Equivalent focal length for MFT lenses

Started Apr 12, 2013 | Discussions thread
Detail Man
Forum ProPosts: 14,969
Re: Equivalent focal length for MFT lenses
In reply to s_grins, Apr 15, 2013

Detail Man wrote:

s_grins wrote:

KenBalbari wrote:

rrr_hhh wrote:

As for the rest, I hate these equivalence debates and won't go further. You have been caught of guard stating that the F stands for focal length while it isn't and you are now trying to rationalize this, using the term aperture in a way most photographers won't use it, unless they are into optics and lens design. Just admit you have goofed with that minor thing,  like I admitted myself above.

But all I was saying is that the f in f/6.7 stands for focal length.  That is correct.

Ken, please stop it.You're doing a great disservice to those whom you wnt to support.

F/5.7 is not a focal lens, it is aperture.

Nobody here thinks that aperture is a diameter of the opening in iris (please wikipedia this word for yourself- iris).

Stop Ballsh^tting and begin to learn things you do not know.

The f-number N is given by:

N = f / D

where f is the focal length, and D is the diameter of the entrance pupil (often called the aperture). It is customary to write f-numbers preceded by f/, which forms a mathematical expression of the entrance pupil diameter in terms of f (a symbol denoting the focal length), and the f-number. For example, if a lens's focal length is 10 mm and its entrance pupil diameter is 5 mm, the f-number is 2 and the aperture size would be expressed as f/2.

Source: http://en.wikipedia.org/wiki/F-number

I am surprised by just how much Wikipedia does not appear to contribute to the forum ...


s_grins wrote:

Thank you for the snip

I thought it appropriate to point out that what Ken stated (regarding the symbolism of the letter "f" in the expression "f/") is correct. You are most welcome for the Wikipedia reference, my friend.

Now, open this link and read this:

"The confusion seems to come from you believing that F-number is the same thing as aperture.  Clearly it isn't.  Did you read the wikipedia article you linked?  The F-number is the ratio of the focal length to aperture diameter.  When I say aperture here, I am always refering to the actual aperture diameter."

There is absolutely nothing incorrect in Ken's statement quoted above. It is refreshing to see people use the term "aperture" to refer (only) to the (effective) diameter of a pupil (the lens-system entrance pupil to be exact), as opposed to the all too common vague and misleading use of the term "aperture" to refer to F-Number (F-Ratio, F-Stop), which we all seem to agree (?) equals the Focal Length divided by the Virtual Aperture Diameter (Entrance Pupil Diameter).

If there is a problem with the accuracy of anything that Ken stated, I do not see one. Please advise.

DM ...

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