kilian@poplar.cray.com (Alan Kilian) (06/05/91)
galt@hellgate.utah.edu (Greg Alt) Says: > It seems that CRT's are a possible health risk and should not be used > right up against your eyes for a long time. That debate rages on and until I see some more articles I am not going to put any CRT based displays right in front of my eyes. The "Light valve" designs seem much safer in the mean time. > but what about LCD screens? > While there is little or no radiation, it is still looking at something > only a few inches away from your face. I would think this is not good > and could cause some pretty bad eyestrain. Well, not really. The screen is only a few inches from your face but it is optically much farther away. Some people say "Optical infinity" but it seems more like one meter or so to me. > I am nearsighted, and my glasses have the effect of bringing objects > about a foot from my eyes. I don't really think that that is correct. When you see an object that is "really" 2 meters away does it look like it's only a foot from your eye? (Sorry about the mixed units there). I don't think it does. I have -4.75 diopters correction so my "optical infinity" is only 1/4.75 meters in front of my eye so optically my glasses take objects at infinity and translate them to 1/4.75 meters away, but the two corrections (My eyes are +4.75 and my glasses are -4.75) cancel and I can see just like "normal" people. Well anyway, I forgot what my point was. > I wonder what the effect of the optics are on the LCD screen. I would > hope they take the screen farther away from your eyes and enlarge it, They do make the screen seem farther away but they don't really "enlarge" it. Well they do, but not really. it's like this: /| / | / | / | / | / | /| | / | | / | | Your eye-----> . | | You are looking this way ---> \ | | \ | | \| | \ | \ | ^ \ | | \ | | \ | | \| | | ^ | | The "real" position ---+ +--- The optical position of the screen. ofn the LCD screen So the screen "looks" bigger because you think it's farther away, but it does not subtend a greater solid angle so it's not really "enlarged" > but does anyone know the sort of lenses that would be used? You could use a 8cm focal length lens 8cm from the screen to get the screen to be at optical infinity. > It would be very good if it would have the effect of taking the picture > out to infinite... > > Also, in a couple weeks, I will start to work on a simple 3D graphics > system that has perspective views. I will write it in Turbo C, and > I will post it (or send it to the new cheap-VR ftp site). I plan on > using a hierarchical structure similar to PHIGS, and it will be flexible > with color and depth cueing. If anyone has comments or suggestions, > please email me... I plan on not supporting lights, but I think I > will leave some hooks to allow expansion... What are you trying to get? There are many public domain 3D graphics systems out there that support all of this. If you are trying to really understand 3D than this is the way to go but if you just want to be able to draw things get something like the simple phigs package from brown university. (Mail to spr@cs.brown.edu because I can't find the IP number) they have a PHIGS package that runs with the X-Window system. -Alan Kilian -Alan Kilian kilian@cray.com 612.683.5499 Cray Research, Inc. | "The Fragile X Syndrome may me the most 655 F Lone Oak Drive | frequent cause of inherited mental Eagan MN, 55121 | retardation". Science 24-May-1991 PP1097
galt@hellgate.utah.edu (Greg Alt) (06/05/91)
In article <1991Jun5.031158.15999@milton.u.washington.edu>, kilian@poplar.cray.c om (Alan Kilian) writes: > galt@hellgate.utah.edu (Greg Alt) Says: > > > but what about LCD screens? > > While there is little or no radiation, it is still looking at something > > only a few inches away from your face. I would think this is not good > > and could cause some pretty bad eyestrain. > > Well, not really. The screen is only a few inches from your face but it > is optically much farther away. Some people say "Optical infinity" but it > seems more like one meter or so to me. Well, that makes sense... So I guess eyestrain would be only as bad as using a normal monitor (more or less). > > I wonder what the effect of the optics are on the LCD screen. I would > > hope they take the screen farther away from your eyes and enlarge it, > > They do make the screen seem farther away but they don't really "enlarge" it. > Well they do, but not really. it's like this: > > /| > / | > / | > / | > / | > / | > /| | > / | | > / | | > Your eye-----> . | | You are looking this way ---> > \ | | > \ | | > \| | > \ | > \ | > ^ \ | > | \ | > | \ | > | \| > | > | ^ > | | > The "real" position ---+ +--- The optical position of the screen. > ofn the LCD screen > > So the screen "looks" bigger because you think it's farther away, but it does > not subtend a greater solid angle so it's not really "enlarged" That's disappointing. I would think it would be good to make the screen appear enlarged, but I guess at a few inches from your face, the display would have a large angle. > > Also, in a couple weeks, I will start to work on a simple 3D graphics > > system that has perspective views. I will write it in Turbo C, and > > I will post it (or send it to the new cheap-VR ftp site). I plan on > > using a hierarchical structure similar to PHIGS, and it will be flexible > > with color and depth cueing. If anyone has comments or suggestions, > > please email me... I plan on not supporting lights, but I think I > > will leave some hooks to allow expansion... > > What are you trying to get? There are many public domain 3D graphics > systems out there that support all of this. If you are trying to really > understand 3D than this is the way to go but if you just want to be able > to draw things get something like the simple phigs package from brown > university. (Mail to spr@cs.brown.edu because I can't find the IP number) > they have a PHIGS package that runs with the X-Window system. I would rather write my own so that it is easy to use with a PC and easy to modify. Actually, I cranked out a big part of it last night. I already have functions to generate all the matrices, and I plan on re-writing them to use fixed-point instead of floating-point (I don't have the $400 for a 387). I also have the hierachical structure setup to allow executing other structures... It will only allow polylines and polymarkers, since the VR system I will make won't be able to handle polygons (386's are too slow). But I will leave hooks for this so that it can be added later (I also have code for fast polygons...) Greg
uselton@nas.nasa.gov (Samuel P. Uselton) (06/05/91)
In article <1991Jun5.031158.15999@milton.u.washington.edu> kilian@poplar.cray.co m (Alan Kilian) writes: >galt@hellgate.utah.edu (Greg Alt) Says: > >> It seems that CRT's are a possible health risk and should not be used >> right up against your eyes for a long time. > >That debate rages on and until I see some more articles I am not going >to put any CRT based displays right in front of my eyes. The "Light valve" >designs seem much safer in the mean time. Just a quick comment on this discussion. I don't claim to be a medical expert OR to play one on TV, however, we (NASA Ames Research Center, NAS Systems Division, Applied Research Branch) commissioned Mark Bolas of Fake Space Labs to do some digging on this topic. Bottom line: Exactly what Alan says, IF you are discussing COLOR CRT's: no conclusive results, lots of opinions, better wait until good studies are complete. However, black & white CRT systems are MUCH lower voltage, lower radiation and EM fields, etc, so no responsible eye researcher seems to claim terrible things about having them close to your face. We are investigating ways of putting color into our boom mounted viewing/tracking system. Mark, Steve Bryson and Creon Levit (our two main VR guys) seem to have a plan for at least some color while still using B&W CRTs. I'll wait until I see details or a demo before I promulgate those rumors further. If you really want to know soon, ask them. > > -Alan Kilian > > -Alan Kilian kilian@cray.com 612.683.5499 > Cray Research, Inc. | "The Fragile X Syndrome may me the most > 655 F Lone Oak Drive | frequent cause of inherited mental > Eagan MN, 55121 | retardation". Science 24-May-1991 PP1097 Sam Uselton uselton@nas.nasa.gov employed by CSC working for NASA (Ames) speaking for myself
fenwick@clipper.ingr.com (Steve Fenwick) (06/06/91)
In article <1991Jun5.031158.15999@milton.u.washington.edu> kilian@poplar. cray.com (Alan Kilian) writes: >galt@hellgate.utah.edu (Greg Alt) Says: > >> It seems that CRT's are a possible health risk and should not be used >> right up against your eyes for a long time. >That debate rages on and until I see some more articles I am not going >to put any CRT based displays right in front of my eyes. The "Light valve" >designs seem much safer in the mean time. (I don't claim to be an eye expert, but I do listen to my opthamologist.) There's a different risk, and much more important, and that's forcing one's eyes to focus at a more-or-less fixed distance for extended (>20 minutes) periods. The eye apparently gets conditioned to this, and tends to lose its ability to focus across a wide range of depths. This is not just a problem at very close (e.g., eyeset) distances, but also for normal CRT users, heavy readers, etc. Give your eyes a break; focus on something other than your CRT at least every 20 minutes. Steve Fenwick -- fenwick@clipper.ingr.com or scf@btr.com | Intergraph APD, 2400 Geng Road | PP-ASEL-IA at last! Palo Alto, California 94303 | Let's bust a cloud! (415) 852-2325/494-8800 |