Originally posted by TonyNorthrup 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 ----------
Originally posted by virgilr 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.
Quote:
...
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."
.
Quote: 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.
.