MCR-20 plus XM-L Alignment Help

[Mattaus]

Hi all,

Hopefully this is the appropriate place to post this. I am busy working on some CAD drawings and need to figure out what height an XM-L emitter needs to be placed in relation to the base of the McR-20 reflector for the best beam. Should the bottom of the LED dome be placed at exactly the same height as the bottom of the opening of the reflector? Or should it be slightly lower/higher than the opening? Tolerances of 0.05mm are workable

I would test this myself except I have no McR-20 reflectors on hand, but I need to determine if the 2 parts will fit in my application before I spend any money testing them! That and I can't afford to wait for one to ship to me because the rest of the project is hinging on this somewhat.

Any help would be highly appreciated.

Thanks,

- Matt

 

[fyrstormer]

Reflector focus is more art than science. You can design a reflector to focus the center of the emitter perfectly, and you can calculate how much of the light will spill out the sides, but there's no way to predict whether you'll like the beam. You just gotta try.

I find it hard to believe you can afford to work on...whatever your project is...but you can't afford a reflector to test with. They don't cost that much. Maybe you can rig up something that uses an adjustable screw to hold the reflector a certain distance above the emitter mounted to a heatsink, and then you can tweak the screw until you get the beam you want. Then you can measure the distance and use that in your CAD drawings.

 

[Mattaus]

Thanks furstormer. I guess I was hoping a for a bit of a 'universally accepted sweet spot' for this emitter/reflector combo. Seems i'll have to do the hard yards...that's what I get for being lazy I guess!

- Matt

 

[fyrstormer]

I'm sure there is a mathematically-calculable range within which the emitter must be positioned, but within that range it's really up to the designer's preference.

 

[Th232]

Well, if you're up for some fun Don has the dimensions for the reflector here. You can take measurements to find out the formula for making the reflector surface, do some ray-tracing to find the focal point of the reflector, then match that up with the apparent die location of the XM-L (I say apparent because the dome will distort things a bit). Then you'll have a reasonable idea of where it should sit.

Or just buy the reflector, make a threaded holder and screw it in/out until you get the best focus.

Edit: Seems Fyrstormer had the same suggestion, so I guess that makes two of us suggesting it.

 

[easilyled]

Mac (cmacclel) would be one of the best people to ask since his EDC-XML series use McR20s and he achieves very nice results. Why not send him a PM?

 

[fyrstormer]

Mac (cmacclel) would be one of the best people to ask since his EDC-XML series use McR20s and he achieves very nice results. Why not send him a PM?

I thought Mac stopped using McR20 reflectors after his first run of EDC-SST50's?

 

[Mattaus]

Might send him a PM anyway just in case. Thanks!

 

[easilyled]

I thought Mac stopped using McR20 reflectors after his first run of EDC-SST50's?

Perhaps you're right. I can't remember which way round it was.
There's still a chance that he'll know the answer to the question, in any case.