DOF head scratching

[xeliex]

Take the following scenario and please answer:

Can you distinguish 3 photos taken using the following theoretical setup?

1) A 4/3 sensor / film equipped with 25mm f/1.4 lens and shot wide open.
2) A 35mm full frame sensor / film equipped with a 50mm f/2.8 shot wide open.
3) A 645 medium format film / sensor (assume same size) equipped with 80mm f/4.5 shot wide open.

I hear opinions on the net saying how differently the DOF "rolls over" between formats and how it is smoother on larger formats compared to the smaller ones? They claim the transition from in-focus to out-of-focus areas is more gradual on the larger formats. Is there truth to that? How can we quantify it if is indeed exists at all?

[Black Pearl]

What are you wanting to shoot and what is your current gear?

[xpatUSA]

Take the following scenario and please answer:

Can you distinguish 3 photos taken using the following theoretical setup?

1) A 4/3 sensor / film equipped with 25mm f/1.4 lens and shot wide open.
2) A 35mm full frame sensor / film equipped with a 50mm f/2.8 shot wide open.
3) A 645 medium format film / sensor (assume same size) equipped with 80mm f/4.5 shot wide open.

I hear opinions on the net saying how differently the DOF "rolls over" between formats and how it is smoother on larger formats compared to the smaller ones? They claim the transition from in-focus to out-of-focus areas is more gradual on the larger formats. Is there truth to that? How can we quantify it if [it] indeed exists at all?

On the assumption that the 3 alternatives are hypothetical, reading this from beginning to end several times will likely answer your question:

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

Written by a scientist but in fairly plain English, it represents more than just an opinion, IMHO. It is my favorite reference for matters related to DOF and should answer the questions posed.

[Stagecoach]

Elie,

There is a rather long thread on this subject here The Falacy of FF Cameras having Flatter DOF

[William W]

. . . I hear opinions on the net saying how differently the DOF "rolls over" between formats and how it is smoother on larger formats compared to the smaller ones? They claim the transition from in-focus to out-of-focus areas is more gradual on the larger formats. Is there truth to that? How can we quantify it if is indeed exists at all?

Those are qualitative opinions / descriptions for the foreground and background blur.

DoF and the Out of Focus Blur (or if you prefer Hekob and Bokeh) are related to DoF, but are different.

The "quality" of the Out of Focus Blurs at both the foreground and background of the Plane of Sharp Focus, have many elements: possibly the format size could be one, BUT the lens which is used to make the image is certainly one element which cannot be underestimated as to the level of affect it will have on the quality of the Blur in the final image.

So therein lies the conundrum: one cannot use the SAME lens to make the contrasts and comparisons between the three images.

***

There are a few Blur analysis calculators available - Bob Atkins has a free one you can down load form his website, from my memory it is called "Blur-calc".

WW

[xeliex]

Guys, thank you. This pdf link is so long and I will go over it. It will take me a long time and I don't know if I will find my answer there.

I have researched this topic a lot and read many posts on this forum and elsewhere yet my question remains unanswered.

Also to answer black pearl, I have medium format, full frame, micro 4/3 etc... What I have, is not the question neither is what I want to photograph.

I also realize that lens properties do come in play a bit. I know the hypothetical 80mm will have less visible barrel distortion compared to the 25mm. But again that is not the question.

At this point I am getting frustrated in finding the answer. Maybe I am having trouble verbalizing it. But please try to help if you know.

If I take a photo with my medium format film camera setup as above and my full frame film film camera as above, as well as my half frame film camera and lens as above, will you be able to tell the difference? How and why? Especially in the depth of field and general relationship of the in focus and out of focus areas......

[xeliex]

I will check Bob Atkins blur calculator. I appreciate your and everyone's response.

[NorthernFocus]

...If I take a photo with my medium format film camera setup as above and my full frame film film camera as above, as well as my half frame film camera and lens as above, will you be able to tell the difference? How and why? ....

I don't understand your conundrum. If you have the gear to run your own tests, why not do so? It is simple enough to do with the ages old slanted yard stick set up. Or the Lens Align tool which is a sophisticated version of the same test. Once you see the results for yourself you can then continue to study the theory if you're still interested.

[xeliex]

I don't understand your conundrum. If you have the gear to run your own tests, why not do so? It is simple enough to do with the ages old slanted yard stick set up. Or the Lens Align tool which is a sophisticated version of the same test. Once you see the results for yourself you can then continue to study the theory if you're still interested.

I have tried my friend but don't have the exact gear to test it out. I do have 80mm on 645 but 40mm ff is the closest. Maybe I can buy something cheap to test it out...

What are your thoughts? Can you see visible differences from a 645 vs say a half frame if shot as above when it comes to dof?

