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Horizontal lens shift - real world data


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#1 of 6 ltlredwagon

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Posted January 14 2013 - 12:49 PM

I am looking at what would be an ideal setup for a school projector, but it requires lens shift and I'm finding it very hard to get practical answers. I have a basic idea of what lens shift is, but I'm having difficulty getting specific answers about how a projector's specs translate into the real world performance. For a variety of reasons the best setup would be as shown in the diagram below. I would need a projector that can shift the image to the right 6.5 feet, at a distance of 19 feet from projector to an 8 foot wide screen. That involves shifting the angle of projection (at least, the apparent angle of projection) from straight ahead (90 degrees) to about 112 degrees. But when I ask people what projectors can do that, and exactly what specs regarding horizontal lens shift (ratios, maximum angle, percentages, etc.) will tell me which projector can accomplish the task, I seem to be getting no data, general data or "tap-dancing" around the issue. If I need to learn about this so I understand it myself, that is fine, just need a source of data. Appreciate any help. The only other relevant point is cost. If there is something in the $3000 range that would do this (less is better) then I would go for it. If the only way to do this is super expensive, then I'll have to figure something out, but I would prefer this arrangement in the room I have available. Doesn't have to be new, either. Good quality used or refurbished would be fine if it does the job. What manufacturer specs regarding horizontal lens shift would tell me that a projector can do this?

#2 of 6 ltlredwagon

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Posted January 14 2013 - 01:07 PM

One other datum that might be relevant - the projector can be mounted at a height that is just about at the vertical center of the screen.

#3 of 6 Jim Mcc

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Posted January 14 2013 - 02:06 PM

Projectors with hor. lens shift normally list the amount of shift as a % of screen width. I've never seen it listed as an angle like you are showing. Just look in the projector's listed specs. Do you have a projector in mind?

#4 of 6 ltlredwagon

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Posted January 14 2013 - 04:28 PM

Thanks Jim. Okay, that starts to make sense if by screen width we're talking about image width. So if my zoom level creates an image 8 feet wide at 19 feet I could move it over 2 ft. to the right with 25% lens shift, 4 ft. at 50%, etc.. Have I got that right? If so, I would need about 80% lens shift to move the image over 6.5 feet. Don't think I've heard of such a projector. Maybe I'll have to rethink everything. I saw an Epson ad online that listed a projector with 10 degree horizontal lens shift. Another site listed lens shift as a ratio between the offset distance and the throw distance. I suppose there is a correlation between these and the percent specification. Don't quite get it yet, but I'll keep at it. I don't have a specific projector in mind, although I've heard that I should be looking at LCD projectors if I'm considering significant lens shift.

#5 of 6 ltlredwagon

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Posted January 14 2013 - 04:47 PM

Hmmm. Just read a pcmag.com review which said the Epson 8350 allows for a horizontal lense shift "by roughly 200 percent total vertically and 100 percent horizontally", but when I checked the actual Epson site brochure it listed max horizontal shift of 47%. I'll keep looking.

#6 of 6 Jim Mcc

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Posted January 14 2013 - 05:37 PM

[quote name="ltlredwagon" url="/t/326851/horizontal-lens-shift-real-world-data#post_4025112"]Thanks Jim. Okay, that starts to make sense if by screen width we're talking about image width. So if my zoom level creates an image 8 feet wide at 19 feet I could move it over 2 ft. to the right with 25% lens shift, 4 ft. at 50%, etc.. Have I got that right? If so, I would need about 80% lens shift to move the image over 6.5 feet. Don't think I've heard of such a projector. Maybe I'll have to rethink everything. I saw an Epson ad online that listed a projector with 10 degree horizontal lens shift. Another site listed lens shift as a ratio between the offset distance and the throw distance. I suppose there is a correlation between these and the percent specification. Don't quite get it yet, but I'll keep at it. I don't have a specific projector in mind, although I've heard that I should be looking at LCD projectors if I'm considering significant lens shift.[/quote] I don't know the answer to your first question. I've never owned a projector with lens shift. And yes, you should be looking for an LCD projector. Why can't you center the projector on screen?




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