Like many a diy-projector junkie, I've been searching long for a diy reflector. Someone posted a link for aluminum hemispheres (thanks, don't remember who) and I thought I would order one to see how it would polish....well it's going to work great. The shipped version is a near perfect 3.5" half sphere, I believe this is close to the same sphere size as the pro reflector. They are available in many sizes, I just chose 3.5" to match the pro reflector. Here's my polishing results, I think it looks even better in person as it's hard to focus well inside a sphere.

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The unpolished hemisphere is on the left, I've achieved close to a mirror finish in about an hour of polishing.

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Here's the tools I used. Mothers mag and al polish, mothers small polish buffer, flexible brillo/sandpaper wheel. I started with the brillo wheel to remove the subtle machining/mold rings inside the raw hemisphere. Then I did this routine for about 45 mins: Load the sphere with polish, drill buff until warm/hot in palm, load more polish etc...I hand wiped the polish about every 3 applications to start clean again. I'll be cutting my bulb notch tomorrow.

Where did you find these spheres, sinner?

that's really neat polishing. What's the lifetime expectancy taking heat of MH lamps into consideration with these type of reflectors?

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Before
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After

Here's the cost (I may produce a few and sell them to make up the cost):

Hemisphere's - ($25 minimum order) $26.50, 2 x 3.5" alluminum, 1x 3.5" stainless steel ( I won't bother with the steel version).
Mother's buff ball- $19
Mothers polish - $4
Sand wheel - $6
Micro Cloth - $2
1 hour labor - ?

$57.50 total

I do have another rough to polish so that would cut the price in half. This won't fade like the pro reflector and I can restore the finish anytime. It will reflect IR heat but my cooling will manage that. It will also wrap my bulb to gather a little more light for my 6" pre condenser ( a true hemisphere). I'll post my tests and the notched version later. You can google "aluminum hemisphere" to find the vendor. If there is demand, I will likely make and sell some more to pay for mine.

just take note eventually the ally will dull due to oxidization. I dont know if this would accelerate due to the higher than usual temps of sitting behind a bulb

and from wikipedia
"Metallic aluminium is very reactive with atmospheric oxygen, and a thin passivation layer of alumina quickly forms on any exposed aluminium surface."

you'll need to keep a layer of wax on there to keep it shiny like that


the stainless sphere might be worth looking into though, i'll polish well and hold it for quite a while (if it doenst turn funny colors).

I've had pretty good luck with other home-polished aluminum reflectors as far as oxidation and fading. I've also used uncoated aluminum first surface mirrors with no issues as well as uncoated concaved mirrors. The only tarnished aluminum I've experienced is very thin aluminum duct flashing I used for heat flashing. The idea behind this is diy restoration when needed instead of buying a new one, I believe these hemispheres are 5/16" thick so there is plenty of solid aluminum to refinish. I have seen stainless steel tarnish pretty easy but I may still experiment with that one too. The stainless hemisphere cost $12 and the aluminum was $6. I'll post it's long term performance. Now I need to cut my bulb notch!

maybe here ?
http://www.wagnercompanies.com/spheres_and_hemispheres.aspx

Here's the cut version:
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Here my mount:
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I need to do new lux measurements, a quick check showed a little less lux at the center and a little more on the outside when compared to the pro reflector. So it appears to me a winning combo of benefits and loss. We'll see if it holds up for a while before needing re-polishing. I believe I'm getting about 129 lumens with this vs about 120 with the pro reflector. Again, the pro is brighter in the center but the fall-off is great to the edge. I know I could polish it even more for better results.

Here's where I bought the hemisphere's, I don't think they are a competitor.

http://sharpeproducts.thomasnet.com/viewit...lls/hemispheres

Any update on this Sinner? I'm tempted to try this. I don't suppose you have a raw spare to sale.

Is there any drawback to using a semi-spherical stainless steel ladle?
I've seen quite a few on my browsing trips for ideas.

How about getting a steel hemi from their catalogue and getting it chromed/hard chromed?

I do have a blank aluminum if you want to try it, how about $10 shipped in the US?

A perfect sphere is optimal for a point source reference, I've seen a few plogs with stainless steel ladles I know some have tarnished too. The steel ladle I used on my very first build did tarnish, not sure if it was stainless.

I don't know how much that would cost but I would be a fun experiment, also what are the effects of heat on chrome?

pm sent

Best I did with a closest sphere was my 4.5" soup ladle, stainless and thicker than most which took to heat better and didn't tarnish. The only problem was that it created alot of heat in the box that eventually warmed up the room quite fast. Don't know if an aluminum would have the same effect.

Well they use chrome plated piston rings, bore liners in engines...

It would be fine I'm sure! No doubt I'll be corrected if I'm wrong