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Author Topic: FOV Equivalences vs Magnification  (Read 56509 times)
01af
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« Reply #60 on: March 03, 2008, 04:11:39 AM »
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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! [...][a href=\"index.php?act=findpost&pid=178659\"][{POST_SNAPBACK}][/a]
It sounds to me you are talking about the quality of bokeh.[a href=\"index.php?act=findpost&pid=178717\"][{POST_SNAPBACK}][/a]
Hell, no! I'm not talking about bokeh! I am talking about the degree (not quality) of blur outside the DOF range.


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Bokeh is a quality of the lens and not related to format.[a href=\"index.php?act=findpost&pid=178717\"][{POST_SNAPBACK}][/a]
Bokeh is not a quality of the lens but a quality of the image. It's determined by a wealth of factors, among them the out-of-focus rendering characteristics of the lens (also often called 'bokeh,' for simplicity's sake). Another factor (of many) is the sharpness gradient we are talking about here. So yes, the image format does affect bokeh.


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My starting point was to agree with the above statement ... but I dont think my test shows this. I can't see a lot of difference between say the H1 at f/4 and the D3 at f/2.[a href=\"index.php?act=findpost&pid=178739\"][{POST_SNAPBACK}][/a]
There isn't supposed to be 'a lot' of difference; it's rather subtle instead. It will be more obvious at close range and less obvious near infinity. And by the way, the format factor between the Hasselblad H1 and the Nikon D3 is not 2 but 1.75 (or even less, depending on how you're calculating). So the equivalent aperture to f/2 on the D3 would be f/3.5 on the H1---provided you are using equivalent lenses (e. g. 45 mm on D3 = 80 mm on H1), shooting from the same point of view, and focusing accurately.

-- Olaf
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Ray
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« Reply #61 on: March 03, 2008, 08:43:37 AM »
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Bokeh is not a quality of the lens but a quality of the image. It's determined by a wealth of factors, among them the out-of-focus rendering characteristics of the lens (also often called 'bokeh,' for simplicity's sake). Another factor (of many) is the sharpness gradient we are talking about here. So yes, the image format does affect bokeh.
[a href=\"index.php?act=findpost&pid=178811\"][{POST_SNAPBACK}][/a]

Bokeh is not a quality of the lens? I've not heard that one before, although I suppose one could argue that all lens attributes such as aberration, sharpness, diffraction, vignetting are only seen in the image and therefore could be described as qualities of the image. However, the image is in part a product of the lens, so that line of reasoning doesn't get us anywhere.

My understanding is that the quality of bokeh is largely dependent upon the degree of divergence of the sagittal and meridional MTF curves, ie. the dotted and solid lines seen on MTF charts. When there's significant divergence of those lines, one can expect the bokeh of OoF areas to be less esthetically pleasing than they otherwise would be if the lines did not diverge.

Sharpness gradient? Is that another term for DoF? I can't see the connection here with sensor format size. You seem to be arguing against yourself. The sensor merely records, as faithfully as it can, the image from the lens. The image with all its qualities of sharpness, DoF, aberrations, nice bokeh, whatever, exists before it's recorded by the sensor. The sensor inevitably introduces its own faults such as noise and aliasing artifacts and is of course limited in the amount of detail it can record.

If a larger format sensor is able to record more detail in the plane of focus, then DoF (on the larger format) will appear to be shallower than the F stop/FL equivalents (for the smaller format) would suggest.

I suspect that claims the DoF 'look' from the larger format cannot be replicated on the smaller format are only true when the larger format has a significantly greater pixel count and is used with appropriately high quality lenses to produce a sharper image at the plane of focus.
« Last Edit: March 03, 2008, 08:45:57 AM by Ray » Logged
01af
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« Reply #62 on: March 03, 2008, 10:22:34 AM »
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Bokeh is not a quality of the lens?[a href=\"index.php?act=findpost&pid=178844\"][{POST_SNAPBACK}][/a]
Exactly.

The lens quality you (and many others) are referring to as 'bokeh' is only one of many factors determining an image's bokeh. There are other factors that are not connected to the properties of the lens. That's why it is unfortunate to call both things 'bokeh' because it will make simple-minded persons believe they're the same ... or there was an 1:1 correlation between them. Of course, there is a correlation---but it's not 1:1.