[xeliex]

Those are qualitative opinions / descriptions for the foreground and background blur.

DoF and the Out of Focus Blur (or if you prefer Hekob and Bokeh) are related to DoF, but are different.

The "quality" of the Out of Focus Blurs at both the foreground and background of the Plane of Sharp Focus, have many elements: possibly the format size could be one, BUT the lens which is used to make the image is certainly one element which cannot be underestimated as to the level of affect it will have on the quality of the Blur in the final image.

So therein lies the conundrum: one cannot use the SAME lens to make the contrasts and comparisons between the three images.

***

There are a few Blur analysis calculators available - Bob Atkins has a free one you can down load form his website, from my memory it is called "Blur-calc".

WW

Still looking at Bob Atkins' calculators. Thank you.

Do you think you'd be able to tell such setups apart from the bokeh?

[William W]

. . . I have researched this topic a lot and read many posts on this forum and elsewhere yet my question remains unanswered . . . I also realize that lens properties do come in play a bit. I know the hypothetical 80mm will have less visible barrel distortion compared to the 25mm. But again that is not the question.

At this point I am getting frustrated in finding the answer. Maybe I am having trouble verbalizing it. But please try to help if you know.

If I take a photo with my medium format film camera setup as above and my full frame film film camera as above, as well as my half frame film camera and lens as above, will you be able to tell the difference? How and why? Especially in the depth of field and general relationship of the in focus and out of focus areas......

It occurs to me that you greatly underestimate the qualitative values that any one particular LENS and any one particular APERTURE which is USED will have upon Out of Focus elements of any image.

Barrel Distortion has little if naught to do with this topic.

The point is - if ALL other parameters such as; Lighting; Subject; all relevant Distances and the Background are kept THE SAME –using a different LENS and/or a different APERTURE will change the quality of the Out of Focus Image areas - often DRAMATICALLY.

So, in my experience once I am familiar with a particular LENS I can often guess correctly that a particular LENS was used – so in that case I might guess the camera format, but that would be because I know that particular lens’s attributes particularly well and therefore I could guess what camera format was used. For example I can often pick the EF 135 F/2 L USM - so therefore I would not guess it was a 645 or 6x6 camera which made the image.

But because which lens and what aperture is used, are two such dominate forces on the outcome of the ‘quality’ of any blur – I think your mission to attribute any specific predictable qualitative characteristics of Blur to Sensor Size is somewhat flawed, even if you can keep all the other parameters the same: and secondly if other parameters change (for example the lighting or background) then I think it would be an uphill battle for anyone to identify the camera format used solely predicated on any qualitative analysis of the Out of Focus Blur of the Image.

WW

[William W]

. . . Do you think you'd be able to tell such setups apart from the bokeh?

If that question means could I make a good estimate as to what camera format has been used, basing my judgements on several aspects of the image - then yes I sometimes can.

Forensic analysis of Images (and also video) forms part of my work.

But that task is made much easier if I am investigating several images as part of a set and also the consideration of other factors, which are not necessarily seen as part of any one of the image(s) which are under scrutiny.

WW

[xeliex]

It occurs to me that you greatly underestimate the qualitative values that any one particular LENS and any one particular APERTURE which is USED will have upon Out of Focus elements of any image.

Barrel Distortion has little if naught to do with this topic.

The point is - if ALL other parameters such as; Lighting; Subject; all relevant Distances and the Background are kept THE SAME –using a different LENS and/or a different APERTURE will change the quality of the Out of Focus Image areas - often DRAMATICALLY.

So, in my experience once I am familiar with a particular LENS I can often guess correctly that a particular LENS was used – so in that case I might guess the camera format, but that would be because I know that particular lens’s attributes particularly well and therefore I could guess what camera format was used. For example I can often pick the EF 135 F/2 L USM - so therefore I would not guess it was a 645 or 6x6 camera which made the image.

But because which lens and what aperture is used, are two such dominate forces on the outcome of the ‘quality’ of any blur – I think your mission to attribute any specific predictable qualitative characteristics of Blur to Sensor Size is somewhat flawed, even if you can keep all the other parameters the same: and secondly if other parameters change (for example the lighting or background) then I think it would be an uphill battle for anyone to identify the camera format used solely predicated on any qualitative analysis of the Out of Focus Blur of the Image.

WW

Well spoken Bill... I understand. So even a 40mm f/1.4 Leica vs a 40mm f/1.4 Voigtlander, both on a 35mm film will have different qualities and feel in the out of the focus areas and their relationships to the in focus areas. If that is the case, then lens design and properties are the confounding variable in my quest to answer my question.

