hm. let me maybe state my argument another way…
i take a LENS out of my pocket. I toss it on the table in front of you. and you say “what can this puppy do? how good is it?”
now, no talk of any surface intensity, because I now have to describe the capabilities of THIS LENS to YOU. I can state that “this lens has diameter x”. i can also state that “this lens has focal length y”. thats all you need to know, to understand mathematically, the capabilities of that lens. The ratio of x and y ? its called the F number.
now, surface brilliance, and megacandelabras, and all the authoritative sounding use of words like flooder/thrower/intensity etc… none of that means anything. For all i care? you can use this lens to transmit the image of a blue fart out of a cow’s @$$ you just lit on fire with a zippo lighter.
because as humorous as that mental image IS? its very very accurate.
you can talk about all the “concepts” you want to. NOTHING else is describing this lenses ability to focus how much light thru it? other than FOCAL LENGTH and DIAMETER. you can talk about surface coatings, and style of lens production as slightly more or less percentage of efficiency? youre only scootching the numbers up and down.
and we really COULD be talking about how bright an image we can transfer onto a camera sensor, of a blue fart coming out of a cows $$... because the image of that blue flame shooting out of that cows
$$ will be BRIGHTER as the f-number goes down, and it will be dimmer as the f-number goes up.
period. end of story. no camera guy… no projector guy… no refractor telescope guy…not ONE of them will correct me, and tell me “no no, only diameter will increase the throw… of the image of a blue flame shootiong out of a cows @$$ onto whatever you wish to throw it onto”
i ask for a definition of “throw”, i get whatever i get
i ask for a mathematical formula? i always get that intensity formula… which means exactly SQUAT to the ability of the LENS to transmit a dimmer or brighter image of the blue fart flame coming out of the cow’s @$$.
=
now, i am correctly stating the lens’s ability to transmit how bright or how dim of an image? because nothing else in the way of a spec exists FOR THE LENS.
if you want to RELATE how many “moon bats” are going to be produced, per unit of time, per unit of area, per unit of whatever… all fine and dandy. But… i keep scratching my head, trying to understand how i am “wrong” using the f-number to describe the abilities of THIS lens o the table right here? before we build a light?
and everyone keeps CORRECTING ME, with the ring of authority… witha smug certainty they are conveying sage knowledge that i am too stupid to grasp? that “only diameter increases throw, focal length is nothing”.
which is DEAD WRONG, and i am DEAD RIGHT.
it doesnt matter how many “moon bats” ar going thru the lens out of the cows @$$… this lens, independent of WHAT you do WITH it? has 2 things that can mathematically describe it. The focal length, the diameter. period. thats IT.
the ratio is the F-number. done.
now… if you tell me the SIZE of the flame shooting out of the cows @$$? i can take the focal length, and tell you at what distance, exactly how tall and wide the projected image of that blue a$$ flame is… and with mathematical certainty. its not a “concept”… its a cold hard fact of geometry. Its honestly not open to mathematical argument.
the diameter and the focal length of the lens? and again thats all there is to mathematically decribe that lenses capcbilities… can be expressed AS a “numerical aperture”, and we can discuss what geometrical percentage OF the number of available moon bats get to fly thru the lens? but once again…
now… how in the &^%$ does it ALWAYS happen, that i get constantly CORRECTED, as if i am somehow WRONG… when i bring up the f number?
because you can make the cow fart harder and make the flame brighter. you can teach the cow to clench its @$$ cheeks together tighter? so the flame is smaller and more intensely bright of a blue flame… but… none of that has the slightest bearing on the capabilities of THIS LENS right HERE on this table.
i can accurately predict any number of things about what the lens can do, and it all flows from only 2 things… focal length and diameter. glass composition and shape are just scootching the percentages up and down a little.
because maybe the WAY you describe the “concept” of “what throw is” needs to be stated a little better… because ALL i keep hearing is “only diameter increases throw, dude…”. All your talk about intensity? is utterly meaningless.
i dont CARE how many moonbats you are making per square kilocandelabra, it doesnt describe the lens… you are describing wat you are going to shove thru the lens, and predicting how many moon bats are going to appear per square foot out the other end.
no one has said one single thing, that makes the f-number NOT a valid mathematical description of the lenses ability to transmit how bright of whatever image later when we build something with it.
and i’m sorry? but the following statement…
“only diameter increases throw”
exactly WHAT impression is that supposed to make in the mind of the new guy? and exactly how am i “wrong”? because i keep getting CORRECTED… as if i am wrong,when i state the f-numbers…. because focal length only affects beamshape, dude…
well, i got news for you? “beamshape” is everything! the f-number is critical! i’m telling you i can geometrically predict all kinds of stuff everyone wants to know, i can relate different size emitters to exact size patches of target, i can adjust focal lengths to illuminate the same size patches between different size emitters.
i can even put numbers on 2 lens compound lens setups… easily.
and all i get is…
1) your WRONG duuuude…. only diameter increases throw, duuuude. Its, like, all about the intensity of the throw, duuuude. Your focal length? its… like… way wrong, duuuuuude.
2) and i got, like, seventeen different kinds of math to back me up? and to accurately predict things? and all i get is told i am wrong. and i really dont think i am.
3) now? its a “concept” not a Law, or an equation? what ARE all you guys SMOKING? I want some of the good stuff.