why silver
Because the reflectance of silver is highest of any material (ie. up to 98.5%). Chrome (53% I think) is actually lower than stainless steel (65%), so chrome plating it would lower the reflectance. The only material competitive with silver is aluminum (95%). This is why mirrors are made from silver or aluminum, or some of their close relatives on the periodic table.
Silver tarnish is oxidization of the surface layer into silver oxide. But if you heat tarnished silver, it drives off the oxygen and becomes pure silver again. I do see some tarnish on the little mounting tabs of my reflector, but none on the main surface. The lamp heats it up enough to un-tarnish it. The mounting tabs don't get hot enough because they lose heat to the mounting hardware that is not exposed to the lamp.
I think you can get silver coated with a transparent lens coating material like magnesium floride, but I have not needed it.
Because the reflectance of silver is highest of any material (ie. up to 98.5%). Chrome (53% I think) is actually lower than stainless steel (65%), so chrome plating it would lower the reflectance. The only material competitive with silver is aluminum (95%). This is why mirrors are made from silver or aluminum, or some of their close relatives on the periodic table.
Silver tarnish is oxidization of the surface layer into silver oxide. But if you heat tarnished silver, it drives off the oxygen and becomes pure silver again. I do see some tarnish on the little mounting tabs of my reflector, but none on the main surface. The lamp heats it up enough to un-tarnish it. The mounting tabs don't get hot enough because they lose heat to the mounting hardware that is not exposed to the lamp.
I think you can get silver coated with a transparent lens coating material like magnesium floride, but I have not needed it.
oh cool, i never knew the reflective percentage of chrome or silver........
you see, I live in florida, where we have a hundred times more humidity than you, you lucky devil!!!
and i don't always run the ac which does reduce moisture inside a home. so in terms of long term use, i think i would be better off highly polishing the stainless steel and then "setting and forgetting"...
after all, my lcd has a low contrast ratio anyways, 200:1.
so i think it would be overboard to pay for silver plating for the reflector.
especially when i move back to Brevard County (space coast) which is one of the most highly corrisive environments in the world. the salt is mixed IN THE AIR with high humidity.
I wish i lived in arizona or s. cali. it's so cool how you can go to a junk yard and pull a 50 year old motorycle or car engine and it's in great shape, here, you can't even leave a tool outside in the summer, it will get surface rust in a matter of hours when conditions are right.
you see, I live in florida, where we have a hundred times more humidity than you, you lucky devil!!!
and i don't always run the ac which does reduce moisture inside a home. so in terms of long term use, i think i would be better off highly polishing the stainless steel and then "setting and forgetting"...
after all, my lcd has a low contrast ratio anyways, 200:1.
so i think it would be overboard to pay for silver plating for the reflector.
especially when i move back to Brevard County (space coast) which is one of the most highly corrisive environments in the world. the salt is mixed IN THE AIR with high humidity.
I wish i lived in arizona or s. cali. it's so cool how you can go to a junk yard and pull a 50 year old motorycle or car engine and it's in great shape, here, you can't even leave a tool outside in the summer, it will get surface rust in a matter of hours when conditions are right.
best reflector
Sounds like you should just go with stainless steel.
I measured my screen Lux with and without my silver reflector, and I found that it adds 22% more light. Apparently, the arc chamber of the MH lamp is not very transparent. So when the light is reflected back through the arc chamber, some of it gets absorbed. Of course, it also has to go through four layers of glass, so that accounts for more loss.
The point is: You can run your projector without any reflector at all, and the screen image will only be about 22% dimmer.
If you are the type who enjoys "holy grail" quests: The very best spherical reflector would be a dichroic glass mirror. (AKA "cold mirror") This is glass with a frequency-selective coating that lets >90% of the IR through, but reflects >90% of the visible light (and UV). If you can buy one of these, then much less heat gets reflected back into the lamp and on into your LCD.
Sounds like you should just go with stainless steel.
I measured my screen Lux with and without my silver reflector, and I found that it adds 22% more light. Apparently, the arc chamber of the MH lamp is not very transparent. So when the light is reflected back through the arc chamber, some of it gets absorbed. Of course, it also has to go through four layers of glass, so that accounts for more loss.
The point is: You can run your projector without any reflector at all, and the screen image will only be about 22% dimmer.
If you are the type who enjoys "holy grail" quests: The very best spherical reflector would be a dichroic glass mirror. (AKA "cold mirror") This is glass with a frequency-selective coating that lets >90% of the IR through, but reflects >90% of the visible light (and UV). If you can buy one of these, then much less heat gets reflected back into the lamp and on into your LCD.
cold mirror
I have a piece about 5" in diameter that I got from Surplus Shed for $5. But that does not work as a spherical reflector (since it is flat). I also have a 5" diameter piece of Rosco Hot Mirror (dichroic, but in the opposite sense) that cost me about $65. That is more like the retail price for a new piece of flat cold mirror.
I have not found any surplus spherical cold mirrors. Any number of custom optical companies would be happy to give you a quote. Maybe something like $500 each, for coating a few of them. The problem with optics is that the economy of scale is huge. It costs almost the same to have one lens or mirror custom made, as it costs for 100 pieces.
