Focusing issue

[Shanghai Steve]

....Get used to it.

That is not for you to tell me, matey.
Jesus wept.

[Donald]

Please note that the trading of personal insults and barbed comments has never been tolerated on this forum and will not be.

People with knowledge and experience are encouraged to share that for the benefit of others and to take part in constructive discussion and debate.

However, throwing personal criticisms, comments and insults around is not part of what this forum is about. I understand it takes place on other forums. It will not take place on here. I would ask everyone to note that.

[xpatUSA]

Please note that the trading of personal insults and barbed comments has never been tolerated on this forum and will not be.

People with knowledge and experience are encouraged to share that for the benefit of others and to take part in constructive discussion and debate.

However, throwing personal criticisms, comments and insults around is not part of what this forum is about. I understand it takes place on other forums. It will not take place on here. I would ask everyone to note that.

My apologies to the Forum for prodding the Gentleman from Shanghai following his outburst re: William W.

I have deleted "Get used to it" from my post but my comment about Bill (WW) remains as-is.

Thank you for the reminder, Donald.

[Shanghai Steve]

Wow. I am unsure exactly what to type here. I certainly don't want to cause a kerfuffle on a forum I have so recently joined. Nor do I believe for one moment that I am God's gift to photography. But can we please have a bit of perspective? What was the nature of this "barbed comment"?

This is all very interesting but perhaps not particularly relevant? People use different focal lengths differently.

That's it.

"...not particularly relevant... question mark"

This is not a barbed commment, nor an emotional one, nor attack nor insult. It is mild language, with italics used to add a mollifying tone and a question mark to further emphasise this.

What is the linguistic alternative to this mildest of language? Silence? I am willing to take the Moderator's advice at this stage. If he tells me never to post any reply to WW which is not effusive praise, I will do so. If he tells me that WW is an unchallengable force, I will accept that. My hands are raised.
I await instruction.

[dem]

The dof calculator doesn't work for macro...

This one does:

http://www.photopills.com/calculators/dof-macro

You can use any DOF calculator for macro if you enter the "effective aperture" (that is the nominal aperture divided by (1+Magnification)). So if you are shooting a Canon camera at f/16 and 1:1 magnification, you need to enter f/16/(1+1) = f/32 into the DOF calculator that has not been adapted for macro. Nikon cameras equipped with their native lenses already show the effective aperture on the LCD, so no adjustment is needed.

This however does not make any difference for application of the Axiom of Depth of Filed in macro photography - whether it is the nominal or the effective aperture, Nikon or Canon, the DOF is still constant for any focal length when the framing is fixed.

I didn't get this from a calculator, I knew this from experience. Three or so years ago I tested how DOF in my close up shots changed when I varied the focal length from 24 to 600 mm while keeping the framing constant. It did not! The perspective distortion and the background changed quite a lot obviously but the edges of the subject looked the same in terms of their sharpness. At the time I did not know about CiC and Bill's tutorials but I learnt a very useful practical lesson from this exercise:

If you are using a zoom lens and are focusing close to its minimal focus distance - as is often the case in close up and bird photography - do not worry about which focal length to use, concentrate on framing and aperture.

Say we are taking a picture of a sparrow facing the camera (say APS-C camera set to f/8.0). If we zoom in so the bird is taking up half of the frame, the tail is going to be out of focus. But zoom back a little, so the sparrow is taking up a third of the frame, and the whole bird is going to be in focus now. It does not matter what the subject-distance is and what the focal length is in this example, it is their ratio (the magnification) that defines the framing and thus the DOF.

Having said that, it is always better to get as close as possible

[george013]

This one does:

http://www.photopills.com/calculators/dof-macro

You can use any DOF calculator for macro if you enter the "effective aperture" (that is the nominal aperture divided by (1+Magnification)). So if you are shooting a Canon camera at f/16 and 1:1 magnification, you need to enter f/16/(1+1) = f/32 into the DOF calculator that has not been adapted for macro. Nikon cameras equipped with their native lenses already show the effective aperture on the LCD, so no adjustment is needed.

This however does not make any difference for application of the Axiom of Depth of Filed in macro photography - whether it is the nominal or the effective aperture, Nikon or Canon, the DOF is still constant for any focal length when the framing is fixed.