[William W]

. . . a 40mm f/1.4 Leica vs a 40mm f/1.4 Voigtlander, both on a 35mm film will have different qualities and feel in the out of the focus areas and their relationships to the in focus areas. . .

I cannot attest as fact for those two particular lenses - but the answer is "yes".

A practical example, - one where I am more comfortable - is using 50mm lenses - I have a few.

In Canon EF Series I own or I have owned or used extensively: EF 50/1.4; EF 50/2.5; EF 50/1.0; EF 50/1.2; EF 50/1.8MkII - l have extensively used all those lenses wide open and also all at around F/2 (except the F/2.5) and yes, they all display different nuance and character in the Out of Focus areas.

Now, whilst I do like spending hours playing these comparison games; I did NEVER have all those lenses all together and at one time, so my comparisons and contrasts of the IMAGES those 50mm lenses will make, has been usually between only two lenses at any one time. Also I have a Rokkor 58/1.2 and I have thrown that into the mix, too.

I think we would be safe to state that it is logical to expect when any two very similar lenses are USED WIDE OPEN then there probably will not be much qualitative difference to the OoF areas of the image, provided that all other conditions are kept the same - so you might not see much difference in blur between the 40mm f/1.4 Leica vs a 40mm f/1.4 Voigtlander when both are wide open, but it's safe to assume that when both lenses are at F/2.8 there is more likelihood that we would see differences in the Blur areas.

On the other hand, I am ignorant of the Lens Optics (the grouping and design) of both those lenses that you mention and if these aspects are markedly different, then we could expect qualitative differences of the Blur even at F/1.4

WW

[William W]

. . . You've really got me thinking now about the "other factors" in this theoretical test and how difficult it would be keep all those "other factors" the same.

I was just thinking - I have a 645 kit. I could use the 80/2.8 at F/2.8 on the 645 camera and make an A/B Test with my 50/1.4 on my 135 format camera - but I cannot use both lenses wide open, in which case the iris/aperture blades are an extraneous and an uncontrolled factor.

I appreciate the Maximum Aperture stipulations that you made concerning the three lenses you described in the opening post - but in reality and off the top of my head I think that we would struggle to find such lenses for a reliable pseudo-practical test anyway . . .

a 25/1.4 - we could use the Panasonic 4/3 lens

a 50/2.8 for 135 format - ? there is a new Sony "Macro" Lens - or maybe Nikkor/Rokkor enlarging lenses ? (is it a fair test use either a macro lens or an enlarging lens?)

an 80/4.5 - ? I am struggling here - maybe an old Mamiya lens ?

The above is basically me thinking out aloud and thinking that it could be useful sharing those thoughts with you; it is not any formulated answer or comment to your query.

WW

[xeliex]

. . . You've really got me thinking now about the "other factors" in this theoretical test and how difficult it would be keep all those "other factors" the same.

I was just thinking - I have a 645 kit. I could use the 80/2.8 at F/2.8 on the 645 camera and make an A/B Test with my 50/1.4 on my 135 format camera - but I cannot use both lenses wide open, in which case the iris/aperture blades are an extraneous and an uncontrolled factor.

I appreciate the Maximum Aperture stipulations that you made concerning the three lenses you described in the opening post - but in reality and off the top of my head I think that we would struggle to find such lenses for a reliable pseudo-practical test anyway . . .

a 25/1.4 - we could use the Panasonic 4/3 lens

a 50/2.8 for 135 format - ? there is a new Sony "Macro" Lens - or maybe Nikkor/Rokkor enlarging lenses ? (is it a fair test use either a macro lens or an enlarging lens?)

an 80/4.5 - ? I am struggling here - maybe an old Mamiya lens ?

The above is basically me thinking out aloud and thinking that it could be useful sharing those thoughts with you; it is not any formulated answer or comment to your query.

WW

Good Sir,

Thank you. I am already learning nuggets of information from your posts.

Wide-open or stopped down is not a real concern but it is a great point you bring up. I really really would appreciate any of your attempts at comparing your 50mm on a full frame vs the 80mm on your 645 and the 25mm on a micro 4/3.

I had sold my panny 25/1.4 and lack a 50mm for full frame (strangely now that I think of it).

I am so happy that you are considering running this.

A reviewer on petapixel said the following about the 645z. Please let me know your thoughts on that statement / assumption:

The depth of field is beautiful. On smaller sensor systems the DoF drops off near instantly when using fast aperture tele lenses. On medium format you just get this beautiful roll off to the out of focus regions. I just can’t get enough of this look.

[george013]

Good Sir,

Thank you. I am already learning nuggets of information from your posts.

Wide-open or stopped down is not a real concern but it is a great point you bring up. I really really would appreciate any of your attempts at comparing your 50mm on a full frame vs the 80mm on your 645 and the 25mm on a micro 4/3.

