Michael's DoF Essay Question and Examples

[bernie west]

Bernie, you are ignoring the effect of the reduced FOV at 200mm (illustrated below).  The background tree just to the left of the subject serves as a reference point to draw an outline of where the 200mm background lines up within the 40mm shot -- it is not surprising to see that it lines up approximately in the middle.  It appears to me that the red sticks are not in the 200mm shot.

if i could work out how to upload images I could point out the red sticks in the 200mm.  They are just above the "mm" in "200mm/f16".  Surely you can see them?

This entire discussion is confused by what represents more or less detail. 

Confused is correct.  Unfortunately, it is you who is confused.  Resolution has nothing to do with DOF.  DOF is concerned with acceptable sharpness.  Of course resolution of distant objects is less with a shorter focal length lens.  But acceptable sharpness (ie. DOF) is greater.  Resolution has nothing to do with DOF.  You are confusing these two terms.

I'm sure both of you and perhaps the OP as well will continue to tell me that I am wrong and just don't understand.  That's fine, I don't care and will not reply any more to this thread since I am satisfied that I have communicated with reasoned argument and valid examples why focal length does not change "DOF".
[a href=\"index.php?act=findpost&pid=188736\"][{POST_SNAPBACK}][/a]

I hope you stick around, because if you do the test I said you will see it is true.  Also you need to disabuse yourself of the incorrect belief that DOF is concerned with resolution.  Once you do these two things, you will be free to enjoy the benefits of varying depth of field for creative effect.  

I apologize if I got off on the wrong foot with the "underwater" comment.  I had just come from a long forum post where one or two people where trying to argue something so counterintuitive, and they just wouldn't listen to reason.  But having said that I am going to give you a little spray .  I have been involved in forum posts about ETTR where some crusty old film guys stuck in the past, wouldn't accept examples and wouldn't do examples or tests themselves.  And I'm sorry, you are like some of these guys.  I have proposed a test, which explains the absolute essence of DOF, and you just resolutely won't do the test.  This says to me, like the crusty old film guys, that you are stuck in your ways and no amount of evidence or anything is going to change your mind.  So, if you are willing to approach this with an open mind, I urge you to stick around and we can try and explain each others point of view better.  However, if you not willing to open your mind a bit, then perhaps it is best if you give up.

[01af]

Resolution has nothing to do with DOF.[a href=\"index.php?act=findpost&pid=188835\"][{POST_SNAPBACK}][/a]

Ouch! Bernie, I guess you want to say the right thing ... but the way you're saying it makes it wrong. DOF surely has to do with resolution! However it is not the same as resolution. And it mustn't get confused with relative blur.

I have been involved in forum posts about ETTR where some crusty old film guys stuck in the past ...[a href=\"index.php?act=findpost&pid=188835\"][{POST_SNAPBACK}][/a]

Huh!? How come? Conceptually, exposing to the right is just another word for exposing for the highlights which crusty old film guys should be very familiar with---at least those who shoot slide film. And the basic rule for negative film, exposing for the shadows, basically is the same again because the shadows in a positive are the highlights in the negative. The reasoning behind it is slighty different for film and digital but the basic concept is the same. So I guess something went severely wrong with that discussion ... well, not unlike here.

-- Olaf

[Ray]

I also found this article by Michael to be contoversial and its conclusion misleading with regard to the way we use DoF in our photographs.

For example, often we use a shallow DoF to make objects in the background less distracting.

In the update to this article, which is a response to a reader's question about using a 300mm lens (from a greater distance) instead of a 200mm at f2.8 for shooting skiers, Michael safely offers the advice that the 300mm lens will provide exactly the same DoF as the 200mm lens.

However, in my view, if the intention of the photographer is to remove as much distracting detail as possible in the background, the longer focal length is a better choice.

If the reader's question had specified different lenses, for example, if the question had been, "I normally use a 300mm lens at f2.8 to photograph skiers, but next Saturday I've been offered a prime viewing position which is much closer to the action and which will allow me to fill the same amount of the frame (with a single skier) using my 85/1.2 at f2.8. Will DoF be the same?", I think Michael would have hesitated to answer in the same way.

