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F2.8 not equal F2.8 ?

 
 
Tom Thackrey
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Posts: n/a
 
      01-18-2004


On 17-Jan-2004, "cwvalle" <(E-Mail Removed)> wrote:

> That is pure junk
> if the lens says it's f2.8 that's what it is...
> If that were not true
> automatic flash units, studio lights, and hand held light meters could not
> be used
> but they obviously can
> That's because f2.8 is f2.8 no matter what camera they are on
> and no matter who made them


That's true. However, f/2.8 is a measure of the focal length divided by the
diameter of the aperture opening. It does not take into consideration any
other factors like the amount or quality of the glass in the lens,
consequently the effective aperture (which is known as a T stop) may be a
larger number than the f number would indicate. I believe Cine lenses use
T/stops because they are more accurate than f/stops when computing exposure.


Most people couldn't tell if their exposure was off by 1/2 stop. TTL meters
measure the light reaching the film/sensor so they in effect compensate for
the difference between f/stop and t/stop. Anyone who's shot exposure
critical stuff in a studio knows better than to take a meter reading at face
value.

f/stop and shutter speed vary a bit between cameras and lenses. Film speed,
too is based on an arbitrary standard. Film processing is another source of
variation. Many photographers test their film, processing, lens and camera
combinations to determine a more precise EI for their particular combination
and preferences.

--
Tom Thackrey
www.creative-light.com
tom (at) creative (dash) light (dot) com
do NOT send email to http://www.velocityreviews.com/forums/(E-Mail Removed) (it's reserved for spammers)
 
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Duncan Allan
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Posts: n/a
 
      01-18-2004
Hence the use of T stops

Duncan

"Tony Spadaro" <(E-Mail Removed)> wrote in message
news:zxqOb.252876$(E-Mail Removed) .com...
> I said nothing about lens brightness - the subject whenever you show up

is
> your dimness. Since even Sigma doesn't claim any increased light
> transmission with their lenses I have to assume you are on another one of
> your little fugues again. Why don't you take it to a psych clinic George,
> they enjoy listening to strange stories from people who think they are

long
> dead pilots.
>
> --
> http://www.chapelhillnoir.com
> home of The Camera-ist's Manifesto
> The Improved Links Pages are at
> http://www.chapelhillnoir.com/links/mlinks00.html
> A sample chapter from my novel "Haight-Ashbury" is at
> http://www.chapelhillnoir.com/writ/hait/hatitl.html
> "George Preddy" <(E-Mail Removed)> wrote in message
> news:bucqi8$87a$(E-Mail Removed)...
> >
> > "Tony Spadaro" <(E-Mail Removed)> wrote in message
> > news:MfmOb.239692$(E-Mail Removed) r.com...
> > > Ahh citizen Putz speaks again.

> >
> > Is that supposed to help your statement that lens brightness doesn't

> matter?
> >
> >

>
>



 
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Roger Halstead
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Posts: n/a
 
      01-18-2004
On Sun, 18 Jan 2004 05:59:04 GMT, "cwvalle" <(E-Mail Removed)>
wrote:

>That is pure junk
>if the lens says it's f2.8 that's what it is...
>If that were not true
>automatic flash units, studio lights, and hand held light meters could not
>be used
>but they obviously can
>That's because f2.8 is f2.8 no matter what camera they are on
>and no matter who made them


I was taught that the f stop or lens speed is based on the *effective*
aperture and not the actual physical size.

So, I'd agree that there may be some small differences, but as you
say, if they aren't what they say then the exposures will be off.

In photography class we were taught the shutter speed varies by a
larger percentage than the lens. That we took as a constant and the
shutter speed was checked on each camera to see if we need to adjust
faster or slower.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com
>
>Carl
>
>
>"George Preddy" <(E-Mail Removed)> wrote in message
>news:bucqi8$87a$(E-Mail Removed)...
>>
>> "Tony Spadaro" <(E-Mail Removed)> wrote in message
>> news:MfmOb.239692$(E-Mail Removed) r.com...
>> > Ahh citizen Putz speaks again.

>>
>> Is that supposed to help your statement that lens brightness doesn't

>matter?
>>
>>

>


 
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Roger Halstead
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Posts: n/a
 
      01-18-2004
On Sun, 18 Jan 2004 07:29:17 GMT, "Tom Thackrey"
<(E-Mail Removed)> wrote:

>
>
>On 17-Jan-2004, "cwvalle" <(E-Mail Removed)> wrote:
>
>> That is pure junk
>> if the lens says it's f2.8 that's what it is...
>> If that were not true
>> automatic flash units, studio lights, and hand held light meters could not
>> be used
>> but they obviously can
>> That's because f2.8 is f2.8 no matter what camera they are on
>> and no matter who made them

>
>That's true. However, f/2.8 is a measure of the focal length divided by the
>diameter of the aperture opening. It does not take into consideration any
>other factors like the amount or quality of the glass in the lens,


It is the *effective* aperture and not the physical size, or at least
that is what they taught in college photography.
Only very simple lenses and mirror telescopes are based truely on the
physical diameter versus the focal length.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

>consequently the effective aperture (which is known as a T stop) may be a
>larger number than the f number would indicate. I believe Cine lenses use
>T/stops because they are more accurate than f/stops when computing exposure.
>
>
>Most people couldn't tell if their exposure was off by 1/2 stop. TTL meters
>measure the light reaching the film/sensor so they in effect compensate for
>the difference between f/stop and t/stop. Anyone who's shot exposure
>critical stuff in a studio knows better than to take a meter reading at face
>value.
>
>f/stop and shutter speed vary a bit between cameras and lenses. Film speed,
>too is based on an arbitrary standard. Film processing is another source of
>variation. Many photographers test their film, processing, lens and camera
>combinations to determine a more precise EI for their particular combination
>and preferences.


