From: Wolfgang Weisselberg on
DanP <dan.petre(a)gmail.com> wrote:
> On 2 June, 02:00, Wolfgang Weisselberg <ozcvgt...(a)sneakemail.com>
>> DanP <dan.pe...(a)gmail.com> wrote:
>> > On 31 May, 02:47, Wolfgang Weisselberg <ozcvgt...(a)sneakemail.com>

>> >> We are talking about stars ... you know, as good as
>> >> infinitely far away point sources as there are?  With
>> >> perfectly parallel rays?
>> > To talk about sorces of perfecly parallel rays is to talk about points
>> > size zero.
>> > For that the focal length has no meaning. a point of size 0 is focused
>> > by all lens to a size zero image.

>> Lenses are imperfect, there's diffraction (and air for us down
>> here) and stars are definitively larger than 0, just very far away.
>> Stop waffling and try it.

> So there is no source of light with perfect parallel rays.

So you try to deny that stars have perfect parallel rays for
the purpose of telescopes and optical lenses on Earth.

>> > You have brought focal lengths to discussion though you did not
>> > express that clearly.
>> > I was talking about lens diameters.

>> So, talk about lens diameter.  Will a lens diameter of 10.000km
>> result in a darker star image than one of 0.0001mm?

> At maximum aperture the 10.000 km will give a brighter picture.
> But set at the maximum aperurte of the .00001mm the results will be
> the same.

Both are f/4 at maximum aperture. Does that change your claim?
Or does "the amount of light let in depends only of exposure
time and f number" hold?

>> >> > And that means the amount of light let in depends only of exposure
>> >> > time and f number. If bigger lenses would let more light in at the
>> >> > same f number then the film would have been over exposed.
>> >> We are not talking about areas, we are talking point sources.
>> > But the above is my answer to the other question.

>> It's wrong.  That's what I tried to point out, but you must
>> do the thinking.

> As far as getting the right exposure time (that depends on the amount
> of light hitting the sensor) no one takes notice of lens diameter or
> focal length, only f number.

Wrong, ask film people. T-stop.

>> > You have started this by questioned my statement "To close the
>> > subject, after some reading and thinking lens diameter does not affect
>> > the amount of light captured. "
>> > Then I said the only thing that matters is the f number.

>> And you are wrong.  T-stop and stars.

No comment?

>> > I think your comparision between EF 70-300mm f/4.5-5.6 DO IS USM:
>> > 82.4mm x  99.9mm and EF 70-300mm f/4.5-5.6 DO IS USM:  82.4mm x
>> > 99.9mm proves my point.

>> That light gets astray?  Suuure.

> It is OK and you notice it in the shallower DOF at low f numbers for
> out of focus area.
> But to get the same results having the same DOF you have to close the
> aperture.

The DOF is shallower for the DO lens at 70mm, wide open than for the
non-DO lens at 70mm, wide open?

> I do not have a theory, it is common knowledge that when you buy a new
> lens you don't care about the lens diameter, only f number.

Your claim is wrong for at least one type of user.

>> > I say it is the size of the diaphragm.

>> You are approximately right for single element lenses.

> You talk like you know more yhan I do. Just tell me where is that the
> entrance pupil and how to measure it.

Peruse the optical formula and apply your optical knowledge.

>> >> >> > So the DO is less brighter that what it should be (internal optics
>> >> >> > should explain why).
>> >> >> Come on, same focal length, you replace a thinner, longer lens
>> >> >> with a fatter shorter one and all you can say is "internal optics
>> >> >> should explain why"?  If that's the case your theory of light
>> >> >> going astray is bogus.
>> >> > If you do that then you lose aperture.
>> >> Explain why.  "you replace a thinner, longer lens with a
>> >> fatter shorter one" and "then you lose aperture."?
>> > Because a smaller lense will not be able to use a wide diaphragm.

>> But the fatter shorter lens is WIDER.  Hello?

> You are mixing things too much, keep focal length the same to compare
> lenses.

70-300mm zoom lens. See above, Mister! The DO is fatter
(i.e. can use a WIDER diaphragm) and is shorter to boot.

>> >> > See the Sigma 120mm-300mm f/2.8http://www.sigmaphoto.com/shop/120-300mm-f28-ex-dg-apo-hsm-sigma
>> >> > It has a size of 112.8 x 268.5 mm giving a theoretical f number of
>> >> > 2.65. Good fast lens but expensive.
>> >> So what's your point?
>> > If you want low f numbers you must have big lenses.

>> Nope.  Simple 1-element 10mm lens, just 1 cm across.  Small
>> lens, low f/stop.

> Yeah, that is for a small sensor.

Not at all. It's a perfectly viable f/1 lens.

