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Author Topic: FOV Equivalences vs Magnification  (Read 55552 times)
Ray
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« Reply #40 on: February 28, 2008, 07:18:26 AM »
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I dont think youl see a lot if diffewrence wich such a wide lens

imo the differences, if there are any,  show in the 50-135 region mainly and at f4 or wider

S
[a href=\"index.php?act=findpost&pid=177912\"][{POST_SNAPBACK}][/a]

Too late, Morgan. Already done! 18mm at f3.5 on the 40D compared with 30mm at F5.6 on the 5D. As you predict, little difference.

[attachment=5315:attachment]  [attachment=5316:attachment]  [attachment=5317:attachment]  [attachment=5318:attachment]  [attachment=5319:attachment]
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EricV
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« Reply #41 on: February 28, 2008, 11:27:19 AM »
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Depth of focus will be similar on different formats, provided the f/stop is properly scaled to the lens focal length squared.  The ratio (lens focal length) / (distance to subject) can be used to determine when this equivalence might be expected to break down.  Using a 30mm lens, focusing on a subject as close as 300mm (roughly 12 inches), this ratio is still only 1/10.  Such a small effect will likely be unobservable, or confused by other effects like diffraction.  None of the images posted so far probe the regime where depth of focus differences might be seen.
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01af
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« Reply #42 on: February 29, 2008, 08:48:55 AM »
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Wow ... what an over-the-top thread, and entirely missing the original question!

To cut to long story short---Morgan is right. With different image formats, depth-of-field sharpness indeed does change differently across the depth of the field. The gradient will be smoother with larger formats. However, with 35-mm format vs. APS-C, the difference is hardly visible (at long range even less than at close range); it'll be more obvious with more dissimilar formats like APS-C vs. medium format, or 35-mm vs. 45", for instance.

But---that wasn't the question.

The question, as I understand it, was dealing with the contradiction of two statements. First statement: At a given distance, image magnification depends on focal length only ... i. e. a longer focal length will yield a larger magnification. Second statement: At a smaller image format, you'll need a shorter focal length for the same apparent magnification.

The solution to this contradiction lies in the word 'apparent'. Statement 1 is dealing with absolute, statement 2 with apparent, or relative, magnification. Relative to what? To the camera's frame size, of course. To make a given subject fill the frame at a given distance, for a frame half the size you'll need half the (absolute) magnification, and thus half the focal length. That's all.

So the answer to the original poster's question is: yes.

Of course, magnification is not the only factor determining an image's appearance (although it's the most significant). Depth-of-field is another. At the same distance and the same (relative) magnification---or in other words, the same angle of view---, the larger format will need a smaller aperture for the same DOF. However, even with the same DOF, the images' appearances still won't be perfectly identical because the gradient of the sharpness within DOF turning into blur beyond DOF will be different---that's what the carried-away discussion above mostly was about.


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Depth of focus will be similar ...[a href=\"index.php?act=findpost&pid=178015\"][{POST_SNAPBACK}][/a]
Eric, nobody here was talking about depth of focus; that's a completely different thing still. Please stop adding confusion to an already way-too-complex thread!

-- Olaf
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Morgan_Moore
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« Reply #43 on: February 29, 2008, 12:49:58 PM »
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Wow ... what an over-the-top thread, [a href=\"index.php?act=findpost&pid=178216\"][{POST_SNAPBACK}][/a]

Possibly for the begineners section but it the look thing is certainly important for me to clarify in my head (which I have not)

My experience is awful with cameras like the D80 and the D200 - horrible to use - now I have a d3 I am getting an cool look back to my DSLR images - but the res is not there compared to my blad,

If however I can convince myself that a 1Ds3 can compare to a 22mp Dback - it might be time to change and that is a big thing to think about

For a beginner laerning the whole game understanding the different formats and looks is part of the learning process too I would sugest - like learning DOF or Camera shake etc

S
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Sam Morgan Moore Cornwall
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juicy
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« Reply #44 on: February 29, 2008, 06:15:40 PM »
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Quote from: Ray,Feb 28 2008, 08:18 AM
Too late, Morgan. Already done! 18mm at f3.5 on the 40D compared with 30mm at F5.6 on the 5D. As you predict, little difference.


Hi!
Why on earth should anyone waste their time with this completely flawed "test"? Next time you could at least try to get sharp images. The 40D image is a horrible mess. Try using a tripod and mlu. Now it's impossible to tell where it's been focused. No point in comparing anything with these images.

