Re: 2197mm Zoom f/3.5 Hand-Held Photo on a P&S Camera

On 04 Nov 2008 08:37:00 GMT, rfischer@xxxxxxxxx (Ray Fischer) wrote:


Stacking two tele-extenders changes your aperture to about f11.

Shall we try to educate this resident troll moron just one more time? Sure, why
not.




On Fri, 24 Oct 2008 22:12:58 +1300, Eric Stevens <eric.stevens@xxxxxxxxx> wrote:

On Thu, 23 Oct 2008 21:39:04 -0500, Si Taylor
<keepyourmail@xxxxxxxxxxxx> wrote:

On Fri, 24 Oct 2008 10:26:05 +1300, Eric Stevens <eric.stevens@xxxxxxxxx> wrote:




OMFG! I cannot even fathom someone being this unbelievably stupid.


Now I know you don't know what you are talking about. A 432mm lense
with an aperture of f3.5 has a diameter of 123mm (quite a lump of
glass for a P&S). A lens assembly with an effective focal length of
2.89 x 432 = 1248mm and a diameter of 123mm has an f number of
1248/123 = 10.15.



On Thu, 23 Oct 2008 12:53:02 -0500, Si Taylor <keepyourmail@xxxxxxxxxxxx> wrote:

The true focal-length in this instance (not 35mm equivalent) is 208.08mm for
that sensor, 72mm x 2.89. You only need a primary lens diameter of 59.45mm to
equal the light-grasp of an effective f/3.5 aperture at that focal-length with
that sensor. 208.08mm / 3.5 = 59.45mm. The extremely high-quality telextender
setup that I use has a full effective aperture of 80mm. This is enough to allow
for an f-stop as large as f/2.6 on the same sensor at that focal length,
208.08mm / 80mm = f/2.6.

You jumble numbers. You talk sh*t. Why should I take you seriously?



Eric Stevens

If you think those grade-school calculations are "jumbled", no wonder that other
idiots and DSLR camera manufacturers can so easily pull the wool over your
ignorant-consumer's eyes.

Follow close:

The camera has a 432mm f/3.5 lens, as advertised. That's the 35MM CAMERA
EQUIVALENT FOCAL LENGTH. That number is only to give you an idea what "reach" it
has, what FOV it's going to provide when shooting, because everyone grew up on
full-frame 35mm cameras. IT HAS NOTHING TO DO WITH THE ACTUAL FOCAL-LENGTH OF
THE P&S's CAMERA LENS. The ONLY reason it acts as the same FOV and zoom-reach as
that 432mm f.l. 35mm-camera's full-frame lens is that the sensor is much smaller
than a 35mm full-frame size. This is no different than why you use the 1.6x crop
factor when figuring out the 35mm eq. focal length of DSLR lenses on the most
common DSLR bodies. This camera has a 6x crop factor. (What an amazingly stupid
name to give it, "crop factor", but then look at the vast majority of idiots
that are ignorantly perpetuating info about cameras online and why that stupid
term has become popular.)

The TRUE focal length of this lens is 72mm when zoomed to that setting. Its
actual, true, in reality, front lens element is only 32mm in diameter (just
measured it for this post). This allows it to have an f/ratio going from f/2.7
to f/3.5 throughout its whole zoom range. (72mm/3.5 = 20.5mm dia. 20.5mm dia. is
all that's really necessary for an aperture of f/3.5 if this was a fixed 72mm
focal-length lens, and if there were no internal stops to ensure full resolution
and sharpness at the full aperture.)

If this lens really was a 432mm focal-length lens then its OEM lens would have
to be at LEAST 123.5mm in dia. (432mm/3.5=123.5mm) That is not going to happen.
The whole camera is only 75mm tall, including the bump in the body for the
built-in flash.

Now we add a high-quality 2.89x, 80mm dia. telextender optical assembly on the
front. This OPTICALLY multiplies its _REAL_ focal length by that amount. (In
practice this is NO different than if you hooked up that camera and lens to the
Keck telescope and obtained images at high-resolution with an enormous
light-grasp. Or practiced the art of "digiscoping" where you might add your
camera to a 6" dia. f/4.5 Newtonian telescope where it might afford a 60x
telextender quotient (eyepiece dependent). But then your aperture would be
limited to the weakest link. In that case it would lower your camera's
performance to an f/4.5 aperture, the same as the telescope's.)

For all intents and purposes, with that 80mm dia. 2.89x telextender, it is now
giving us the 35MM EQUIVALENT FOCAL LENGTH reach of a 35MM CAMERA'S 1248mm lens.
2.89 x 432mm (35mm eq.)

This is not the TRUE focal length of this lens. In reality it is now behaving as
a 2.89 x 72mm focal length = 208.08mm. Its TRUE focal-length. One only needs a
59.45mm diameter lens to give that TRUE focal-length an f/ratio of f/3.5.
(208.08mmx3.5=59.45mm)

I'm using a telextender with a full 80mm diameter. Far more diameter than is
needed to afford an f/ratio of f/3.5. Zero light-loss (except for minor
air-to-glass transitions), zero f/ratio lost. Would that the original camera
manufacturer had originally built-in more aperture into their own lens affixed
to the camera, then that telextender lens could provide enough light gathering
ability for an f/2.6 aperture at a 35MM EQUIVALENT FOCAL-LENGTH 1248mm zoom lens
(2.89x432mm).

You have to figure the f/ratio from its TRUE focal-length and TRUE lens
diameters, not its imaginary 35mm equivalent focal length. You must use the
actual physical dimensions, not its advertised human-perception 35mm eq. value
which only give you a familiar idea its performance.

Got it? Did you follow any of that at all? Probably not. I explained it by
approaching it from every way that you might possibly misinterpret things again,
in the hopes that it might get through that pea-brain of yours and others'
similarly sized brains, but I still I feel it was just more wasted typing.

If, however, that intermittently shorted lightbulb in that empty little cavity
you have in that excuse you call a head finally did illuminate by a few
nanowatts, from at least one of the various ways I've proved it, then now do you
see why I'm laughing so hard at these moronic resident-trolls that don't know a
thing about optics and photography? The same relentless and idiotic band of
R.P.D. virtual-reality-living trolls that have been mindlessly parroting the
same stupid nonsense for years now, post after post, their whole pathetic lives.
Even worse are those that are so stupid as to ignorantly believe them without
bothering to figure it out on their own. Worse than that are those that haven't
bothered to correct the resident-trolls' blatant stupidity and reveal their
ignorance to the world, their stupidity borne of their entrenched
virtual-life-psychosis, to finally make them come to terms with the real world
and FACTS.

Hey, everyone is saying it in this newsgroup, it MUST be true. Right?

Fucking retards, all around.

Note to self: Never underestimate the stupidity of humanity -- ESPECIALLY
online.

.

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