:

You seem obsessed with this footnote at the CiC Calculator

Notes: the "focusing distance" is measured as the distance between camera sensor and subject, and the "lens focal length" is the actual lens focal length (without multipliers).

Let me explain what the author of that footnote means.

‘ “focusing distance” ‘ – means the distance measured from the Film Plane to the Plane of Sharp Focus

‘ "lens focal length" is the actual lens focal length (without multipliers)’ has NOT taken into account FOCUS BREATHING.

GEORGE - please read this again:

‘ "lens focal length" is the actual lens focal length (without multipliers)’ has NOT taken into account FOCUS BREATHING. - the number that we MUST put into the CiC Calculator is the EFFECTIVE FOCAL LENGTH

The phenomenon of FOCUS BREATHING was first mentioned by Dan K in Post #6 and again, by dem, in post #7, viz:

Originally quoted by Dan K:
I suspect the answer is that the functional focal length of macro lenses at minimum focusing distance is typically less than the nominal focal length because of the movement of the lens elements when focusing close.

Originally quoted by dem:
The problem with the calculator is that it does not know anything about "focus breathing" that depends on the lens design. A 100 mm lens is a 100 mm lens only when focused on infinity. Focus it on a nearby object and the actual focus length [sic] will get shorter.

Moreover, if those two statements did not clearly describe and explain that in is NOT the NOMINAL FOCAL LENGTH which is required to be put into the CiC Calculator to get the correct answer, then surely Post #19 is very clear:

Originally quoted by William W:
[the question] was about the CiC calculator which requires the Focal Length data to be inputted (more correctly NOT the NOMINAL Focal Length but the EFFECTIVE Focal Length) and Rob was asking why the CiC Calculator was not working for him and the answer is because he was not putting in the correct Focal Length, so, logically Rob needed to find out HOW to get the correct Focal Length. That can be achieved if we know the MINIMUM WORKING DISTANCE. The MWD can be measured by observation or found in some data sheets.

***

6. Some other notes:

a) I shall NOT transcribe from first principles the formulae required to prove that we can use the MINIMUM WORKING DISTANCE of the Lens to calculate the EFFECTIVE FOCAL LENGTH at the MINIMUM FOCUS DISTANCE.

You have a choice to accept my word on that or otherwise do the research and the study yourself.



b) I have already wished you well in your reading of Ilford Manuals of Photography – I hope you enjoy them: I have said that before when you previously mentioned on another thread that you purchased them.

But understand that there is a difference between me wishing you well in you purchase and me “recommending” that you make a purchase.

If I “recommend”, then there is a certain amount of “responsibility” which I have.

I have no responsibility for your purchases, as I did not recommend them to you.

That is an important concept and I wanted the record quite clear on that point.


c) I cannot find any other simpler method of laying out the points above.

I do sincerely hope that you take the time to read through them very carefully so that you gain a complete understanding of the concepts I have outlined.

WW

[Saorsa]

We used to call the forward extension of the lens in close focus the bellows extension factor. Even when it was the focusing helix and not a bellows that moved the lens forward. That was used to calculate exposure.

The focal length of a lens that is engraved on the lens is the FL when focused at infinity. It doesn't usually matter much until you start getting in to close working distances.

[ajohnw]

Hi folks,

First post!

As part of this article: https://www.cambridgeincolour.com/tu...cro-lenses.htm, there is a magnification factor calculator. I am using a Canon 100ml macro lens, and the closest focusing distance is 300mm. However, when I use the 300mm measurement in the calculator, I get a message which reads "Focusing distance must be at least four times the focal length". I'm probably overlooking something obvious, but just don't understand. If someone can enlighten me I would be most grateful.

Thanks and bests,
Rob.

It's probably done that way because the approximations break down if the focus distance is shorter than the factor mentioned. They can only be approximations anyway and the factor mentioned indicates that they can be wildly out if shorter.

It's not really possible to know exactly what is going on in a real rather than web calculator macro lens. This for instance is the data on the Olympus one - unusually complete going on others I have seen.



