DOF... where's it going?!

Phil V said:
No - the subject is the same size.

Are you suggesting that the subject in your earlier point was the same size? because that wasn't ever made clear. And is of course the fundamental point.
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I thought I'd kinda made it clear with one of these:

Davince said:
Yes but I'm not changing output magnification by digitally cropping - I'm just selecting a smaller area
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Davince said:
Absolutely, but as you go on to say cropping has nothing to do with output whatsoever, it is merely chopping bits of an image off.
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Davince said:
Erm... yes I am? The screen displays at 72ppi, (okay some 100 but you know waht I mean) so output is set at that for digital display. If I crop an image in photoshop, without resampling, then I am doing EXACTLY that, I am digitally 'cutting bits of the print off'. Nothing else. I am just removing pixels, not altering the remaining in any shape or form.
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Davince said:
Zooming in will affect it, of course it will, but I'd have said 'cropping and zooming' or 'cropping and magnifying'
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Davince said:
Just got in from a shoot, hence no reply's, but I can't say this any more times, I'm not sure why I'm saying it again frankly, but as it's being bought up time and time again, I'll give it one last go...

I have simply cropped the image. The image IS NOT MAGNIFIED IN ANY SHAPE OR FORM. If I posted the whole image, it would simply have taken up more of the screen space.
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And as you say, it's fundemental, and why I got just a tad annoyed. Cropping is the act of chopping off extraneous parts, literally, cutting. It is NOT zooming, magnifying, scaling, changing perception, wheeling your chair in or out...

So, as I say, and as you've just said, CROPPING does not change DOF. So as I say... Hoppy may be the expert but we only have common language to impart knowledge. He is completely wrong to claim that cropping changes DOF, he is completely correct to claim that altering your perspective on a viewed image, be it digitally displayed or physically displayed, and be your perspective changed by magnification at output, or by holding it closer to you, changes DOF.
 
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Davince said:
I thought I'd kinda made it clear with one of these:
...
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What's that old saying about a picture being worth a thousand words. This is the proof. I now appreciate what you were trying to say, but it never really came out the way you thought it did.
 
To the OP - Much better if you explain things properly rather than get annoyed. Perception.
 
Davince said:
So, as I say, and as you've just said, CROPPING does not change DOF. So as I say... Hoppy may be the expert but we only have common language to impart knowledge. He is completely wrong to claim that cropping changes DOF, he is completely correct to claim that altering your perspective on a viewed image, be it digitally displayed or physically displayed, and be your perspective changed by magnification at output, or by holding it closer to you, changes DOF.
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"Depth of Field" is a totally subjective thing, as at the minute level there is zero depth to the focus. You only get thing in perfect focus on one infinitesimally small plane, as soon as you leave that plane there's lots of things determining whether it appears in focus or not.

I'd just take on board what Hoppy is saying as it's not wrong.
 
Phil V said:
What's that old saying about a picture being worth a thousand words. This is the proof. I now appreciate what you were trying to say, but it never really came out the way you thought it did.
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LOL also that old saying about 'assume', as I assumed that bit was clear. Guess it comes from my design background and use of the term cropping - cropping and resizing/resampling/magnification are very different animals.
 
chphotos said:
To the OP - Much better if you explain things properly rather than get annoyed. Perception.
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Honestly? I'd had a stressful day with a problematic shoot and was at the limit of my articulation when I said that I was only cropping the image, and that I hadn't changed the zoom or magnification in any way shape or form, nor resampled the image. I assumed that made it clear

As Phil says I should have used images, but I posted from my phone and it was late, so sorry for offence caused.

But as Phil V confirms above, cropping the image (the act of removing unwanted bits of an image) doesn't change dof, so it's fairly academic now :)
 
ernesto said:
read what?

If there is a bandwagon going by than I am on it.
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LOL in all fairness, so are many people on internet forums so can't blame you, these bandwagons all look so pretty :p

I was generally meaning the thread above, which was supposed to be a plea for help on a problem which appears to be equipment based, but turned into a debate on Hoppy incorrectly claiming that cropping an image changes it's DOF, when in fact it doesn't, changing the pov or magnification changes the dof, not the crop (as Phil clearly states that the cropped image has no difference in DOF from the uncropped image above it).

Hoppy hasn't been by to comment on it yet mind.
 
Yes, I was only messing around.

