Equivalent focal length for MFT lenses

Started Apr 12, 2013 | Discussions thread
Detail Man
Detail Man Forum Pro • Posts: 16,688
Re: Equivalent focal length for MFT lenses

GeorgianBay1939 wrote:

Of course, you, DM, and KB are correct.  Many of the others have an incorrect understanding of focal ratio, f-stop, (what we commonly refer to as the f/ ) when setting the APERTURE in a lens.

"In optics, the f-number (sometimes called focal ratio, f-ratio, f-stop, or relative aperture) of an optical system is the ratio of the lens's focal length to the diameter of the entrance pupil. It is a dimensionless number that is a quantitative measure of lens speed, and an important concept in photography"

The above is from the WIKIPEDIA ARTICLE ON F-NUMBER.

Unfortunately some photographers use the term "aperture" instead of "relative aperture" or f/stop when discussing these matters.   Many books on photography also screw up learners heads by misusing the terms.  Even the wiki entry referred to above has a stupidly misleading caption to the well-known diagram on the right hand side of the page.

WIKI CAPTION FOR ABOVE DIAGRAM:  "Diagram of decreasing apertures, that is, increasing f-numbers, in one-stop increments; each aperture has half the light gathering area of the previous one."

It would be clearer if the caption said "Diagram of decreasing apertures (or entrance pupils), corresponding to increasing f-numbers for a fixed focal length lens."  (I would leave the discussion of the geometric series of f-stops and SS to another paragraph.  Sufficient for the newbie camera operator to learn that f/ = F/A where F=Focal length in mm, and A= Aperture Diameter in mm.)


I have recently returned to photography and tried to read various texts, articles and forums relating new techniques to modern camera optics and electronics.   Huge difficulty with the amount of very confusing information out there.  So I am indebted to guys like you, KB, GB, Macx, Hogan, AO, crames Tan68, Anders, and others who are trying to help clean up the language used on these forums.

Well, I stepped in on this occasion because those who were incorrect were attempting to criticize one who was absolutely correct. Seemed a bit absurd to me. The vague and unclear use of the term "aperture" when in actuality referring to F-Ratio, and the use of the term "exposure" when (whether or not understood) what is actually being described is exposure scaled (in some linear or non-linear manner) by post-processing operations seem endemic.

It is not the lack of understanding and the resulting incoherence in communication that is as irritating as the proffering of attitudes that simply because a given individual does not themselves choose to desire to understand a subject running deeper than their own personal level of comprehension (as well as their personal desire to comprehend), they sometimes manage to convince themselves that it is incumbent upon others to translate their own communications and discourse to linguistic metaphors which are wholly unclear and misleading to others who, for whatever reason(s), have come to understand a subject on a more comprehensive level.

It is one thing to not understand while acknowledging that one does not understand. To accede to deeper understanding is a volutary and willfull process involving intention and effort.

It is quite another thing to not understand, deny to one's own consciousness an appreciation of the extent to which they do not understand, and further denounce the the substance and the purpose of the deeper understanding of others as being in some way either impractical or irrelevant to the subject(s) at hand. Such constitutes navel-gazing of the highest order, as well as a consummate lack of interest in learning through listening, consumed by speaking only ...

GOLLYWOP'S ARTICLE  is a good start to help new photographers get a clear understanding of Exposure Vs Brightening.  Unfortunately many folks still believe in the Exposure Triangle and the software houses will continue to mislabel their sliders.

My vote was for "Scalar Badness" (in place of post-"Exposure") - but some self-proclaimed "intuits" among us seem deeply bolted into the floor of their Cathedral of Equivocations.

Hopefully GB will write an article on equivalence to help clear up the huge misunderstandings on the subject.

Well, of course, he has. As of the new anonymously sanitized regime, the link is no longer blocked.

But somehow there are some outstanding images out there by folks who are obviously disadvantaged by not understanding the fundamentals.  Imagine how much better they could be if they learned the basics. 

They might argue that the fact that all of the stars occasionally align in their favor is an emblem of some inborn talent (where inspiration is 98% persiration). Understanding the underlaying principles of the machinery surely does not harm. It can, however, tend to cause us to experiment less. The more that I know, the less that I attempt (knowing the limitations).

Over seven years, seven cameras, and some knowledge learned, my "keeper" rate is still a few percent, and my "polished gem" rate is still around one percent. However, my expectations surrounding my work product have also increased. Probably better than them staying the same. And such just might be the case had I not endeavored to try to understand more about things.

Regards, DM

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