Daekar
Enlightened
Since these things seem to be so useful for great throw from otherwise fairly normal setups and don't require a whole lot of work I thought it might be good to set up a spot for those like myself who need a bit of guidance in deciding whether they want an Aspheric lens for their favorite light. I will do the best to add information I think is useful for people as I learn it, but chances are there are many more people out there that already know this stuff. I'm hoping you'll post your knowledge, and I'll add it to this post as things go.
First things first...
Q: What is an Aspheric Lens?
A: According to Wikipedia, an aspheric lens (also an aspherical lens or an asphere) is "is a lens whose surfaces have a profile that is neither a portion of a sphere nor of a circular cylinder."
Q: OK... great. What's that mean to me?
A: The upshot of aspheres seems to be that they can eliminate spherical aberration, an imperfection inherent in light which passes through a simple spherical lens. That means greater control of light (read: focus) with less size, weight, and expense. In the context of flashlights, this means that a single asphere can take a large percentage of some emitter's output which is being emitted in multiple directions and collimate it - in other words, it bends it to all go in the same direction. This means higher concentrations of light at longer distances, and that means more throw! Take a look at this picture shamelessly hotlinked from http://www.yoptics.com:
For more information on lenses in general, see here.
Q: Fantastic! So I can just go buy the cheapest asphere I can find, stick it on the head of my light, and I'll get world-class throw, right?
A: Not quite. There are a few qualities possessed by any lens which we need to consider: Overall Diameter, Effective Diameter, Center Thickness, Edge Thickness, Focal Length, and Reflectivity.
Overall Diameter:
Sometimes aspheres like this one don't follow a single line all the way across - they have extra material on the sides to help the user mount them in whatever device or fixture is required. For flashlights, your bezel needs to be at least this size or it will require machining to fit a lens that has a larger Overall Diameter. This also means that the whole surface of the lens isn't necessarily optically functional, something else to remember in your design considerations.
Effective Diameter:
This is the important part of the lens, the optically functional portion which actually does the work in refracting the light to a collimated beam. In the picture linked to in Overall Diameter, this is the big curvy part.
Center Thickness:
If you've been snooping around on http://www.surplusshed.com, you've no doubt noticed that, for a specified diameter and material, the shorter the focal length is, the bigger and rounder the lens is. Center Thickness is related to this - it's simply the measurement of the width of the lens at its thickest point, which in an asphere is the center. Center Thickness is important because the larger this value is, the more the lens will protrude from the bezel of a light unless you put crenelations on it like this one.
Edge Thickness:
Like in this image, already referenced, the Edge Thickness is simply the width of the optically non-functional bit that sticks out around the... edge.
This is important to us because a larger value for edge thickness means that the crown that holds the lens on may not screw down all the way, or if the edge is very thick, it may not even screw on at all! Obviously, despite the fact that edge thickness isn't an optical property, it can still make or break an asphere mod. I haven't gotten a chance to find out, but I believe if the edge thickness is too great it can be ground or abraded down to the required size (within limits of course) if sufficient machining on the light head assembly itself isn't possible. That's an area where I'm fuzzy, so I'd appreciate confirmation/refutation of that by a knowledgeable party. :thinking:
Focal Length:
Those of you unfamiliar with basic optics should probably read the Wiki on lenses, which will give you a general idea of how things work, it should give you a good idea of what focal length is in general. Go read it now. Are you back? Good. You may have noticed that in many diagrams, you have two theoretical light beams diverging from one point. If you're talking about an asphere and an LED, that point is the LED. Of course, LEDs aren't a true point-source of light, but they're as close as we've got. Anyway, the focal length simply refers to how far away from the lens the emitter needs to be to make optical use of it - or to put it another way, how far away it needs to be to make the best focused throwing beam. Along with Effective Diameter, this is the most important optical quality of any lens.
Reflectivity:
Not so much a lens property as a property of any matter, reflectivity refers to how much light bounces off of any object. In our flashlight lens, reflectivity is BAD and results in optical inefficiency. Essentially, we just don't want light being reflected back at the emitter - we want it ALL going out the front. Reflectivity can never be completely eliminated, but it can be effectively reduced with an anti-reflective coating, sometimes called a non-reflective coating or something similar. In the process of searching for an appropriate lens for your application you may not have a choice between a coated or non-coated lens, but if you do you should get the coated one. I believe DIY anti-reflective coatings are available for treating lenses that don't already have them, but I haven't gotten a chance to look for them yet.
Those are the basics of aspheres as I understand them. Again, if anything is unclear or even worse, incorrect, please tell me! :candle:
Q: Yeah, yeah, that's all great, just tell me what lens fits my light.