I didn't get this from a calculator, I knew this from experience. Three or so years ago I tested how DOF in my close up shots changed when I varied the focal length from 24 to 600 mm while keeping the framing constant. It did not! The perspective distortion and the background changed quite a lot obviously but the edges of the subject looked the same in terms of their sharpness. At the time I did not know about CiC and Bill's tutorials but I learnt a very useful practical lesson from this exercise:

If you are using a zoom lens and are focusing close to its minimal focus distance - as is often the case in close up and bird photography - do not worry about which focal length to use, concentrate on framing and aperture.

Say we are taking a picture of a sparrow facing the camera (say APS-C camera set to f/8.0). If we zoom in so the bird is taking up half of the frame, the tail is going to be out of focus. But zoom back a little, so the sparrow is taking up a third of the frame, and the whole bird is going to be in focus now. It does not matter what the subject-distance is and what the focal length is in this example, it is their ratio (the magnification) that defines the framing and thus the DOF.

Having said that, it is always better to get as close as possible

That's funny. I was trying to build a program to show the behaviour of the dof and other variables while changing certain input. And there it is.

The idea behind it is that the formulas are using the f-number. And that is a simplification. Basicly dof and also diffraction are based on the light cone formed by aperture diameter and image distance. When focusing on infinity image distance equals focal length. And that gave the possibility to use the F-number in the formula. As long there is not much difference between those it doesn't make much difference. Closer the difference is growing. With a magnification of 1, sizes original and image are the same, image distance is twice the focal length. And that's corrected with a so called "effective aperture".

Another issue in the tables is the distance.From what is it calculated? From the sensor or the optical middle of the lens? I always play with distances which equals the focal length and less. When less an imaginair image must be the result. In the "normal "dof calculator the distance is calculated or expected from the optical middle of the lens. In the macro dof calculator it is the sensor plane.

Macro lenses, or some, are changing there focal length despite being a prime.

There are many rules of thumb in photography land. Don't forget they were originated far before the pc. Now we can check those rules for any situation and condition as long we trust and understand those progs. But it doesn't mean they're useless.

George

[xpatUSA]

This one does:

http://www.photopills.com/calculators/dof-macro

You can use any DOF calculator for macro if you enter the "effective aperture" (that is the nominal aperture divided by (1+Magnification)). So if you are shooting a Canon camera at f/16 and 1:1 magnification, you need to enter f/16/(1+1) = f/32 into the DOF calculator that has not been adapted for macro. Nikon cameras equipped with their native lenses already show the effective aperture on the LCD, so no adjustment is needed.

That's a good tip and a cracking good calculator which agrees well with my own spreadsheet which is based on angular measure (Cone of Confusion) in accordance with here:

http://www.dicklyon.com/tech/Photogr...Field-Lyon.pdf

This however does not make any difference for application of the Axiom of Depth of Field in macro photography - whether it is the nominal or the effective aperture, Nikon or Canon, the DOF is still constant for any focal length when the framing is fixed.

I didn't get this from a calculator, I knew this from experience. Three or so years ago I tested how DOF in my close up shots changed when I varied the focal length from 24 to 600 mm while keeping the framing constant. It did not! The perspective distortion and the background changed quite a lot obviously but the edges of the subject looked the same in terms of their sharpness. At the time I did not know about CiC and Bill's tutorials but I learnt a very useful practical lesson from this exercise:

If you are using a zoom lens and are focusing close to its minimal focus distance - as is often the case in close up and bird photography - do not worry about which focal length to use, concentrate on framing and aperture.

Say we are taking a picture of a sparrow facing the camera (say APS-C camera set to f/8.0). If we zoom in so the bird is taking up half of the frame, the tail is going to be out of focus. But zoom back a little, so the sparrow is taking up a third of the frame, and the whole bird is going to be in focus now. It does not matter what the subject-distance is and what the focal length is in this example, it is their ratio (the magnification) that defines the framing and thus the DOF.

I put Dem's bird into my spreadsheet as 100mm tall, projecting onto the image plane as 7.5mm tall (1/2 a 15mm frame height) and set the marked focal length as 50mm:

mag, f-effective, actual aperture diameter, dist, DOF (where dist is from subject to image plane):

1:13 55.8mm 6.25mm 770mm 86mm*

Still at 50mm, stepping back to 1105mm distance for 1/3 frame height:

1:20 52.5mm 6.25mm 1105mm 186mm*

Then I set 5mm (1/3 of 15mm frame height) and iterated the marked focal length to get the same ~770mm distance - it came to 35mm:

1:20 36.8mm 4.38mm 772mm 130mm*

* These total DOF numbers are based on my monitor's CoC and my viewing distance. Other calculators will give different DOF numbers but all we're doing here is comparing.

