Aspheric questions...

22 posts / 0 new
Last post
DARCANGEL
DARCANGEL's picture
Offline
Last seen: 8 hours 11 min ago
Joined: 04/11/2012 - 00:06
Posts: 959
Location: the nickel city,New York
Aspheric questions...

I have been researching aspheric lenses and I have been curious what most of you guys do to start an aspheric mod?I want to start a mod and wondering if most try to pick a lens size based on the dimensions of the host rather than doing a build starting with a lens and modding around that.My ultimate goal is to use the new xp-g2 as the emitter because of it's specs,and would like some advice as where to go from there.I also see a number of options like aspheric condenser lenses and many different options and prices.Since the xp-g2 is so new,I anticipate some experimenting will be essential,but I want a push in the right direction.There are so many options'any help would be appreciated.

gcbryan
Offline
Last seen: 4 months 1 day ago
Joined: 05/07/2010 - 20:42
Posts: 2541
Location: Seattle,WA

I’m not familar with the XP-G 2. How is it different than the XP-G?

Generally speaking the XR-E is the smallest and has the greatest surface brightness which equates to throw.

Most aspherics from places like DX only tell you the diameter so you buy something that will fit your host or if you have a bench grinder (for instance) you can get something close and make it fit.

You also need the emitter to focus when the aspheric is in place but DX doesn’t tell you what the back focal length is so you just have to hope that you can make it work.

Depending on your host you may have some adjustment there that you can make (screwing the head in or out).

Chicago X
Chicago X's picture
Offline
Last seen: 6 years 3 months ago
Joined: 07/22/2011 - 16:13
Posts: 4013
Location: See Name

I work with the lens first, as the back focal length (BFL) is one of the most important considerations for host selection.

http://wardogsmakingithome.org/index.html

War Dogs, Making it Home - Rescue Dogs for Returning Vets

DARCANGEL
DARCANGEL's picture
Offline
Last seen: 8 hours 11 min ago
Joined: 04/11/2012 - 00:06
Posts: 959
Location: the nickel city,New York

Chicago X wrote:
I work with the lens first, as the back focal length (BFL) is one of the most important considerations for host selection.
That said,is there a formula that I can follow to determine ideal bfl,in reference to the emitter type?BTW,I chose the xp-g2 because it's new and uncharted territory and I'm up for the challenge,not sure if I'm on a fools mission or not.
gcbryan
Offline
Last seen: 4 months 1 day ago
Joined: 05/07/2010 - 20:42
Posts: 2541
Location: Seattle,WA
DARCANGEL wrote:

Chicago X wrote:
I work with the lens first, as the back focal length (BFL) is one of the most important considerations for host selection.
That said,is there a formula that I can follow to determine ideal bfl,in reference to the emitter type?BTW,I chose the xp-g2 because it’s new and uncharted territory and I’m up for the challenge,not sure if I’m on a fools mission or not.

I just looked up XP-G2. It’s 20% more efficient than XP-G.

It’s not uncharted territory…it’s charted just like all the other emitters.

It won’t throw as far as the XR-E.

There isn’t an ideal bfl. You just have to get the emitter at the right point with regard to the lens. A shorter bfl will give you a larger hotspot and a longer one will give you a smaller hotspot but they will both be the same brightness and will throw the same.

There aren’t that many choices regarding aspherics so you generally buy what you can and hope one of them with have the right bfl for your application.

Chicago X
Chicago X's picture
Offline
Last seen: 6 years 3 months ago
Joined: 07/22/2011 - 16:13
Posts: 4013
Location: See Name

I’m not aware of a formula.

The “ideal” BFL would likely change depending on diameter of the lens, as the angle of emission is a fixed number.

http://wardogsmakingithome.org/index.html

War Dogs, Making it Home - Rescue Dogs for Returning Vets

DARCANGEL
DARCANGEL's picture
Offline
Last seen: 8 hours 11 min ago
Joined: 04/11/2012 - 00:06
Posts: 959
Location: the nickel city,New York

Well,thanks that makes more sense,and maybe xre is the way to go,I have heard xp-g2 would be more ideal in an aspheric but from what gcbryan said,not as bright.Do you you guys reccommend a certain lens over another for a large thrower?

zizo
Offline
Last seen: 7 months 2 weeks ago
Joined: 06/11/2011 - 15:52
Posts: 94
Location: CA, USA

I recommend the 67/75 mm lens from lck-led with a xm-l U2. It’s very bright and the beam is wide enough to be useful at close range.

