From: Paul Furman on
Miles Bader wrote:
> "jaf" <me(a)here.com> writes:
>
>> You missed the point.
>> The questions were rhetorical.
>> A lens may have both T & f scales but it only has one aperture.
>> It only has one aperture ring.
>>
>> The light getting to the film plane is the same regardless of which scale you look at.
>
> Obviously, but the scales are different on some lenses -- the
> relationship between the scales is only fixed for a given lens, not
> generally, whereas the relationship between the t-stop numbers and the
> "amount of light" passed through is fixed for all lenses.
>
> Frankly, I'm not sure _what_ you're trying to argue...
>
> The meaning of t-stop and f-stop seems obvious, and the difference is
> clearly useful in some applications. Your tone gives the impression
> that you somehow disagree, but it's not clear how or why.

F/stops are measured with a ruler.
T-stops are measured with a light meter.

--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam
From: Miles Bader on
Paul Furman <paul-@-edgehill.net> writes:
>> The meaning of t-stop and f-stop seems obvious, and the difference is
>> clearly useful in some applications. Your tone gives the impression
>> that you somehow disagree, but it's not clear how or why.
>
> F/stops are measured with a ruler.
> T-stops are measured with a light meter.

Right, exactly.

I still am confused about what the [jaf's] argument is here -- there
doesn't seem anything at all controversial or vague about this
subject...

-Miles

--
x
y
Z!
From: jaf on

"Kennedy McEwen" <rkm(a)nospam.demon.co.uk> wrote in message news:Hy8eOXEfNNrKFw4b(a)kennedym.demon.co.uk...
> In article <us2dnbICTrEPSj7XnZ2dnUVZ_oSdnZ2d(a)giganews.com>, jaf
> <me(a)here.com> writes
>>
>>"Miles Bader" <miles(a)gnu.org> wrote in message
>>news:874orgcg1q.fsf(a)catnip.gol.com...
>>> "jaf" <me(a)here.com> writes:
>>>> I read it.
>>>> "(in a sense, T-stops are absolute and f-stops are relative)"
>>>>
>>>> Absolute to what?
>>>>
> Absolute to an aperture with 100% transmission. That is what the "T" in
> "T-stop" stands for!
>
>>>> Relative to what?
> Dimensionally relative to the Focal length. That is what the "f" in
> "f-stop" stands for, and is completely independent of actual optical
> transmission.
>
>>> I think the meaning is that t-stops have a fixed relationship to an
>>> external reference -- e.g., using t-stops, you can calculate exposure
>>> using an external meter, and directly use the indicated settings on your
>>> camera. That can't always be done using f-stops, but if you calculate
>>> the correct exposure at a single f-stop, then other f-stops using the
>>> same lens etc will have a fixed relationship to that (so f2 always lets
>>> through twice as much light as f2.8).
>>> -miles
>>>
>>
>>You missed the point.
> No, he hit the point precisely. You seem to have some difficulty making
> a point.
>
>>The questions were rhetorical.
> That may be so, but they were questions and could be answered factually
> and meaningfully.
>
> Common f-stops on similar lenses produce common depth of field but not
> necessarily the same exposure.
>
> Common t-stops on similar lenses produce common exposures but not
> necessarily the same depth of field.
>
>>A lens may have both T & f scales but it only has one aperture.
>>It only has one aperture ring.
>>
>>The light getting to the film plane is the same regardless of which
>>scale you look at.
>>
> That is true for a SINGLE lens. However it is certainly untrue for
> different lenses. Since you seem to have lost the plot, the OP was
> asking about how one lens compares to another.
> --


The OP stated "It just seems odd to me that two, 50mm lenses, set at f8 for example, would give
different amounts of light."

I stated they do not.
My reply was directed at the spec's in question. 50mm @ f8.

Some other pinheads decided to hijack the the thread into a babbling idiot contest about using different scales.
As if different scales make a difference even though the aperture can only be set on one reading.

Now we a blessed by your inability to see the forest because the trees are in the way.
Thanks for stopping by.



