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Discussion Starter · #1 ·
I put my projector into letterbox mode, and stuck my uh480 anamorphic lens in front.


Movies look great, but when measuring the projected aspect ratio (either with a 2.35 movie, or just by putting up the zoom bars on my projector) - the calculated ratio is 2.47 : 1! My throw ratio is 1.5.


This is a minor hindrance for creating a screen, I almost blindly bought a 2.37 screen thinking that was my ratio.


The weird part is, if I zoom in/out as much as I want on the projector, the ratio is still around 2.46-2.47.


I read in the UN480 manual that a very close/low throw ratio (1.3) could result in an aspect ratio of nearly 2.5 being thrown. But even if I adjust my TR to be much higher (2.0 and above), the AR is still measuring out to be 2.46ish.


I.e. at the smallest measurements, it's 175.5" wide and 71" tall = 2.47.


-ELmO
 

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moving your projector back to about 20-22' still makes it 2.46? Projector and lens are square to the screen and each other? Sounds like one of the lenses may have moved inside the case.
 

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Discussion Starter · #3 ·
I haven't been moving my projector back to change throw ratio, I've been decreasing the image size (thereby decreasing image width, increasing throw ratio) and the aspect ratio is still saying roughly around there (2.46).


I wil decrease to as small an image as possible tonight, and measure its resulting AR.


The thrown image looks fine, I haven't moved the lens "much" so not sure when the lens may have moved if thats the case.


-ELmO
 

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It sounds like the lens is not "straight". A prism based lens will either widen or shorten the width of the image if the lens is rotated either clock wise or counter clock wise. Your actually best to have a screen up first, then add the lens.


Just work off the image height of the native 16:9 image to work out the ideal height.
 

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Discussion Starter · #5 ·
OK , I played with it a little more tonight.


At the very smallest image that I project, I end up with nearly 2.37 (as expected!).


In the middle of the zoom range (who knows what my TR is at that point) it does start goign up to 2.42'ish.


Where I'm at right now is 2.47.


That's OK i'm ordering a screen soon so we'll see how it turns out.
 

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Quote:
Originally Posted by elmalloc /forum/post/18156938



That's OK i'm ordering a screen soon so we'll see how it turns out.

A prisms lens like yours is a fixed set of optics designed for 1.33x expansion.

This is intersting though, as I did notice that when I was making my cheap DIY prisms lenses that the amount of prism displacent was TR dependent - IE you set it up for 2.0:1, then use it at 1.5:1, the longer TRs actually needed more prism displacement and shorter TRs did not need as much or there was over shoot at the shorter throw. The variances you are reporting seem a bit far as the most I ever seemed to see was the differecne bewteen 2.35 and 2.40, so not too much, but it was there.


I am assuming that you have masked up a frame with masking tape so you have a point of reference?
 

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Discussion Starter · #7 ·
Yes, I have measured the amount of pincushioning as a point of reference. The carada frame is 3.25" on each side. I will be projecting a bit over the frame, which will "straighten out" some of the pincushioning in those last 1-2" anyway.


Yes, if you dig deep into some manuals you can see a low TR (1.3 even) can result in 2.5 aspect ratios being thrown. Makes sense if you think about it.


I am ending up with a 2.47 ratio being tossed which is probably a hindrance with geometry (if i was a perfectionist), but I am happy with what I'm seeing.


I am at max zoom out, and I'm hiting 2.47'ish. At the min zoom it is as expected (nearly 2.37 on the dot).


My TR is 1.48'ish (16ft throw and resulting in 14.5ft wide 2.47 image - lol).


-ELmO
 

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It will be interesting to see how this pans out for you.
 

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Discussion Starter · #9 ·
I agree. I may be dumping about 1.8K into Carada's screen, and it will be throwing money away if it doesn't work because they don't take returns on custom sizes.


I am sort of interstedin screen reseearch's 4K material, but that will get very expensive unless I frame it myself - and even then, I didn't end up going in walls. I'm getting some zen acoustic adagios/adagio jr for my center next week. Don't think many people have heard of those speakers (I haven't really either) - so that will be a fun "surprise" I hope.
 
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