I had sold my panny 25/1.4 and lack a 50mm for full frame (strangely now that I think of it).

I am so happy that you are considering running this.

A reviewer on petapixel said the following about the 645z. Please let me know your thoughts on that statement / assumption:

The depth of field is beautiful. On smaller sensor systems the DoF drops off near instantly when using fast aperture tele lenses. On medium format you just get this beautiful roll off to the out of focus regions. I just can’t get enough of this look.

May I formulate your question in a different way. With some introduction.
When focused on a subject the light cone aperture-image distance is pinned just on the sensor/film. The light cone from a subject before or after that subject creates a circle on the sensor/film. When the subject distance changes, the image distance changes.
Sharp is said to be when that circle when printed on a A4 doesn't exceed a diameter of 0.25mm. This is related to the sensor size.
Out off focus are all those distances that creates a light cone with a to big top circle on the sensor, producing a bigger circle on a A4 print.

So when I understood the question, you're looking for the behaviour of that out off focus part, how fast does that change in a token image when looking at a different subject distance.

George

[dem]

Here is a theoretical amount of blur as a function of subject-background distance for a full frame 50mm f/2.8 and an equivalent M43 25mm f/1/4 set up:

http://howmuchblur.com/#compare-1x-5...m-wide-subject

You can only see one line in the graph because the two lines go exactly on top of each other. So theoretically the images should look identical in terms of their blur. Of course, the images will look different in real life because of 101 differences in lens and camera construction and signal and image processing involved. The formulas used in this type of calculators never take into account, for example, how many aperture blades there are, how sharp they are etc... etc... That's why an OOF light source is often rendered not as a perfect circle but as a polygon, "cat eye", "onion rings", "double circle" and whatever names people come up with. Same goes for tree branches against the sky and other high contrast subjects that are a challenge to blur in a pleasing way.

Would I be able to tell which photo came from a full frame camera and which came from an equivalent m43 set up? I'm sure some difference in the background blur will be easy to spot but might be difficult to link to a particular camera/lens combo. There might also be a noticeable difference in tonal range, micro-contrast and dynamic range - this is what I will be looking for first, not the blur. Though if you stick an old lens on a full frame camera and compare it against a shiny Zuiko that costs 10-20 times more, the viewer can be easily confused.

[xeliex]

Here is a theoretical amount of blur as a function of subject-background distance for a full frame 50mm f/2.8 and an equivalent M43 25mm f/1/4 set up:

http://howmuchblur.com/#compare-1x-5...m-wide-subject

You can only see one line in the graph because the two lines go exactly on top of each other. So theoretically the images should look identical in terms of their blur. Of course, the images will look different in real life because of 101 differences in lens and camera construction and signal and image processing involved. The formulas used in this type of calculators never take into account, for example, how many aperture blades there are, how sharp they are etc... etc... That's why an OOF light source is often rendered not as a perfect circle but as a polygon, "cat eye", "onion rings", "double circle" and whatever names people come up with. Same goes for tree branches against the sky and other high contrast subjects that are a challenge to blur in a pleasing way.

Would I be able to tell which photo came from a full frame camera and which came from an equivalent m43 set up? I'm sure some difference in the background blur will be easy to spot but might be difficult to link to a particular camera/lens combo. There might also be a noticeable difference in tonal range, micro-contrast and dynamic range - this is what I will be looking for first, not the blur. Though if you stick an old lens on a full frame camera and compare it against a shiny Zuiko that costs 10-20 times more, the viewer can be easily confused.

Very interesting link and thoughts, dem, thank you. Theoretically this is what I am thinking as well; which disagrees with the statement of the petapixel reviewer that I have quoted right above. Don't you think? This seems to be an ongoing belief.

[xeliex]

May I formulate your question in a different way. With some introduction.
When focused on a subject the light cone aperture-image distance is pinned just on the sensor/film. The light cone from a subject before or after that subject creates a circle on the sensor/film. When the subject distance changes, the image distance changes.
Sharp is said to be when that circle when printed on a A4 doesn't exceed a diameter of 0.25mm. This is related to the sensor size.
Out off focus are all those distances that creates a light cone with a to big top circle on the sensor, producing a bigger circle on a A4 print.

So when I understood the question, you're looking for the behaviour of that out off focus part, how fast does that change in a token image when looking at a different subject distance.

George

George, you very intelligently expressed my question and simultaneously explained those focus prism drawings that accompany dof right ups.

Just to clarify in case we have a misunderstanding. Yes, I want to know what does sensor / medium size have to do with the out of focus areas quality and their relationships to the in focus area, if all or most other factors are kept stable (same effective field of view, aperture width, etc...)