John




From: Floyd L. Davidson on
"jaf" <me(a)here.com> wrote:
>"Kennedy McEwen" <rkm(a)nospam.demon.co.uk> wrote in message news:Hy8eOXEfNNrKFw4b(a)kennedym.demon.co.uk...
>> In article
>> <us2dnbICTrEPSj7XnZ2dnUVZ_oSdnZ2d(a)giganews.com>, jaf
>> <me(a)here.com> writes
>>>
>>> "Miles Bader" <miles(a)gnu.org> wrote in message
>>> news:874orgcg1q.fsf(a)catnip.gol.com...
>>>> "jaf" <me(a)here.com> writes:
>>>>> I read it.
>>>>> "(in a sense, T-stops are absolute and f-stops are relative)"
>>>>>
>>>>> Absolute to what?
>>>>>
>> Absolute to an aperture with 100% transmission. That
>> is what the "T" in "T-stop" stands for!
>>
>>>>> Relative to what?
>> Dimensionally relative to the Focal length. That is
>> what the "f" in "f-stop" stands for, and is completely
>> independent of actual optical transmission.
>>
>>>> I think the meaning is that t-stops have a fixed relationship to an
>>>> external reference -- e.g., using t-stops, you can calculate exposure
>>>> using an external meter, and directly use the indicated settings on your
>>>> camera. That can't always be done using f-stops, but if you calculate
>>>> the correct exposure at a single f-stop, then other f-stops using the
>>>> same lens etc will have a fixed relationship to that (so f2 always lets
>>>> through twice as much light as f2.8).
>>>> -miles
>>>>
>>>
>>>You missed the point.
>> No, he hit the point precisely. You seem to have some
>> difficulty making a point.
>>
>>>The questions were rhetorical.
>> That may be so, but they were questions and could be
>> answered factually and meaningfully.
>> Common f-stops on similar lenses produce common depth
>> of field but not necessarily the same exposure.
>> Common t-stops on similar lenses produce common
>> exposures but not necessarily the same depth of field.
>>
>>>A lens may have both T & f scales but it only has one aperture.
>>>It only has one aperture ring.
>>>
>>> The light getting to the film plane is the same
>>> regardless of which scale you look at.
>>>
>> That is true for a SINGLE lens. However it is
>> certainly untrue for different lenses. Since you seem
>> to have lost the plot, the OP was asking about how one
>> lens compares to another.
>> --
>
>The OP stated "It just seems odd to me that two, 50mm lenses, set at f8 for example, would give
>different amounts of light."
>
>I stated they do not.

And that was of course a mistake, because they *can*
have different light transmission characteristics. One
easy way to visualize that is to use the exact same lens
as your example: set it to f/8, and use it with and
without an ND filter on the front. Same focal length,
aperture, and f/8 either way, but a different "lens
design" in terms of light transmission with and without
the ND filter. As someone else pointed out, the DOF
will be the same in both cases because the f/stop is the
same, but the exposure will be different because the
t/stop is different.

>My reply was directed at the spec's in question. 50mm @ f8.

As has been noted, f/8 refers to a physical set of
measurements, not to how much light actually passes
through the lens.

>Some other pinheads decided to hijack the the thread
>into a babbling idiot contest about using different
>scales. As if different scales make a difference even
>though the aperture can only be set on one reading.

The *fact* is that T-stops are a measure of light
transmission. Hence when the aperture of one lens is
set to f/8, it might be t/9, while another lens might be
t/11.

If both lenses are set to f/8, the exposure will be
*different*. To get an identical exposure using the two
lenses it is necessary to set both to the same T-stop
rather than the same F-stop.

The point of course is that on any single lens there is
as you say a constant and direct relationship between
f/stops and t/stops, but any two different lens designs
can have *different* relationships. On one the t/stop
might be, across the board, 1/3 of an f/stop lower than
the f/stop scale; but on another lense it may be 2/3 of
an f/stop lower than the f/stop scale. That means
setting the two at the same f/stop will result in 1/3 of
an f/stop *different* exposure!

Or, as one example that I posted earlier... with mirror
lenses it might be significantly greater. 1/3 of an
f/stop isn't much to most people, but an f/8 mirror
lense might be more than 1 whole f/stop lower when light
transmission is measured, and actually could be a t/11
when set to f/8.

>Now we a blessed by your inability to see the forest
>because the trees are in the way. Thanks for stopping
>by.

At some point this all might actually become more clear
to you, but you really are going to have to slow down
and *look* at what people are saying. Several people have
tried different ways of describing it, but you are refusing
to read what they say... and *you* are the only one who
is not agreeing!

