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Newbie Lens/Focal Length Question



 
 
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  #21  
Old January 18th 05, 02:29 PM
Nostrobino
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wrote in message
oups.com...
Nostrobino wrote:

No offense, but there are already so many well-meaning people

ignorantly
misusing "prime lens" in this way, it sure would be nice if we could

stop
encouraging innocent newbies to parrot the same mistake.


No offence, but if you could start spelling "offence" properly -- as it
was originally spelled in English --


Many words are spelled differently in American English than in British
English, and this is one of them. Many are pronounced differently too; for
example we say and write "aluminum" where they use "aluminium." We also say
"fenders" where the Brits say "wings," they call "petrol" what we call
"gasoline," and so on.

It is not the SPELLING of "prime" I'm objecting to, but its misusage. Spell
it "pryme" if you like. Just don't use it for "fixed focal length," please.

N.


  #22  
Old January 18th 05, 03:59 PM
Don Stauffer in Minneapolis
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Capt Donkey Smile wrote:

Hello,

Please correct me where I am wrong.

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

I understand that 50mm sees things pretty much as I see it. I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

If I wanted 10x zoom, would I be looking for an effective focal length
of 500mm?

Thanks

You are basically correct in the first part of your statement.
Certainly not all lenses can zoom, or change their focal length.

The statement 10X zoom is ambiguous. In MOST cases it merely means the
ratio of the longest focal length to the shortest. A 30 - 90 mm lens is
a 3X zoom. It says nothing about how the telephoto focal length compares
to a standard 50mm (film equivalent).

There is no well defined term for what you are looking for, but it is
frequently called power or magnification. That is, a 100 mm lens may be
said to have a power or magnification of 2. This is NOT, however, the
same thing as the term 'magnification' used in lens design or camera
design. Since most folks (except those using macro lenses or
supplemental lenses) don't need to use the real, technical magnification
I won't say anything more about that term.
  #23  
Old January 18th 05, 03:59 PM
Don Stauffer in Minneapolis
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Capt Donkey Smile wrote:

Hello,

Please correct me where I am wrong.

I understand that the focal length of the lens can be varied and in
doing so you change the "zoom" of the lens.

I understand that 50mm sees things pretty much as I see it. I have a
1.6x crop so to see things through the camera as I see it, I 'd shoot
at 50/1.6= ~30mm.

If I wanted 10x zoom, would I be looking for an effective focal length
of 500mm?

Thanks

You are basically correct in the first part of your statement.
Certainly not all lenses can zoom, or change their focal length.

The statement 10X zoom is ambiguous. In MOST cases it merely means the
ratio of the longest focal length to the shortest. A 30 - 90 mm lens is
a 3X zoom. It says nothing about how the telephoto focal length compares
to a standard 50mm (film equivalent).

There is no well defined term for what you are looking for, but it is
frequently called power or magnification. That is, a 100 mm lens may be
said to have a power or magnification of 2. This is NOT, however, the
same thing as the term 'magnification' used in lens design or camera
design. Since most folks (except those using macro lenses or
supplemental lenses) don't need to use the real, technical magnification
I won't say anything more about that term.
  #24  
Old January 18th 05, 04:06 PM
Nostrobino
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"Charles Schuler" wrote in message
...


No offense, but there are already so many well-meaning people ignorantly
misusing "prime lens" in this way, it sure would be nice if we could stop
encouraging innocent newbies to parrot the same mistake.


No offense taken, but you have stated one point of view.
From the dictionary at PhotoNotes.Org:


"Prime lens.

A lens with a fixed focal length - its field of view cannot be changed. At
least, not without the addition of supplemental lenses or teleconverters.

Generally, prime lenses are lighter, sharper, cheaper and of higher
optical quality than zoom lenses, since it's easier to build a prime lens
than a zoom. By tradition, common prime lenses used by 35mm cameras are
lenses with 28, 50, 85, 100 and 135mm focal lengths."



Check other sources ... the definition of a prime lens, as presented, is
widely used.


Yes, unfortunately the misusage is now very widespread and has found its way
into many places that should never have accepted it as proper.

Charles, I'm sure whoever compiled that "dictionary" at PhotoNotes.Org meant
well and believed that's what "prime lens" means, just as everyone else who
misuses it (including anyone else who compiles an online reference) believes
that's what it means. After all, who would DELIBERATELY misuse a word in
this way?

But of course anyone can put together whatever definitions for words he
likes, call it a "dictionary" and publish it online.

Note that the very exhaustive and authoritative Canon Lens Glossary at
http://www.usa.canon.com/html/eflens...y/index_p.html does
not even mention "prime lens." Isn't it surprising that a term that now has
such currency in these newsgroups isn't even mentioned at Canon?

Nor has any lens literature I've ever seen from Minolta over the last 25+
years referred to any FFL lens as "prime" (unless used correctly, e.g. to
distinguish a long telephoto from its matched extender) and I would be
surprised if any other major lens manufacturer did. This is a misusage that
appears to have started on the old Fidonet (which is where I first saw it)
and spread like a weed through the magic of the Internet and especially
Usenet. I believe this happened because there just never was much CORRECT
usage of the term (there was no need for it at all, except to distinguish
the camera lens from some auxiliary attachment), making the term relatively
easy to misappropriate.