Note that the F ratio changes with magnification factor. This can be down to the behaviour of the lens itself. Not that it matters really with TTL metering as we don't need to work it out. If the figures given were studied they might indicate that the focal length of the lens is changing as the magnification is varied. In real terms it might or it might not depending on how close it is to the various approximations that are about.

It seems I have F5.6 at 1:1. Does that mean I have a greater depth of field ? It might or it might not. It could just indicate that at this magnification I am taking shots from a field that is larger than the sensor where the real depth of field is more like F2.8. I do know on another set up that I use more often that I am not getting the depth of field that the crop factors suggest. Something I am going to look at closely at some point over the winter. I mostly use a zoom lens plus close up lens and may well find that the focal length set on the zoom matters for certain reproduction ratios. I've tended to always use it from 3 to 400mm away from the subject.

Before saying unusually complete data on the lens I should really look at the data that came with my other macro lenses but can't remember seeing anything of interest in them so hardly looked.

As I mentioned earlier the simple calculation I posted could be useful for choosing a macro lens as none that I am aware of specify working distances. The sum will by the look of it give people some idea of what they are about to buy. If I had done this before buying the Olympus one I might have not bought it at all however it's still a useful prime to have but not too good for skittish insects.

John
-

[xpatUSA]

Just a bit of added data:

The only true macro lens I own is the Sigma 50mm f/2.8 EX DG. As the barrel extends to focus, Sigma kindly reveals magnification marks.

At 1:1 magnification, "the distance" is marked on the focusing ring as 0.188m - the which distance being less than the theoretical thin-lens 0.2m. Effectively a 47mm focal length perhaps, depending on who you believe in this benighted thread.

With the focusing ring set at 0.2m distance, the magnification mark on the barrel shows as 1:1.6 **.

** On Sigma lenses, the magnification ratio is marked backasswards (image to object).

[george013]

George, I shall try one last time to explain.

I ask you to read very carefully and do not rephrase or use words that I do NOT write.

I shall go through my commentaries, step by step and define the key words, as I proceed.

If your goal is to seek the understanding of the concepts, then it is my advice that it will serve you little purpose to continue any arguments about inconsequential matters such as: the type of tape measure that I use; or to misquote me or imply words and phrases that I stated when I did not.

Just don't get angry. But don't you see how silly this is? You measure with a flex measure lint from point A to point B without knowing exactly where point B is. And then saying there's a difference of 2mm on 312mm being 0.6%, probably due to Canon rounded.



***

1. The Initial Question posted on the thread.

The initial question was about using the CiC Calculator to assess if a Lens actually could achieve 1:1 or x1.0 Magnification.

Rob asked the question because when he put in the MINIMUM FOCUS DISTANCE and the FOCAL LENGTH of his lens he got an answer which was not x1.0.

The reason he got that WRONG answer was because he used the NOMINAL FOCAL LENGTH of the Lens.

What he needed to put into the CiC calculator to get the correct answer was the EFFECTIVE FOCAL LENGTH of the Lens.

No, he got a fault message. The calculator just doesn't go further as a magnification of 1. Den explained why.
And than a part I don't understand. It's written under the calculator to use the "nominal" focal length. But you just keep insisting on using the effective focal lenght = image distance. I just keep asking myself why? Use some numbers with which you get a magnification of 1, and you know. So simple. WHY DON"T YOU DO THAT?
Twice in this thread you used the image distance in stead of the focal length and twice you get a magnification of 0.63 and twice you state that the Canon figures must be wrong and twice you don't search the fault in your way of thinking.