A: Sorry, no can do, these things are very specific and there is no "one size fits all" solution. As mods are created and people learn more, we might be able to create a list, but it might not be as easy as that - I expect most lenses/lights will require at least minor modification to fit together, and further modding to get the focus exactly right.
Q: OK, so you can't tell me what to get... what do I use to measure my light?
A: To get the lens diameter I used a pair of 6" calipers graduated in 0.001" increments. To get the focal length I used a depth micrometer, like the one pictured in this Wiki article (the bottom micrometer in the image). If you don't have access to those tools (which is likely) you can probably use metric ruler for the lens diameter and a rod which you stick down in the reflector and then make a mark on it where the lens would sit. Just measure that distance with the ruler. Remember that all lenses are specified in metric (mm), so if you don't have a metric measuring device, just multiply your result in inches by 25.4 to get millimeters. It's important to be as accurate as possible, but remember that most lens specs are given in whole numbers as opposed decimals or fractions of a millimeter.
Q: OK, I know this probably won't be a simple "drop-in" procedure and I'm pretty sure I know what size lens I need. Where to I get it?
A: Well... so far, finding a lens has been the hard part for me. The best I can do is post a few websites which either sell lenses online or will custom-make lenses to order. That of course would be the best solution, but it's expensive. I'll give what I have:
The Surplus Shed - I believe this is where many CPFers get their lenses. They have a large inventory of many different sizes at smashing prices - but it takes some searching. Try the lens finder available in the drop-down menu, but also manually search their lens inventory - they seem to have different things in both places.
ThorLabs Optics - Link is a page with lenses already listed, homepage is http://www.thorlabs.com. They seem to cater to industry, but may be a viable option, especially for modders who are looking to produce asphere lights in slightly greater volume.
Asphericon - Similar to Thorlabs, this company doesn't seem to sell directly on the internet. However, for larger orders or custom orders they may be just the ticket.
YOptics - Already mentioned, this seems to be a smaller business which has focused their efforts in the aspheric realm on custom lenses.
Edmund Optics - Link is a page with lenses already listed, homepage is http://www.edmundoptics.com. Seems to cater to industry but may sell in small volumes.
OptoSigma - Link is a page with lenses already listed, homepages is http://www.optosigma.com. An optics and hardware company, they have a wide variety of different lenses and film coatings, not just aspheres and non-reflective.
Lightpath - Deals primarily in custom lenses, presumably with larger volumes than the average person would need. Possibly a good volume-modder resource.
Mellesgriot - Link is a page with lenses already listed, homepage is http://www.mellesgriot.com. Similar to Optosigma listed above, but seems to be very internet-shopping-friendly. Not a high-volume-only merchant.
LedSpot - A merchant that doesn't actually carry any aspheres, but they do carry LED lenses specifically designed for different applications. The "real spot" product for the Cree XR-E seems to fairly well reproduce an asphere effect.
Modding Tips:
~ Greenlight pointed out the following to remember:
*ADDITION* It seems that the general consensus is that the reflector WILL increase the total light out the front, but the type of reflector matters. 2xTrinity made mention of an elliptical reflector with two focal points - one for the source and one for entry into an asphere. With the proper elliptical setup, you could use not only a Cree, which is the best current LED for the aspheres, but a Seoul P4, or an incandescent or HID light as well! I think it would be worth exploring this combination. Hopefully one of the modders will take notice and start offering an HID/elliptical/asphere combination throw light! I'll try to learn a bit about elliptical reflectors as well, as they seem to be a good accessory for making aspheres more useful.
~ Someone in another thread mentioned that to attain the smallest hotspot and therefore the greatest throw, use a larger lens. This makes the size of the LED die closer to a point-source relative to the size of the lens. This means it may not be possible to stick a tiny asphere in a Draco to get a micro-throw-monster.
Light Dimensions:
I've got measurements for the following lights. I'll try to add dimensions as they become available to me so there will eventually be measurements for all of my lights except the PT Apex and SF L2.
Lumapower MRV
Overall Reflector Length = 31.2039mm
Inner Reflector Length = 30.4622mm
Lens Diameter = 41.9608mm
Lens Thickness = 2.0701mm
Lumapower D-mini
Overall Reflector Length = 25.8064mm
Inner Reflector Length = n/a
Lens Diameter = 30.8102mm
Lens Thickness = 1.9050mm
Lumapower M1 Tactical
Overall Reflector Length = 20.4978mm
Inner Reflector Length = n/a
Lens Diameter = 30.7848mm
Lens Thickness = 2.1590mm
Seems to be able to accept this lens without modification per this thread.
