As you can see from the graph above, the difference in anti-reflective performance for single layer 550nm λ/4 MgF2 lenses (up to 0.4% for reds and up to 1% for violets) causes Duv increase and overall CRI distortion. And green }P tint, by the way.
As far as I see the VIS 0 and the VIS EXT are the best anti-reflective coatings we could use for flashlights. The performance of VIS 0 and VIS EXT coatings is in all respects far superior to the usual, common λ/4 MgF2 @ 550nm; be it for throwers, flooders or whatever.
So, how about asking lens manufacturers to coat their lenses with VIS 0 or VIS EXT? For affordable price, of course. Believe it, my dears. Thanks. O:)
Forget about Edmunds-coated lens in a production flashlight.
But there are many manufacturers that can provide quality multi-layer coatings, also in China.
I agree with you that it would be a worthwhile improvement.
If we are to believe in the faithfulness of the anti-reflection coatings' graph, I cannot agree with the suitability of VIS-NIR or UV-VIS. They would work, I know, but they would induce some other sort of Duv and CRI distortions. Too many up and downs in the VIS-NIR or UV-VIS curves between 400 and 700nm, this is the reason. VIS-EXT and VIS-0, on the other hand, look more faithful, staying at ≈0.5% and below between 400 and 700nm.
Edmunds coated? Does Edmunds posseses the patents of the above shown coatings? Patents expire, doesn't it?
Now, onto the “there are many manufacturers that can provide quality multi-layer coatings, also in China” thing, I agree.
I was also thinking in multi-layer coatings before I stumbled onto the Edmunds article. So, I've taken some additional time to check the following:
I am no expert in this stuff, but if the above graph is indicative of the effectiveness of a multilayer λ/4 MgF2 coating, it certainly looks good. With three layers at 450, 550 and 650nm the result should be great. Four layers looks very neat. With five λ/4 MgF2 layers at the proper stepping the result would be gorgeous.
Average <0.5% reflection over the visible range at 0 degree is a kind of high-standard that many manufacturers reach.
I don’t know how many layers does it take to reach it but I know that each layer is a different material, so MgF2 doesn’t repeat (if it is present at all).
BTW a coating optimized for incidence angles a little higher than 0 degrees would work better with flashlights - because (manufacturing precision aside) 100% of light hits at least one lens surface at angle.
I mean: light coming from straight under the lens passes through the lens straight. But there is so little of it coming exactly straight from the single point that it’s 0% of the total output. If light goes straight towards the lens from any other point - it doesn’t refract on the
first surface but refracts on the second.
With strong aspheric lenses the incidence angles may be quite large even when the lens is focused.
When a light is out of focus, the average angle is large.
With TIRs it’s quite similar.
With windows it’s a bit different, the light going straight ahead from the entire led surface will come out straight as well as some that was bounced off the optics.
But we can’t hope for manufacturers to design custom coatings for us…even if some actually could do this.
And coatings designed to work best at moderate angles are quite rare.
I agree those two coatings fall into a clear 2nd tier on that plot. I say that because I just assume that better performance = more cost or difficulty. Also, in a perfect world where LEDs didn’t have a tendency towards being green shifted and still having a blue spike, I wouldn’t say that… but they do. I think the placement of the peaks in these coatings could help reduce the peaks in the output spectrum that deviate from the ideal BB spectrum
In my experience better performance quite often does not necessarily involves higher cost. For me, great performance and affordable cost is a very real thing. Things change and we evolve, its all in the amount of light we let in. ;-)
Concerning what you say about the peaks in led spectral power distributions, to reduce green and blue peaks the λ/4 MgF2 coating must not be set straight at these frequencies, i.e. not “tuned” for 455nm or 550nm. Maybe a multilayer coating set at 410, 500, 605 and 670nm, or sort of. Heck, it's almost 10 AM here and I'm yet to go to bed, so we'll see later LoL.
BTW, this is not necessarily a goal worth pursuing but when you look at a lens at angle, you see a colourful residue reflection. That’s how you tell that a lens is coated.
Some lenses have the reflection very weak and white which makes it pretty much invisible.
I remember Dale saying that when he showed his lights with UCL2 lenses, he would often get fingerprints on the lens…because people would feel an urge to check whether the lens was there.
I understood the UCL and UCLp lens from https://flashlightlens.com/ were superior in that they had less impact on duv and CRI - I think TK mentioned this a while back. Anyone know if that's still accurate?
They currently sell UCL (98-99%) and UCLv3 (98-99%) in glass, and UCLp (97%) in Acrylic. The v3 is AR coated Borofloat
Yes - the UCL and UCLp I've used in the past are super clear, but you can still catch a tinted color in a reflection off the lens.
There's a ∅22.6 × 1.75mm available size, that conforms to the lens size listed for the Convoy S21A (∅22.8 × 1.5mm). However, although paying nearly €4 for a lens is a thing I could probably allow to happen, the shipping cost :facepalm: to where I live is a whole different story.
Yes, the number is the incidence angle at which the coating works best.
If you’re concerned about zoomie flood more than throw than yes, 45 would be about as good as it gets. Same with mule. If it’s zoomie with moderately strong (or weak) lens but you care about throw, the actual angles are going to be close to 0 degrees. Overall, something in between should work best.
If it’s a reflector light, beam is going to hit the lens (actually: the window) at near-0 angle. Spill - still less than 45 unless you have a very shallow reflector. I think for reflector lights the optimal option would be near 0. Considering that most coatings on the market are designed to work at exactly 0 - that’s not perfect but close.
Not aware of any tests on UCL's in general. Not sure if/where there are AR lens tests here on BLF. With all the crazy testing equipment we got here, I can't recall seeing any AR lens tests to show the changes in duv and CRI.
I've only tested for lumens and throw. I've seen maybe 2% to 5% bumps. 5% more typical from regular non AR glass.
0K but, does it really matters? Where are those VIS-x lenses, after all.
So there is a myriad of AR-coatings out there. 0K, maybe not a myriad but a nice bunch.
The question is what can we aim to get a chance to see manufactured. Since I guess λ/4 MgF2 is public domain, we could probably get someone interested in manufacturing :???: 4-layer λ/4 MgF2 coated lenses. As I see it that coating covers ±40nm very well, and so I would specify the 4 layers to be optimized for 430, 510, 590 and 670nm. That would deliver balanced performing lenses. Or it should, doesn't it?
That’s a good question. I’m truly not an optics expert and my intuition is relatively (on my personal scale) weak in this area. I don’t see how layering works honestly. I could only imagine its extremeley irradic and sort of an empirical method of discovery. What I mean is that my assumption is that the behavior of two layers is not an additive function of the two individuals, but rather something significantly different.
I’m going to buy some UCLv3 lenses and see how they look. I’ve only heard great things.
Reality is created from above to below (as above so below). It all starts with an idea, a thought pattern which is energized and eventually materializes if all its requirements are met. Thus, when something “is not known” it is a lot better to stay in a positive mindset. It's extremely important if the aim is to succeed.
I didn't create the λ/4 MgF2 coating or any of the other ones. I think multiple layers of such coating side by side results in a “flat” reflectivity curve at ≈1.3% reflectance, which is the lowest reflectance value delivered by the coating. It may be argued that ≈1.3% isn't the best thing, but everything between 400 and 700nm at ≈1.3% is excellent consistency; to preserve Duv and CRI consistency matters. For this reason I was speaking about the VIS coatings above, and also about the FS-BBAR-397-727 from Torr Scientific Ltd:
Now that I look at it more carefully, if the graph is accurate I'm not that sure. Performs best “in the green”, around 515nm. Despite performing better overall, green is not what we want.