DEFINITIONS:

LENS = unless otherwise stated, “Lens” means a typical lens that we use on a typical camera

MINIMUM FOCUS DISTANCE = the distance from the Film Plane to the Plane of Sharp Focus when the Lens’s Focus Turret is set at the minimum focussing distance

NOMINAL FOCAL LENGTH = the “nominated” Focal Length of the Lens, what is written in the nomenclature. The NOMINAL Focal Length of a Lens is approximately the EFFECTIVE FOCAL LENGTH of the Lens when the Lens is focused at Infinity

EFFECTIVE FOCAL LENGTH = is the ACTUAL FOCAL LENGTH of a Lens for the purposes of calculations, such as Field of View (just as one example). If the Optics of the lens are known, then the EFFECTIVE FOCAL LENGTH can be computed mathematically for any specific FOCUS DISTANCE. However a key point to note is mostly all Lenses exhibit a feature referred to as FOCUS BREATHING

FOCUS BREATHING = is the change in the ACTUAL FOCAL LENGTH of a Lens as the lens is focused at different FOCUS DISTANCES.

(BTW - FOCUS BREATHING is NOT the correct term to be applied to the common phenomenon of many ZOOM LENSES which will change the Plane of Sharp Focus when the Lens is being zoomed. The correct term to use for that phenomenon is to designate the Lens as a “Non-parfocal Lens”, a more recent term “Varifocal Lens” is also often used)

PLANE OF SHARP FOCUS = is the PLANE at the SUBJECT which is in SHARP FOCUS

***

The effective focal length is the same as the image distance. Not important further.

2. My initial response:

To answer Rob’s question I responded with Post #13, the four key points made in that post are:

a) The formula “x4” is only good for a single element lens – (I.E. for a lens that has ONE bit of glass)

b) The CiC Calculator requires that the EFFECTIVE FOCAL LENGTH of the Lens put into the box “Focal Length”

c) There is complicated mathematics involved in attaining the value of the EFFECTIVE FOCAL LENGTH of a Lens

d) Notwithstanding the complexity of the mathematics mentioned in point c) above, there is a really simple method of calculating the EFFECTIVE FOCAL LENGTH of the lens by using the WORKING DISTANCE

DEFINITIONS:

WORKING DISTANCE = is the distance from the FRONT NODAL POINT of the FRONT ELEMENT of a LENS to the PLANE OF SHARP FOCUS. WORKING DISTANCE is often abbreviated to “the distance from the front of the Lens to the Subject".

3. Points for GEORGE to NOTE CAREFULLY –

This concept seems to be confusing you.

WORKING DISTANCE indeed is a mathematically useful distance.

WORKING DISTANCE when it is used as a technical term it is not affected by lens hoods, filters, flash heads or any other physical element.

It seems that another area of confusion for you is my use of this phase in post #13 “(Subject to Front Nodal Point)”.

That phrase was used because I assumed that most Photographers would know what the WORKING DISTANCE was.

The reason I used the phrase “(Subject to Front Nodal Point)” was to emphasize that for the purposes of using the CiC Calculator it would be necessary to measure WORKING DISTANCE very accurately – not just from the Plane of Sharp Focus to the "front" of the Lens – BUT to the ‘front nodal point’ referring specifically to the ‘front nodal point’ of the FIRST ELEMENT in the LENS’S ASSEMBLY.

If there was any confusion using the terminology ‘front nodal point’ in Post #13, then surely it was clarified by –

a) the Image #4 in Post 21:

IMAGE #4


b) also the text in Post #32:



***

.
Working distance has been discussed long enough. I'm still waiting for some examples that shows your approach on the net. John did answer your demand, I'm still waiting.

4. SUMMATION of my commentaries:

One of the key purposes of my commentaries in this conversation was to inform the readership that there is a very simple method of calculating the EFFECTIVE FOCAL LENGTH of the lens, so that number can then be used as the “focal length” in the CiC Calculator.

To attain the EFFECTIVE FOCAL LENGTH of the macro lens, all you need to do is accurately measure the MINIMUM WORKING DISTANCE and then divide that number by two.

This will give you the EFFECTIVE FOCAL LENGTH of the Lens at the MIMNIMUM FOCUS DISTANCE and this is the number which can then be used in the CiC Calculator in the “Lens Focal Length” field.

DEFINITIONS:

MINIMUM WORKING DISTANCE = is the WORKING DISTANCE when the lens is at the MINMUM FOCUS DISTANCE.