Still concerned about that expert who convinced you that the focal plane is not flat though. How did they demonstrate that to the point where it convinced you?
 
LOL good good, bad weekend work wise so humour detector is slightly askew. In fact it's on the floor and has been stamped on.

I was persuaded on the focal plane because, when push comes to shove, I have the mathematical capabilities of a goldfish and they wielded a sharp sword of trigonometry around which went way over my head. Most importantly - I have (had? lol) the utmost respect for them so was perhaps a little more easily lead. I shall be having words though, having now researched it lol - every day is a school day, just got to be careful who your teacher is :p

Thank you abdoujaparov, glad I explained clear enough for someone! :)
 
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Davince said:
LOL in all fairness, so are many people on internet forums so can't blame you, these bandwagons all look so pretty :p

I was generally meaning the thread above, which was supposed to be a plea for help on a problem which appears to be equipment based, but turned into a debate on Hoppy incorrectly claiming that cropping an image changes it's DOF, when in fact it doesn't, changing the pov or magnification changes the dof, not the crop (as Phil clearly states that the cropped image has no difference in DOF from the uncropped image above it).

Hoppy hasn't been by to comment on it yet mind.
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What is DoF? It is the zone of acceptable sharpness perceived in an image. That part is easy, it's the bit you're talking about, no disagreement there.

But measuring it in a quantifiable way, as you have done in your OP, is more difficult because it's not a sharp/unsharp line drawn in the sand, but an ever shifting zone of sharp, acceptably sharp, and blurred. And the degree of acceptable/unacceptable sharpness changes according to the numerous aspects of magnification at play. For that reason, DoF calculators specify clear parameters and values, as they must do, and if you adhere to them you'll get the right answer, and you won't if you don't.

You said the DoF in the OP was 30cm, calculated from the uncropped image. You then present a cropped version (we still don't know how much it was cropped) and asked where that 30cm of DoF had gone. Well, from the image you presented, it was never there - you've reduced it by cropping and changed the forumla. If you want the DoF back, then look at the full uncropped image from the correct distance and it will reappear. Example, when you checked the image on the LCD, it probably looked fine at the time of shooting - it always does.

DoF is one aspect of your question, that I think we've done to death, the other part is why are the faces unsharp? The explanation for that is equally simple - the image is back-focused, around the guy's ear, and that unarguable fact coupled to less DoF that you estimated is the answer.

If I was to hazard a guess as to why it's back focused, unless your camera has taken a hefty whack recently I'd say it was nothing more complicated than user error - easily done with poor light in the heat of the moment. But check it anyway, as per the test outlined in post #72.

Edit: Of course Nikon will want you to send it in for them to look at, what did you expect them to say? Either way, they'll send you a bill too.
 
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HoppyUK said:
you've reduced it by cropping and changed the forumla.
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I'm getting a little confused. Is it the crop that does this on its own (assuming no enlargement, which is the case here), or do you also have to change the distance at which you view it? Because I dunno about other people, but I never move my head closer to the screen to look at things unless there's text I can't read. I mean, I'm sure I'd do it without thinking if I was holding an actual print, but never when looking at a computer monitor.
 
abdoujaparov said:
I'm getting a little confused. Is it the crop that does this on its own (assuming no enlargement, which is the case here), or do you also have to change the distance at which you view it? Because I dunno about other people, but I never move my head closer to the screen to look at things unless there's text I can't read. I mean, I'm sure I'd do it without thinking if I was holding an actual print, but never when looking at a computer monitor.
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The actual image never changes, but cropping and output size and viewing distance change magnification and therefore the perceived DoF. It's no different to changing lens focal length of moving closer/further to the subject when shooting, but nobody seems to argue about that.

DoF calculations were all drawn up (and internationally agreed) long ago when we all looked at prints - and they were generally small like 10in or A4 max. Anything bigger went on the wall and you stood back to look at them, so everything worked fine and well.

Digital viewing on screen changes the fundamentals of DoF calcs in a new way - we tend to view them at a certain fixed distance, and we also change their size at lot. Most commonly, as seems to be the case here, we make them bigger, often much bigger like pixel peeping at 100%, and when you then look at what appears sharp on screen and compare it to what a DoF calculator says, they're often a long way apart.

