Originally Posted by AV_Integrated
That's because their calculator (mostly) sucks. I have a huge issue with how lens shift calculators are shown. In the case of the 3100, the neutral position of the lens (no offset) is at 0% above/below the center line of the screen. So, the 26.5" is above the center line, not above the top of the screen.
This is correct. I agree.
In my first post, I can see where my verbiage is confusing. I start out referencing screen center but then talk about lens center and the top of the screen.
Originally Posted by b curry
The +/- 60% vertical lens shift is referenced from the screen center.
If you have a 91" diagonal, 16:9 screen, the screen viewable height is ~45".
45" X .60 = 27"
So, for a ceiling mount, you should be able to mount the projector with reference to the lens center at a maximum of ~27" above the top of the viewable area of the screen.
You've indicated that you want to mount the top of the screen ~2 feet down from the 8 foot ceiling. So, the projectors lens center mounting position could be anywhere that it fits in that 24" from the top of the screen to the ceiling.
The Epson 3100 is listed as 6.2" high. I don't know what mount you want to use but figure 4-6 inches minimum for the mount height plus the projector and that places the bottom of the projector at ~7 feet from the floor. That leaves you plenty of vertical lens shift or in other words, you will not use all of the vertical lens shift available and it will maybe leave you enough room so you don't bump your head.
The bold line should read: So, for a ceiling mount, you should be able to mount the projector with reference to the lens center/screen center at a maximum of ~27". I referenced the top of the viewable area so as to not include the screen frame.
Sorry my F-up.
Originally Posted by AV_Integrated
I think this is, by far, the first calculator I've seen which is actually straightforward to use for lens shift inclusion:
You put in the room height and the model of the projector and image diagonal, then you can just get the measurements you are after. You can move the projector up and down, move the lens shift around, and you can see it all happen and get real measurements! So, with a 91" diagonal, and the proejctor about 9' from a screen that is exactly 24" from the ceiling, the center of the lens must be 19.7" from the top of the ceiling (or more) and exactly on center. I would shoot to put the lens closer to 22" from the ceiling for a bit of flexibility.
Compared to this line of junk... https://files.support.epson.com/pdc/...ml5/index.html
I have book marked that new calculator, and encourage people to use it when they start needing to play with lens shift. Plus, the guy is a forum member which means we can give him some feedback. He was quick to add imperial (inches) to a previously metric only chart.
While the Epson HTML5 calculator may not be as intuitive as the JACK LIU Projection Calculator, it gives you what you need and it does give you additional information in regards to lens shift that the Jack Liu calculator does not.
As it's not typically possible to use the full range of both vertical and horizontal lens shift together, the Epson HTML5 version does give you a very good tool and reference to this point. If you enter the information correctly and completely on the first screen and click on the gray box "Lens shift checker", you will get a pop-up screen with your screens viewable area superimposed on a highlighted octagonal area that represents the screens total mounting area based on both the horizontal/vertical lens shift extremes as well as combinations of both horizontal/vertical lens shift.
You're able to drag the screen to any position inside the highlighted area and get instant corresponding values indicated for both the horizontal/vertical lens shift.
The truncated corner areas of the mounting rectangle coincide with and indicate the limitation of using both horizontal/vertical. The "cross-hairs" indicate the screen center but they also give you some indication of what part of the lens the panel image is projected through.