all right, lets have it... whats the BEST lens you ever observed?

Flashlight Modding and DIY Parts
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okay, in another thread? i am deciphering the edmunds optics “math model” of how to make what might well be, the perfect zoomie-thrower… my gut tells me? that the optical engineers at edmunds optics, a high end custom lens and off the shelf facility?? were not commissioned to write their engineering paper “lightly” and off the top of their heads…

so far? the only “criteria” seems to be… basically stating it? “use the absolute lowest f-number possible”… period.

then? whatever light you shove under it? performs at its best. flooder, thrower, doesnt matter how you roll with it… looking like the lowest f-number is where its “at”.

so… just in case the optical engineers know what they are doing? whats the BEST lens you ever used?

1) most distance you ever got? acceptable observation. describe the lens… where it came from… what was the claimed focal length? what was its diameter? best OBSERVED results are fine.

2) maybe you know of the “lowest f number” lens you ever used… someone here, has to have the lowest f-number lens, theres always a winner… what is it? down and dirty, lowest f-number wins in this category.

3) maybe its some lens you always MEANT to buy? and never got around to it… where is it? how much is it? how big of a diameter, and low of a focal length (f number…) is it?

4) best METER WHACKER counts too, thats observed results… what single zoomie lens? made your meter wish it didnt have batteries in it, when you sizzled it with the uber-lens that shocked you?

==

i want some “candidates”… i am basically looking for the lowest f-number… but anything “best” counts too… lets leave no stone unturned. if you were proud of some lens, brag it up!

aspheric… plano…. regular convex… anything considered… nothing is off the table at this point…

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The best lens I have ever observed…, nothing off the table…, that must be this one, my long distance phase contrast 40x Leitz fluorescence objective, super performance, a beauty! :heart_eyes:

(Sorry, got carried away there, different hobby :wink: )

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is it for what? gas chromatography system? scanning electron microscope? lasers? what?

its show and tell… you showed… now tell! 9it does look cool, whatever the &^%$ it does, lol)

looks like a microscope objective, but, looks are prolly deceiving… spill it!

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telescope eyepiece maybe?

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microscope objective… “kinky”… (but, many points awarded for originality? and is that alow f number of .6??)

NEEEEXT !!

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Correct :partying_face: , 40x phase contrast microscope objective, f=160mm, which was the microscope world standard up to when infinity optics were introduced, numerical aperture is 0.6, chamber thickness of the sample can be corrected for from 0.6 to 1.6mm thickness.

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hey! everyone look at the big brain on djozz! he used the MAGIC WORD “numeric aperture”!

freeze, mister…. you freeze right there…

i “bulldogged” my way through the “engineering equations” from EdmundsOptics engineering paper? I got some numbers…

i understand “what” an f-number is, and how it sets up an angle of acceptance to a lens?
edmunds optics INSISTS on using “numeric aperture”, which is the same thing, just stated a different way (wikipedia, f-number and NA are the same thing, just stated in different math)

so… if i said “instead of a single lens numeric aperture, i am supposed to select TWO lenses, such that the RATIO of focal lengths ”creates” a numeric aperture, at will, by selection of the ratio”

would THAT make more sense to you than to me?

at that point, i am just bulldogging thru the equations, trying to get numbers that seemed to make sense…

i SOLVED for answers, which seem to make sense? but… how do i set those focal lengths UP? how do i VISUALIZE them

are both lenses at their own focal length form the light source? some other configuration?

hey, you used the magic word… spill it, LMAO

(tired of being ALONE, trying to answer questions above my pay grade, LMAO)

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or… i could assign myself some classroom time, i guess…

focal length 160mm.
NA = 0.6

in the engineering paper, we started with the “given” of 60 degs, plus minus 30…
NAbeam = sin(theta/2) = sin (60/2) = sin(30) = .5

here? lets say i want the f-number instead of the NA off of his microscope lens…

NA = sin (x/2) = .6

hmmmm

sin(x/2) = .6

sin(30)=.5 but, we want .6
sin(40) = .64 so, it should be between 30 and 40
sin(35) = .57
sin(36) = .5877
sin(37)= .6018 very close
sin (36.9) = .6004 lets call that close enough for government work, shall we?

but, its the sin of the half angle, so… (36.9 * 2) = 73.8 full angle, angle of acceptance in his microscope objective

but, numerical apertures dont relate to the human brain real well (at least, not MY weird eccentric brain)… f numbers? do relate well, we visualize the ratio better that way…

what lens f-number would satisfy this, FL=160mm ? well, we get the angle from this much…

the FL = 160mm, thats the base of the triangle, the centerline in my other CAD example… we already KNOW the angle is approximately 36.9 degrees half angle, we found that too….

we need the lens diameter. since this is a half angle, we will find the radius of the lens… and twice that is the diameter

chief soch-cah-toa is consulted, and says the sin of that angle? is the opp over the hypotenuse… the cos of that angle, is the adjacent over the hypotenuse… and the tan of that angle, is the opposite over the adjacent…

before, i had to find the hypotenuse, just as a stepping stone to finding… the adjacent was the focal langth…. i dont need that useless hypotenuse, i already have the adjacent = 160mm… that means the opposite is the radius of the lens…

so… tan (36.9) = opp-radius / FL-160mm
tan(36.9) = Radius/160
tan(36.9) i can get… thats .750821