***

5. The CiC Calculator and what number is really need to be put into it:

You seem obsessed with this footnote at the CiC Calculator

It's there for a reason. The maker of the calculator knows best what input is needed: he programmed it. In this one it's the focal length. But if you insist on using something else, then you'll get a magnification of 0.67 in stead of 1. And of course it's Canon's fault.

Let me explain what the author of that footnote means.

‘ “focusing distance” ‘ – means the distance measured from the Film Plane to the Plane of Sharp Focus

‘ "lens focal length" is the actual lens focal length (without multipliers)’ has NOT taken into account FOCUS BREATHING.

That was the for you too simple division by 4. Minimal focal distance as given by Canon of 300 with a magnification of 1 gives a focal length of 75. Use the calculator with focus distance of 300 and a focal length of 75 and you get a magnification of 1.

GEORGE - please read this again:

‘ "lens focal length" is the actual lens focal length (without multipliers)’ has NOT taken into account FOCUS BREATHING. - the number that we MUST put into the CiC Calculator is the EFFECTIVE FOCAL LENGTH

The phenomenon of FOCUS BREATHING was first mentioned by Dan K in Post #6 and again, by dem, in post #7, viz:





Moreover, if those two statements did not clearly describe and explain that in is NOT the NOMINAL FOCAL LENGTH which is required to be put into the CiC Calculator to get the correct answer, then surely Post #19 is very clear:



***

6. Some other notes:

a) I shall NOT transcribe from first principles the formulae required to prove that we can use the MINIMUM WORKING DISTANCE of the Lens to calculate the EFFECTIVE FOCAL LENGTH at the MINIMUM FOCUS DISTANCE.

You have a choice to accept my word on that or otherwise do the research and the study yourself.



b) I have already wished you well in your reading of Ilford Manuals of Photography – I hope you enjoy them: I have said that before when you previously mentioned on another thread that you purchased them.

But understand that there is a difference between me wishing you well in you purchase and me “recommending” that you make a purchase.

If I “recommend”, then there is a certain amount of “responsibility” which I have.

I have no responsibility for your purchases, as I did not recommend them to you.

That is an important concept and I wanted the record quite clear on that point.


c) I cannot find any other simpler method of laying out the points above.

I do sincerely hope that you take the time to read through them very carefully so that you gain a complete understanding of the concepts I have outlined.

WW

I always buy for my own responsibilty. Of course I checked the Manual on the net. You only pointed me to it.

Please, play with the calculator with figures that gives a guaranteed magnification of 1. All this writing and quoting would be for nothing. It's also in the formulas Den gave 2+m+1/m=L/f. L being focus distance and f being nominal focal length.

George

[xpatUSA]

This should clear it all up nicely as regards:

Front Nodal Point

'NoParallax' point

Principal Point

Principal Plane

Entrance Pupil

Center of Perspective

Thin Lens

Thick Lens

http://www.janrik.net/PanoPostings/N...allaxPoint.pdf

Lots of ray-tracing diagrams and 5-dollar words that hurt the brain . . .

[joebranko]

Wow. No kidding!

[William W]

Thanks for the paper.

This should clear it all up nicely as regards: . . .
Thin Lens
Thick Lens
http://www.janrik.net/PanoPostings/N...allaxPoint.pdf
Lots of ray-tracing diagrams and 5-dollar words that hurt the brain . . .

Yes.

What I found most refreshing upon reading that paper was that the author took somewhat of a practical approach in avoiding the detailed mathematics when he needed to address the difference of applications when comparing the simplicity of Thin Lenses to the complexity of, “Real Lenses (Thick Lens Model) . . . We do not have space enough here to discuss these issues in full detail, but a brief summary should answer the questions well enough for our purposes.” [Theory of the “No-Parallax” Point in Panorama Photography Version 1.0, February 6, 2006, Amended April 20, 2015, Rik Littlefield (ibid)].

WW

[William W]

Just don't get angry.

I am not nor never was: my intention was to assist your learning

***

But don't you see how silly this is?

Yes. Now I do.

WW