Cheers,
J
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Morgan_Moore
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« Reply #45 on: February 29, 2008, 06:32:14 PM »
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Hi!
Why on earth should anyone waste their time with this completely flawed "test"? Next time you could at least try to get sharp images. The 40D image is a horrible mess. Try using a tripod and mlu. Now it's impossible to tell where it's been focused. No point in comparing anything with these images.

Cheers,
J
[a href=\"index.php?act=findpost&pid=178333\"][{POST_SNAPBACK}][/a]

If the 40D is like the D200 or D80 - its always a horrible mess - immpossible to tell where its been focussed - its the beacause of the small chip  

Too much DOF declining at to shallow a rate !
« Last Edit: March 01, 2008, 01:40:21 AM by Morgan_Moore » Logged

Sam Morgan Moore Cornwall
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Sheldon N
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« Reply #46 on: February 29, 2008, 08:27:12 PM »
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Sam -

Why don't you bang out a quick test - don't you have a MFDB and a Nikon D3?

Just use a normalish lens, focus on a close subject and include middle distance and far distance background subjects (still life of some sort). Then downrez the MFDB shot to the same resolution as the D3 and compare the quantity (not quality) of the background blur of the middle distance and far distance subjects.

If I were ambitious I'd compare my 5D and 4x5 film, but it would take me a few weeks to have the film processed and scanned.
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Ray
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« Reply #47 on: March 01, 2008, 12:51:04 AM »
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Wow ... what an over-the-top thread, and entirely missing the original question!

To cut to long story short---Morgan is right. With different image formats, depth-of-field sharpness indeed does change differently across the depth of the field. The gradient will be smoother with larger formats. However, with 35-mm format vs. APS-C, the difference is hardly visible (at long range even less than at close range); it'll be more obvious with more dissimilar formats like APS-C vs. medium format, or 35-mm vs. 45", for instance.

[a href=\"index.php?act=findpost&pid=178216\"][{POST_SNAPBACK}][/a]


Depth of focus will be similar ...

Yes! It's over the top, but all my tests have shown that magnification is very similar. The issue has naturally gravitated towards the 'resolution' of that similar magnification. That's now become the issue, and it's the central issue which has flowed on from a beginner's question.

Morgan has suggested that comparisons will vary with focal length. I've tested the extremes of 250mm versus 400mm, and 18mm versus 30mm. I've now gone somewhere in the middle and compared 58mm on the 40D with 105mm on the 5D.
Surprisingly, the results are different. I didn't expect it and I was already composing in my mind some derogatory comments, before I saw the results.
In this range between 50mm and 105mm, with my lenses at least, the results tend to suggest the larger format produces slightly less DoF for the equivalent FL and F stop.

Has this anything to do with the mathematical formula presented as evidence for this effect? Who knows? Once again, it all boils down to 'knowing thy lenses'! Because my Canon 24-105 behaves like this is no guarantee that all lenses will behave similarly.

Of course I offer the results at maximum quality jpeg comprerssion. First the over all scene.

[attachment=5345:attachment]

Then for dedicated pixel peepers, a 100% crop of of the 5D at f8 versus the 40D at f5, with the same zoom lens. The 5D is marginally sharper and more detailed, but not by much. There are all sorts of issues such as, is the 24-105 sharper at 105mm than at 58mm? (The FoV's are the same but the nomenclature may be erroneous.)

[attachment=5346:attachment]

Let the results speak for themselves. The image headings should provide sufficient information. You can see from the following 2 images that DoF resolution does in deed vary noticeably with the these focal lengths (but not greatly). Perhaps Roger Clark should re-examine his views.

[attachment=5347:attachment]  [attachment=5348:attachment]

The bottom left hand corner is slightly nearer than the plane of focus, yet it is still marginally sharper in the 40D shot, confirming that at these focal lengths, something different is happening. The larger format does indeed tend to produce a slightly shallower DoF.
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Morgan_Moore
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« Reply #48 on: March 01, 2008, 01:45:02 AM »
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Sam -

Why don't you bang out a quick test - don't you have a MFDB and a Nikon D3?