So DoF calculations are a bit out of kilter these days, and that's made worse by most folks not fully understanding the importance of output size and viewing distance. But that's not the DoF calculator's fault and at the very least the DoF standard is a fixed reference point that everyone uses, and you're free to modify it according to individual needs.
 
HoppyUK said:
What is DoF? It is the zone of acceptable sharpness perceived in an image. That part is easy, it's the bit you're talking about, no disagreement there.

But measuring it in a quantifiable way, as you have done in your OP, is more difficult because it's not a sharp/unsharp line drawn in the sand, but an ever shifting zone of sharp, acceptably sharp, and blurred. And the degree of acceptable/unacceptable sharpness changes according to the numerous aspects of magnification at play. For that reason, DoF calculators specify clear parameters and values, as they must do, and if you adhere to them you'll get the right answer, and you won't if you don't.

You said the DoF in the OP was 30cm, calculated from the uncropped image. You then present a cropped version (we still don't know how much it was cropped) and asked where that 30cm of DoF had gone. Well, from the image you presented, it was never there - you've reduced it by cropping and changed the forumla. If you want the DoF back, then look at the full uncropped image from the correct distance and it will reappear. Example, when you checked the image on the LCD, it probably looked fine at the time of shooting - it always does.

DoF is one aspect of your question, that I think we've done to death, the other part is why are the faces unsharp? The explanation for that is equally simple - the image is back-focused, around the guy's ear, and that unarguable fact coupled to less DoF that you estimated is the answer.

If I was to hazard a guess as to why it's back focused, unless your camera has taken a hefty whack recently I'd say it was nothing more complicated than user error - easily done with poor light in the heat of the moment. But check it anyway, as per the test outlined in post #72.

Edit: Of course Nikon will want you to send it in for them to look at, what did you expect them to say? Either way, they'll send you a bill too.
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I notice you completely and utterly ignored the very simple, straight forward question posted above with two images. I can only imagine that to be because you know you can't answer it without proving your argument invalid. You have two choices, you either explain how those two images have a different depth of field, or you simply state you are wrong because there is no difference in DOF, and the only difference between the two images is that one is cropped. It's not zoomed, it's not magnified, its not resampled it's not resized, it's cropped.

So which is it?

We haven't 'done it to death' because you've offered nothing at all to substantiate your IMO very clearly flawed claim, and until you answer the above question one way or the other, I have nothing to base any change of opinion on at all.

To your second point... you think it's focused on the ear? Or are you just trying to shift things to make me look bad? I'm not an expert, I make mistakes, I have a very, very long road of learning ahead of me. I don't however need glasses. If you think that the ear in this shot is more in focus than the eye, then we probably have an explanation for you attitude toward dof...

Eyes_zps77acb1aa.jpg
 
HoppyUK said:
So DoF calculations are a bit out of kilter these days, and that's made worse by most folks not fully understanding the importance of output size and viewing distance. But that's not the DoF calculator's fault and at the very least the DoF standard is a fixed reference point that everyone uses, and you're free to modify it according to individual needs.
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And yet you're happy to immediately quote cropping as the problem from an on-screen image. How bizarre...

Oh... any answer on the two posted images yet? no?
 
I think I understand all that. However, in this case, if the OP had posted the full image, then there would have been more photo filling my screen, but the portion comprising the heads (ie, the OP's crop) would have been exactly the same size, and my eyes would have been exactly the same distance from the screen (because I wouldn't have moved backwards simply because there was a big image on my screen). Has the DoF changed?

(I appreciate that the OP's DoF calculations may be moot because looking at a screen is not the same as holding an A4 print, but I'm really struggling to understand your claim that the crop, in itself, changed the DoF calculation in the current context, ie on a screen)
 
abdoujaparov said:
I think I understand all that. However, in this case, if the OP had posted the full image, then there would have been more photo filling my screen, but the portion comprising the heads (ie, the OP's crop) would have been exactly the same size, and my eyes would have been exactly the same distance from the screen (because I wouldn't have moved backwards simply because there was a big image on my screen). Has the DoF changed?

(I appreciate that the OP's DoF calculations may be moot because looking at a screen is not the same as holding an A4 print, but I'm really struggling to understand your claim that the crop, in itself, changed the DoF calculation in the current context, ie on a screen)
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What if the original image was 900pix across and the crop (say half the original image) was also 900 pix across, there's your magnification difference, but it's not immediately clear from the original posts whats going on.
 
abdoujaparov said:
I think I understand all that. However, in this case, if the OP had posted the full image, then there would have been more photo filling my screen, but the portion comprising the heads (ie, the OP's crop) would have been exactly the same size, and my eyes would have been exactly the same distance from the screen (because I wouldn't have moved backwards simply because there was a big image on my screen). Has the DoF changed?