>> > But big lenses in
>> > itself does not guarantee more light.
>> > Lenses are advertised by their f number, not lens diameter.

>> Lower "f numbers" do not necessarily mean more light.  Take a
>> f/2.8 lens and add a ND-filter to the design.

> Fine, put your hand in front of the lenses and you get even less
> light.

But with a well placed center pass ND lens you get perfect
bokeh, see Sony's 135mm STF (Smooth Transition Focus) lens.

-Wolfgang
From: LOL! on
On Wed, 2 Jun 2010 17:44:30 +0200, Wolfgang Weisselberg
<ozcvgtt02(a)sneakemail.com> wrote:

>DanP <dan.petre(a)gmail.com> wrote:
>> On 2 June, 02:00, Wolfgang Weisselberg <ozcvgt...(a)sneakemail.com>
>>> DanP <dan.pe...(a)gmail.com> wrote:
>>> > On 31 May, 02:47, Wolfgang Weisselberg <ozcvgt...(a)sneakemail.com>
>
>>> >> We are talking about stars ... you know, as good as
>>> >> infinitely far away point sources as there are? �With
>>> >> perfectly parallel rays?
>>> > To talk about sorces of perfecly parallel rays is to talk about points
>>> > size zero.
>>> > For that the focal length has no meaning. a point of size 0 is focused
>>> > by all lens to a size zero image.
>
>>> Lenses are imperfect, there's diffraction (and air for us down
>>> here) and stars are definitively larger than 0, just very far away.
>>> Stop waffling and try it.
>
>> So there is no source of light with perfect parallel rays.
>
>So you try to deny that stars have perfect parallel rays for
>the purpose of telescopes and optical lenses on Earth.
>
>>> > You have brought focal lengths to discussion though you did not
>>> > express that clearly.
>>> > I was talking about lens diameters.
>
>>> So, talk about lens diameter. �Will a lens diameter of 10.000km
>>> result in a darker star image than one of 0.0001mm?
>
>> At maximum aperture the 10.000 km will give a brighter picture.
>> But set at the maximum aperurte of the .00001mm the results will be
>> the same.
>
>Both are f/4 at maximum aperture. Does that change your claim?
>Or does "the amount of light let in depends only of exposure
>time and f number" hold?
>
>>> >> > And that means the amount of light let in depends only of exposure
>>> >> > time and f number. If bigger lenses would let more light in at the
>>> >> > same f number then the film would have been over exposed.
>>> >> We are not talking about areas, we are talking point sources.
>>> > But the above is my answer to the other question.
>
>>> It's wrong. �That's what I tried to point out, but you must
>>> do the thinking.
>
>> As far as getting the right exposure time (that depends on the amount
>> of light hitting the sensor) no one takes notice of lens diameter or
>> focal length, only f number.
>
>Wrong, ask film people. T-stop.
>
>>> > You have started this by questioned my statement "To close the
>>> > subject, after some reading and thinking lens diameter does not affect
>>> > the amount of light captured. "
>>> > Then I said the only thing that matters is the f number.
>
>>> And you are wrong. �T-stop and stars.
>
>No comment?
>
>>> > I think your comparision between EF 70-300mm f/4.5-5.6 DO IS USM:
>>> > 82.4mm x �99.9mm and EF 70-300mm f/4.5-5.6 DO IS USM: �82.4mm x
>>> > 99.9mm proves my point.
>
>>> That light gets astray? �Suuure.
>
>> It is OK and you notice it in the shallower DOF at low f numbers for
>> out of focus area.
>> But to get the same results having the same DOF you have to close the
>> aperture.
>
>The DOF is shallower for the DO lens at 70mm, wide open than for the
>non-DO lens at 70mm, wide open?
>
>> I do not have a theory, it is common knowledge that when you buy a new
>> lens you don't care about the lens diameter, only f number.
>
>Your claim is wrong for at least one type of user.
>
>>> > I say it is the size of the diaphragm.
>
>>> You are approximately right for single element lenses.
>
>> You talk like you know more yhan I do. Just tell me where is that the
>> entrance pupil and how to measure it.
>
>Peruse the optical formula and apply your optical knowledge.
>
>>> >> >> > So the DO is less brighter that what it should be (internal optics
>>> >> >> > should explain why).
>>> >> >> Come on, same focal length, you replace a thinner, longer lens
>>> >> >> with a fatter shorter one and all you can say is "internal optics
>>> >> >> should explain why"? �If that's the case your theory of light
>>> >> >> going astray is bogus.
>>> >> > If you do that then you lose aperture.
>>> >> Explain why. �"you replace a thinner, longer lens with a
>>> >> fatter shorter one" and "then you lose aperture."?
>>> > Because a smaller lense will not be able to use a wide diaphragm.
>
>>> But the fatter shorter lens is WIDER. �Hello?
>
>> You are mixing things too much, keep focal length the same to compare
>> lenses.
>
>70-300mm zoom lens. See above, Mister! The DO is fatter
>(i.e. can use a WIDER diaphragm) and is shorter to boot.
>
>>> >> > See the Sigma 120mm-300mm f/2.8http://www.sigmaphoto.com/shop/120-300mm-f28-ex-dg-apo-hsm-sigma
>>> >> > It has a size of 112.8 x 268.5 mm giving a theoretical f number of
>>> >> > 2.65. Good fast lens but expensive.
>>> >> So what's your point?
>>> > If you want low f numbers you must have big lenses.
>
>>> Nope. �Simple 1-element 10mm lens, just 1 cm across. �Small
>>> lens, low f/stop.
>
>> Yeah, that is for a small sensor.
>
>Not at all. It's a perfectly viable f/1 lens.
>
>>> > But big lenses in
>>> > itself does not guarantee more light.
>>> > Lenses are advertised by their f number, not lens diameter.
>
>>> Lower "f numbers" do not necessarily mean more light. �Take a
>>> f/2.8 lens and add a ND-filter to the design.
>
>> Fine, put your hand in front of the lenses and you get even less
>> light.
>
>But with a well placed center pass ND lens you get perfect
>bokeh, see Sony's 135mm STF (Smooth Transition Focus) lens.
>
>-Wolfgang