[a href=\"index.php?act=findpost&pid=178353\"][{POST_SNAPBACK}][/a]

Because Ive been extremely busy shooting real pictures for real clients

I may do now its the weekend


S
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Sam Morgan Moore Cornwall
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Ray
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« Reply #49 on: March 01, 2008, 03:42:25 AM »
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Because Ive been extremely busy shooting real pictures for real clients

I may do now its the weekend
S
[a href=\"index.php?act=findpost&pid=178393\"][{POST_SNAPBACK}][/a]

We're all busy, whether it's shooting real pictures for real clients or mowing the lawn.

The main point about my latest test comparing the 40D at 58mm and the 5D at 105mm, is that the 40D is actually slightly sharper a little bit in front of the focus point and also slightly sharper a little bit behind the focus point.

At the precise focus point the 5D is slightly sharper. This would be proof that there is no misfocussing.
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Morgan_Moore
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« Reply #50 on: March 01, 2008, 04:58:20 AM »
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We're all busy, whether it's shooting real pictures for real clients or mowing the lawn.

The main point about my latest test comparing the 40D at 58mm and the 5D at 105mm, is that the 40D is actually slightly sharper a little bit in front of the focus point and also slightly sharper a little bit behind the focus point.

At the precise focus point the 5D is slightly sharper. This would be proof that there is no misfocussing.
[{POST_SNAPBACK}][/a]

OK [a href=\"http://81.5.138.214/smmcom/format_test/index.html]Check This Out[/url]


S
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Sam Morgan Moore Cornwall
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Ray
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« Reply #51 on: March 02, 2008, 06:10:41 AM »
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Quote from: juicy,Mar 1 2008, 09:15 PM
Quote from: Ray,Feb 28 2008, 08:18 AM
Too late, Morgan. Already done! 18mm at f3.5 on the 40D compared with 30mm at F5.6 on the 5D. As you predict, little difference.
Hi!
Why on earth should anyone waste their time with this completely flawed "test"? Next time you could at least try to get sharp images. The 40D image is a horrible mess. Try using a tripod and mlu. Now it's impossible to tell where it's been focused. No point in comparing anything with these images.

Cheers,
J
[a href=\"index.php?act=findpost&pid=178333\"][{POST_SNAPBACK}][/a]

I didn't notice this cheeky little comment. 'Why should anyone waste their time..?' No good reason at all to ever waste your time. No need to ask that, surely.

What the question should be is, "Why does the 40D image look unsharp? Is it because I didn't use tripod and MLU or is it simply OoF?

The answer is, the 40D shots are sometimes not focussed properly. Why didn't I pick it up? Because I'm comparing a consumer grade zoom at f5.6 with another consumer grade zoom at F3.5. Considering the 5D is less demanding on lenses because of its wider pixel spacing, I figured the 5D shot probably should be sharper with a sharp lens at f5.6.

The other problem is the difficulty of accurately manually focussing a wide angle image through a small viewfinder. One reason I bought the 10D was because the LivewView feature allows for more accurate manual focussing, but also because it's supposed to have more accurate autofocussing, period.

In these tests, I used both cameras in autofocus mode, being careful to focus on the same spot in each scene with both cameras. It looks as though the 40D with EF-S 17-55/2.8 is not focussing as accurately as the 5D with EF lenses.

This is a surprise to me. The following images show the problem.. same camera, same lens, same f stop, same focussing point. In autofocus mode, the 40D is focussing slightly in front. This is a recently acquired camera and lens which I've not had chance to use much.

Since the 5D doesn't have LiveView and is difficult to precisely manual focus through the viewfinder, I can never be certain that the focussing of the 5D is the same as the manual focussing with LiveView on the 40D, with the EF-S 17-55 at least.

[attachment=5363:attachment]  [attachment=5364:attachment]  [attachment=5365:attachment]
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Morgan_Moore
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« Reply #52 on: March 02, 2008, 07:18:56 AM »
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Why would anyone waste thier time with this stuff ?

Well, If you are considering spending money on a specific system it is good to know what you are buying into

especially when acceptable A3 resolution is provided by cameras from $1000 to $20000 (ish)

I bought my blad when the highest res DSLR was the Kodak14n - resolution was a major factor - no longer so IMO

S
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Sam Morgan Moore Cornwall
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01af
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« Reply #53 on: March 02, 2008, 11:19:27 AM »
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[...] the results tend to suggest the larger format produces slightly less DoF for the equivalent focal length and f-stop.[a href=\"index.php?act=findpost&pid=178384\"][{POST_SNAPBACK}][/a]
No, they don't. The depth-of-field is the same---after all, that's how equivalent f-stop is defined in this context. But the larger format has more blur outside the DOF range. Don't confuse more blur with less DOF!

