Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!husc6!purdue!bu.edu!slehar From: slehar@thalamus.bu.edu (Steve Lehar) Newsgroups: comp.sys.sgi Subject: Re: photographing the screen Message-ID: Date: 25 Oct 90 13:10:39 GMT References: <26308.27257d14@kuhub.cc.ukans.edu> Sender: news@bu.edu.bu.edu Organization: Boston University Center for Adaptive Systems Lines: 64 Photographing the IRIS screen and making slides is the most effective way of presenting your results at conferences and meetings, etc. I have done this several times, and the resolution of the slide captures everything on the screen with good fidelity, especially if you zoom your imagex up 2x. I usually use a regular 35mm camera on a tripod in a darkened room. Be very careful about reflections on the screen- it is amazing how you can look at the screen and see no reflections, but when you look at the pictures you see a prominent reflection from a power or "on-line" light of a printer or computer, or from a tiny crack in the window shade. Your brain filters these things out because they are at a different focus- until captured on the photograph. Be very careful to level the camera- in the viewfinder measure the angle between the bottom of the screen and the bottom of the viewfinder- get them exactly parallel. This is another thing that you might not notice otherwise, but looks very odd when you project your slides to the audience with a 2 degree list to starboard. Likewise, center the screen exactly in the frame. Move the pointer to the bottom-right of the screen where it disappears except for one last pixel. Again, if you are not thinking, you will not notice the pointer because you are so used to seeing it. When you see the photographs however it will appear prominantly distracting. Another thing that strikes you when you see the slides is the curvature of the lines due to the curved screen. You normally pay no attention to this because your eye compensates for it- like looking at a line of lattitude on a globe (looks straight) compared to seeing a projection of that globe onto a flat map (looks curved). Make sure that you are looking straight-on at the screen, so that the curve-up at the top of the screen is symmetrical with the curve-down at the bottom. This is done by aligning the camera exactly on the normal to the center of the screen. The curvature can be minimized by setting the camera far from the screen and using a zoom lens. Use a film speed that will "average over" many screen refresh cycles. If you set your exposure to 1/30 of a second for instance, you are unlikely to catch exactly one screen refresh, probably 0.9 or 1.2 or something, which will create funny looking results where there is a gap or an overlapping region. If you set for 1 second, then some parts of the screen will have been refreshed 30 times, and some parts 29, or 31 times. This ratio is sufficient to make the difference not noticable. I.e. use a long exposure time- this means of course that you must either use a remote cable trigger, or a delayed trigger, to avoid shaking the camera with your finger. When using a built-in light meter, zoom the lens to remove all the background blackness, set the lens till the light meter is satisfied, then un-zoom again for taking the pictures. In other words, don't let the border blackness (off the screen) influence the reading of the light meter. Straddle the settings that the light meter recommends- i.e. take three exposures for each frame, at three adjacent settings, to make sure that one of them is ok. The perfect setting may well depend on the type of image you have- are you interested in the detail in those dark corners, or do you want to examine the brighter regions. -- (O)((O))(((O)))((((O))))(((((O)))))(((((O)))))((((O))))(((O)))((O))(O) (O)((O))((( slehar@park.bu.edu )))((O))(O) (O)((O))((( Steve Lehar Boston University Boston MA )))((O))(O) (O)((O))((( (617) 424-7035 (H) (617) 353-6741 (W) )))((O))(O) (O)((O))(((O)))((((O))))(((((O)))))(((((O)))))((((O))))(((O)))((O))(O)