Anyway---we are not talking about lens bokeh here. If anything then it's image bokeh.


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My understanding is that the quality of bokeh is largely dependent upon the degree of divergence of the sagittal and meridional MTF curves ...[a href=\"index.php?act=findpost&pid=178844\"][{POST_SNAPBACK}][/a]
Sigh. You've heard some techno-babble and now you're confusing one facet for the whole picture.


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Sharpness gradient? Is that another term for DoF?[a href=\"index.php?act=findpost&pid=178844\"][{POST_SNAPBACK}][/a]
No, it's not. The correlation between the two terms is similar to that between speed and distance ... or between temperature and heat ... or between voltage and current ... you get the picture (or not).


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I can't see the connection here with sensor format size.[a href=\"index.php?act=findpost&pid=178844\"][{POST_SNAPBACK}][/a]
You can't? That's funny because in photographic imaging, frame format is connected to almost everything.

-- Olaf
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EricV
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« Reply #63 on: March 03, 2008, 11:26:52 AM »
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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]
Haha, so after telling me to drop out of this thread, because the beginning question was not about DoF, it seems you have now decided to jump all the way in?  The blur formula quoted earlier shows that at equivalent focal length and aperture, not only is DoF equivalent, but blur at any distance beyond focus is also the same.  So your statement above is simply incorrect.
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01af
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« Reply #64 on: March 03, 2008, 02:34:52 PM »
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... after telling me to drop out of this thread ...[a href=\"index.php?act=findpost&pid=178872\"][{POST_SNAPBACK}][/a]
No-one told you to drop out. I just asked you to stop babbling about depth-of-focus as if it was the same as depth-of-field---which it isn't.


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So your statement above is simply incorrect.[a href=\"index.php?act=findpost&pid=178872\"][{POST_SNAPBACK}][/a]
You should look at images rather than formulas.

-- Olaf
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Ray
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« Reply #65 on: March 03, 2008, 05:40:11 PM »
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The lens quality you (and many others) are referring to as 'bokeh' is only one of many factors determining an image's bokeh. There are other factors that are not connected to the properties of the lens. That's why it is unfortunate to call both things 'bokeh' because it will make simple-minded persons believe they're the same ... or there was an 1:1 correlation between them. Of course, there is a correlation---but it's not 1:1.

When referring purely to the image, everything is connected to the property of the lens. All photographic images are a product of the lens properties and the target properties. Obviously, to determine the quality of 'bokeh', the target being photographed has to be 3-dimensional in relation to the plane of focus. There has to be at least one area in the image which is OoF.

If you want to get semantic about this, you could therefore claim that the quality of 'bokeh' is determined by an interaction of lens properties and target properties, just as the property called 'lens resolution' is associated with a target containing something to resolve. A lens can only resolve a certain number of line pairs per millimetres if the lines exist.

Since this situation is obvious and always implied, when you claim bokeh is not just a property of the lens, I can't help wondering what you are talking about.

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Anyway---we are not talking about lens bokeh here. If anything then it's image bokeh.
Sigh. You've heard some techno-babble and now you're confusing one facet for the whole picture.
No, it's not. The correlation between the two terms is similar to that between speed and distance ... or between temperature and heat ... or between voltage and current ... you get the picture (or not).
You can't? That's funny because in photographic imaging, frame format is connected to almost everything.

Frame format is not connected to the image before it's recorded. You can examine the whole image circle in as much detail as you want on a ground plate of glass. All the characteristics which we talk about such as quality of OoF blobs, sharpness, chromatic aberration, peripheral resolution fall-off, vignetting etc etc are all there.

You can then apply a frame of any size you want for the purpose of composition or for the purpose of cutting out the inferior parts of the image which are usually near the periphery of the image circle. The frame or format is ideally not supposed to alter the image in any way. It's merely a method of selecting which part of the image you want to record.

Got it?
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EricV
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« Reply #66 on: March 03, 2008, 06:09:12 PM »
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You should look at images rather than formulas.
-- Olaf
What makes you believe your statement that "an object at a certain distance beyond DOF will appear ... more blurred in a large-format shot"?  I contend that this statement is wrong, based on a mathematical formula derived from a geometric model of image blur.  Since you do not believe in formulas, can you produce images to demonstrate your claim?
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Eric Myrvaagnes
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« Reply #67 on: March 03, 2008, 06:30:36 PM »
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The lens quality you (and many others) are referring to as 'bokeh' is only one of many factors determining an image's bokeh. There are other factors that are not connected to the properties of the lens. That's why it is unfortunate to call both things 'bokeh' because it will make simple-minded persons believe they're the same ... or there was an 1:1 correlation between them. Of course, there is a correlation---but it's not 1:1.