Karma is wonderful. Now you know what it feels like trying to educate YOU.

LOL!

From: DanP on
On 2 June, 16:44, Wolfgang Weisselberg <ozcvgt...(a)sneakemail.com>
wrote:

> >> Lenses are imperfect, there's diffraction (and air for us down
> >> here) and stars are definitively larger than 0, just very far away.
> >> Stop waffling and try it.
> > So there is no source of light with perfect parallel rays.

Your previous quote: "stars are definitively larger than 0, just very
far away." is incompatible with parallel rays.

> Both are f/4 at maximum aperture.  Does that change your claim?
> Or does "the amount of light let in depends only of exposure
> time and f number" hold?

No, both set at f/4 will let in the same amount of light.

> Wrong, ask film people.  T-stop.
>
> No comment?

T-stop depends on the quality of the glass, not lens diameter.


> The DOF is shallower for the DO lens at 70mm, wide open than for the
> non-DO lens at 70mm, wide open?

Yes. At 70mm f/4 has shorter DOF than f/4.5.


> > Yeah, that is for a small sensor.
>
> Not at all.  It's a perfectly viable f/1 lens.

If you want to talk about lens diameter keep all other things equal.


> But with a well placed center pass ND lens you get perfect
> bokeh, see Sony's 135mm STF (Smooth Transition Focus) lens.

By all means use it. Just keep it out of the discussion, you are
introducing way too many variables, T-stops, filters and sensor sizes.


DanP
From: whisky-dave on

"Wolfgang Weisselberg" <ozcvgtt02(a)sneakemail.com> wrote in message
news:uraid7-2en.ln1(a)ID-52418.user.berlin.de...
> DanP <dan.petre(a)gmail.com> wrote:
>> On 2 June, 02:00, Wolfgang Weisselberg <ozcvgt...(a)sneakemail.com>
>>> DanP <dan.pe...(a)gmail.com> wrote:
>>> > On 31 May, 02:47, Wolfgang Weisselberg <ozcvgt...(a)sneakemail.com>
>


>> So there is no source of light with perfect parallel rays.
>
> So you try to deny that stars have perfect parallel rays for
> the purpose of telescopes and optical lenses on Earth.

No one heard of gravitational lensing ?

The light coming from any star will be shaped by any large object so I
can;t see how any light sources can be truly parallel to each other if they
are apart they will have differing gravitational attractions to the nearest
mass.


From: RichA on
On Jun 3, 5:49 am, "whisky-dave" <whisky-d...(a)final.front.ear> wrote:
> "Wolfgang Weisselberg" <ozcvgt...(a)sneakemail.com> wrote in message
>
> news:uraid7-2en.ln1(a)ID-52418.user.berlin.de...
>
> > DanP <dan.pe...(a)gmail.com> wrote:
> >> On 2 June, 02:00, Wolfgang Weisselberg <ozcvgt...(a)sneakemail.com>
> >>> DanP <dan.pe...(a)gmail.com> wrote:
> >>> > On 31 May, 02:47, Wolfgang Weisselberg <ozcvgt...(a)sneakemail.com>
>
> >> So there is no source of light with perfect parallel rays.
>
> > So you try to deny that stars have perfect parallel rays for
> > the purpose of telescopes and optical lenses on Earth.
>
> No one heard of gravitational lensing ?
>

There's never a mini black hole around when you need one.