Lens modding for a sharp, spotlight style beam?

Flashlight Modding and DIY Parts
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I’d like to replace the lens on the Convoy M21A (Exact same head as the C8) to make a sharply focussed spotlight beam with hard edges with near zero spill. (Similar to the Convoy Z1 zoomie on full zoom).

How do you determine the correct aspheric lens? I’m not sure about things like refractance index and focal length etc?
The current flat lens is 42mm wide and there’s 31mm between emitter and lens.

I would get the Z1 however it has a larger head and I’d like to cut down on bulk and it will never need the zoom out feature.

Here’s a beamshot of the Z1 zoomed in for illustration:

[Album] imgur.com
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Welcome to the forum adamsthws

I dont think just swapping the lens will accomplish what you want.

Aspheric lenses need to be very close to the LED. Im pretty sure you would need to delete the reflector, and raise the LED on a shelf, so it sits much closer to the lens.

imo the M21A is good at what it does, and if you want a different beam pattern, this is your excuse to shop for a different light :wink:

1 Thank
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Thanks for the advise Jon!

In the Z1, any idea how I might find out what the distance is between the Z1 lens and the emitter when fully zoomed in? (Without having to buy one).

I’m wondering about milling a slot within the M21a head, so the Z1 lens could sit closer to the emitter. The dimensions of the lens and head should (in theory) allow for this.

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no experience with the Z1 myself

maybe ask Simon (Convoy), what distance a Z1 lens needs to be from the LED in an M21a. And if he has any suggestions to convert your M21a…

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Thanks for signing up, adamsthws!

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Welcome adamsthws.

Buying aspheric lenses from a cheap Chinese vendor is a crap shoot , you might get something usable, might not. Some of them don’t focus properly.

Buying from a reputable vendor can cost a lot more but they’ll be much more trustworthy about their specifications. Example - 40mm Dia x 32mm FL, NIR I Coated, Molded Aspheric Condenser Lens Look for something with the shortest possible focal length

If you really like making stuff with your own hands then have at it, buy a lens and make it work… BUT… if all you want is a smaller package aspheric light then do like jonslider suggested and just buy a new light. While lens quality can vary ceap Chinese aspheric lights generally suit the purpose.

Bear in mind that smaller aspherics will have a larger spot than the Z1.

2 Thanks
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That’s super advice, thanks Pinky!

I’m not sure any flashlights exists for my specific use case so I’m keen to custom build something and the modding process is something I’ll find enjoying.

(I’m essentially building a portable stage light / spot light that is part of a mobile art installation. Flashlight weight, bulk and aesthetics are all important factors).

I’ve ordered a handful of lenses from AliExpress to experiment with. Even if they’re crap they should help me learn more about lenses and what might fit in the modified M21a’s head.

A lot of the AliExpress lenses don’t mention focal length and only mention dimensions, luckily Convoy helpfully list the dimensions of the z1 lens so I ordered a few similar to this with slight variations in lens widths an heights.

I’ll keep this post up to date with my findings, whatever the outcome may be!

1 Thank
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This post might be helpful

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There is no cheap method:

You either buy an expensive aspheric lens with data available to plug into a simulator (more effort but will yield the most precise results)

Or get the Z1 and experiment with LEDs (the 5050 Yinding Glass sounds perfect for this use case)

An alternative low effort idea is just get an LEP but good entry level ones are usually £100