If you want something economical, you have to find it already being mass-produced for some other application. For example, there are some small halogen floodlamps that have a built-in cold mirror reflector. A few very brave (or foolish?) builders have cut those up with abrasive disk tools, so they can slip a bare MH arc chamber inside to make their own DIY MH dichroic floodlamp.
Edmond Optical has some dichroic elliptical reflectors for <$100, but that requires a different projector design. (There are threads on that here, if you are interested: Use the search buttom.)
I think the only reasonable DIY approach is to make your own custom reflector from aluminum, polish it up very well, and then put a piece of hot mirror or IR selective film between the light engine and the fresnels.
I have a piece about 5" in diameter that I got from Surplus Shed for $5. But that does not work as a spherical reflector (since it is flat). I also have a 5" diameter piece of Rosco Hot Mirror (dichroic, but in the opposite sense) that cost me about $65. That is more like the retail price for a new piece of flat cold mirror.
I have not found any surplus spherical cold mirrors. Any number of custom optical companies would be happy to give you a quote. Maybe something like $500 each, for coating a few of them. The problem with optics is that the economy of scale is huge. It costs almost the same to have one lens or mirror custom made, as it costs for 100 pieces.
If you want something economical, you have to find it already being mass-produced for some other application. For example, there are some small halogen floodlamps that have a built-in cold mirror reflector. A few very brave (or foolish?) builders have cut those up with abrasive disk tools, so they can slip a bare MH arc chamber inside to make their own DIY MH dichroic floodlamp.
Edmond Optical has some dichroic elliptical reflectors for <$100, but that requires a different projector design. (There are threads on that here, if you are interested: Use the search buttom.)
I think the only reasonable DIY approach is to make your own custom reflector from aluminum, polish it up very well, and then put a piece of hot mirror or IR selective film between the light engine and the fresnels.
i'm going with the quiche mold you found. thanks for all your help, you kick butt.
your dog does too. LOL
how long you think that quiche mold will take to ship from Maple country to florida?
your dog does too. LOL
how long you think that quiche mold will take to ship from Maple country to florida?
As I recall, the shipping was pretty fast. No import duty fees or problems with customs at all. The only problem was that the shipping cost more than the mold. They told me they could ship more than one for the minimum shipping fee. (I think maybe 3?) If there is anybody else interested in one in your area, then you could buy them all together and save a few bucks.
BTW, that is an uneditted photo of my dog: He just loves to have his picture taken!
BTW, that is an uneditted photo of my dog: He just loves to have his picture taken!
yeah, i figured it was fast,
i use to order alot of parts for my antique british bike and they came faster than any of the domestic shipments that came from out west.
your dog looks like one of the animals in a south park episode when they were making a "cute animals shot with wide-angle lenses" video.
LOL it was so funny.
my dog is half lab and acts like that too. (worse watch-dog you could possibly have) but he's half pitbull and will fight other dogs, just not people cause the lab in him makes him want to please everyone.) but he can't stand other dogs, it's a weird thing.
like Mr. Jeckle and Dr. Hyde.
i use to order alot of parts for my antique british bike and they came faster than any of the domestic shipments that came from out west.
your dog looks like one of the animals in a south park episode when they were making a "cute animals shot with wide-angle lenses" video.
LOL it was so funny.
my dog is half lab and acts like that too. (worse watch-dog you could possibly have) but he's half pitbull and will fight other dogs, just not people cause the lab in him makes him want to please everyone.) but he can't stand other dogs, it's a weird thing.
like Mr. Jeckle and Dr. Hyde.
guy grotke,
the link you had up is down, do you have a more recent link for these? i know this thread has been dead a while, but i figured i'd give it a shot
the link you had up is down, do you have a more recent link for these? i know this thread has been dead a while, but i figured i'd give it a shot
quiche molds
Shiney stainless steel nearly perfect half-spheres in various sizes:
http://www.dr.ca
Then click on Pastry Moulds/Rings/Shapes in the left pane.
Then click on Stainless Steel Moulds in the right pane.
Then scroll down to Stainless steel half sphere moulds. (NOT Ovale)
They have various different sizes, so you can pick one to match the size of your lamp. A 12 cm diameter is about right for a Ushio retrofit lamp. Smaller would be okay for double-ended lamps, but using a larger one than you need doesn't hurt anything but your wallet.
Shipping to the US costs more than one of these molds. Find a friend or three and order several together, since their shipping charge is about the same for 3 as for 1.
Shiney stainless steel nearly perfect half-spheres in various sizes:
http://www.dr.ca
Then click on Pastry Moulds/Rings/Shapes in the left pane.
Then click on Stainless Steel Moulds in the right pane.
Then scroll down to Stainless steel half sphere moulds. (NOT Ovale)
They have various different sizes, so you can pick one to match the size of your lamp. A 12 cm diameter is about right for a Ushio retrofit lamp. Smaller would be okay for double-ended lamps, but using a larger one than you need doesn't hurt anything but your wallet.
Shipping to the US costs more than one of these molds. Find a friend or three and order several together, since their shipping charge is about the same for 3 as for 1.
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