can someone help me with this fresnel lens?

Sorry, I know this is a little OT, but since astronomy deals with optics, I
thought that someone might be able to help me with the following situation:

I recently acquired a fresnel lens from a projection tv. It is about
36"x36".
My original purpose was going to be to use it for melting metals, etc but
the focal point appears diffused. It ignites paper and boils water after a
time, but won't melt metals very well. Since this is a lens, is there any
way I can add an additional fresnel (or even glass) lens at the focal point
to decrease it even further so I get higher melting points?

Thanks in advance,
JR


.

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