The front and the rear limit of DOF are determined by some well-defined level of sufficient sharpness. But that does not say anything about how exactly the sharpness gradually will turn into blur beyond those limits. With focal length and aperture being equivalent (i. e. same point of view, same angle of view, and same DOF), an object at a certain distance beyond DOF will appear blurred in a small-format shot and more blurred in a large-format shot.

-- Olaf
« Last Edit: March 02, 2008, 11:22:08 AM by 01af » Logged
juicy
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« Reply #54 on: March 02, 2008, 12:07:43 PM »
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I didn't notice this cheeky little comment. 'Why should anyone waste their time..?' No good reason at all to ever waste your time. No need to ask that, surely.

What the question should be is, "Why does the 40D image look unsharp? Is it because I didn't use tripod and MLU or is it simply OoF?

The answer is, the 40D shots are sometimes not focussed properly. Why didn't I pick it up? Because I'm comparing a consumer grade zoom at f5.6 with another consumer grade zoom at F3.5. Considering the 5D is less demanding on lenses because of its wider pixel spacing, I figured the 5D shot probably should be sharper with a sharp lens at f5.6.

The other problem is the difficulty of accurately manually focussing a wide angle image through a small viewfinder. One reason I bought the 10D was because the LivewView feature allows for more accurate manual focussing, but also because it's supposed to have more accurate autofocussing, period.

In these tests, I used both cameras in autofocus mode, being careful to focus on the same spot in each scene with both cameras. It looks as though the 40D with EF-S 17-55/2.8 is not focussing as accurately as the 5D with EF lenses.

This is a surprise to me. The following images show the problem.. same camera, same lens, same f stop, same focussing point. In autofocus mode, the 40D is focussing slightly in front. This is a recently acquired camera and lens which I've not had chance to use much.

Since the 5D doesn't have LiveView and is difficult to precisely manual focus through the viewfinder, I can never be certain that the focussing of the 5D is the same as the manual focussing with LiveView on the 40D, with the EF-S 17-55 at least.

[attachment=5363:attachment]  [attachment=5364:attachment]  [attachment=5365:attachment]
[a href=\"index.php?act=findpost&pid=178610\"][{POST_SNAPBACK}][/a]

HI!

After writing 10000 posts how different test should be conducted I expected you to nail it immediately but that was not the case. For this kind of test it's absolutely vital that focusing is accurate and the possible camera shake is eliminated completely. Otherwise the test IS waste of time...      


Cheers,
J
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Ray
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« Reply #55 on: March 02, 2008, 04:04:48 PM »
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HI!

After writing 10000 posts how different test should be conducted I expected you to nail it immediately but that was not the case. For this kind of test it's absolutely vital that focusing is accurate and the possible camera shake is eliminated completely. Otherwise the test IS waste of time...       
Cheers,
J
[a href=\"index.php?act=findpost&pid=178670\"][{POST_SNAPBACK}][/a]

Possible camera shake was eliminated. Tripod and remote cord were used and an ISO of 400 for a fast shutter speed. But you are right. I should have nailed it immediately. No matter how many posts I have, I continue to contribute here because I've still got something to learn. At least I've learned something from this exercise and that's what counts, isn't it?  

When you don't see me here anymore, it'll be because I've nothing more to learn, or because I'm dead, or because my interests have shifted.

The fact is, I bought this 40D and 17-44 EF-S lens just before leaving Bangkok a few weeks ago. I haven't used it much and so took this opportinity to put it through a few tests in relation to this 'DoF versus format' issue. The 40D has developed such a reputation for having more accurate focussing, the fact that it could have less accurate autofocussing than my 2+ year old 5D is the last thing that occurred to me. I was prepared to believe that the sharper results from the 5D were due to a combination of larger sensor, a greater pixel count, and a lens used at a smaller and sharper aperture..

The outcome of these preliminary tests for me, is that my new 40D with EF-S 17-55 lens doesn't appear to be autofocussing accurately, which is very annoying because I'll now have to do more tests with line charts to confirm that it's not autofocussing accurately before taking the camera/lens in for calibration.

