Equivalent focal length for MFT lenses

Started Apr 12, 2013 | Discussions thread
GeorgianBay1939 Veteran Member • Posts: 4,036

Detail Man wrote:

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 ...

It took me several attempts to understand the topic sentence of the above paragraph.  You might find the FOG INDEX interesting and this SELF EVALUATIONmight be instructive. 

Another article which has a huge Fog Index is the one YOU REFERRED TO in your earlier post to KB relating to "the inverse square law".  That has to be one of the worst pieces of writing that I have seen in a long time.

Compare that article with this description of POINT SOURCES, LINE SOURCES, PLANE SOURCES.

(Albeit, you need to change the vocabulary from "radiation intensity" to "ILLUMINANCE " in those diagrams.)

Magick, eh?

The inverse square law is true for a point source.

For a line source illuminance is proportional to (perpendicular) distance from the line source.

For a plane source illuminance is independent of distance from the plane source.

(You would be amazed at the number of wrong articles in photo magazines that insist on applying the "inverse square law" inappropriately!)

The saddest part about the use of sloppy language it that it prohibits the user from communicating ... in both directions.  It also prevents the user from learning deeper since his/her conceptual frameworks are badly screwed up.  It takes a certain amount of honesty to recover from such impediments.

It is for the above reason that I applaud efforts by Gollywop and GB to clean up the language at least in this forum.

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.

I know that he has written about it many times here.  Please send a link to his "article".  Many thanks.

I have to admire his patience.

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.

INDEED!!!!!  Isn't that what it's all about?   

Regards, DM

Now I HAVE to reply to KB.


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