DARCANGEL
DARCANGEL's picture
Offline
Last seen: 8 hours 11 min ago
Joined: 04/11/2012 - 00:06
Posts: 959
Location: the nickel city,New York

zizo wrote:
I recommend the 67/75 mm lens from lck-led with a xm-l U2. It's very bright and the beam is wide enough to be useful at close range.
Cool,thanks!I like that idea too,I have also seen lenses with a.r. coatings on them,is this practical to consider a coated lens or not worth the money?I understand the concept of surface brightness in an aspheric,but I like the xml die for a larger useful beam.edit:spelling sorry
gcbryan
Offline
Last seen: 4 months 1 day ago
Joined: 05/07/2010 - 20:42
Posts: 2541
Location: Seattle,WA

You can always just slightly defocus the aspheric by unscrewing the head for a larger beam and you still have the option for a tight beam by screwing it back in.

It really just depends on what you are looking for regarding throw. If you want the most throw a tightly focus XR-E will give you the most.

If you want a wide beam at the expense of some throw then there are many options.

NightCrawl
Offline
Last seen: 3 years 6 months ago
Joined: 01/22/2012 - 08:20
Posts: 3071
Location: Karlsruhe, Germany

On the topic of aspheric lenses.. would cutting the dome be a huge improvement?

bibihang
bibihang's picture
Offline
Last seen: 2 weeks 1 day ago
Joined: 11/10/2011 - 09:32
Posts: 2387
Location: Malaysia
NightCrawl wrote:

On the topic of aspheric lenses.. would cutting the dome be a huge improvement?

Cutting dome will only improve the throw for reflector configuration. This is because after de-doming a LED more light will go to the sideway and hits the reflector, thus increasing in throw.

However, since aspherical lens collect lights that emitted out from the front of the LED, de-doming a LED will decrease the throw in this case.

DARCANGEL
DARCANGEL's picture
Offline
Last seen: 8 hours 11 min ago
Joined: 04/11/2012 - 00:06
Posts: 959
Location: the nickel city,New York

Can anyone verify if lck led is a good vendor?I'm liking that 75mm lens.

NightCrawl
Offline
Last seen: 3 years 6 months ago
Joined: 01/22/2012 - 08:20
Posts: 3071
Location: Karlsruhe, Germany

bibihang wrote:
NightCrawl wrote:

On the topic of aspheric lenses.. would cutting the dome be a huge improvement?

Cutting dome will only improve the throw for reflector configuration. This is because after de-doming a LED more light will go to the sideway and hits the reflector, thus increasing in throw. However, since aspherical lens collect lights that emitted out from the front of the LED, de-doming a LED will *decrease* the throw in this case.

Greatly explained, thank you! Smile

 

@DARCANGEL: Erik trusts them, so I think you are good to go.

gords1001
gords1001's picture
Offline
Last seen: 1 year 4 months ago
Joined: 05/07/2012 - 14:02
Posts: 5276
Location: wigan england

I used them this month, very pleased.

zizo
Offline
Last seen: 7 months 2 weeks ago
Joined: 06/11/2011 - 15:52
Posts: 94
Location: CA, USA

One factor that you are not considering is the apparent surface area of the LED created by LED’s dome. De-doming an LED will decrease the die image size and increases the lux with an aspheric lens. I’ve tried this with both Xm-l and Xr-e LEDS with a gain in lux.