(I appreciate that the OP's DoF calculations may be moot because looking at a screen is not the same as holding an A4 print, but I'm really struggling to understand your claim that the crop, in itself, changed the DoF calculation in the current context, ie on a screen)
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Please read it again :)
 
HoppyUK said:
Please read it again :)
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Well, I was being polite. Your argument is a bait-and-switch. Your claim is that cropping changes the DoF, but your explanation depends on the viewing distance being changed because of the crop.
 
abdoujaparov said:
Well, I was being polite. Your argument is a bait-and-switch. Your claim is that cropping changes the DoF, but your explanation depends on the viewing distance being changed because of the crop.
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Yes, of course. I never said anything else. Cropping changes the DoF calculation which is the point of the OP's question. He's estimated it at 30cm, but from what's been posted it's actually less than that.

And from the even closer crop that's just been posted above of the guy's ear, it's much less still - and we don't have to move closer to the screen to see it!
 
abdoujaparov said:
Well, I was being polite. Your argument is a bait-and-switch.
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Possibly the best explanation I've ever seen for this type of post!

Hoppy, you haven't commented on the two photos question, or the ear being in focus question, Obviously those are pivot to your point of view here, please could you just clarify for us thickies?

Do you still think the ear is the point of focus? And was there a difference in the DOF of the two images posted earlier? Not hard questions for such an esteemed expert.
 
Imagine that the OP had posted the full photo. Imagine that without moving my head, I had masked off with tape all of my computer screen except the portion that coincides with the OP's crop. Has that changed the DoF, yes or no? If it has, I'll concede that I don't understand your explanation.
 
Davince said:
I notice you completely and utterly ignored...

<snip>
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Look at the image in your OP - the point of sharpest focus is around the guy's chain, cheek and ear, not his eyes.

I have answered all your questions and explained all the reasons, several times now in what appears to be an entirely thankless quest to help. Nothing has changed from my first (correct) post on this thread, including your ability to understand and accept the facts. I can do no more.
 
HoppyUK said:
He's estimated it at 30cm, but from what's been posted it's actually less than that.
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No, the DOF calculator estimated it at 30cm. It is less than 30cm. Holy bats*** mother of all merciful, we should try a thread to find out why there is the discrepancy!!!!!

Oh no, wait, someone will just keep switching and changing their comments, ignoring questions that could clarify things and start making conflicting comments when their argument is proven flawed just to confuse the hell out of people.
 
HoppyUK said:
Look at the image in your OP - the point of sharpest focus is around the guy's chain, cheek and ear, not his eyes.

I have answered all your questions and explained all the reasons, several times now in what appears to be an entirely thankless quest to help. Nothing has changed from my first (correct) post on this thread, including your ability to understand and accept the facts. I can do no more.
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Where do you answer, and explain your opinion, of which of the two images posted one above has what dof?

I am confused by the ear comment. This is the same photograph, a different area of it. Are you now also claiming that changing which part of a photo you look at changes where it is focused? Have I somehow managed to magically move the focus so the eyes are the sharpest bit? If so please advise how as I think I'll probably be able to patent that ability.
 
abdoujaparov said:
Imagine that the OP had posted the full photo. Imagine that without moving my head, I had masked off with tape all of my computer screen except the portion that coincides with the OP's crop. Has that changed the DoF, yes or no? If it has, I'll concede that I don't understand your explanation.
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he won't answer, for exactly the same reason he won't answer the question with two photographs, because it is to his explanation of the theory what Thatcher was to coal miners...

Phil, however, was good enough to give a straight answer, which already proved Hoppy incorrect :)
 
And Just to add, Hoppy... you originally said the point of focus was on his chain. He, like most human beings, has eyes that are set back from the front of his face, he's also turning his head, pivoting as we all do at the rear most point of his neck, so his eyes will be very close to in focal plane to the chain where you can see it. So yes, with his eyes being closest to the focal plane, so will the chain be. The chain also is highly reflective and so is obviously going to give the highest contrast in the photograph and look relatively sharp. His ear doesn't. never did. In fact you only started on that attack when I started asking awkward questions...
 
