17 inch 16:9 assault on high end project

[Hezz]

Here is the model that I thought I was showing above. You can see the fan mockup and the magnetic shield in place over where the transformer will be mounted.

If you look closely you can somewhat make out the mirror mounting mechanism. Two bars mount the mirror at four points which can be shimmed with felt washers to get the exact angle. Also the whole mount can pivot up and down in one degree of freedom to set the vertical angle of the mirror.

Since this thing is so big I am thinking of covering the large lower chamber with thin clear acrylic to make it more see through. It will be like a museum piece. The lower chamber will be sealed off from the other chambers and will vent hot air out the back near the top.

Hezz

[Guy Grotke]

Since that mirror is just part of the condensor system, I don't think using a standard second surface mirror would make any difference. And you can get a 12" by 12" mirror tile at a building supply store for about $1 US.

That would be considerably less than what you would pay for such a piece of 3/4" aluminum, not to mention the weight difference. I also think you will have a very hard time getting a piece of aluminum plate to be as optically flat and reflective as the $1 mirror tile.

The mirror tile would also have an advantage of being the same thickness as the first surface glass mirror you mentioned buying later. That would mean your geometry would not change switching between the two glass mirrors.

[Hezz]

Guy,

I always thought that a cheap mirror would be OK in the light engine but the guys that have experimented with them have always found the first surface mirrors to be far better because the regular mirrors create a small ghosting effect. The reason for this is because since the light is hitting a clear piece of plastic or glass at very close to brewsters angle a lot of light is reflected by the plastic surface itself and is slightly out of focus compared to the mirror surface.

I don't think that flatness is an issue at all and all of the highest quality mirrors ar made by hand by amateur telescope makers, granted it is a lot more work and costs more than a cheap mirror but I figure the metal will cost me about 20 - 25 USD at a specialty metals store if I can find a remnant. The machining would be expensive and would put it out of the cost ballpark except that I am machining it myself.

Anyway, I checked at my local Home Depot and they only sell mirror tiles in whole boxes and they are not big enough. I need a 13.5 x 15 inch mirror. And even if I decide not to make the machined mirror I can make a cheap homemade mirror out of a piece of thin aluminum bonded to some MDF.

After all, this is intended to be a high end project so why not go for it.

Hezz

[Hezz]

It seems that the fresenl lens that I ordered from Lumenlabs is the wrong focal length for the DIYprojectorcompany 135 mm diameter triplet.

There was some discussion on another forum about some of the Lumenlabs fresnels being the wrong size so I measured mine. Mine was one of the right ones at 790 mm FL. But it turns out that I am going to need something like a 600 mm FL fresnel. I will have to look for one or else try and use a large homemade singlet.

When I measured the lens to LCD distance of my lens it seemed to be 15.75 inches and about the same for each orientation. I tried the lens in both directions as most lenses are designed to work in one direction only. I could not detect the difference with my crude methods but perhaps I need to test this lens again to make sure I am using it in the right orientation.

Here is a sketch of the fresnel requirements for the lens with the 15.75 lens to LCD distance. I hope that it isn't too large to post.

Hezz

[Hezz]

I spent most of the day testing and measuring the 135 mm diameter lens and it turns out that indeed it does focus from different distances depending on how it is turned. At a distance of about 11 feet from the wall I get the short distance of rear lens to LCD of 15.5 inches and when turned around I get a rear lens to LCD distance of 18.5 inches. At this point holding the lens by hand it was difficult to tell if there ws an imaging quality difference. Subjectively, the longer distance seemed to have a slight egde in image quality and the projected image is slightly smaller which is what I need.

I have determined that I may just be able to get by with the Lumenlabs fresnel if I use a 15.4 inch LCD instead of a 17 inch one. Based on my projector to wall distance I will have to use the 15.4 LCD because my wall space is insufficient for the 17 inch LCD and I can't move the projector any closer to the wall.

Here is an updated sketch of the lens and fresnel light cones. These focusing distances are for an approximate 11 foot lens to wall distance. The 790 mm FL fresnel will just barely fit it's light cone into the aperture of the 135 mm lens if I use a 15.4 inch LCD.

Hezz

[Hezz]

I am also going to have to increase the LCD to rear lens distance on the projector and even though this give the projector a rerally long snout it looks as if I have no choice unless I want to flip the bill of 135 USD to get a 600 mm FL fresnel from Edmonds optic. I tried searching the internet for 600 - 650 mm FL fresnels but I have had no luck so far. I am going to try to get by with this fresnel and the worst that will happen is that I will have some reduced light output.

Here's model with new lens adapter plate. I have some pictures in the works but I want to wait on those and get more of them developed at once.

I also have a design idea to enhance the light output of the light engine but I need to flesh that out a little more. I am going to have to redesign the whole reflector assembly to adapt to the 15.4 inch LCD.

Hezz

[Mikey p]

Hezz,
I thought L.L. was replacing the first batch of lenses with the new 650mm one. Or is it just the people who got the 990mm ones?

Mike

[Guy Grotke]

These are not just for replacing the ones they sent out that were made wrong. They should have these new 650 mm fl fresnels for sale as well. Definitely, check with LL before you spend so much!

Did you really measure your LL "790 mm" lens focal length? When I measured mine, I think it was actually more like 767 mm!

[KodSnoba]

HEZZ:

I bought first surface mirror from Delphy Glass company.
It is 12x16 inch mirror. Price was 24.95 US$ plus shipping to Europe 14.00 US$.
I think they will cut you a custom size. You could ask them.
Their web page:

http://www.delphiglass.com/

My mirror is 2 mm thick. They sell this mirrors for use in making caleidoscopes :-)

Cheers !

[KodSnoba]

Actually it is 1.5 mm thick

It is amazing that it survived trip from USA to Europe

:-))