willie
willie's picture
Offline
Last seen: 4 months 3 weeks ago
Joined: 08/16/2011 - 14:19
Posts: 824
Location: Houston
DARCANGEL wrote:

zizo wrote:
I recommend the 67/75 mm lens from lck-led with a xm-l U2. It’s very bright and the beam is wide enough to be useful at close range.
Cool,thanks!I like that idea too,I have also seen lenses with a.r. coatings on them,is this practical to consider a coated lens or not worth the money?I understand the concept of surface brightness in an aspheric,but I like the xml die for a larger useful beam.edit:spelling sorry

Typically AR coatings will give 5% increase my understanding. My preferred vendor Optolife offers coating on some lenses. Not every aspheric lens offered by them will give good results for flashlight use. I have a 80mm (A142) that seems to have potential but it not listed on the site anymore. I have had good success with their 50mm A293 or A293MC AR coated. Looks like I will give the 75mm lck-led a try.

NightCrawl
Offline
Last seen: 3 years 6 months ago
Joined: 01/22/2012 - 08:20
Posts: 3071
Location: Karlsruhe, Germany

zizo wrote:
One factor that you are not considering is the apparent surface area of the LED created by LED's dome. De-doming an LED will decrease the die image size and increases the lux with an aspheric lens. I've tried this with both Xm-l and Xr-e LEDS with a gain in lux.

So.. no dome -> smaller but brighter hotspot with aspheric?

gcbryan
Offline
Last seen: 4 months 1 day ago
Joined: 05/07/2010 - 20:42
Posts: 2541
Location: Seattle,WA

For those who have removed the dome…did it affect the tint and did it affect the life of the emitter since it’s not now protected?

zizo
Offline
Last seen: 7 months 2 weeks ago
Joined: 06/11/2011 - 15:52
Posts: 94
Location: CA, USA
gcbryan wrote:
For those who have removed the dome…did it affect the tint and did it affect the life of the emitter since it’s not now protected?

Yes, the tint is warmer and more yellow. I haven’t used my de-domed Xm-l leds much, but my de-domed Xr-e has been running a about a year and I don’t see any drop in lux.

bibihang
bibihang's picture
Offline
Last seen: 2 weeks 1 day ago
Joined: 11/10/2011 - 09:32
Posts: 2387
Location: Malaysia
zizo wrote:
One factor that you are not considering is the apparent surface area of the LED created by LED’s dome. De-doming an LED will decrease the die image size and increases the lux with an aspheric lens. I’ve tried this with both Xm-l and Xr-e LEDS with a gain in lux.

Is it? I think I saw from somewhere in this forum or other forum (can’t remember anymore) that someone explained this in details.

Note that the LED die surface area is always remain the same no matter you de-dome it or not. The dome is to collect the light emitted from the die and projected them towards a specific direction, kind of acting as an aspherical lens though. But if you de-dome it, the light would become more “scattered” since there is nothing to focus the beam.

But if you said that you have tried it practically and confirmed that you got higeher lux after de-doming the LED (every factors else remain the same), then I don’t know what’s happening behind.

EDIT: Found it, as explained by ma_sha1. You may read the following comments below, though the discussion went a bit ugly in the end… Big Smile

Manny
Manny's picture
Offline
Last seen: 1 year 1 month ago
Joined: 05/23/2012 - 06:13
Posts: 571
Location: Scottsdale, Arizona 85259
gcbryan wrote:
DARCANGEL wrote:

Chicago X wrote:
I work with the lens first, as the back focal length (BFL) is one of the most important considerations for host selection.
That said,is there a formula that I can follow to determine ideal bfl,in reference to the emitter type?BTW,I chose the xp-g2 because it’s new and uncharted territory and I’m up for the challenge,not sure if I’m on a fools mission or not.

I just looked up XP-G2. It’s 20% more efficient than XP-G.

It’s not uncharted territory…it’s charted just like all the other emitters.

It won’t throw as far as the XR-E.

There isn’t an ideal bfl. You just have to get the emitter at the right point with regard to the lens. A shorter bfl will give you a larger hotspot and a longer one will give you a smaller hotspot but they will both be the same brightness and will throw the same.

There aren’t that many choices regarding aspherics so you generally buy what you can and hope one of them with have the right bfl for your application.


XR-E can throw !!!!