The matter of DoF and 'look' variation with format seems to remain unresolved, so you'll just have to do the tests yourself. Sorry!  
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Ray
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« Reply #56 on: March 02, 2008, 04:17:06 PM »
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No, they don't. The depth-of-field is the same---after all, that's how equivalent f-stop is defined in this context. But the larger format has more blur outside the DOF range. Don't confuse more blur with less DOF!

The front and the rear limit of DOF are determined by some well-defined level of sufficient sharpness. But that does not say anything about how exactly the sharpness gradually will turn into blur beyond those limits. With focal length and aperture being equivalent (i. e. same point of view, same angle of view, and same DOF), an object at a certain distance beyond DOF will appear blurred in a small-format shot and more blurred in a large-format shot.

-- Olaf
[a href=\"index.php?act=findpost&pid=178659\"][{POST_SNAPBACK}][/a]

It sounds to me you are talking about the quality of bokeh. If so, this is another issue. Bokeh is a quality of the lens and not related to format.
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juicy
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« Reply #57 on: March 02, 2008, 04:18:27 PM »
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Possible camera shake was eliminated. Tripod and remote cord were used and an ISO of 400 for a fast shutter speed. But you are right. I should have nailed it immediately. No matter how many posts I have, I continue to contribute here because I've still got something to learn. At least I've learned something from this exercise and that's what counts, isn't it?   

When you don't see me here anymore, it'll be because I've nothing more to learn, or because I'm dead, or because my interests have shifted.

The fact is, I bought this 40D and 17-44 EF-S lens just before leaving Bangkok a few weeks ago. I haven't used it much and so took this opportinity to put it through a few tests in relation to this 'DoF versus format' issue. The 40D has developed such a reputation for having more accurate focussing, the fact that it could have less accurate autofocussing than my 2+ year old 5D is the last thing that occurred to me. I was prepared to believe that the sharper results from the 5D were due to a combination of larger sensor, a greater pixel count, and a lens used at a smaller and sharper aperture..

The outcome of these preliminary tests for me, is that my new 40D with EF-S 17-55 lens doesn't appear to be autofocussing accurately, which is very annoying because I'll now have to do more tests with line charts to confirm that it's not autofocussing accurately before taking the camera/lens in for calibration.

The matter of DoF and 'look' variation with format seems to remain unresolved, so you'll just have to do the tests yourself. Sorry! 
[a href=\"index.php?act=findpost&pid=178713\"][{POST_SNAPBACK}][/a]

This DoF topic IS interesting. We all have learned something (good technique and questioning everything is needed to get valid results, if nothing else).  

Didn't mean to offend you, just teasing a bit.  

Cheers,
J
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Ray
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« Reply #58 on: March 02, 2008, 04:30:30 PM »
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This DoF topic IS interesting. We all have learned something (good technique and questioning everything is needed to get valid results, if nothing else).  

Didn't mean to offend you, just teasing a bit.   

Cheers,
J
[a href=\"index.php?act=findpost&pid=178718\"][{POST_SNAPBACK}][/a]

No offense taken, but I'm really annoyed with myself. I don't believe my 40D and 17-55 lens is covered by an international warranty; one reason I got it at such a good price.
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Morgan_Moore
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« Reply #59 on: March 02, 2008, 05:51:14 PM »
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No, they don't. The depth-of-field is the same---after all, that's how equivalent f-stop is defined in this context. But the larger format has more blur outside the DOF range. Don't confuse more blur with less DOF!

The front and the rear limit of DOF are determined by some well-defined level of sufficient sharpness. But that does not say anything about how exactly the sharpness gradually will turn into blur beyond those limits. With focal length and aperture being equivalent (i. e. same point of view, same angle of view, and same DOF), an object at a certain distance beyond DOF will appear blurred in a small-format shot and more blurred in a large-format shot.

-- Olaf
[a href=\"index.php?act=findpost&pid=178659\"][{POST_SNAPBACK}][/a]

My starting point was to agree with the above statement

BUT I dont think my test shows this

I cant see a lot of difference between say the H1 at F4 and the D3 at F2

Maybe I havent looked close enough at what DOF is provided

Can you grab a couple of my images, or take some your self that shows this??

(both my test and Rays have shown that we have difficulty gaining accurate focus on some cameras, that appear to be slightly miscalibrated - but that is a different story)

S
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Sam Morgan Moore Cornwall
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