Originally Posted by Gary Lightfoot
Around 2 x screen heights for me with a 2.35 screen.
THX recommend 2.4 x SH for optimal viewing for both tv and commercial, so they don't feel there's an issue with closer than 3xSH. CEDIA do have different documents for tv and projected images though, and tell you which one to use. I believe the tv version recommends 3xSH (along similar lines to what GeorgeAB has already said) but the projected version (CEB23) says the same as SMPTE - 3xSH plus or minus 1SH, with client preference being paramount (and even suggests they see where they like to sit in a commercial theatre).
Sony's 1,5 x SH for 4k doesn't seem very practical (except for commercial IMAX maybe) - at that distance if you were sat in the center of the screen, the vertical viewing angle is at around 35 degrees IIRC which is the maximum recommended (and where THX say the front row should be in their certified theatres). For comfortable viewing it should be around 15 degrees. If you wanted less than 35 degrees vertical with 4k, you'll have to lower the screen onto or into the floor, or raise the seating.
We have binocular vision of around 120 degrees, and 2 x SH for scope is only 61.8 degrees (less for 16:9), so still not taxing our vision that much - a little eye movement needed maybe, but still not in the realms of having to move your head. Movies that have scenes with people at the extremes are composed and designed that way. If the director wanted them closer in your field of view, and knowing how close people sit in a commercial theatre, he would have placed them closer together, so he's placed them at the edges for a reason.
Here are some factors that reduce the human visual system's ability to detect pixel structure in a video image:
1. Motion in the image
2. Reduced image brightness (many projection systems have too large of a screen for the lumen output of the projector selected)
3. Three chip projectors with poor red, green, and blue chip alignment/registration (as much as +/- an entire pixel in some)
4. Lower cost anamorphic lenses in projection systems
5. Less than 20/20 visual acuity in the viewer
6. Poor lens quality in lower cost projectors
7. Projection screens that are textured, using a granulated high gain coating, perforations, or a woven material
I have been certified with THX since 2002 and was brought in years later as a consultant for the development of their calibrator certification program. Much of what THX has done over the decades has genuinely benefited the motion imaging industry and home entertainment. I have been an avid and vocal proponent of their efforts. However, we don't agree on their viewing distance recommendations. It's also worth pointing out that they are not a standards body, like SMPTE and the ITU. They are fundamentally a consulting service. It's my opinion that they value image width for a sense of immersion over image sharpness. For me, immersion is much more than image width. The quality of the picture has as much to do with eliciting the willing suspension of disbelief as size does. If I detect pixel structure in the image, it is a distraction for me.
The SMPTE recommendations regarding seating distances are for commercial cinema. We all recognize that cinema audiences are not all discriminating viewers who value the fine details of a well crafted and executed image. Image excellence is a science as well as an art. However, the dramatic impact of cinematic art is wholly enhanced and fostered by the best technical presentation, whether the audience is conscious of the technical details or not.
Over the decades of my enjoyment of cinema and avid study of its characteristics and myriad of components, I have grown more discriminating regarding picture quality. I appreciate a sharp, clear, well defined picture more now than in my youth. A more natural electronic image is a sharper image. I have actually found myself sitting progressively farther from the screen in a commercial cinema as I have aged. A soft image is not acceptable any more. I sit in the next to the last row at IMAX. The last row would be better, but then I end up under the back surround speakers instead of forward from them.
Many home cinemas I have visited have an unacceptably soft picture to me, caused by one or more of the factors in the above list. What I am used to viewing in my company's demo theater is very sharp. It has Joe Kane Productions designed, single chip, 1080p, DLP projector and JKP's exceptionally smooth, 2.35:1, 0.9 gain, Da-Lite Affinity screen. For CinemaScope movies, I use the zoom and shift method, rather than anamorphic, to preserve the exceptional lens clarity of the projector. I sit at three screen heights for this constant image height system.
Best regards and beautiful pictures,
G. Alan Brown, President
A Lion AV Consultants affiliate
"Advancing the art and science of electronic imaging"