.750821 = Radius/160
(.750821 * 160) = radius ?

radius = 120.132mm

radius is half the lens diameter, which would be…
240.264mm diameter, 160mm FL

which would be a F-number of…
.6659 plus a spray of insignificant digits… lets round that off to a nice round .666 f-number

===

since they were designing a microscope, instead of a 8-inch refracting telescope? that would be a LITTLE bit hard to squeeze a 240mm dimeter lens with 160mm FL under the microscope for the objective… so, they PROBABLY went the route of… consulting the engineers at edmunds scientific, who are now on our BLF payroll? they decided that might have trouble sourcing that particular objective in a single lens design and fitting it under the microscope, LMAO… so… the engineers at edmunds optics? said they should probably just set up a RATIO of FOCAL LENGTHS to accomplish the desired and required numerical aperture, which is another way of saying in order to create the desired f-number of .666, set a ratio of the focal lengths up to accomplish it.

and, once they were “given” one NA of the first suitable lens they sourced? they PROBABLY solved for the other part of the ratio, based on the given lens value they sourced…

because a RATIO has an infinite number of solutions… you can solve for either lens, once you are “given” one of them…

=

this is either starting to make sense and i am getting my head wrapped around this? or, my brain is just being warped to an unusual degree, as in “past eccentric” and into “complete weirdo” zone… i am strangely comfortable with either one, as long as i can get results…

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back to show and tell! no on else has a cool best lens they encountered?

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Sorry its not nearly in the same league as Djozz, but I really like the Ahorton lens that I bought a couple of a few years ago. For its size they work really well. Focal length aprox 12mm, dia 26.2mm

Keep up the good work sedstar, I now see where you are coming from. I dont understand all the calculations (yet), but your heart and mind are definitely in the right place. :student:

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no, i definitely remember the “ahortons”…

when i first hit my night vision site? an “ahorton” was a figure of merit for our early infrared zoomies.

i wonder if the “fl” of 12.x mm ? is the “back focal length”, and it has an “effective FL” of a different value?

aspheres get thick, lol

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Oh no, its not the best out there, but I dont have anything else to compare it with, so its the best Ive seen :wink: For its size, it does a good job. I used one as a helmet mounted light (slightly defocused) for mtb night riding.

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Best for me so far was this one. It has a the opposite of a low f-number. I've bought some bigger lens since with much smaller f-numbers, but they can't even get close in performance. I don't know the math, etc behind these lens. I'm assuming f-number is focal length. I'm I over simplifying the meaning?

I still haven't built a real host for this lens.

https://budgetlightforum.com/t/-/21450

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well, yeah… thats the sort of thing thats a decent candidate…

you think the focal length is 4-1/2… getting on almost 5 inches, huh?

100mm lens…

call 4 inches 100mm… say 125mm focallength? seem about right?

thats not a bad lens… definitely something to work with…

excellent candidate lens!

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if we call it a 125mm FL lens, we’re talking F-number in the … oh… F 1.25 region…

not shabby, by half…

two of them touching, used as one lens? would yield one lens of 62.5mm FL… actually a little more than that, its a little thick, but still…

then, the F-number goes down to something like… F-number = 0.625

which is definite “food for thought” about a beast of a zoomie…

makes me wonder about getting a pre-collimator working under it, lol…. but? excellent candidate.

(just edging out the “microscope objective” as a good candidate to build a zoomie out of, lol wink)

16

So I was a bit off base. I take it that f-number is FL divided by the lens' diameter?

I had a hard time nailing down focal length. Well, let me rephrase that. I half assed tried to measure it a couple times, and got different results. Figured I would nail it down when I built a host for it. I have 4 of these lens. I wanted to build a triple (3 emitters, one per lens) monster. If you want me to try to measure something using 2 of them, I can try to hobble something together (talking cardboard prototype here). I just need clear layman instructions as I'm a fish out of water with aspherics.

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oh… focal length? we talk about it like its a “constant” for the lens? in reality, its not… it varies somewhat.

the “actual focal length” is more of the “length” you will measure, focused up out far… at what they call the “infinity point” for the lens. and its in focus after that forever. hence the infinity point name.

at distances closer? the focal length actually gets longer… and if you were focusing up your emitter across the ROOM, you would get a “focal length” that seemed longer than it actually “was”.

if you insist on focusing up just inches away? (macro photography, anyone?) your “100mm focal length lens” will require a couple of FEET to focus up, lol… thats why macro photography dudes, have those L_O_N_G focusing tubes added to their lens, to get close-ups…

but, your estimates are close enough for government work.

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Surplus shed 55 x 38 FL coated aspheric lens for use on a Mag I had a while back it threw like crazy


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QUOTE
So I was a bit off base. I take it that f-number is FL divided by the lens’ diameter?
ENDQUOTE

yup! the lower the (unit-less) figure? the more light the lens will pass…

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That's a beaut there AlexGT. Just stunning.

That might explain my two different results trying to measure FL. One measurement I took focusing 10 feet away to a wall. The other was to that tree in the beam shots. I just realized I could fab up pretty true spacers for between the 2 lens by rotating PVC pipe on my table saw.

EDIT: Since, no one ever duplicated my results (or at least no one said they did), I can measure the other lenses for consistency. They are still unopened in their original packing.