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05-16-2014, 08:03 PM - 2 Likes   #1
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Pretty Good Video on Equivalence

.

If the numbers bore you, if you just like plain talk and reasonable examples, this is a fairly good video (if a bit long) :



A still from the video showing same FOV on FF ("1x") and m43 ("2x"), and the settings (f-stop, ISO) that would be needed to get the same image in DOF & noise:




He gets into which camera companies are 'lying' by not converting aperture (f-stop) when they convert focal length, but I don't think they're 'lying' as much as just sticking to convention, even if that convention is misleading.

Anyway, enjoy.

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05-16-2014, 08:23 PM   #2
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I stopped watching soon as he said something about the myth one format has "less bokeh". Less bokeh? What the heck is that? Bokeh is not a measure of how shallow your DOF is. It's smooth, creamy, harsh, nervous, etc. A property of the lens not the camera body or sensor.
05-16-2014, 10:42 PM   #3
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It depends on how you define bokeh. If you agree that if bokeh is related to the out-of-focus portions of an image. And if how out-of-focus portions are is related to depth of field, then from some peoples point of view less-out-of-focus portions = less bokeh. After all how could you rate the bokeh of the lens from images where everything is in focus?

He busts the myths that smaller sensors have more depth-of-field (and by association "less" bokeh) with examples of the same lens on different sensor sizes. The mathematics behind this isn't at all difficult to understand. What he is saying is you need to apply a crop factor to not only the focal length but also to the ISO and f-stop. When you can get the same image quality (in terms of noise, DOF and by association bokeh) from the same lens regardless of sensor size.

Watch the video. He explains the mathematics and gives many photo examples. A picture is worth a thousand words.

Bokeh is more a personal preference than anything else in my opinion and like pornography you'll find many definitions. As Supreme Court Justice Potter Stewart famously said about pornography (substitute "Bokeh"): "I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description ["hard-core pornography"]; and perhaps I could never succeed in intelligibly doing so. But I know it when I see it, and the motion picture involved in this case is not that".
05-16-2014, 11:18 PM   #4
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I've watched half of it - there are some things I think are being overlooked here mainly the properties of depth of field and focal length in relation to distance to the point of focus. As well he seems to directly associate crop factor to focal length. I find this all a bit misleading

05-16-2014, 11:42 PM   #5
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ISO 800 is the same (noise-wise) as ISO 3200?? I don't think so...
05-17-2014, 12:22 AM   #6
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QuoteOriginally posted by OregonJim Quote
ISO 800 is the same (noise-wise) as ISO 3200?? I don't think so...
It usually is if sensor capturing ISO800 image is 1/4th the size of the sensor capturing ISO3200 image.
05-17-2014, 01:47 AM - 1 Like   #7
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I stopped watching when I realized it's a video about dumbing down photography. Which was before the 1min mark.

And no, companies aren't lying nor are they sticking to conventions; they're sticking with physics. How is that misleading, only an "equivalence" fan can explain, once and again, and again, and again...

Last edited by Kunzite; 05-17-2014 at 01:53 AM.
05-17-2014, 05:31 AM - 3 Likes   #8
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QuoteOriginally posted by Kunzite Quote
I stopped watching when I realized it's a video about dumbing down photography. Which was before the 1min mark.

And no, companies aren't lying nor are they sticking to conventions; they're sticking with physics. How is that misleading, only an "equivalence" fan can explain, once and again, and again, and again...
Well, you might want to watch the video, because I do explain the physics. If you disagree with my math, just let me know where my math is wrong and I'll happily fix it.

Re: my usage of bokeh, it seems like everyone knew what I meant. I'm aware of the technical definition of bokeh, but I'm also aware of how people commonly use it as jargon to mean the amount of background blur. Saying, "Small sensors have less bokeh" (as a myth) was more concise than saying, "Small sensors are less able to create a shallow depth of field."

Anyway, I get your point, but I still think my use of the term communicated the message more clearly to most viewers than if I'd avoided using the term because my usage didn't strictly match the official definition.

05-17-2014, 07:26 AM   #9
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Posted last night on my phone before bed, so it was too brief.

I won't go on and on, but in terms of sensor size, crop factor and shallow depth of field effects (what the presenter calls bokeh), he really is misleading.

Firstly, shallow depth of field is a purely optical phenomenon (as well as "deep" depth of field, for lack of a better description). The focal length, aperture and focal distance from subject of the lens determine the "amount" of in-focus material before and behind the in-focus subject. This has NOTHING TO DO with the size of the sensor!