So, at constant distance and zooming out, the DOF changes significantly (e.g. 130mm vs. 86mm), as has already been said in the quote.

Also, an interesting result is that stepping back gets you more DOF than zooming out - hadn't realized that until now.

Unusually for photography, Dem's experience appears to match theory

[William W]

As an aside.

An observation from a long time Member of CiC directed as: A welcome to a new Member of CiC -

It seems you've got your nose put out of joint, which is...sigh-inducing. I am also surprised that you are surprised that at some point in your impromptu tutorial, someone pointed out that your plethora of facts don't in fact, make much difference. Or have I stumbled into the internet equivalent of a closed shop?

No.

No nose has been put out of joint: nor has one stumbled into a “closed shop”

Nor (as an incidental comment) was the previous an “impromptu tutorial”, au contraire – the commentaries probably did, indeed, make a difference. That goes back to the point about “relevance” – what is relevant to one might be irrelevant or modestly relevant to another. . . just like we all use Focal Lengths differently – we all use information differently.

Reviewing this conversation:

> Post #25 addressed the link made between WA lenses and how they might ‘give you greater depth of field’. Considering also the comment 'If your pictures aren't any good, get closer' then Post #25 explained that the DoF remains constant, if the Framing remains constant.

> Post #26 commented that Post #25 was not clear and that it was not understood.

> Hence Posts #31; 32 and 33 sought to explain the relationship between DoF and Framing. This is what generally happens at CiC, if someone mentions that they do not understand something then other Members seek to assist that understanding.

As one himself is a teacher, one would understand that modern pedagogy infers that a best practice primary tool in written intercourse to several recipients, is a multiplicity of different approaches with similar content. Hence Posts 31; 32 and 33 have similar content and various different approaches and deliveries on the same topic.

> Post #34 asked about a question of relevance of Posts 31; 32 and 33.

> Post #37 answered that question of relevance – and went on to explain to a new Member how the conversations at CiC tend to flow and how, mostly all Members’ commentaries, forward the conversation and do not seek to critique previous commentaries, per se.

Note there is abundant space in conversations to question an opinion; argue a point of fact within the content; proffer an alternative point of view; seek validation for references or experience to back up an opinion. This happens all the time. 99.9% of the time is made with polite discourse. Also worth mentioning, on the odd occasion when a Member does overheat, there is usually always a very quick resolution to that tempest, accompanied by a sincere apology.

> Post #37 also pointed out that here at CiC conversations (threads) tend to meander and wander off into tangent conversations. This happens especially with dormant threads which are revived or very long threads when the question or problem designated in the Original Post has been considerably covered and addressed.

***

> Post #44 asked for “instruction” as to how one should proceed as a Member of CiC.

This commentary is NOT that ‘instruction’.

This commentary is however an observation and a dissection of part of the forgone conversation and how this conversation occurs to a long term member here at CiC.

Hopefully this whole conversation (this thread) is an example to one so one might see how CiC Forums actually do work: how the conversations are inclusive; vibrant; positive and abundantly welcoming of knowledge and experience from ALL members: certainly CiC is NOT a closed shop.

My opinion is that many other Members have a similar view of CiC as described above.

That opinion is predicated on the anecdotal evidence that CiC has bubbled along for many years without very many hiccups or unpleasant moments and all without very much Moderator intervention.

WW

[William W]

. . . You can use any DOF calculator for macro if you enter the "effective aperture" etc . . .

Ta. Never thought of that. I have rewritten a few notes.

Thank you very much

WW

[William W]

. . . an interesting result is that stepping back gets you more DOF than zooming out - hadn't realized that until now.

Ta also. Another gem.

As you probably know I don't do much Macro Photography and even rarer do I make any commentary on it - but I have put that in my notes also.

Thanks.

WW

[Shanghai Steve]

As an aside.

An observation from a long time Member of CiC directed as: A welcome to a new Member of CiC -



No.

No nose has been put out of joint: nor has one stumbled into a “closed shop”

Nor (as an incidental comment) was the previous an “impromptu tutorial”, au contraire – the commentaries probably did, indeed, make a difference. That goes back to the point about “relevance” – what is relevant to one might be irrelevant or modestly relevant to another. . . just like we all use Focal Lengths differently – we all use information differently.

Reviewing this conversation:

> Post #25 addressed the link made between WA lenses and how they might ‘give you greater depth of field’. Considering also the comment 'If your pictures aren't any good, get closer' then Post #25 explained that the DoF remains constant, if the Framing remains constant.

