From: Remmy Martin on
On Mon, 14 Jun 2010 18:45:43 +0200, Wolfgang Weisselberg
<ozcvgtt02(a)sneakemail.com> wrote:

>DanP <dan.petre(a)gmail.com> wrote:
>> On Jun 9, 11:46�pm, Wolfgang Weisselberg <ozcvgt...(a)sneakemail.com>
>> wrote:
>>> DanP <dan.pe...(a)gmail.com> wrote:
>>> > Big lens: 42mm diameter, 50mm focal length, f/1.2 aperture.
>>> > Small lens: 18mm diameter, 50mm focal length, f/2.8 aperture.
>>> > Set them both to f/2.8 or smaller and you get the same light.
>
>>> So use a 200mm as the big lens and a 50mm as the small lens
>>> and answer again.
>
>> 200mm?
>> I am talking about lens diameter not focal length.
>
>And I am trying to point out that a 200mm f/2.8 lens at f/2.8 will
>capture more light from a star than a 50mm f/2.8 lens at
>f/2.8.

Not true. It depends on the duration that you are capturing photons through
either optic as well as any AR coatings that may or may not exist on those
optics' surfaces, including what wavelengths that you are trying to image.
What is true, however, is that the 200mm lens can have more resolving
power, but only if it is figured to diffraction-limited quality.

Yes, I realize it is an exercise in futility in trying to educate you.
About as much futility as you are experiencing in trying to educate DanP.
But others reading this who have an IQ above 100 will be able to glean some
knowledge from the above.

>
>It's patently obvious that a 200mm f/2.8 lens has a larger
>diameter than a 50mm f/2.8 lens.
>
>-Wolfgang
From: Wolfgang Weisselberg on
Remmy Martin <remmymartin(a)gooddrinksnotspam.net> wrote:

> Yes, I realize it is an exercise in futility in trying to educate you.
> But others reading this who have an IQ above 100 will be able to glean some
> knowledge from the above.

You belong to the IQ-below-70 group.
Plonk.

-Wolfgang