Fish eye frustration

[MoreGooder]

I have spent well over $200 on various ashperical lens since Jan 1. All of them have been completely unsatisfactory. The problem is that while I have found how to create a nice even flood mode, the focus mode is horrible. There's the image of the die on the wall with a large floody area around it. I cannot get rid of the flood portion at all.

In contrast, the cheep plastic lens that comes with the X2000 light from DX works marvelously. It produces the best, brightest and tightest spot and an even flood.

So, what am I missing? So far the closest aspherical glass lens that comes remotely close to what I'm after is this one from Thor Labs:

http://www.thorlabs.com/thorProduct.cfm?partNumber=ACL3026

If anyone out there can point me in the right direction for a nice flood to throw lens about 25 - 30mm in overall diameter, I would be eternally gratefull.

MG

 

[Paul Baldwin]

Hi,
I didn't realise you intended to buy quite so many lenses for your torch, especially after seeing the price of some of them! From what I've seen from playing with aspherics the halo when zoomed is the nature of the beast. I've bought various focusing torches and the one with the most obvious halo is the mag aspheric. I put a lot of that down to its size and being a far better quality lense than the cheap platic ones it transmits more of the 'wasted' light making it more noticeable. When in use outside you probably won't even be aware of it on a distant object?

 

[MoreGooder]

Hi,
I didn't realise you intended to buy quite so many lenses for your torch, especially after seeing the price of some of them! From what I've seen from playing with aspherics the halo when zoomed is the nature of the beast. I've bought various focusing torches and the one with the most obvious halo is the mag aspheric. I put a lot of that down to its size and being a far better quality lense than the cheap platic ones it transmits more of the 'wasted' light making it more noticeable. When in use outside you probably won't even be aware of it on a distant object?

My observation is that because some of the light is wasted as a flood area around the focused image, there is lower lux produced at the hotspot. This makes sense of course.

My new theory is that the larger the diameter and the longer the focus, the larger the focused floody ring.

Intuitively, you would think that a larger diameter asphere would collect more of the light, which it does. However, the side effect is a lower lux due to more spill around the image.

Perhaps a simple spherical plano lens is the answer. Does anyone care about spherical aberation in a flashlight's hotspot? I think not. Afterall, this plastic lens from the X2000 is not aspherical plano. It's clearly a spherical plano.

The aspherical lenses I have make excellent magnifying lenses for finding splinters though! It's like having a miniature microscope in your fingers, especially the thor lens I linked to above.

My next attempt, and probably my last, will be a 24mm lens with the longest backfocus distance I can find (gotta have a long BF to get an even flood in flood mode)

 

[Paul Baldwin]

I remembered seeing a post by Moviles before, the diagram seems to back up your thoughts? http://www.dealextreme.com/forums/Forums.dx/Forum.12834~threadid.482270
That suggests to me you would get a better definition from hotspot to outer ring with less inbetween.

 

[panicmechanic]

I'm not an expert in aspherics, but I have some here from DX, and can test with different emitters. Which emitter do you intend to use?
I've seen the described effect with some lenses, but it was almost invisible with DX sku.5297 on XP-G. However, there are some issues:
There is a small darker spot in flood mode, some rings when zooming in, both hardly visible. But you can zoom in on the die without halo, only haven't compared projection sizes.
I have these lenses to test (sku #s from DX):
- 66mm*24mm sku.13618
- 44mm sku.4558
- 28mm sku.5297
- 22mm*7.15mm sku.13570
- 50mm*18mm sku.12834
- 63.5mm*23.5mm sku. 13736
- 66mm*24mm sku.13618
- 50mm FORD/Hella Foglight lens
and then some...

 

[MoreGooder]

I'm not an expert in aspherics, but I have some here from DX, and can test with different emitters. Which emitter do you intend to use?
I've seen the described effect with some lenses, but it was almost invisible with DX sku.5297 on XP-G. However, there are some issues:
There is a small darker spot in flood mode, some rings when zooming in, both hardly visible. But you can zoom in on the die without halo, only haven't compared projection sizes.
I have these lenses to test (sku #s from DX):
- 66mm*24mm sku.13618
- 44mm sku.4558
- 28mm sku.5297
- 22mm*7.15mm sku.13570
- 50mm*18mm sku.12834
- 63.5mm*23.5mm sku. 13736
- 66mm*24mm sku.13618
- 50mm FORD/Hella Foglight lens
and then some...

XP-G R5.

Coincidently, I have the dx 5297 28mm on its way to me now. It was my last hope, and at 1.97, not a big investment. Im glad you've had good results, and I look forward to testing it even more now.

But, I wonder why the emitter matters? Is it because the lens on the LED is not really producing a perfect beam? Perhaps a decapitated emitter would nullify this effect, (in a most innefficient way)

FYI, The lens quest is a part of this project:
http://www.candlepowerforums.com/vb/showthread.php?t=257706

A lens with a poor flood is definitely not what I'm after.

Anyway thanks for the help thus far.lovecpf

 

[MoreGooder]

Oh, one other observation. The smaller the ratio of focus length to lens thickness, the larger the die image. Large die image = lower lux.

 

[znomit]

But, I wonder why the emitter matters? Is it because the lens on the LED is not really producing a perfect beam? Perhaps a decapitated emitter would nullify this effect, (in a most innefficient way)

For an aspheric you want an emitter that puts more light out the front. You might be better off with an XRE.

