GH2 Micro Four Thirds Equivalence Explained

M

mpgxsvcd

Veteran
Too many people think that F number is the only thing that determines the Bokeh of an image. The focal length actually does more to compress the background of the image than the focal ratio does.

This video shows how a longer focal length lens does more for shallow depth of field and background compression than a fast focal ratio lens.

http://www.youtube.com/watch?v=_SJFeia_DqY


If you think you really want shallow depth of field with Micro Four Thirds then you will probably want to get the 35-100mm F2.8 lens. It will be expensive but it will finally be the first reasonably fast longer focal length lens with image stabilization.

The video also shows a Konica 35-70mm F2.5-F3.5 macro manual focus lens that can be found on ebay for about $35. Until the 35-100mm F2.8 is released that is the best lens I have seen for shallow depth of field with M4/3s.
 
This is not news to seasoned pros. The challenge actually is to balance what we know about the relationship between focal length and bokeh with what we NEED in terms of framing AND the accountability of relative sensor sizes.
I've come to the conclusion that the 'magic bullet' is Super35 or S35 sensor cameras, which split the difference between the huge bokeh/focal length ratio of full frame and the rather diminished bokeh/focal length ratio of Micro 4/3.
Trouble is.... Micro 4/3 has taken off in a big way for lower budget operators, dashing any hopes of a an S35 revolution of the same magnitude.
 
Zephyrnoid said:
I've come to the conclusion that the 'magic bullet' is Super35 or S35 sensor cameras, which split the difference between the huge bokeh/focal length ratio of full frame and the rather diminished bokeh/focal length ratio of Micro 4/3.
Click to expand...

Except it didn't really. Super35 was out long before Micro4/3.
 
35mm and 16mm coexisted for decades, and each is still being used. Neither is "better" than the other.

FF, S35, m43, and others can also coexist; none is inherently "better" than the other.

For what I shoot and how I work, I currently prefer m43 cameras. They weigh less, cost less, and produce comparable images with smaller lenses. Its easier to simultaneously get exposure and sharp focus in available light, and easy enough to selectively focus on a subject when desired.

Losing a background with long lenses is simple and easy; heck, the 14-140 does adequately well at this on the longer end. Its mostly a call of how far back you want to shoot from the subject; standard in ENG was about 10-15 feet, or slightly more with 1/3" cams. Some directors/producers still keep this notion and want to set that far back with larger sensor cameras, which doesn't always work with a sensible lens and a desire for extreme closeups.

Selective focus with a shorter focal length lens is one of my favorite looks, for whatever reason... crank it wide open and get the lens as close to the subject as possible. This is obviously more possible when you're 1) familiar with the subject (as you're right on top of them), 2) a one-man-band or not much more. Throw in too many people operating on the camera side or a fidgety, uncomfortable subject and such situations rapidly grow untenable.
 
Background blur is quite complex, and certainly the iris plays a part, especially wide open.
 
not all that complex:


Hyperfocal distance:
hyperfocal.gif

Near distance of acceptable sharpness:
neardistance.gif

Far distance of acceptable sharpness:
fardistance.gif

is the hyperfocal distance, mm
is the lens focal length, mm
is the focus distance
is the near distance for acceptable sharpness
is the far distance for acceptable sharpness
is the f-number
is the circle of confusion, mm

[TD="align: right"]where:
[/TD]

[TD="align: right"] H
[/TD]

[TD="align: right"] f
[/TD]

[TD="align: right"] s
[/TD]

[TD="align: right"] D[SUB]n[/SUB]
[/TD]

[TD="align: right"] D[SUB]f[/SUB]
[/TD]

[TD="align: right"] N
[/TD]

[TD="align: right"] c
[/TD]

f-number is calculated by the definition N = 2[SUP]i/2[/SUP] , where i = 1, 2, 3,... for f/1.4, f/2, f/2.8,...
Calculations using these equations must use consistent units. When focal length and circle of confusion have units of millimeters, the calculated hyperfocal distance will have units of millimeters. To convert to feet, divide H by 304.8. To convert to meters, divide H by 1000.
 
Thanks MPG,

Again you have posted a good and clear explanation for average users who need some explanations.

The critiques you got here seem a little off base to me - of course seasoned professionals don't need this explanation. They're...uh...seasoned professionals.
And in this setting I'd also like to add that splitting hairs over a definition of a term or a release date or a crop factor decimal point is all totally irrelevant to the people you made this video for.

I give this video another A+ for all us non-pro, casual, or beginner users.
 
mcbob said:
not all that complex:


Hyperfocal distance:
hyperfocal.gif

Near distance of acceptable sharpness:
neardistance.gif

Far distance of acceptable sharpness:
fardistance.gif

is the hyperfocal distance, mm
is the lens focal length, mm
is the focus distance
is the near distance for acceptable sharpness
is the far distance for acceptable sharpness
is the f-number
is the circle of confusion, mm

[TD="align: right"]where:[/TD]

[TD="align: right"] H [/TD]

[TD="align: right"] f [/TD]

[TD="align: right"] s [/TD]

[TD="align: right"] D[SUB]n[/SUB] [/TD]

[TD="align: right"] D[SUB]f[/SUB] [/TD]

[TD="align: right"] N [/TD]

[TD="align: right"] c [/TD]

f-number is calculated by the definition N = 2[SUP]i/2[/SUP] , where i = 1, 2, 3,... for f/1.4, f/2, f/2.8,...
Calculations using these equations must use consistent units. When focal length and circle of confusion have units of millimeters, the calculated hyperfocal distance will have units of millimeters. To convert to feet, divide H by 304.8. To convert to meters, divide H by 1000.
Click to expand...

That does not explain why lenses with the identical "numbers" have markedly different background blur. For example, the Helios 58 and the Rokkor 58.
Other examples include the wide variety of 50/1.4 by various manufacturers.
I'm sure the curvature of the lens, as well as the corner sharpness, both play a role, in addition to the pronounced effect of the iris which always is most apparent wide open.
At the other end, stopped down it is well-known that diffraction comes into play. Lastly, even within closely matched lenses, the circle cone of focus is a spot, rather than a point, hence the necessary and equally ambiguous term "circle of least confusion".
 
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