Del, if you spent as much energy reading properly and trying to understand what has been posted, as you do jumping up and down and ignoring the basic facts of physics and the evidence of your own eyes, then you'd get it.

DoF is less than you calculated, but that appears to be my fault. The image is back-focused, so that's the camera's fault. You don't understand plain English, but that's not your fault either. If your are really as keen to learn as you claim, then go back and read the whole thread with some honest endeavour.
 
HoppyUK said:
Del, if you spent as much energy reading properly and trying to understand what has been posted, as you do jumping up and down and ignoring the basic facts of physics and the evidence of your own eyes, then you'd get it.

DoF is less than you calculated, but that appears to be my fault. The image is back-focused, so that's the camera's fault. You don't understand plain English, but that's not your fault either. If your are really as keen to learn as you claim, then go back and read the whole thread with some honest endeavour.
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Hoppy, dearest, it really is very, very simple. Stating the same thing over and over, doesn't make you correct.

Now then... All you have to do is answer two questions:

1:Is there any difference in DOF in these two images on your screen:

Lge_zps4e5b71fb.jpg


sm_zps65c2c7e6.jpg
[/QUOTE]

If so, how has it appeared?

2: Are the ears in this image, more in focus than the eyes.
Eyes_zps77acb1aa.jpg


If you answer no, then why do you claim it is backfocus that is the problem. If the answer is yes, what makes you say they are more in focus than the eyes, given that there is little definition and lots of blur, what makes you classify them as in focus and the eyes out?

If you cannot answer those two questions, why? What is it that is so hard about even giving me one word answers - yes or no, won't take any time, will it? certainly not as much time as you've spent so far answering :)

Phil answered no problem, why can't you?
 
Thank you.

What I know about photography could be written on the sensor of a cheap point-and-shoot, but I know a little more about formal logic. You seem to assume that cropping implies a change of viewing distance. I'd suggest that that assumption died for most people when the computer became the predominant way of viewing images. When you said "if you have cropped half the frame area, you'll lose about a third of your estimated DoF" on the first page, it would have been very helpful if you'd added "because of the change in viewing distance", so we could have avoided four pages of confusion.
 
abdoujaparov said:
Thank you. When you said "if you have cropped half the frame area, you'll lose about a third of your estimated DoF" on the first page, it would have been very helpful if you'd added "because of the change in viewing distance", so we could have avoided four pages of confusion.
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Exactly. You'll note he refuses to answer the above, because to do so proves him incorrect on his claim that cropping changes DOF, it's the change of pov historically associated with a cropped image that does that. Still not sure why he isnt answering the question of if he thinks the ear or eye is more in focus... Any idea? LOL
 
Davince said:
I've been scratching my head over this last couple of weeks, and as embarrassing as it is in it's basic nature, I'm going to have to throw it out there in confusion.

A couple of nights a week I do some shots at a local bar, but I keep having issues with DOF - a prime example being this shot (cropped in to highlight focus issue):

SnL0604-4-4_zps3fbe9fb6.jpg


Taken at ISO 1250, 1/3rd sec, f/5.6, Focal lenght 50mm, Subject Distance 1.5m,

By my reckoning, and confirmed by various DOF calculators that should give me a DOF of about 30cm, not far off 50/50 split front and rear.

So how the hell is the bloke on the left so out of focus?! they were nigh on dead in line, certainly not with one even near 15cm fore of the other, I wondered if it was movement blur rather than focus, but I use this shot as an example as they were like statues in it.

Am I being thick? Am I missing something obvious looking for a complex answer?

Or is my expectation of what is 'acceptable' focus just to high? Personally don't think this is acceptable but I'm getting loads of them like this last couple of shoots!

One issue I have been having there is with the lighting system used which has been playing havoc with the camera but can't imagine it changing the focal perceptions of the camera?!!
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The next object behind the happy couple is too far away to be in focus

high ISO = high noise = lower resolution
you are not accurately focused on the eyes
you have a little movement blur

What you need is some off camera flash, triggered by a little on camera flash. The focus assist on the on camera flash will nail the focus. The off camera flash will both light the subject well, and get your apeture/shutterspeed/iso back to a more acceptable level

Off camera flash can be as simple as bouncing a single flashgun off the ceiling / wall
 
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