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd(a)apaflo.com
From: jaf on

"Floyd L. Davidson" <floyd(a)apaflo.com> wrote in message news:871vm9o20n.fld(a)apaflo.com...
> "jaf" <me(a)here.com> wrote:
>>"Kennedy McEwen" <rkm(a)nospam.demon.co.uk> wrote in message news:Hy8eOXEfNNrKFw4b(a)kennedym.demon.co.uk...
>>> In article
>>> <us2dnbICTrEPSj7XnZ2dnUVZ_oSdnZ2d(a)giganews.com>, jaf
>>> <me(a)here.com> writes
>>>>
>>>> "Miles Bader" <miles(a)gnu.org> wrote in message
>>>> news:874orgcg1q.fsf(a)catnip.gol.com...
>>>>> "jaf" <me(a)here.com> writes:
>>>>>> I read it.
>>>>>> "(in a sense, T-stops are absolute and f-stops are relative)"
>>>>>>
>>>>>> Absolute to what?
>>>>>>
>>> Absolute to an aperture with 100% transmission. That
>>> is what the "T" in "T-stop" stands for!
>>>
>>>>>> Relative to what?
>>> Dimensionally relative to the Focal length. That is
>>> what the "f" in "f-stop" stands for, and is completely
>>> independent of actual optical transmission.
>>>
>>>>> I think the meaning is that t-stops have a fixed relationship to an
>>>>> external reference -- e.g., using t-stops, you can calculate exposure
>>>>> using an external meter, and directly use the indicated settings on your
>>>>> camera. That can't always be done using f-stops, but if you calculate
>>>>> the correct exposure at a single f-stop, then other f-stops using the
>>>>> same lens etc will have a fixed relationship to that (so f2 always lets
>>>>> through twice as much light as f2.8).
>>>>> -miles
>>>>>
>>>>
>>>>You missed the point.
>>> No, he hit the point precisely. You seem to have some
>>> difficulty making a point.
>>>
>>>>The questions were rhetorical.
>>> That may be so, but they were questions and could be
>>> answered factually and meaningfully.
>>> Common f-stops on similar lenses produce common depth
>>> of field but not necessarily the same exposure.
>>> Common t-stops on similar lenses produce common
>>> exposures but not necessarily the same depth of field.
>>>
>>>>A lens may have both T & f scales but it only has one aperture.
>>>>It only has one aperture ring.
>>>>
>>>> The light getting to the film plane is the same
>>>> regardless of which scale you look at.
>>>>
>>> That is true for a SINGLE lens. However it is
>>> certainly untrue for different lenses. Since you seem
>>> to have lost the plot, the OP was asking about how one
>>> lens compares to another.
>>> --
>>
>>The OP stated "It just seems odd to me that two, 50mm lenses, set at f8 for example, would give
>>different amounts of light."
>>
>>I stated they do not.
>
> And that was of course a mistake, because they *can*
> have different light transmission characteristics. One
> easy way to visualize that is to use the exact same lens
> as your example: set it to f/8, and use it with and
> without an ND filter on the front.

Hey PINHEAD,
Why don't you try it with the lens cap on.
See if you get the same light measurement.
Filters are irrelevant to the question the OP asked!

> Same focal length,
> aperture, and f/8 either way, but a different "lens
> design" in terms of light transmission with and without
> the ND filter.

Hey PINHEAD,
Filters are irrelevant to the question the OP asked!

As someone else pointed out, the DOF
> will be the same in both cases because the f/stop is the
> same, but the exposure will be different because the
> t/stop is different.
>
>>My reply was directed at the spec's in question. 50mm @ f8.
>
> As has been noted, f/8 refers to a physical set of
> measurements, not to how much light actually passes
> through the lens.
>

Hey PINHEAD,
Not relevant whether it's physical, metaphysical or fixation on your part.
It has no relevance to the question the OP asked!

>>Some other pinheads decided to hijack the the thread
>>into a babbling idiot contest about using different
>>scales. As if different scales make a difference even
>>though the aperture can only be set on one reading.
>
> The *fact* is that T-stops are a measure of light
> transmission.

The fact is, you are a <expletive deleted> PINHEAD!
T stops are irrelevant to the question the OP asked!
Filters are irrelevant to the question the OP asked!

>Hence when the aperture of one lens is
> set to f/8, it might be t/9, while another lens might be
> t/11.

Hey PINHEAD,
T stops are irrelevant to the question the OP asked!

>
> If both lenses are set to f/8, the exposure will be
> *different*.

Hey PINHEAD,
NO THEY WON'T

To get an identical exposure using the two
> lenses it is necessary to set both to the same T-stop
> rather than the same F-stop.

Hey PINHEAD,
T stops are irrelevant to the question the OP asked!

>
> The point of course is that on any single lens there is
> as you say a constant and direct relationship between
> f/stops and t/stops, but any two different lens designs
> can have *different* relationships. On one the t/stop
> might be, across the board, 1/3 of an f/stop lower than
> the f/stop scale; but on another lense it may be 2/3 of
> an f/stop lower than the f/stop scale. That means
> setting the two at the same f/stop will result in 1/3 of
> an f/stop *different* exposure!
>

Hey PINHEAD,
T stops are irrelevant to the question the OP asked!

> Or, as one example that I posted earlier... with mirror
> lenses it might be significantly greater. 1/3 of an
> f/stop isn't much to most people, but an f/8 mirror
> lense might be more than 1 whole f/stop lower when light
> transmission is measured, and actually could be a t/11
> when set to f/8.
>

Hey PINHEAD,
T stops are irrelevant to the question the OP asked!

>>Now we a blessed by your inability to see the forest
>>because the trees are in the way. Thanks for stopping
>>by.
>
> At some point this all might actually become more clear
> to you, but you really are going to have to slow down
> and *look* at what people are saying. Several people have
> tried different ways of describing it, but you are refusing
> to read what they say... and *you* are the only one who
> is not agreeing!

Hey PINHEAD,
T stops are irrelevant to the question the OP asked!
Try answering the OP's question without T stops.


John