Anyway---we are not talking about lens bokeh here. If anything then it's image bokeh.
[a href=\"index.php?act=findpost&pid=178857\"][{POST_SNAPBACK}][/a]
The condescending tone you are using here is, IMHO, inappropriate. If, in fact, you know better than anyone else on this thread the "correct" meaning of "Bokeh", you should be able to provide a reference to some reliable and authoritative sources for your approved definition of "Bokeh".

Out of curiosity, I just spent a half hour googling "bokeh" to see what others claim it refers to. The most generally accepted notion I could find included three main points:
(1)   The word (originally "boke") comes from a transliteration of a Japanese word for "blur" or "fuzziness";
(2)   In photography, the term refers to the out-of-focus parts of an image; and
(3)   The (purely subjective) quality of "bokeh" in an image depends on characteristics of the lens and the shape of the diaphragm.

I suppose one could argue that the diaphragm isn't part of the lens (Why? Because it isn't made of glass?), but even so, that is the only characteristic I have found that might fit your description of "other factors [sic]".

Has the ISO agreed on a more precise definition? Please enlighten us.
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-Eric Myrvaagnes

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01af
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« Reply #68 on: March 04, 2008, 08:50:36 AM »
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When referring purely to the image, everything is connected to the property of the lens.[a href=\"index.php?act=findpost&pid=178937\"][{POST_SNAPBACK}][/a]
While this statement is true, it is not the complete truth. There are many factors affecting the appearance of the image besides lens properties. Actually, lens properties generally are of secondary importance overall.


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If you want to get semantic about this ...[a href=\"index.php?act=findpost&pid=178937\"][{POST_SNAPBACK}][/a]
I don't. It's you who unnecessarily is forcing the thread into this direction.


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... just as the property called 'lens resolution' is associated with a target containing something to resolve.[a href=\"index.php?act=findpost&pid=178937\"][{POST_SNAPBACK}][/a]
Your analogy is flawed. I repeat it again: I am *NOT* talking about lens properties. Because that's not what this thread is about in the first place. It's you who keeps talking about lens properties.


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... I can't help wondering what you are talking about.[a href=\"index.php?act=findpost&pid=178937\"][{POST_SNAPBACK}][/a]
I am talking about images and their appearance, or 'flavour,' or characteristics, and if and how frame format has an influence on that.


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Frame format is not connected to the image before it's recorded.[a href=\"index.php?act=findpost&pid=178937\"][{POST_SNAPBACK}][/a]
 

Of all properties of an image, the format is one of the most basic ones.


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You can examine the whole image circle in as much detail as you want on a ground plate of glass. All the characteristics which we talk about such as quality of OoF blobs, sharpness, chromatic aberration, peripheral resolution fall-off, vignetting etc etc are all there.[a href=\"index.php?act=findpost&pid=178937\"][{POST_SNAPBACK}][/a]
Sure. It does absolutely completely entirely not matter whether the image is on a ground glass, on film, on a sensor, or in a digital file. Did anyone deny this? Not? So why do you bring this up now, of all things?


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The frame or format is ideally not supposed to alter the image in any way. It's merely a method of selecting which part of the image you want to record.[a href=\"index.php?act=findpost&pid=178937\"][{POST_SNAPBACK}][/a]
And you really believe that selecting what's to be in an image doesn't affect the image in any way?  

-- Olaf
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01af
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« Reply #69 on: March 04, 2008, 08:53:25 AM »
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What makes you believe your statement that "an object at a certain distance beyond DOF will appear ... more blurred in a large-format shot"?[a href=\"index.php?act=findpost&pid=178944\"][{POST_SNAPBACK}][/a]
Images. Unfortunately, they're not mine, and they are not on the Internet, so no URL. They were shot with several different format digital cameras at short distance (approx. 1 - 2 ft or so). The differences in the DOF and blur characteristics were obvious.