Now, the field of view of the lens at this point comes in to play, since, as focal length increases, field of view decreases. This then influences the interpretation of composition of the photographer in terms of how much of the subject will be in the photographed frame.

So if one wants to fill the frame with the subject, they can either move closer to the subject, therefore influencing the depth of field plane of the image captured by the lens, or they can use a lens with a higher focal length and move back away from the subject to fill the frame in which case the optical characteristics of the lens will influence the depth of field plane. The inverse is true, move back or use a lower focal length to change the amount of subject that fills the frame - again, the optical influence on depth of field comes into play.

Where sensor size does affect the depth of field captured is in the field of view captured by the sensor- because it influences the distance the lens and sensor are from the subject to be in focus. Essentially the "crop factor" of the sensor captures a percentage of the field of view the lens can render- descending from full-frame down to the various tiny sensors used in point and shoot and smart phones. So, to be able to frame a subject in the same way with an equivalent lens on two different size sensors, the photographer will need to move further away from the subject to increase the field of view captured on a smaller sensor than they would need to on a larger size sensor. This then changes the in-focus regions before and behind the sharpest focal point in the image rendered by the lens.

At around the 15 minute mark in the video, the presenter makes a comparison between the out of focus rendering of two images captured with the same lens on a full frame and MFT sensor. He describes the difference between the burring of the background behind the subject between the two sensor formats, noting that the MFT image shows less of the blurring effect of shallow depth of field (OK, he called bokeh. Whatever). But what he DIDN'T mention at all, was that to get the same framing of the subject at the equivalent focal length used, the MFT image would have required moving the camera away from the subject substantially further than the 35mm full frame image. That was in my opinion completely misleading as there was no mention of the relationship between focal length, aperture and DISTANCE TO SUBJECT.

Take the example of 35mm and 4x5 film formats. The influence of field of view is obvious- the same focal length lens requires the photographer to move much closer on 4x5 to get the same framing as on 35mm due to the greater angle of view captured by the wider negative. So shallow depth of field is more pronounced because the photgrapher is simply closer to the subject (at equivalent f/stop).
05-17-2014, 08:16 AM   #10
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QuoteOriginally posted by TonyNorthrup Quote
Well, you might want to watch the video, because I do explain the physics. If you disagree with my math, just let me know where my math is wrong and I'll happily fix it.

Re: my usage of bokeh, it seems like everyone knew what I meant. I'm aware of the technical definition of bokeh, but I'm also aware of how people commonly use it as jargon to mean the amount of background blur. Saying, "Small sensors have less bokeh" (as a myth) was more concise than saying, "Small sensors are less able to create a shallow depth of field."

Anyway, I get your point, but I still think my use of the term communicated the message more clearly to most viewers than if I'd avoided using the term because my usage didn't strictly match the official definition.
I have problems with your pronunciation of bokeh. It's "Boke-AH", not "Boke-AY". Everyone needs to say it like me!

I do agree with the other poster though that it would only take a moment to articulate the difference between bokeh and DOF, and your viewers might appreciate knowing the difference.

By the way thanks for stopping in and I'm curious, how did you know your video was linked in here?

.

---------- Post added 05-17-14 at 09:48 AM ----------

QuoteOriginally posted by virgilr Quote
Posted last night on my phone before bed, so it was too brief.

I won't go on and on, but in terms of sensor size, crop factor and shallow depth of field effects (what the presenter calls bokeh), he really is misleading.

Firstly, shallow depth of field is a purely optical phenomenon (as well as "deep" depth of field, for lack of a better description). The focal length, aperture and focal distance from subject of the lens determine the "amount" of in-focus material before and behind the in-focus subject. This has NOTHING TO DO with the size of the sensor!
The size of the sensor affects what FL you need to use to get the same FOV, though, so it is a factor.

QuoteQuote:

...

Where sensor size does affect the depth of field captured is in the field of view captured by the sensor- because it influences the distance the lens and sensor are from the subject to be in focus. Essentially the "crop factor" of the sensor captures a percentage of the field of view the lens can render- descending from full-frame down to the various tiny sensors used in point and shoot and smart phones. So, to be able to frame a subject in the same way with an equivalent lens on two different size sensors, the photographer will need to move further away from the subject to increase the field of view captured on a smaller sensor than they would need to on a larger size sensor. This then changes the in-focus regions before and behind the sharpest focal point in the image rendered by the lens.
The photographer doesn't need to move at all if he/she uses the equivalent focal length from the same position, ie the FL that gives the same FOV between formats. When they do that, and use the same F-stop, the larger format will have less DOF. I think this is the point Tony was trying to get across, and this is exactly what photographers talk about when they use shorthand like "FF gives shallower DOF."