The fact is, using the 85/1.8 for the same shots, would have introduced the risk of all sorts of distracting background skiers being visible and more prominent, not only because the background is more extensive (wider FoV) but also because smaller images (secondary skiers) would 'appear' sharper because they are smaller, yet retain the same absolute resolution as the blurrier looking objects (subjects) in the 300mm shots.

Nevertheless, we have to thank Michael for pointing out this phenomenon, that although a background object might look blurrier when using a longer lens from a greater distance, the actual detail in that blurry object is approximately the same as the detail in the smaller, and therefore sharper looking, object in the wider-angle shot taken from a closer distance.

I didn't know that when I first read this article. Of course, being a natural skeptic, I had to check this out for myself, and sure enough my own tests demonstrated that it is approximately true, but not precisely, as the OP's comparison demonstrates and as Olaf has mentioned several times.

[bernie west]

Ouch! Bernie, I guess you want to say the right thing ... but the way you're saying it makes it wrong. DOF surely has to do with resolution! However it is not the same as resolution. And it mustn't get confused with relative blur.

Ok, perhaps I am using the wrong terminology.  When I talk about resolution I mean it in the sense of resolving detail.  Clearly longer focal length lenses have greater resolving power than shorter focal lengths.  So it is possible, and this has come up with some of the examples Tony has shown, that  whilst some things might be within DOF, for example a sign, you may not neccessarily be able to read the sign (in a short focal length image).  But this isn't a limitation of DOF, it is a limitation of the resolving power of the lens.  But this is a red herring anyway.  Because to be able to bring the longer focal length image into acceptable sharpness, one would have to go back so far, that one wouldn't be able to resolve the writing on the sign anyway.

Huh!? How come? Conceptually, exposing to the right is just another word for exposing for the highlights which crusty old film guys should be very familiar with---at least those who shoot slide film.

I don't want to open another can of worms, but it had to do with them not understanding the concept of sensor linearity and that if you half exposure you lose half your tonal values.  I provided linear tiffs which showed just this, but their only reply to that was that I must have done something wrong.  When I suggested that they do the test themselves... Silence...

So I guess something went severely wrong with that discussion ... well, not unlike here.
-- Olaf
[a href=\"index.php?act=findpost&pid=188841\"][{POST_SNAPBACK}][/a]

LOL.

[barryfitzgerald]

There are some interesting DOF articles online..
http://www.dofmaster.com/dof_imagesize.html
http://www.vanwalree.com/optics/dof.html

I won't disagree that DOF (overall DOF is very close if subject size is maintained...though not always the case..see above)

I will argue the following though..

Focal length "IS PART" of the formula, why do we still see people saying its got nothing to do with it..its there! Check your maths. I dont want to see any more nonsense about its nothing to do with it, its in black and white in the formula..!

The effect of focal length on DOF can be wiped out with distance to subject (which is what MR test was about..again, this is not set in stone though, take note of hyperfocal distances, macro etc)

You do not always "have" a subject in shots! (ala landcapes etc)
It is not practical to shoot an F1 race with a 20mm lens, or capture a bald mountain eagle flying ala close up shot with a 50mm lens.

Not all lenses can maintain subject size do to optical design. WA lenses are not good close up..limited in that regard, telel lenses have min focus distances too.

People tend to use longer focal lengths to "compress" the background more, even if you have the same DOF with a shorter FL one, the effect is not the same.

And the point that is not mentioned in the LL article is..

That the distribution of the DOF (front and rear) is NOT the same for different focal lengths, even if the overall DOF is the same or nearly the same. A long tele lens has a near 50/50 (almost) front to back DOF. A super WA lens 20mm say, has an average 1/3rd front to 2/3rds back DOF distribution. A very important point to remember...

[dwdallam]

I'm sure both of you and perhaps the OP as well will continue to tell me that I am wrong and just don't understand.  That's fine, I don't care and will not reply any more to this thread since I am satisfied that I have communicated with reasoned argument and valid examples why focal length does not change "DOF".
[a href=\"index.php?act=findpost&pid=188736\"][{POST_SNAPBACK}][/a]

No. I said before I'm not disagreeing with what is solid science, and you guys can hammer that out. In fact, if what is a fact is a fact, then someone is incorrect and someone is correct because there cannot be two truths to a single equation. So if anything is trivial, its debating a priori facts of math and science--that is, physics. It's just a matter of finding the information on the subject, a subject that has already been put to rest, and understanding that information.