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I contend that this statement is wrong, based on a mathematical formula derived from a geometric model of image blur.[a href=\"index.php?act=findpost&pid=178944\"][{POST_SNAPBACK}][/a]
After some more thinking about it, I don't insist in the words 'more blurred.' But I do insist in 'blurred in a different (smoother) way.'


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Since you do not believe in formulas ...[a href=\"index.php?act=findpost&pid=178944\"][{POST_SNAPBACK}][/a]
Actually, I am an engineer, and I do believe in formulas as much as you do. However I am aware that formulas usually don't reflect the real world but the (often simplified and/or idealized) models that we make to describe, and to grasp, the world ... or part thereof. So formulas don't always tell the full truth---the COC formula discussed above, for example, does not take lens aberrations or diffraction effects into account. And currently I am wondering if it is accurate at all distances or only at distances much longer than focal length.

If that formula was accurate at all distances (which, to me, still is subject to further investigation) then it would suggest that 'equivalent f-stop' (with regard to DOF), for the larger frame format, is not simply small format's f-stop multiplied by form factor but somewhat greater (greater aperture number, that is, not wider aperture), depending on focus distance.

Be q the quotient of the linear sizes of the formats (also known as 'crop factor'), d the focus distance, f_small and f_large the equivalent focal lengths of the small and the large formats, and k_small the  f-stop number for the smaller format, then the equivalent f-stop number of the larger format, k_large, according to that COC formula, was:

k_large = q * [(d - f_small) / (d - f_large)] * k_small

(With d approaching infinity, the factor in brackets [] approaches 1, and thus it turns into the well-known formula k_large = q * k_small.)

With this modified equivalent f-stop, the COC curves of both formats, according to the COC formula given further up this thread, will match exactly across all object distances. This suggests that the blur beyond the DOF range, at equivalent focal lengths and equivalent f-stops, was exactly the same for all frame formats.

But as a matter of fact, the blur is not equal for all formats. So the COC formula obviously is over-simplified. I suspect it is meant for long focus distances but becomes increasingly inaccurate at shorter focus distances. Or maybe it does describe the sizes of the circles of confusion accurately but not the characteristic, or appearance, of the blur. I don't know.

An interesting question ...

-- Olaf
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01af
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« Reply #70 on: March 04, 2008, 08:55:38 AM »
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... you should be able to provide a reference to some reliable and authoritative sources for your approved definition of "bokeh".[a href=\"index.php?act=findpost&pid=178953\"][{POST_SNAPBACK}][/a]
Maybe I should indeed but you already did.


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The most generally accepted notion I could find included three main points:
(1)   The word (originally "bo-ke") comes from a transliteration of a Japanese word for "blur" or "fuzziness";
(2)   In photography, the term refers to the out-of-focus parts of an image;[a href=\"index.php?act=findpost&pid=178953\"][{POST_SNAPBACK}][/a]
See? Point (2) is exactly what I said.


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(3)   The (purely subjective) quality of "bokeh" in an image depends on characteristics of the lens and the shape of the diaphragm.[a href=\"index.php?act=findpost&pid=178953\"][{POST_SNAPBACK}][/a]
It does indeed. But there are other factors also.


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... that is the only characteristic I have found that might fit your description of "other factors" [sic].[a href=\"index.php?act=findpost&pid=178953\"][{POST_SNAPBACK}][/a]
Other factors include, but are not restricted to:
- depth-of-field (... doh!);
- distance of out-of-focus objects (how far out of focus are they);
- shape and structure of out-of-focus objects;
- brightness of out-of-focus objects;
- contrast of out-of-focus objects;
- ratio of areas of in-focus vs. out-of-focus parts of the image;
- print size;
- the eyes of the beholder;
- etc. ...

-- Olaf
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EricV
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« Reply #71 on: March 04, 2008, 11:11:36 AM »
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Images ... were shot with several different format digital cameras at short distance (approx. 1 - 2 ft or so). The differences in the DOF and blur characteristics were obvious.
After some more thinking about it, I don't insist in the words 'more blurred.' But I do insist in 'blurred in a different (smoother) way.'
-- Olaf
[a href=\"index.php?act=findpost&pid=179033\"][{POST_SNAPBACK}][/a]
Hmm, I think we might actually agree now :)  I do not trust the formula we have been discussing to be valid at very short distances, so this is precisely where to look for format differences.

