EDIT: Hit something that posted the thread as I was correcting the title it should read
What Makes A Zoomable Focus Round Rather Than Square
Mods .... if you happen to see and can amend would be appreciated and if so just delete top part of thread to here
AS per title ... if I zoom an LED Lenser to max the hot spot is round rather than square with the contacts showing like an SK98 .. is there anything you can do with an SK98 to make it round rather than square i.e. change the LED or is it something that's actually built into the reflector or elsewhere????
If possible I'd also like a "tighter" focus .. I believe and XP-L Hi might help do that???
Ok, a few things here.
Lensers and Coasts use a TIR optic, this is a Total Internal Reflection lens. These lights tend to project a circle more so. Although this is often largely because the movement on the lens is limited, to prevent it projecting the LED image.
I have a P5 (it's a Poplite, but essentially identical to a Led Lenser P5), it uses an XR-E LED. If I unscrew the bezel I can move the lens further away from the LED and get it to project the LED dye and bond wires, exactly the same as the SK68 does.
The only thing I would say is, when doing this with the P5 the LED projection appears dimmer than when you get a round hot spot. I suspect that in order to project the LED, you have to move the lens too far from the optic and you loose lumens.
So my hunch is, most TIR optics are most efficient and will produce the most lux before projecting the LED image. Although on some examples, at full zoom, even though the hot spot looks round, if you rotate the light, you'll see the hot spot might be a little more square than you first thought. But this can be true of SMO reflector lights too that focus the beam tightly.
Most other zooming lights use an aspheric lens. These work quite differently to a TIR optic. And max lux is normally achieved when the LED image is projected. Why this is true with aspherics and how it differs to a TIR I do not know.
If you want a more round image with an aspheric, then the easiest thing is to slightly defocus the light. You'll loose a bit of lux, but will get a more useful beam.
Other options include using different LEDs. XP-G2's don't have visible bound wires running across the dye, but they do have a somewhat dappled look and when fully projected with give a weird spotty looking image. Again slightly defocusing will give a cleaner beam.
Another option is to use a round LED. Many Nichia LEDs have a round dye. So at full projection it will be a round beam. But you'll still see the LED detail, so the advantage is minimal.
This is a Nichia 219a in a Z8 (similar size to an SK68). The beam looks better in the pics than in person, as the projection was slightly dappled. But it worked quite well, although limited lumens.
I've also used the Cree XB-D in these small torches and they work quite well as they are largely round without visible bound wires.
Re: your second question though "If possible I'd also like a "tighter" focus .. I believe and XP-L Hi might help do that???"
Sadly there isn't a straight forward answer here. There are several things at play.
1. The LED
The LED itself will alter the beam profile. But there are a few things going on. With an zoomy used for throw, the surface brightness of the LED is important.
As a rule, smaller LED's have a higher surface brightness than larger ones (although this isn't always true). So these tend to throw further.
The old Cree XR-E is a great example. Very limited lumens, but a very small dye and high surface brightness make for a very good thrower. The EZ900 variant had an even smaller dye and can produce kick *** lux numbers today still. Nearly all original and older SK68's used to use the XR-E. Which is why they used to throw well for their size.
Something like an XM-L (or XM-L2) is a much bigger LED, but will have a lower surface brightness than the XR-E. This means, you get a lot more lumens, but the throw isn't as good. But the beam will be a lot broader. In small zoomy lights, the throw can be quite underwhelming with an XM-L emitter.
Where it gets difficult is, today the XP-E2 is the small Cree LED. But I'm lead to believe the XP-G2 has the same surface brightness, but 2.2 times the area. This means that the throw will be similar from both, but the XP-G2 will have a bigger beam and more lumens.
Other LEDs like Nichia's tend to be slightly bigger than the XP-G2 and with a lower surface brightness and lower lumen output. So while they can work in a zoomy, you won't be getting the most throw available.
2. The lens itself.
There are several factors of the lens that will affect throw and beam profile. The quality of the optic. And the focal length.
Given the same lens, an XM-L will result in a much larger projection than an XR-E. But it is possible to use a different lens on the XR-E and get a similar size projection to the XM-L.
But like reflector lights, this will often result in the need for a larger lens to achieve what you are wanting. Which means a physically larger light.
When you say "tight" beam, I'm not 100% sure what you mean though. As an SK68 with an XR-E can produce a tight beam, but it's limited physical size and lumen output limit it's throw ultimately. The same LED in a larger light could well throw further.
Or you can have larger lights with smaller beams.
Something I've not covered yet are de-domed LED's. A dome on a LED is like a small lens and changes the beam profile and angle the light is emitted at. Most Cree and some other LEDs you can remove this dome. The result is a more focused beam, but also a narrower beam. This will result in more throw. However can cause a tint shift.
The XP-L HI is essentially a de-domed emitter. It doesn't have a dome, it has a flat silicon cover. XP-L HI or a de-dome XP-L or XM-L2 will all give very very similar beams and outputs.
Here is an example of a de-domed emitter. These two torches are idential zoomys (Zeusray) with the same output and the same LEDs. As you can see the right hand beam, the de-domed one, is smaller, brighter and more intense.
To expand on the above. Here is an SK68 with the XR-E, now remember this is a small lens, so the image projection is fairly large considering the size of the LED. This is compared to the de-domed XM-L2 in the Zeusray. A bigger LED, but also a bigger lens. They result in almost the same size beam. But the higher lumen output, combined with the bigger lens mean the Zuesray is brighter and will throw further.
This is the same Zeusray again. But the other light is using an XP-G2, but has the same sized lens as the Zesray. See how when the lenses are the same size, that the smaller LED gives a smaller projection.
These throw a similar distance (the Zuesray slightly better). The XP-G2 is a much tigher laser like beam, but arguably less useful as it does light up a much smaller area.
And here is another example of different size LEDs in the same size lens. Here is an SK68 with an XR-E and the Trusfire Z8 with an XM-L (an XM-L Sk68 would look the same).
As you can, the Z8 illuminates a much bigger area. But what you can't see in these pics (because of the auto exposure on the camera I was using), is that the SK68 lights up it's area brighter. And will shine quite a bit further, despite probably only making 1/3rd the lumens.
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I'm not sure if I've answered your question or not, but hope I've given you enough info to help you understand the differences.