I think I already said also that I tend to agree prima facia about the Dof not changing--since I'm not  interested in light and lens physics discussions--although I'm wondering how this works, when you have no detail  to bring back, no matter how far you stand back. But I'll just give you that.

However, as you agree, using a longer lens, as in my examples, will render the background "more out of focus" given similar parameters as is the case in my test images. And that is what I'm talking about.

[jani]

What an amazing discussion.

People are accusing Tony for being blind, but yet they cannot see themselves that the 40mm and 200mm shots were framed differently; dwdallam didn't move straight backwards.

This can easily be seen from the base which the "Aladdin" whatsit is standing on, as well as the tilt of the scene, and the whatsit itself.

I guess you all need eye surgery!  (Or perhaps stepping back into the next room and closing the door will help.)


dwdallam; what you observe is how it is, but your own description of what you see is at best imprecise, and it's difficult to be precise when discussing this unless you also have the technical vocabulary, as e.g. Olaf has. I don't have that vocabulary down pat, and I only very rarely need to use DOF tables/calculators for my own photography.

But I'm pretty sure we're all seeing the same thing, plus/minus needed eye surgery, retina defects, eyes overflowing over with tears and closed doors.

[bernie west]

What an amazing discussion.
[a href=\"index.php?act=findpost&pid=190818\"][{POST_SNAPBACK}][/a]

What a pointless post.

Putting eye surgery aside, I think it is clear some people need brain surgery!  Do you not understand how perspective can change with focal length?  If you can't get past this point, then you've got no hope of understanding DOF!

[Tony Beach]

I have already written and vowed to not engage in this discussion anymore, so I will not address the topic.  However Bernie, I have a hard time deciding what I dislike more, your condescending remarks, your disingenuous apology, or your "surgery" insults.  Disagreeing with someone does not give you a license to be abusive and if that is the tenor of this website then I will happily spend my time elsewhere.

[bernie west]

I have already written and vowed to not engage in this discussion anymore, so I will not address the topic.  However Bernie, I have a hard time deciding what I dislike more, your condescending remarks, your disingenuous apology, or your "surgery" insults.  Disagreeing with someone does not give you a license to be abusive and if that is the tenor of this website then I will happily spend my time elsewhere.
[a href=\"index.php?act=findpost&pid=190880\"][{POST_SNAPBACK}][/a]

I was actually replying to Jani's surgery remarks.  I guess the tone of my last post was set by Jani's post which I found condescending.  I suppose you didn't find it condescending because he was supporting you.  Funny how it works out like that...

As for my apology, it actually was sincere.  I'd buy you a beer if you were nearby  

As for the avoiding the discussion, well that's your choice.  But now that you've popped back in, you may as well give it another go.  At least do the rest of us who didn't give up the fight the courtesy of trying and reporting back about the test I proposed.  Is that crickets I hear??

[dwdallam]

What an amazing discussion.

People are accusing Tony for being blind, but yet they cannot see themselves that the 40mm and 200mm shots were framed differently; dwdallam didn't move straight backwards.

This can easily be seen from the base which the "Aladdin" whatsit is standing on, as well as the tilt of the scene, and the whatsit itself.

I guess you all need eye surgery!  (Or perhaps stepping back into the next room and closing the door will help.)
dwdallam; what you observe is how it is, but your own description of what you see is at best imprecise, and it's difficult to be precise when discussing this unless you also have the technical vocabulary, as e.g. Olaf has. I don't have that vocabulary down pat, and I only very rarely need to use DOF tables/calculators for my own photography.

But I'm pretty sure we're all seeing the same thing, plus/minus needed eye surgery, retina defects, eyes overflowing over with tears and closed doors.
[a href=\"index.php?act=findpost&pid=190818\"][{POST_SNAPBACK}][/a]

The shots were framed as closely as I could manually adjust my footsteps and ball head/tripod. I would say the frames are within 1" of each other in all ways.

"dwdallam; what you observe is how it is, but your own description of what you see is at best imprecise,"

And I think I've admitted that three or more times now.

Do you have any new information to add? If so, please share it.