 

[rmteo]

Coincidently, I have the dx 5297 28mm on its way to me now. It was my last hope, and at 1.97, not a big investment. Im glad you've had good results, and I look forward to testing it even more now.

I have the DX 5297, same problem as with several others. Does not come even close to the performance of the plastic lens in the X2000.

 

[MoreGooder]

I have the DX 5297, same problem as with several others. Does not come even close to the performance of the plastic lens in the X2000.

LOL.... *sigh*
I wish I had posed this topic in the forums before I spent $200 on my lens experiment.

Thanks for the news..... I think.

 

[Codiak]

LOL.... *sigh*
I wish I had posed this topic in the forums before I spent $200 on my lens experiment.

Thanks for the news..... I think.

Your not the only one doing lens experiments.
I've had good success with plano-convex rather then aspherics. and fl of 50 does give me a nice tight hot spot with just a touch of halo.

To reduce the halo I'm going to be making my tubes between and post lense lightly dimpled with fine grain sand blasting then painted flat black.
By reducing reflected light within the tubes the halo will be reduced.

I would note I'd posted a question about using a ashperic + reflector and while I've yet to try it, Diahard has done in with one of their flashlights

 

[rmteo]

LOL.... *sigh*
I wish I had posed this topic in the forums before I spent $200 on my lens experiment.

Sorry, did not mean to discourage you. I am doing a commercial product and locating a lens to give good flood-to-throw performance has been challenging to say the least. After playing around with quite a few OTS components (just like yourself), I decided to go the custom route. There are several companies in the US that will design/produce plastic lenses to your spec. Also, for prototypes, there is a process called SPDT (single point diamond turning) where they machine the lenses on special CNC machines. One company quoted to produce 5 prototypes based on the following specs:

28mm Dia Aspheric Condenser Lens
Clear Aperture: 25mm
BFL: 13mm
EFL: 30mm
Center Thickness: ~11mm
Edge Thickness: 2mm
Here is their reply:

Rough Order Magnitude (ROM) for 5 acrylic aspheric condenser lenses to be SPDT is: ~ $950.00ea + $350.00 setup (5-6weeks delivery).

The total cost for 5 prototypes is $5,100. You really don't want to know what the tooling cost will be for production units. Lets just say that it will not leave you much change from $40,000. 🙁

 

[MoreGooder]

I tried the XP-G with the plastic x2000 lens. Interesting results. I had to position the lens further away from the XP-G by about 3mm from the XR-E's focus position. This must be due to the significant difference in the dome of the two lenses.

With the beam focused, it is extremely bright and practically zero spill. NO halo at all.

I think I'm just going to order the x2000 or equivalent ebay version for my custom builds. Toss the flashlight and keep the plastic lens. I have googled like crazy trying to find the plastic lens for sale all by itself to no avail.

 

[Apollo Cree]

There are a lot of amateur telescope makers who grind their own mirrors for use in telescopes. They're usually grinding glass in a concave shape to make a mirror for a Newtonian refractor. They're also usually grinding a larger diameter and a longer focal length than a flashlight lens.

However, maybe there's a way to adapt the techniques to make your own lenses.

 

[IMSabbel]

There are a lot of amateur telescope makers who grind their own mirrors for use in telescopes. They're usually grinding glass in a concave shape to make a mirror for a Newtonian refractor. They're also usually grinding a larger diameter and a longer focal length than a flashlight lens.

However, maybe there's a way to adapt the techniques to make your own lenses.

Thats the whole reason why _a_spheric lenses are that much more expensive to manufacture.
All the home-grown telescope lenses are spheric.

 

[MoreGooder]

There are a lot of amateur telescope makers who grind their own mirrors for use in telescopes. They're usually grinding glass in a concave shape to make a mirror for a Newtonian refractor. They're also usually grinding a larger diameter and a longer focal length than a flashlight lens.

However, maybe there's a way to adapt the techniques to make your own lenses.

Interesting suggestion, but I don't have the skills, time or money to take that approach.

And the winner is...... The inexpensive plastic lens that comes with the X2000. All other lenses for an LED DIY flashlight are just not worth the effort given the poor price/performance ratio.

 

[rmteo]

The X2000 and C30 DX lights use the same lens. SKU 18697 at <$10 is the cheapest source for these lenses.

 

[IMSabbel]

I really wonder what magic they are using in those lights 🙂

To be honest, when i got mine i was totally surprised, too. The rather shoddy build quality was just as expected, but the totally smooth flood plus nice nice die-projection was not...

 

[Paul Baldwin]

After some intense googling it appears that the Chinese sites refer to these type of lenses as a condenser lens aswell. http://www.busytrade.com/selling_leads/info/999627/Led_Lenses.html
http://www.made-in-china.com/showro...etailUqtxNQmumRre/China-Condenser-Lens-2.html

The first link appears to list the characteristics of the X2000 and C30 family lense very closely?

"2. And the lens can be adjusted by the distance between the LED and the real need condenser angle (45-80 degrees)
3.Can be established with all kinds of high-power LED, the spot is very uniform, no stray light, no black hole, no shadows or dark, light transmittance and high rate of utilization for large-angle focus of the lighting"

That company appears to have a thousand item minimum order tho, maybe worth contacting them for supplier details?

 

[MoreGooder]

Thanks a ton Paul! I sent inquiry for the "condenser lens 2". Hopefully, a small volume sell is possible.

I have also offered to send one of these lenses to an R&D engineer at Thor Labs. Some analysis by a pro with the proper equipment is definitely needed.