That's all for now! Hopefully it will be useful. It would be great for some people will contribute more information to add, I'm only a beginner! :wave:
First things first...
Q: What is an Aspheric Lens?
A: According to Wikipedia, an aspheric lens (also an aspherical lens or an asphere) is "is a lens whose surfaces have a profile that is neither a portion of a sphere nor of a circular cylinder."
Q: OK... great. What's that mean to me?
A: The upshot of aspheres seems to be that they can eliminate spherical aberration, an imperfection inherent in light which passes through a simple spherical lens. That means greater control of light (read: focus) with less size, weight, and expense. In the context of flashlights, this means that a single asphere can take a large percentage of some emitter's output which is being emitted in multiple directions and collimate it - in other words, it bends it to all go in the same direction. This means higher concentrations of light at longer distances, and that means more throw! Take a look at this picture shamelessly hotlinked from http://www.yoptics.com:
For more information on lenses in general, see here.
Q: Fantastic! So I can just go buy the cheapest asphere I can find, stick it on the head of my light, and I'll get world-class throw, right?
A: Not quite. There are a few qualities possessed by any lens which we need to consider: Overall Diameter, Effective Diameter, Center Thickness, Edge Thickness, Focal Length, and Reflectivity.
Overall Diameter:
Sometimes aspheres like this one don't follow a single line all the way across - they have extra material on the sides to help the user mount them in whatever device or fixture is required. For flashlights, your bezel needs to be at least this size or it will require machining to fit a lens that has a larger Overall Diameter. This also means that the whole surface of the lens isn't necessarily optically functional, something else to remember in your design considerations.
Effective Diameter:
This is the important part of the lens, the optically functional portion which actually does the work in refracting the light to a collimated beam. In the picture linked to in Overall Diameter, this is the big curvy part.
Center Thickness:
If you've been snooping around on http://www.surplusshed.com, you've no doubt noticed that, for a specified diameter and material, the shorter the focal length is, the bigger and rounder the lens is. Center Thickness is related to this - it's simply the measurement of the width of the lens at its thickest point, which in an asphere is the center. Center Thickness is important because the larger this value is, the more the lens will protrude from the bezel of a light unless you put crenelations on it like this one.
Edge Thickness:
Like in this image, already referenced, the Edge Thickness is simply the width of the optically non-functional bit that sticks out around the... edge.
This is important to us because a larger value for edge thickness means that the crown that holds the lens on may not screw down all the way, or if the edge is very thick, it may not even screw on at all! Obviously, despite the fact that edge thickness isn't an optical property, it can still make or break an asphere mod. I haven't gotten a chance to find out, but I believe if the edge thickness is too great it can be ground or abraded down to the required size (within limits of course) if sufficient machining on the light head assembly itself isn't possible. That's an area where I'm fuzzy, so I'd appreciate confirmation/refutation of that by a knowledgeable party. :thinking:Focal Length:
Those of you unfamiliar with basic optics should probably read the Wiki on lenses, which will give you a general idea of how things work, it should give you a good idea of what focal length is in general. Go read it now. Are you back? Good. You may have noticed that in many diagrams, you have two theoretical light beams diverging from one point. If you're talking about an asphere and an LED, that point is the LED. Of course, LEDs aren't a true point-source of light, but they're as close as we've got. Anyway, the focal length simply refers to how far away from the lens the emitter needs to be to make optical use of it - or to put it another way, how far away it needs to be to make the best focused throwing beam. Along with Effective Diameter, this is the most important optical quality of any lens.
Reflectivity:
Not so much a lens property as a property of any matter, reflectivity refers to how much light bounces off of any object. In our flashlight lens, reflectivity is BAD and results in optical inefficiency. Essentially, we just don't want light being reflected back at the emitter - we want it ALL going out the front. Reflectivity can never be completely eliminated, but it can be effectively reduced with an anti-reflective coating, sometimes called a non-reflective coating or something similar. In the process of searching for an appropriate lens for your application you may not have a choice between a coated or non-coated lens, but if you do you should get the coated one. I believe DIY anti-reflective coatings are available for treating lenses that don't already have them, but I haven't gotten a chance to look for them yet.
Those are the basics of aspheres as I understand them. Again, if anything is unclear or even worse, incorrect, please tell me! :candle:
Q: Yeah, yeah, that's all great, just tell me what lens fits my light.
A: Sorry, no can do, these things are very specific and there is no "one size fits all" solution. As mods are created and people learn more, we might be able to create a list, but it might not be as easy as that - I expect most lenses/lights will require at least minor modification to fit together, and further modding to get the focus exactly right.
Q: OK, so you can't tell me what to get... what do I use to measure my light?
