Aspherics : Increased throw or simply more narrow beam?

I like aspheric's when I want a light that has a narrow beam with no spill. This is, in effect, a spotlight. You can seach for something at a distance without it shining in your neighbor's windows for example.

They don't seem to throw any further than a well designed reflectored light but the common reputation is that they do throw further.

Maybe they do in theory or with a well matched optical setup. DEFT seems to prove this out. But for the average light where you put in an aspheric with its focal length matched to its distance from the emitter in my experience they don't really throw any further.

Am I incorrect in my thinking? If so, please point it out.

I have used 3 flashlights (all with leds) , 1 6P clone, 1 light with a 40 mm head and one with a 50 mm head and have replaced the reflectors with aspherics...28 mm, 35 mm and 40 mm and the aspheric versions don't really throw any further.

They do a good job as spot lights and a 40 mm aspheric does throw further than a 35 mm aspheric but within each light they illuminate the same (far) tree whether it's with a reflector or with an aspheric.

It's easier to see that tree in most cases with the aspheric since there is no distracting spill but the distance is the same.

It depends to a degree on the reflector that the light comes with but if it's a decent (for throw) reflector it does just as well as the aspheric.

Why are most of the posts on here to the contrary?

Thanks.

gcbryan said:

Am I incorrect in my thinking? If so, please point it out.

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Yes. You can have a bad match with both reflectors and aspherics. That said A perfectly matched lens will beat a "perfectly" matched reflector of the same diameter. It does matter somewhat what the LED is paired with those two options but unless you have an unusually strange spatial distribution, such as with a "batwing" LED, this rule holds.

saabluster said:

Yes. You can have a bad match with both reflectors and aspherics. That said A perfectly matched lens will beat a "perfectly" matched reflector of the same diameter. It does matter somewhat what the LED is paired with those two options but unless you have an unusually strange spatial distribution, such as with a "batwing" LED, this rule holds.

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How how would you define "perfectly matched?".

I would define "matched" as an aspheric with the same diameter as the reflector and with a focal length that is able to focus the emitter.

That would be "matched". What would "perfectly matched" be?

I guess it would be a short enough focal length to gather a lot of light and a long enough focal length to result in a narrow beam?

Also, what magnitude are we talking about here? Is a well matched aspheric going to just out throw a well matched reflector or is it going to do it by quite some distance?

Re: Aspherics: Increased throw or simply more narrow beam?

gcbryan said:

Am I incorrect in my thinking? If so, please point it out.

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I'd say so.

Theory: An XR-E outputs more light forward than out to the sides. It should be quite easy to get good throw from one with a suitable lens and relatively harder to get good throw with even a good reflector. The amount of light projected forward by a K2 is much more similar to the amount projected out to the sides, so the two systems would be on a much more even footing. However, even then a lens will transmit a greater proportion of light than a reflector will reflect, so the lens should still have better throw. (As I understand it that's the main reason that a refractor telescope performs much much better for a given diameter than a reflector telescope.)

A graph I made a while back using some data from another CPFer...



Practice: I simply haven't found any small reflectors that throw well. I have found small lenses that throw well. Neither of those findings is surprising since I use XR-Es (see theory above), and I've used reflectors where I've wanted spill and been very happy with the results. I do have large reflectors that throw well with incandescent bulbs, but compared to my latest setup with that 66 mm DX lens (thrown together though it was) they don't come anywhere close if comparing similar power levels. The throw from a 100 W incandescent with 130 mm reflector is about the same as a 1.2 W XR-E with that big lens. The incan has a wider and more illuminated beam though.

It's good you're still experimenting with lenses. I hope you're using XR-Es.

TorchBoy, yes, of course (regardling the use of XR-E R2).

I have the Uniquefire HS-809 (XR-E R2) with a 45 mm diameter reflector and it's 56 mm deep. It throws well.

The hotspot is just as tight as the emitter image is when used with an aspheric. To get an aspheric to focus in this light (after removing the reflector) I had to grind it down to 40 mm so it's not a direct comparison but the reflector hotspot throw just as far as the emitter image with the aspheric.

I have an Aurora with a 40 mm head and a reflector that is 35 mm in diameter (also using XR-E R2). I replaced the reflector with a 35 mm aspheric. The aspheric doesn't seem to throw any further than the reflector.

I like the spotlight/no spill aspect of this set-up and I didn't like the look of the beam with this particular SMO reflector so I keep the Aurora as my aspheric "spotlight".

The Uniquefire HS-809 I'm keeping as a reflectored thrower rather than as an aspheric since it seems to throw just as far and it puts more light around the subject so makes it easier to locate some subjects (as compared to the aspheric).

The aspheric just seems to waste a lot of light since it just cuts off anything that isn't in its center of focus.

I understand the beam angle of the XR-E and that it's not so efficient in a reflector unless it's really deep but my reflector is fairly deep (HS-809).

Conversely, with an aspheric, that portion of the emitter not directly at the focal point of the aspheric seems to be wasted as well so as far as efficiency is concerned it seems like it kind of a wash.

Re: Aspherics: Increased throw or simply more narrow beam?

gcbryan said:

I have the Uniquefire HS-809 (XR-E R2) with a 45 mm diameter reflector and it's 56 mm deep. It throws well.

... my reflector is fairly deep (HS-809).

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That's a beauty reflector! Some calculating indicates it could be capturing the outer 67° or thereabouts or the XR-E's light. Are you making fair comparisons with similarly premium aspheric lenses? And where is the HS-809 available from? Your post seems to be the only mention of it that Google knows about.

Re: Aspherics: Increased throw or simply more narrow beam?

TorchBoy said:

That's a beauty reflector! Some calculating indicates it could be capturing the outer 67° or thereabouts or the XR-E's light. Are you making fair comparisons with similarly premium aspheric lenses? And where is the HS-809 available from? Your post seems to be the only mention of it that Google knows about.

Click to expand...

Sorry...typo...HS-802...Uniquefire HS-802 from DX. I don't know about premium aspheric lenses as they it came from DX as well. I used the 50 mm lens ground down to 40 mm. A lot of that was ground down the lip.

It is comparing a 40 mm aspheric with a 45 mm reflector due to the focal length of the aspheric and where it had to fit. So, as I mentioned in that case it's not a totally comparable thing.