By the way, for those interested in performing actual image tests, it is not necessary to have two cameras with different formats.  A single camera with a zoom lens will do just fine, if you are careful to crop the image in proportion to the focal length, to maintain the same field of view, and then enlarge the final image to the same size.
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Ray
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« Reply #72 on: March 04, 2008, 10:40:22 PM »
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Other factors include, but are not restricted to:
- depth-of-field (... doh!);
- distance of out-of-focus objects (how far out of focus are they);
- shape and structure of out-of-focus objects;
- brightness of out-of-focus objects;
- contrast of out-of-focus objects;
- ratio of areas of in-focus vs. out-of-focus parts of the image;
- print size;
- the eyes of the beholder;
- etc. ...


[a href=\"index.php?act=findpost&pid=179034\"][{POST_SNAPBACK}][/a]

I'm glad you agree with the points I made a few posts ago. In order to examine qualities of the lens, the target has to contain features relevant to those qualities being examined. No point in shooting a misty dawn scene over a placid lake, in order to examine lens resolution. No point in shooting a smooth, evenly lit wall to look for chromatic aberration and color fringing. No point in shooting a 2-dimensional target in order to examine DoF issues. This is a given. I'm surprised it's necessary to raise the issue. Why are we discussing such obvious factors?

The matter that's being questioned here relates specifically to the effect of format size on DoF qualities. Any other variation such as lens resolution, bokeh quality, sensor pixel count, system resolution etc will produce its own different 'look'.

Currently, the highest resolving systems, in terms of picture resolution rather than lp/mm, are MFDBs. Perceptions of differences in DoF (after matching FoV and shifting to equivalent f stops) are in my opinion likely to be due to factors other than format size, such as lens properties, system resolution, bokeh quality, lack of, or presence of an AA filter and so on.
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Ray
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« Reply #73 on: March 04, 2008, 10:51:35 PM »
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By the way, for those interested in performing actual image tests, it is not necessary to have two cameras with different formats.  A single camera with a zoom lens will do just fine, if you are careful to crop the image in proportion to the focal length, to maintain the same field of view, and then enlarge the final image to the same size.
[a href=\"index.php?act=findpost&pid=179069\"][{POST_SNAPBACK}][/a]

This approach ignores system resolution. If I crop a 5D image to match the FoV of a 40D image, I end up comparing a 4.8mp image with a 12.3mp image.
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01af
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« Reply #74 on: March 05, 2008, 03:16:39 AM »
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... it is not necessary to have two cameras with different formats.  A single camera with a zoom lens will do just fine ...[{POST_SNAPBACK}][/a]
This approach ignores system resolution. If I crop a EOS 5D image to match the FoV of a EOS 40D image, I end up comparing a 4.8 mp image with a 12.3 mp image.[a href=\"index.php?act=findpost&pid=179222\"][{POST_SNAPBACK}][/a]
But you can always scale your 12.3 MP image down to 4.8 MP. So within limits, this approach is valid I think.

By the way, I constructed a COC formula that takes the effects of shorter focus distances into account properly. Of course, even though it's way more complex than the COC formula given above it still is a simplification as it is based on nothing but the simple thin-lens equation and the theorem of intersecting lines (and some basic algebra). So it takes neither a non-zero distance of nodal planes nor diffraction effects into account.

I evaluated the improved COC formula with a function plotter, and it indeed suggests a difference in the COC curves for different formats ... albeit a minuscule one. For larger formats, COC at object distances beyond DOF is slightly smaller than for smaller formats. While this seems counter-intuitive, it does make sense. A COC growing at a slower rate in the blurred area beyond DOF will make for a smoother transition from perceived sharpness to blur.

For further discussion of this topic, I'd like to suggest to start a new thread elsewhere because we have come a long way from the original question, and this definitely is no beginner's topic anymore. I wonder if the original poster is still with us ...

-- Olaf

P.S. For a follow-up, see [a href=\"http://luminous-landscape.com/forum/index.php?showtopic=23713]here[/url].
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Farkled
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« Reply #75 on: March 05, 2008, 01:21:41 PM »
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Still here and reading (albeit not totally understanding) with interest.  Also marveling at what a slight imprecision in the use of language has wrought.
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« Reply #76 on: March 05, 2008, 11:30:52 PM »
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Still here and reading (albeit not totally understanding) with interest.  Also marveling at what a slight imprecision in the use of language has wrought.
[a href=\"index.php?act=findpost&pid=179363\"][{POST_SNAPBACK}][/a]

So how has this 'helped you' ?