A: To get the lens diameter I used a pair of 6" calipers graduated in 0.001" increments. To get the focal length I used a depth micrometer, like the one pictured in this Wiki article (the bottom micrometer in the image). If you don't have access to those tools (which is likely) you can probably use metric ruler for the lens diameter and a rod which you stick down in the reflector and then make a mark on it where the lens would sit. Just measure that distance with the ruler. Remember that all lenses are specified in metric (mm), so if you don't have a metric measuring device, just multiply your result in inches by 25.4 to get millimeters. It's important to be as accurate as possible, but remember that most lens specs are given in whole numbers as opposed decimals or fractions of a millimeter.
Q: OK, I know this probably won't be a simple "drop-in" procedure and I'm pretty sure I know what size lens I need. Where to I get it?
A: Well... so far, finding a lens has been the hard part for me. The best I can do is post a few websites which either sell lenses online or will custom-make lenses to order. That of course would be the best solution, but it's expensive. I'll give what I have:
The Surplus Shed - I believe this is where many CPFers get their lenses. They have a large inventory of many different sizes at smashing prices - but it takes some searching. Try the lens finder available in the drop-down menu, but also manually search their lens inventory - they seem to have different things in both places.
ThorLabs Optics - Link is a page with lenses already listed, homepage is http://www.thorlabs.com. They seem to cater to industry, but may be a viable option, especially for modders who are looking to produce asphere lights in slightly greater volume.
Asphericon - Similar to Thorlabs, this company doesn't seem to sell directly on the internet. However, for larger orders or custom orders they may be just the ticket.
YOptics - Already mentioned, this seems to be a smaller business which has focused their efforts in the aspheric realm on custom lenses.
Edmund Optics - Link is a page with lenses already listed, homepage is http://www.edmundoptics.com. Seems to cater to industry but may sell in small volumes.
OptoSigma - Link is a page with lenses already listed, homepages is http://www.optosigma.com. An optics and hardware company, they have a wide variety of different lenses and film coatings, not just aspheres and non-reflective.
Lightpath - Deals primarily in custom lenses, presumably with larger volumes than the average person would need. Possibly a good volume-modder resource.
Mellesgriot - Link is a page with lenses already listed, homepage is http://www.mellesgriot.com. Similar to Optosigma listed above, but seems to be very internet-shopping-friendly. Not a high-volume-only merchant.
LedSpot - A merchant that doesn't actually carry any aspheres, but they do carry LED lenses specifically designed for different applications. The "real spot" product for the Cree XR-E seems to fairly well reproduce an asphere effect.
Modding Tips:
~ Greenlight pointed out the following to remember:
I would imagine he's correct, painting the inside black would certainly make the beam more distinct. Given the same amount of light directly impacting the lens however, I would imagine a reflector might make use of the side light and make a lightsaber with a small spill or less powerful secondary beam. Which is best is probably a subjective or application-specific decision.
*ADDITION* It seems that the general consensus is that the reflector WILL increase the total light out the front, but the type of reflector matters. 2xTrinity made mention of an elliptical reflector with two focal points - one for the source and one for entry into an asphere. With the proper elliptical setup, you could use not only a Cree, which is the best current LED for the aspheres, but a Seoul P4, or an incandescent or HID light as well! I think it would be worth exploring this combination. Hopefully one of the modders will take notice and start offering an HID/elliptical/asphere combination throw light! I'll try to learn a bit about elliptical reflectors as well, as they seem to be a good accessory for making aspheres more useful.
~ Someone in another thread mentioned that to attain the smallest hotspot and therefore the greatest throw, use a larger lens. This makes the size of the LED die closer to a point-source relative to the size of the lens. This means it may not be possible to stick a tiny asphere in a Draco to get a micro-throw-monster.
Light Dimensions:
I've got measurements for the following lights. I'll try to add dimensions as they become available to me so there will eventually be measurements for all of my lights except the PT Apex and SF L2.
Lumapower MRV
Overall Reflector Length = 31.2039mm
Inner Reflector Length = 30.4622mm
Lens Diameter = 41.9608mm
Lens Thickness = 2.0701mm
Lumapower D-mini
Overall Reflector Length = 25.8064mm
Inner Reflector Length = n/a
Lens Diameter = 30.8102mm
Lens Thickness = 1.9050mm
Lumapower M1 Tactical
Overall Reflector Length = 20.4978mm
Inner Reflector Length = n/a
Lens Diameter = 30.7848mm
Lens Thickness = 2.1590mm
Seems to be able to accept this lens without modification per this thread.
That's all for now! Hopefully it will be useful. It would be great for some people will contribute more information to add, I'm only a beginner! :wave:
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