There are, on the other hand, variable prime lenses (i.e., prime lenses of
variable focal length) marketed by Zeiss, Schneider and others and
catalogued just that way: "variable primes." Obviously this proves that
"prime" CANNOT POSSIBLY mean fixed focal length, since a focal length cannot
be fixed and variable at the same time.

N.


  #25  
Old January 18th 05, 05:59 PM
Charles Schuler
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Well, I learned something (variable primes)! Thanks.

Yes, anybody can compile a dictionary and anybody can "bend the rules" and
sometimes these alterations become permanent. Language evolves over time.
Too bad that change can lead to confusion.

Stay well.


  #26  
Old January 18th 05, 06:40 PM
John McWilliams
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Nostrobino wrote:
There are, on the other hand, variable prime lenses (i.e., prime lenses of
variable focal length) marketed by Zeiss, Schneider and others and
catalogued just that way: "variable primes." Obviously this proves that
"prime" CANNOT POSSIBLY mean fixed focal length, since a focal length cannot
be fixed and variable at the same time.


Is this, then, relying on manufacturer's marketing departments to define
prime for us?

Afaik, the use of the term prime in these NGs is pretty uniformly
understood to mean a lens of a fixed focal length. Not to be confused
with prime real estate, nor numbers, etc.

--
John McWilliams
  #27  
Old January 18th 05, 06:41 PM
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I have found that when I set the my 24-70 zoom to 55mm on my 20D that
the eye not using the camera and the eye using the camera see the same
scale in the image. That is the brain can combine the image from both
eyes wihout confusion. This is how I would define "as I see it", that
is the same scale, rather than the same angular coverage (which would
take something like a 15mm lens.)

  #28  
Old January 18th 05, 06:41 PM
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I have found that when I set the my 24-70 zoom to 55mm on my 20D that
the eye not using the camera and the eye using the camera see the same
scale in the image. That is the brain can combine the image from both
eyes wihout confusion. This is how I would define "as I see it", that
is the same scale, rather than the same angular coverage (which would
take something like a 15mm lens.)

  #29  
Old January 19th 05, 01:03 AM
Tom Monego
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It has been written that the eye sees an image equivelent to an 85mm lens. This
is real difficult to determine since the eye scans and the brain interprets, ad
two eyes into the equation and it is really difficult. But the established 35mm
eqivelent focal length of the eye is 85mm. Again this is not an exact science.
"Normal" lenses only mean that the focal length is equal to the diagonal of the
film. Funny the 35mm diagonal is 44mm, but Leitz though 50 was a better number
so 50mm became the standard for 35mm.
One more thing, if an APS sensor has a 1.6 crop ratio it means the 35mm
equivelent would be 50 x 1.6 or 80mm, so on an APS sensor a 50mm would be close
to the size image an eye sees.

Tom


In article .com,
says...

I have found that when I set the my 24-70 zoom to 55mm on my 20D that
the eye not using the camera and the eye using the camera see the same
scale in the image. That is the brain can combine the image from both
eyes wihout confusion. This is how I would define "as I see it", that
is the same scale, rather than the same angular coverage (which would
take something like a 15mm lens.)


  #30  
Old January 19th 05, 03:44 PM
Nostrobino
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"John McWilliams" wrote in message
...
Nostrobino wrote:
There are, on the other hand, variable prime lenses (i.e., prime lenses
of variable focal length) marketed by Zeiss, Schneider and others and
catalogued just that way: "variable primes." Obviously this proves that
"prime" CANNOT POSSIBLY mean fixed focal length, since a focal length
cannot be fixed and variable at the same time.


Is this, then, relying on manufacturer's marketing departments to define
prime for us?


No, it's just accepting that manufacturers like Zeiss who have been making
photographic lenses for 100 year or so do know correct terminology, and use
it.



Afaik, the use of the term prime in these NGs is pretty uniformly
understood to mean a lens of a fixed focal length.


It is commonly MISUNDERSTOOD that way, yes, more so all the time as the weed
of misuse spreads--unfortunately. Newcomers pick up the misuse from people
they believe are more knowledgeable than they (and therefore likely to use
terminology correctly), which clearly is how THOSE people picked it up
themselves.

I am not aware of any major camera manufacturer that misuses "prime lens" in
this way in its own literature. Nor is there any possible logical foundation
for the misuse. Again, "prime" is used properly here in its dictionary
senses of primary, chief, first in order, etc. There is NO dictionary
definition for "prime" meaning fixed focal length, single focal length, or
fixed or single anything else.

It's a term that evidently was picked up and misunderstood by someone who
then misused it, and the misusage was picked up by others, has spread and
continues to spread. It's still wrong. If a million people call a cabbage a
cantaloupe, a cabbage is still not a cantaloupe.


Not to be confused with prime real estate, nor numbers, etc.


Or beef, etc. We can agree that there are many meanings for "prime" that
have nothing to do with lenses.

N.


 




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