Glass concave mirror, would it work?

[JTT3]

I was wondering if something like this could be used in an early acetylene headlight. Thoughts?

https://www.ebay.com/itm/374234401037?m ... media=COPY

[Dan Hatch]

One question would it handle the heat? Then you need to worry about the focal point.

[Greg Griffin]

A mirror is a reflector. A Mangin mirror (for a gas headlight) is a lens. The nickled reflectors sold by the vendors were OK until I got my Mangin mirrors, which are better. You could give the concave mirror a try and if it works then the hobby gains another resource.

[JTT3]

Does anyone have Gene Majre’s contact info?
He restores headlights & sidelights. He was usually at Chickasha in the south building. Thought I’d see if he had any reflectors. Thanks for any help.

[jiminbartow]

The less curvature, the further away the focal point is. The more curvature, the closer the focal point is to the light source. I would imagine you would prefer for the focal length to reach further into the night.

[Drkbp]

I haven't used those (the link you posted) as I found some Lancaster Mangins
that snug up to the shape of the rear of the headlight buckets properly.

I believe you will have mounting difficulties and possible problems as Dan notes.
There are "plate" mirrors in some late Victor acetylene lamps and are mounted
in steel straps. I believe they were directed mostly at the truck market.

The one on the left below is out of a 6" Victor type driving lamp I have mounted on
my running board. The plate mirror seems to work as well as the Mangins. There
is quite a bit of vibration while driving so I haven't tried to mount a "plate" in
my John Brown 16's. The plate type might fit an E&J but I don't have one to try.

I find gas lights very reliable for ten years since I set them up
with a Prest-O-Lite "B" tank.

[TRDxB2]

The focal point of a mirror is the point at which light rays from an object converge or diverge after reflecting off the mirror. The "object", burner, of an acetylene headlight is similar to a headlight filament with respect to proper aiming. If the "object" is at the focal point the reflector will project the maximum about of concentrated light forward. If it is offset, the light projected will be scattered. So the question is what does the focal point of the reflector need to be capture the maximum amount of light from the burner?
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[Jerry VanOoteghem]

So the question is what does the focal point of the reflector need to be capture the maximum amount of light from the burner?

Do you mean where does the focal point of the reflector need to be?

If so, then the real question is, where does the burner need to be with respect to the reflector's focal point. Since the burner position is adjustable, but the reflector's focal point is not.

[KWTownsend]

John-
Those look like they would work.
A friend of mine recently purchased some of these:

https://www.ebay.com/itm/283428097530?_ ... R4LJk8ubZQ

-Keith

[TRDxB2]

So the question is what does the focal point of the reflector need to be capture the maximum amount of light from the burner?

Do you mean where does the focal point of the reflector need to be?

If so, then the real question is, where does the burner need to be with respect to the reflector's focal point. Since the burner position is adjustable, but the reflector's focal point is not.

The focal point of the mirror needs to be within the adjustment points of the burner. Same method used for adjusting electrical headlights

[Allan]

The burner mounts are adjustable fore and aft within the lamps. On my 1912 van the reflectors have a slightly different curvature, so the burners are set at different locations between lamps.

Allan from down under.

[Drkbp]

You set the burner pipe center ( the flame) at the focal point of the Mangin.

The standard focal point is 2-7/16" from the mirror back and the dimension "F"
in the chart below.

"D" is the 1-3/8" dimension of a 6" #3209 Mangin in the chart already posted above.

That leaves the burner center one-inch in front of the Mangin rim and centered, more
or less, in the burner adjustment slots in the John Brown gas headlights.

I shine mine on one of the shop overhead doors about 50 fifty feet away when I set them up.
I had just come back from a drive in photos below and was closer to the door but that's the idea.

The two Browns are down lower with the Victor up higher. The dark spot at the top is the burner
shadow in the Victor which I can move while driving and was aimed up a little for some reason.

[TMiller6]

The eBay mirror with its 11.8” focal length is essentially a shaving mirror. I don’t think it would work well in a headlight.

[KWTownsend]

So according to Ken, the focal point needs to be about 62mm?

[Drkbp]

Keith,

James Lyons helped us understand the Mangins in 2015 and I saved that post.
I had already found the focus position earlier that year and was driving with the
Prest-O-Lite tank. You can't be too far off if you just mount the burner stand in the
slot. I noticed last night that I had the burner stand a little to the front of the slot
to focus.

I measured my right front headlight setup last night with a small tape measure and
find it "aligns" with that discussion.
I am sure he wouldn't mind me posting that explanation. He is in the field so
he has the equipment to determine what we are using. Hope he chimes in.

Ken

[ShirkWood]

An alternative might be what I did on my 1910 2-cyl. Buick. It had what resembled a convex clock glass like was used on an old mantle clock. It had a sheet metal frame around it with three tabs to connect it to the lamp body. New convex clock glass was cheap. I had a glass shop make them a "mirror" for me. They look good, are close to the curvature needed, and cost relatively little.

[Drkbp]

Verne,
Did you have the clock glass silvered?
Really neat idea!

It would be easy enough to mount a clock glass in the headlight
and light a good burner set as far forward in the burner slot as
you can get. Getting the burner forward may help save the clock glass.

If the clock glass survived driving around burner lit for a couple of miles,
you could have the "front" of the glass silvered and shellac it. I set my
mirrors on a couple of strips of 2-inch webbing to snug up.

Even if it can't be focused, you could probably easily drive with them.
(Thank you Keith for great photo of lit acetylene headlamp with proper flame.)

Ken