.
QuoteQuote:
At around the 15 minute mark in the video, the presenter makes a comparison between the out of focus rendering of two images captured with the same lens on a full frame and MFT sensor. He describes the difference between the burring of the background behind the subject between the two sensor formats, noting that the MFT image shows less of the blurring effect of shallow depth of field (OK, he called bokeh. Whatever). But what he DIDN'T mention at all, was that to get the same framing of the subject at the equivalent focal length used, the MFT image would have required moving the camera away from the subject substantially further than the 35mm full frame image. That was in my opinion completely misleading as there was no mention of the relationship between focal length, aperture and DISTANCE TO SUBJECT.
I think you got it wrong - At the 15 min mark he's showing f/2.8 and f/5.6 on the same camera, same lens, just to show the DOF difference. At 16:00 he's showing f/2.8 on both FF and m43, showing how the DOF ("bokeh") is different, and I think this his distance to subject was the same and he used a different FL, judging by the relative perspective I see in the background. Tony, is that correct? (I'll paste the still below.)



The subject is shifted along the focal plane, either she moved slightly to the right or the FF camera was on a different tripod right next to the m43 camera, but the perspective looks the same.

Right after that he shows how you'd get equivalent images, or what you would have to do if you wanted to (for some strange reason ) match the m43 DOF - stop down to f/5.6 and up the ISO to get the same shutters speed (and noise = ISO 3200 on FF = ISO 800 on m43, sensor efficiency being similar.) Same distance to subject.




.

Last edited by jsherman999; 05-17-2014 at 08:53 AM.
05-17-2014, 08:48 AM   #11
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QuoteOriginally posted by Not a Number Quote
It depends on how you define bokeh.

I believe there is only one definition for it. How a lens renders out of focus ( pleasant, harsh, average). Not how much is out of focus ( less, more, a lot).
05-17-2014, 09:03 AM   #12
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QuoteOriginally posted by tuco Quote
I believe there is only one definition for it. How a lens renders out of focus ( pleasant, harsh, average). Not how much is out of focus ( less, more, a lot).
Agreed, bokeh is related to and affected by some of the same factors that affect DOF, but it's not the same thing. Two different 50mm lenses on the same camera from the same position and same F-stop can have very different bokeh... although in that case it wouldn't look like what people would call 'more' or 'less' bokeh, it would be 'more smooth' or 'more harsh'.

The best 'shallow DOF' shots are taken with the right settings to get the shallow DOF, but also with lenses that give naturally smooth bokeh. Nikon 200 f/2 on FF is about as good as it gets, IMO, although I'd love to see what Pentax could come out with.

Last edited by jsherman999; 05-17-2014 at 09:14 AM.
05-17-2014, 03:47 PM   #13
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'Equivalence' may have some technical validity, but this clumsy video takes the whole silly sensor format debate to a new low.
05-17-2014, 06:34 PM   #14
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QuoteOriginally posted by rawr Quote
'Equivalence' may have some technical validity, but this clumsy video takes the whole silly sensor format debate to a new low.
Why do you say that?

There are a lot of photographers who would never bother to read through Joseph James' entire article, but could watch a video like this and 'get it.' I like the effort.
05-17-2014, 08:20 PM - 2 Likes   #15
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QuoteOriginally posted by jsherman999 Quote
I think you got it wrong - At the 15 min mark he's showing f/2.8 and f/5.6 on the same camera, same lens, just to show the DOF difference. At 16:00 he's showing f/2.8 on both FF and m43, showing how the DOF ("bokeh") is different, and I think this his distance to subject was the same and he used a different FL, judging by the relative perspective I see in the background. Tony, is that correct? (I'll paste the still below.)



The subject is shifted along the focal plane, either she moved slightly to the right or the FF camera was on a different tripod right next to the m43 camera, but the perspective looks the same.

Right after that he shows how you'd get equivalent images, or what you would have to do if you wanted to (for some strange reason ) match the m43 DOF - stop down to f/5.6 and up the ISO to get the same shutters speed (and noise = ISO 3200 on FF = ISO 800 on m43, sensor efficiency being similar.) Same distance to subject.
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Right! Thanks for answering that . My other crop factor video (which I cross-reference in the beginning) shows those shots being taken. I had a tripod mounted 70-200 f/2.8 and swapped between a 5D Mark III (at 200mm) and an E-M10 (at 100mm). Chelsea might have moved because she's organic--a crime surpassed only by my casual use and pronunciation of 'bokeh'.
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