> Post #26 commented that Post #25 was not clear and that it was not understood.

> Hence Posts #31; 32 and 33 sought to explain the relationship between DoF and Framing. This is what generally happens at CiC, if someone mentions that they do not understand something then other Members seek to assist that understanding.

As one himself is a teacher, one would understand that modern pedagogy infers that a best practice primary tool in written intercourse to several recipients, is a multiplicity of different approaches with similar content. Hence Posts 31; 32 and 33 have similar content and various different approaches and deliveries on the same topic.

> Post #34 asked about a question of relevance of Posts 31; 32 and 33.

> Post #37 answered that question of relevance – and went on to explain to a new Member how the conversations at CiC tend to flow and how, mostly all Members’ commentaries, forward the conversation and do not seek to critique previous commentaries, per se.

Note there is abundant space in conversations to question an opinion; argue a point of fact within the content; proffer an alternative point of view; seek validation for references or experience to back up an opinion. This happens all the time. 99.9% of the time is made with polite discourse. Also worth mentioning, on the odd occasion when a Member does overheat, there is usually always a very quick resolution to that tempest, accompanied by a sincere apology.

> Post #37 also pointed out that here at CiC conversations (threads) tend to meander and wander off into tangent conversations. This happens especially with dormant threads which are revived or very long threads when the question or problem designated in the Original Post has been considerably covered and addressed.

***

> Post #44 asked for “instruction” as to how one should proceed as a Member of CiC.

This commentary is NOT that ‘instruction’.

This commentary is however an observation and a dissection of part of the forgone conversation and how this conversation occurs to a long term member here at CiC.

Hopefully this whole conversation (this thread) is an example to one so one might see how CiC Forums actually do work: how the conversations are inclusive; vibrant; positive and abundantly welcoming of knowledge and experience from ALL members: certainly CiC is NOT a closed shop.

My opinion is that many other Members have a similar view of CiC as described above.

That opinion is predicated on the anecdotal evidence that CiC has bubbled along for many years without very many hiccups or unpleasant moments and all without very much Moderator intervention.

WW

Oh dear God!

[george013]

That's a good tip and a cracking good calculator which agrees well with my own spreadsheet which is based on angular measure (Cone of Confusion) in accordance with here:

http://www.dicklyon.com/tech/Photogr...Field-Lyon.pdf



I put Dem's bird into my spreadsheet as 100mm tall, projecting onto the image plane as 7.5mm tall (1/2 a 15mm frame height) and set the marked focal length as 50mm:

mag, f-effective, actual aperture diameter, dist, DOF (where dist is from subject to image plane):

1:13 55.8mm 6.25mm 770mm 86mm*

Still at 50mm, stepping back to 1105mm distance for 1/3 frame height:

1:20 52.5mm 6.25mm 1105mm 186mm*

Then I set 5mm (1/3 of 15mm frame height) and iterated the marked focal length to get the same ~770mm distance - it came to 35mm:

1:20 36.8mm 4.38mm 772mm 130mm*

* These total DOF numbers are based on my monitor's CoC and my viewing distance. Other calculators will give different DOF numbers but all we're doing here is comparing.

So, at constant distance and zooming out, the DOF changes significantly (e.g. 130mm vs. 86mm), as has already been said in the quote.

Also, an interesting result is that stepping back gets you more DOF than zooming out - hadn't realized that until now.

Unusually for photography, Dem's experience appears to match theory

What is meant with your monitors CoC?

George

[xpatUSA]

What is meant with your monitors CoC?

George

Yes, that was a bit confusing, sorry.

Basically, the standard CoC for a DOF calculation is based (among other things) on a print size, often 8x10" viewed at one ft distance.

Because I don't print, I use instead my monitor dot pitch and viewing distance. That gives a Cone angle of Confusion of 0.522mrad.

[Cantab]

Yes, that was a bit confusing, sorry.

Basically, the standard CoC for a DOF calculation is based (among other things) on a print size, often 8x10" viewed at one ft distance.

Because I don't print, I use instead my monitor dot pitch and viewing distance. That gives a Cone angle of Confusion of 0.522mrad.

Ted, as someone who is not an engineer and knows virtually nothing about these technical calculations, I'm curious whether there's a significant difference in the cone angle of confusion as calculated for your monitor and as used for an 8"x10" print?

[xpatUSA]

Ted, as someone who is not an engineer and knows virtually nothing about these technical calculations, I'm curious whether there's a significant difference in the cone angle of confusion as calculated for your monitor and as used for an 8"x10" print?

