Searching for the Best Aspheric Lens

Want to build a mega thrower aspheric from scratch. Based on what I have read, I want the following in a lens:

  • Big as possible to capture as much of the emitted light as possible
  • Short focal length for the same reason
  • Low beam degree angle (Don’t know technical term for this) for a tight concentrated beam
  • Highest transmission rate for efficiency (i.e. High quality glass with no bubbles and low in iron)
  • Precision ground for uniform and accurate collection and projection of light

What is readily available out there? Links would be appreciated. Don’t want to spend much, but I’m guessing anything that fits the above parameters will not be cheap. None of the lenses at DX seem to fit the bill.

I know that I ordered a lot of lenses from china sellers(I went for bigger 70 mm ones) and non of them have performance like branded aspherics Crelant/Dereelight/Tiablo… They were blurry and poor performing…

Flashlight manufacturers probably requires QC from aspheric manufacturers…

For big 70 mm ones you can not go wrong with Crelant or Xsearcher although Xsearcher throws slightly better with same emitter and current.

I wish you very best luck building throw monster… Add wavien collar and you will be around 1 milion candela/lux for sure.

I am afraid an aspheric lens for a flashlight is always a trade-off: to get the smallest hotspot you need a long focal length, but to get the led focussed with a long focal length lens it needs to be far away from the led so you will not capture much light.

But if you want a lens close to the led (and thus capture more light) that can focus it in a hotspot the focal length needs to be short which leads to a bigger hotspot.

To capture a lot of light with a long focal length lens far away from the led, the only way is to use a large diameter.

But going short focal length and at the same time getting the most concentrated beam is sort of defying basic optics.

Thank you both. Good info.

djoss, just to make sure we’re on the same page. I think you are talking about the focal point after the lens. I imagine I want a focal point of infinity after the lens. When I said “Short Focal Length”, I was thinking of the distance the emitter needs to be behind the lens to achieve focus. Is that there right wording for that?

I apologizes for the noob question. I now see I should have tried to study some basic aspheric lens concepts before starting this thread.

EDIT: Please ignore this post. I see you were addressing the distance behind the lens. I will edit the OP.

You mean something like this

Left Tiablo 50 mm aspheric right Dereelight 50 mm aspheric you can actually see focal difference here:

from my limited experience, crelants aspheric SUCKS BAD! mine was loaded with pits and air bubbles, and others had said it was a common thing with them

I rescued quite a few condensor lenses from old slide projectors (most are glass and around 50mm), some of them make good aspherics for flashlights.

My Crelant 7G5V2 with collimator head kind of sucks… I wouldn’t recommend it for anyone. I regretted my decision to buy it after 30 minutes of playing with it.

Well I am not to happy with Crelant either…

They are kind of blurry… But they will still have massive throw in that size but not as good as Dereelight Xsearcher lenses which has much cleaner and eye pleasant beam.

Derellight probably has better vendor for aspherical lenses.

In old days dereelight(2008. i think) was selling all desired parts to costumers worldwide. You could easily get lenses from them… And after some while they had some post failure rate and no profit and they are not selling any more i think?
But you could ask them for XS lenses? You never know…

Thank you all for your suggestions.

djoss, I have some surplus warehouses around here. I will check them out for old slide projectors. They have a lot of video projectors. Sometimes the broken ones go real cheap. May have to crack one open if I can get cheap enough to risk it.

Here’s a link. Old camera optics work great but my old Canon 50mm f1.4 costs about $100 used. A 50mm F1.8 generally sells for about $40. Of course with aspherics no led works quite as well as the old XR-E’s they just had the highest apparent surface brightness and narrow beam angle ideally suited for aspheric use. 50mm definitely is a good focal length to use. I tried various longer length lenses like a 200mm but it ends up being more like a laser pointer than a flashlight. The 50mm seems the perfect length for long distance spotting.

Thank you Mr_Krabs. Good info. I’ll check it out.

Cool 8)