(originally posting in CIH forum but I hope the mods won't mind me keeping my build thread up-to-date)
Well, I finally got my, now fully working, lens hung tonight and spent some time dialing it in. After careful set up I must say that it offers a stunning picture... I'm a really happy camper.
I'm by no means an expert but here is my story.My setup:
Screen: 54" CIH DIY curved screen (to a 41' radius) with Seymour AV Center Stage XD fabric.
Projector: JVC RS-40
Lens: Prismasonic HD-6000RSetting up the projector and lens
1. The first step was to ensure the projector was mounted completely level front to back and level relative to the screen right to left (which is also level btw
2. Next I zoomed and offset the 16:9 image to over scan slightly the height of the screen. You can see in the pics below that the geometry distortion I was seeing was limited to barreling on the bottom edge. The top edge was flat and the side were very slightly trapezoid (wider at the bottom). I put this down to the offset optics of the JVS lens itself.
3. I made sure that the image was exactly centered on my screen.
4. After carefully setting the projector focus I brought the HD-6000 lens into the path and noticed that the now stretched image was projecting slightly to one side. I tweaked my lens ceiling mounting so that the lens was square to the projector lens -- if off even slightly, one side of the expanded image would be closer to the edge of the screen than the other side which results in subsequent distortion. Note that my custom ceiling mount was not connected to the projector mount so it is possible to be out of alignment hence the need for this step.
5. After the lens mount was square I tilted the actual a-lens on its pivot to ensure I had even distortion along the top and bottom edges of the image. In my case (and I guess I did something right calculating screen radius) because I was able to end up with an image with zero (honestly less that 1/8") distortion -- no barrel, no pincushion at all! The only distortion was was present was an emphasized trapezoid distortion on the sides particularly in the lower corner. I presume that the a-lens is amplifying the projector lens error(?) Maybe it is introducing so additional distortion but frankly this is the easiest type of distortion to mask off.
6. I went back to step 1 and did everything again with very minor tweaks.Focus:
There have been reports that the focus of the HD-6000 differs from the center to the edges. With my curved screen I could not detect this at all. I've tried to provide some photos but its hard with my pocket digital camera. I did find the focus adjustment on the HD-6000 is on a very fine thread. It takes a turn or two to see any notable effect and there seems quite a range over which it is hard to discern any difference. The strategy I used was to get my wife to turn the focus so it was clearly degrading the image, then turn about 8 turns the other way until again it was clearly degrading. Then winding back to roughly the center between these points. This seemed to work fine, but honestly I could have turned the focus an entire turn in either direction without any noticeable change.
After this procedure I must say that I was very impressed. Some screen shots follow but I was hard pressed to see much of a difference in any part of the image. There was a small, but noticeable softening of the image (which I imagine would be a positive for a DLP projector). I took screen shots at the left/center edge and true center so you can judge for yourselves. Again, note that my camera quality is not the best.Vignette
There is absolutely no trace of any vignette effects. My lux measurements between the center and corners of the screen proved that there was no measurable additive effect of the lens. I presume this is because the lens is quite a bit larger than needed at my TR.Geometric Distortion
My curved screen was designed to eliminate barreling at a throw distance of 18'. Clearly this has worked out perfectly to compensate for the pincushion on the upper and lower edges. The only distortion I can see is the exaggerated trapezoid in the lower section of the sides.Brightness
I need to check my results again because I was rushed, but I only measured a 1% reduction in brightness caused by the lens. The image is noticeably brighter then when I was zooming.. Given the less than marketed brightness of the JVC projectors this is great news. I am still able to get a bright enough image without resorting to high-lamp (although the iris is max open).CA
I would say that it is almost unseen to the eye if it exists at all. I don't know how to properly test this and separate the effect from the slight convergence error in the projector...Overall
Fantastic. Whether through my care in setup or just a great lens I know my widescreen image in my humble little theater is substantially better than what I've viewed in demo rooms at my local so called "high-end" AV stores.
Is the initial discounted prices still available? If so, my recommendation is to jump on this lens!I'll have an update on my lift automation solution soon.
Barrel distortion on lower edge with 16:9 and no anamorphic lens (as a result of my curved screen):
The same barrel distortion can be seen here:
With a-lens, the distortion has gone, but the trapezoid distortion is more apparent in the lower corners:
Focus, first without the a-lens, then with (darker because I reduced the exposure):
Center of screen, first without the a-lens, then with (camera location moved slightly):
Without lens, then with (far left of screen):
Eye Candy (without, then with lens):
Final note. The HD-6000 does indeed scale by x1.35, however my screen is built as a native 2.4:1 (with adjustable masking) so it worked out perfectly.