[dwdallam]

I have already written and vowed to not engage in this discussion anymore, so I will not address the topic.  However Bernie, I have a hard time deciding what I dislike more, your condescending remarks, your disingenuous apology, or your "surgery" insults.  Disagreeing with someone does not give you a license to be abusive and if that is the tenor of this website then I will happily spend my time elsewhere.
[a href=\"index.php?act=findpost&pid=190880\"][{POST_SNAPBACK}][/a]

Why do you think one person's comments represent the entire web forum community? It's a fallacy called "Specific to the General." I get your point, but don't let one person run you off (operative word being "one").

[dwdallam]

I don't even know what the argument is.

If this statement is wrong, then we need a discussion. If it is right, then we've concluded what I set out to question, and we need a new thread on the physics of DoF regarding photography:

"Using a longer length lens will give a greater illusion of a blurry background when compared to a shorter lens and all things aperture, distance to subject, frame fill, and print size are equal."

[bernie west]

I don't even know what the argument is.

If this statement is wrong, then we need a discussion. If it is right, then we've concluded what I set out to question, and we need a new thread on the physics of DoF regarding photography:
[a href=\"index.php?act=findpost&pid=190902\"][{POST_SNAPBACK}][/a]

I think the statement is wrong in relation to DOF.  And as I've said a number of times, the physics, charts, equations and what not don't really matter in this discussion.  That is because we are comparing two situations where we (you) have minimised the differences between the two situations, to just the variables we are comparing.  It seems to be the almost perfect experiment, where we don't have to bother with equations.  In addition to all this, equations really don't matter anyway.  And the reason for this is that ultimately the only important thing for DOF determination is the eyes.  Once again for Tony et al, DOF is a visual perceptual phenomenon.  If you see acceptable sharpness, then the image IS acceptably sharp.  No amount of fussing over the FOV or level of blurriness in the background will change this fact.  If you can see it with your eyes, then it is real.  And I (and most others too) can see that DOF is larger with shorter focal length lenses (when all else that is important is equal).

[jani]

What a pointless post.

I'm glad you realise that, and decided put it in your introduction, but that still leaves the question why you bothered to post it.

Putting eye surgery aside, I think it is clear some people need brain surgery!  Do you not understand how perspective can change with focal length?

Yes, I do, which should be clear from the part of the post which you didn't bother to read. You seem to obsessed with insulting other people.

However, perspective doesn't change as unevenly as illustrated in dwdallam's shots, if that's what you're implying.

I was actually replying to Jani's surgery remarks. I guess the tone of my last post was set by Jani's post which I found condescending.

Here's a mirror. Please make use of it and guess three times why the tone of my post was such, and why I thought it funny to read your own, condescending "surgery" remark, while missing what's right there in front of your own two eyes. Perhaps that's condescending, I thought it witty when I wrote it. I'm sorry that I insulted you then.

The shots were framed as closely as I could manually adjust my footsteps and ball head/tripod. I would say the frames are within 1" of each other in all ways.

I don't know where that 1" is - on your screen, in the full resolution image on your screen, but the point here was that ridiculing others for needing eye surgery when they themselves don't even bother looking at the examples you posted is slightly less than clever.

What you did was fine enough; it illustrated what you wanted to ask about.

"dwdallam; what you observe is how it is, but your own description of what you see is at best imprecise,"

And I think I've admitted that three or more times now.

Do you have any new information to add? If so, please share it

Yes, but please continue reading past the point which you quoted. It seemed, from your then-currently last post on the topic, that you still struggled with an apparent disconnect between what you saw and how the DoF "should" work according to physics.

I was trying to contribute by telling you that there isn't such a disconnect.

[bernie west]

To be honest, I don't know why I am replying to this dribble, but here goes.

However, perspective doesn't change as unevenly as illustrated in dwdallam's shots, if that's what you're implying.

So you're implying that he is lying then??  This seems to be the same type of response I used to get from the kooky old film guys when I presented evidence to them about sensor linearity.

Here's a mirror. Please make use of it and guess three times why the tone of my post was such

1.  You're rude?
2.  You have no idea?
3.  You have nothing to contribute to the discussion?

How did I do?

Why don't you actually contribute something to this discussion and address some of the entirely valid and useful points myself and others have made from our side of the discussion?  Or just throw more insults around.  You decide.

[michael]

I haven't read this whole thread, but unfortunately it seems to have degenerated into a rude pissing contest.

It's therefore now closed.

Michael