Finally I have found myself a room to create my HT... the cellar (it's dark ). It's quite small but good enough. It means the projection distance will be 291 cm. I use a 15,4 wuxga screen, unsplit.

With dazzzla's tool I calculated the distance between the triplet and the LCD: 603,73mm. Leaving a gap of 20mm between the field fresnel and the LCD means a fresnel/triplet distance of 623,73mm. Using a 500mm triplet with a diameter of 100mm it will look like this:

What you see is the diagonal of the LCD (15,4 inch or 392mm). Considering the width and the height of the LCD screen: these light rays will fall even closer to the middle of the triplet!!!!


Now, as you can see it's a bit tight.

But does it work? And does it work well? Or do we say the cone is too small... I've heard conflicting opinions. One says it's best to get a small and bright ARC projection as possible because the edges of the triplet are less perfect, others say it's best to project the arc as big as possible to get the most uniform and bright picture.

As I think, I can tweak a bit. Because I could bring the bulb (lamp) closer to the first fresnel, so that the focal point of the field fresnel increases, right?

So what shall I do?

Kick

Keep building !

You're gonna be using the LL 650mm fresnel, or something else ? How large will your projection be ?

Things look good, so really just keep building and if anything, keep room in the light engine side for making adjustments for brightness/vignetting balance... that's about all you can do.

What lamp are you planning to use ?

gs

Thanks for the reply. I'm gonna use a 630 fresnel from www.diy-beamer.com (Austria, Europe). My projection will be about 1,6 meters (62 inch) by 0,9 meters (35 inch). With a 400 watt HQI-TS Daylight Powerstar bulb (5200 K / 36.000 lumen) I think the picture should be bright enough. I'm not sure how much gain I'm gonna use yet (although I can darken the room entirely).

Ok I will continue this setup . And you confirm I can ajust later with the lamp, that's cool.

So but what are your thoughts of the 'best' ARC projection at triplet?