Hello Bruce,

For the "standard" print, it depends on the ppi being printed at:

8x10” Print 300ppi: 0.28mrad (just a bit less than the average human vision).

8x10” Print 150ppi: 0.56mrad (a bit more like my monitor) More notes from my spreadsheet: Based on human vision only: Normal Human vision: 0.29mrad = 1 minute of arc per Snellen's test chart.

My personal myopic vision: 0.75mrad (from viewing said chart on my screen at an appropriate distance).

And finally:

My NEC P232W Monitor: 0.5217mrad (from 0.265mm dot pitch divided by 500mm viewing distance).

[george013]

Hello Bruce,

For the "standard" print, it depends on the ppi being printed at:

8x10” Print 300ppi: 0.28mrad (just a bit less than the average human vision).

8x10” Print 150ppi: 0.56mrad (a bit more like my monitor) More notes from my spreadsheet: Based on human vision only: Normal Human vision: 0.29mrad = 1 minute of arc per Snellen's test chart.

My personal myopic vision: 0.75mrad (from viewing said chart on my screen at an appropriate distance).

And finally:

My NEC P232W Monitor: 0.5217mrad (from 0.265mm dot pitch divided by 500mm viewing distance).

I think you're confusing magnification with quality. The minimum light cone from human eye to a subject doesn't change with screen/print quality. So 0.29mrad doesn't change. I don't know if those figures are correct.

George

[xpatUSA]

I think you're confusing magnification with quality.

Please explain what is meant by "quality".

Please read and understand what cone angle I'm discussing here:

http://www.dicklyon.com/tech/Photogr...Field-Lyon.pdf

The minimum light cone from human eye to a subject doesn't change with screen/print quality.

Trivial but nevertheless correct.

So 0.29mrad doesn't change.

Only if "0.29mrad" continues to represent normal human visual acuity. If 0.29mrad represents something else, such as an 8x10" print at 300 ppi and viewed at 1 ft, that would be a mere coincidence.

I don't know if those figures are correct.

Assuming that you claim or imply that those figures are incorrect, here is an example:

I said that 8x10" printed at 150 ppi and viewed from 1 ft = 0.56mrad. Easy for your eyes to resolve, not so easy for mine without glasses.

The calculation is simple enough:

150 ppi = 5.91 p/mm = 0.169mm printing pixel pitch.

Viewing distance of 1 ft = 304.8mm.

Small angle approximation = 0.169/304.8 = 0.555mrad.

Is this example correct or not for calculating the cone angle for the resolution of the print?

[george013]

Please explain what is meant by "quality".

Please read and understand what cone angle I'm discussing here:

http://www.dicklyon.com/tech/Photogr...Field-Lyon.pdf



Trivial but nevertheless correct.



Only if "0.29mrad" continues to represent normal human visual acuity. If 0.29mrad represents something else, such as an 8x10" print at 300 ppi and viewed at 1 ft, that would be a mere coincidence.



Assuming that you claim or imply that those figures are incorrect, here is an example:

I said that 8x10" printed at 150 ppi and viewed from 1 ft = 0.56mrad. Easy for your eyes to resolve, not so easy for mine without glasses.

The calculation is simple enough:

150 ppi = 5.91 p/mm = 0.169mm printing pixel pitch.

Viewing distance of 1 ft = 304.8mm.

Small angle approximation = 0.169/304.8 = 0.555mrad.

Is this example correct or not for calculating the cone angle for the resolution of the print?

The subject of this thread is focusing issue, concerning the camera/lens.
Let's say a point of 0.3mm is experienced as a point and not as a circle at a distance of 1m. Assuming you need to enlarge your sensor 10 times, than you can calculate the max. coc: 0.3/10=0.03mm. It's independent of how that circle on the print/screen is shown. In print a higher dpi will give a higher quality, basicly.

What you calculate is the size of the dot at a certain distance. If it's 0.3mm at 1 m than at 10 meter it will be 3mm. Still independent of the printresolution/quality. Your approach with the angle is the same.

George

[xpatUSA]

The subject of this thread is a focusing issue, concerning the camera/lens.

Then we need no longer discuss DOF or the calculation thereof.

[pat3pee]

I came across these websites re AUTO FOCUS problems. The one shows 8 possible reasons for not getting the right focus and the second is IMO for focus nerds but interesting if you have the patience and need for fine tuning the auto focus system.

https://www.youtube.com/watch?v=gEDzAMm1FCc

https://www.youtube.com/watch?v=7zE50jCUPhM

Cheers
Patrik