What was the agenda behind your question ?

Were you trying to evaluate buying into different systems or what..?

S
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« Reply #77 on: April 03, 2008, 07:50:53 PM »
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Hi all-

I agree with the last poster that there is so much discord because of a word, and slight imprecision in using that word makes a big difference.  The poster a while back, though, is correct:  Bokeh is an IMAGE property, not a property of a lens, thus it depends on background, lighting, etc, and included in that are lens factors for how the out of focus area of an image is rendered.  Of course lenses matter- but so does technique and what background you choose to shoot.  Bokeh is AFFECTED by lenses, but lenses do not "have" bokeh.

Probably the most important factor for how  lens affects bokeh is spherical aberration.  THe degree of correction of spherical aberration is related to the shape of the out of focus circle of confusion-- specular highlights can be a nice smooth gaussian blur or a donut, with the donut being worse for an images bokeh, in most people's opinions.

I have a primer on Bokeh if anyone is interested.  Farkled- it may be more useful than just arguing about words etc.

http://bokehtests.com/Site/About_Bokeh.html

Klaus
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Farkled
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« Reply #78 on: April 04, 2008, 12:15:36 AM »
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So how has this 'helped you' ?

What was the agenda behind your question ?

Were you trying to evaluate buying into different systems or what..?

S
[a href=\"index.php?act=findpost&pid=179488\"][{POST_SNAPBACK}][/a]

No agenda.  Just trying to understand why a 300mm lens performs as a 450 on a 1.5 crop body and wondering if the two images are, in fact, close enough to being the same magnification as to make no never mind.

Simplistically stated, if one considers 50mm to be normal, then a 300mm is a 6X power, a 400mm is an 8X power.  So when I mount a 300mm on a 1.5x crop body, it is still a 6X - nothing changed except that we now call it the equivalent (same as) a 450mm.  Basically we are cropping and "blowing up" or enlarging the image.

I was just wondering if, for all intents and purposes, while in the field and shooting wildlife, if a 300 on a crop body would be the "same" as a 450 on a FF body - leaving aside issues of resolution, IQ, DoF, bokeh, etc.  Yes, it's a question that betrays ignorance, which is why it was asked in the Beginners Corner.  Silly or not, that question kept me from buying a DSLR for almost a year.  I like long lenses and their effects and I wanted to understand before jumping in with a couple grand.  Obviously, I never got an understandable answer - so I asked it here.

I bought an Olympus OM2 around 1980 and it served me well until 2005 when the winder clutch died.  I have a Tokina 400mm that took some seriously good candids and wild life shots (glass quality aside.)  Trying to take serious images with a Canon S2 IS drove me nuts so I finally came up with the money for a 40D as well as a 70-300 IS lens.  Despite not having an answer, I am happily taking pictures that I enjoy, but I'd still like to know.
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Ray
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« Reply #79 on: April 04, 2008, 01:19:34 AM »
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Trying to take serious images with a Canon S2 IS drove me nuts so I finally came up with the money for a 40D as well as a 70-300 IS lens.  Despite not having an answer, I am happily taking pictures that I enjoy, but I'd still like to know.
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Canon's first DSLR was a cropped 35mm format. Many people complained because the wide angle lenses they'd been using with their 35mm film cameras were no longer wide angle. Others rejoiced because their telephoto lenses became effectively 1.6x longer in focal length.

The wide angle disadvantage has now been addressed with lenses such as the EF-S 10-22mm, so in terms of magnification and 'field of view' the cropped format would appear to have the advantage with regard to the effective range of focal lengths available. Even the longest and most expensive lens that Canon make, the 1200mm F5.6, becomes effectively a 1920mm lens on the 40D.

However, one could get the same effect using that 1200mm lens on a 21mp 1Ds3 and cropping the image in Photoshop to the same field of view. You would then be comparing almost identical images that would differ only in pixel count. The 40D shot would be 10mp and the cropped 1Ds3 shot would be around 8mp.

The 40D image might be very marginally sharper or more detailed, but it's doubtful you would notice it.
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