 
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George Preddy
Guest
Posts: n/a
 
      01-18-2004

"cwvalle" <(E-Mail Removed)> wrote in message
news:IgpOb.6789$(E-Mail Removed) m...
> That is pure junk
> if the lens says it's f2.8 that's what it is...


It is "what it is." F2.8 is a distance measurement proportional to focal
length, nothing more. Glass is not considered, which is why you do have to
adjust lighting.

> If that were not true
> automatic flash units, studio lights, and hand held light meters could not
> be used
> but they obviously can
> That's because f2.8 is f2.8 no matter what camera they are on
> and no matter who made them
>
> Carl
>
>
> "George Preddy" <(E-Mail Removed)> wrote in message
> news:bucqi8$87a$(E-Mail Removed)...
> >
> > "Tony Spadaro" <(E-Mail Removed)> wrote in message
> > news:MfmOb.239692$(E-Mail Removed) r.com...
> > > Ahh citizen Putz speaks again.

> >
> > Is that supposed to help your statement that lens brightness doesn't

> matter?
> >
> >

>
>



 
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George Preddy
Guest
Posts: n/a
 
      01-18-2004

"Tony Spadaro" <(E-Mail Removed)> wrote in message
news:yyqOb.252878$(E-Mail Removed) .com...
> There can indeed be a small difference in actual light transmission. But
> George is, as usual, so full of sh-tuff his eyes are brown.


IOWs: George is right.

>
> --
> http://www.chapelhillnoir.com
> home of The Camera-ist's Manifesto
> The Improved Links Pages are at
> http://www.chapelhillnoir.com/links/mlinks00.html
> A sample chapter from my novel "Haight-Ashbury" is at
> http://www.chapelhillnoir.com/writ/hait/hatitl.html
> "cwvalle" <(E-Mail Removed)> wrote in message
> news:IgpOb.6789$(E-Mail Removed) m...
> > That is pure junk
> > if the lens says it's f2.8 that's what it is...
> > If that were not true
> > automatic flash units, studio lights, and hand held light meters could

not
> > be used
> > but they obviously can
> > That's because f2.8 is f2.8 no matter what camera they are on
> > and no matter who made them
> >
> > Carl
> >
> >
> > "George Preddy" <(E-Mail Removed)> wrote in message
> > news:bucqi8$87a$(E-Mail Removed)...
> > >
> > > "Tony Spadaro" <(E-Mail Removed)> wrote in message
> > > news:MfmOb.239692$(E-Mail Removed) r.com...
> > > > Ahh citizen Putz speaks again.
> > >
> > > Is that supposed to help your statement that lens brightness doesn't

> > matter?
> > >
> > >

> >
> >

>
>



 
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George Preddy
Guest
Posts: n/a
 
      01-18-2004

"Tony Spadaro" <(E-Mail Removed)> wrote in message
news:zxqOb.252876$(E-Mail Removed) .com...
> I said nothing about lens brightness - the subject whenever you show up

is
> your dimness. Since even Sigma doesn't claim any increased light
> transmission with their lenses


What do you think DG stands for? You have no clue.


 
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George Preddy
Guest
Posts: n/a
 
      01-18-2004

"Duncan Allan" <(E-Mail Removed)> wrote in message
news:budeos$bu0$1$(E-Mail Removed)...
> Hence the use of T stops
>
> Duncan


Don't confuse the animals.


 
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Duncan Allan
Guest
Posts: n/a
 
      01-18-2004
I'll avoid the confusion George.

Makes me laugh when mags and comments relate to 1/3rd stops when it really
is academic. I've just underrated film by 1/2 stop on tyranny to get the
depth and works fine now as it did 30 years ago.

regards

Duncan
"George Preddy" <(E-Mail Removed)> wrote in message
news:budhfc$n2p$(E-Mail Removed)...
>
> "Duncan Allan" <(E-Mail Removed)> wrote in message
> news:budeos$bu0$1$(E-Mail Removed)...
> > Hence the use of T stops
> >
> > Duncan

>
> Don't confuse the animals.
>
>



 
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Alfred Molon
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Posts: n/a
 
      01-18-2004
In article <(E-Mail Removed)>,
(E-Mail Removed) says...

> In photography class we were taught the shutter speed varies by a
> larger percentage than the lens. That we took as a constant and the
> shutter speed was checked on each camera to see if we need to adjust
> faster or slower.


Not sure if I understand you - are you saying that 1/30s lasts more or
less than 33.33 ms on different cameras ?

--

Alfred Molon
------------------------------
http://groups.yahoo.com/group/Olympus_405060/
Olympus 5050 resource - http://www.molon.de/5050.html
Olympus 5060 resource - http://www.molon.de/5060.html
 
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