Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!munnari.oz.au!sirius.ucs.adelaide.edu.au!chook.ua.oz From: francis@chook.ua.oz (Francis Vaughan) Newsgroups: comp.misc Subject: Re: photo of crt Message-ID: <780@sirius.ucs.adelaide.edu.au> Date: 27 Feb 90 09:25:48 GMT References: <146@tslwat.UUCP> Sender: news@ucs.adelaide.edu.au Lines: 78 From article <146@tslwat.UUCP>, by louk@tslwat.UUCP (Lou Kates): > Does anyone have any experience in taking photos of what is on a CRT screen? > What lighting, if any, should be used, what f stop, what shutter speed? I > am using a 35 mm camera. > > Lou Kates, Teleride Sage Limited, ...!watmath!looking!tslwat!louk > 519-725-0277 I have done this quite a bit. My method is reasonably simple and gives very good results. 1. Get a tripod. 2. Use a good slow film (I use 100 ASA kodacolor for prints and kodachrome 64 for transparencies. 3. Very carefully set the camera up on the tripod so that the camera is square on. I used to use a program that generated a course grid on the screen. You may have some problems focusing close enough to the screen with a normal lens. A macro lens may be needed. Try to get the screen to fill to viewfinder. 4. Do the photography in a completely dark room. Even a small amount of ambient light will degrade the contrast of the image. 5. Set up the monitor so that it looks good in the dark. Mostly you will find that the brighness and contrast are too high as people crank it up to compete with the normal lighting. A test pattern of colours ranging from darks to full on brights is good (I used to use on with three HLS circles, a lot like the ones a Mac uses on the control panel for setting colours). Tweak the contrast and brightness so that the gradation of colours and brightnesses is seen across the range. Watch out that the bright bands don't have any flare. 6. Work out the exposure. The method I use is about as good as I can think of. Fill the screen with pure 100% white. (This must be done after the tweaks done in 5 for obvious reasons.) Start with an f stop of about 22. Now, using the cameras internal meter work out the exposure time (often in the order of seconds). You may need to juggle the f stop if the camera will not give a long enough exposure. Once you have the exposure time set, open the lens f stop by two and a half stops (ie, if set to f11 open it to mid way between f5.6 and f4). Once this is done you may need to trade f stops for exposure time. IE close down one stop (ie f8 to f11) double the exposure time. Do this enough to get the exposure time into the seconds. If the exposure is much less than a second you will get dark bands on the photo due to a lack of synchronisation between the raster scan and the shutter. A long exposure lets this even out. A high f number also helps to improve the depth of field, very useful if the screen is curved. (If the screen is curved you may get some distortion of the image, this can be aleviated by using a longer focal length lens, and shooting from a longer distance, so long as you have a choice of lenses or a zoom, never use a wide angle lens. 7. Take the pictures. A cable release is very useful to help eleminate camera shake. 8. Process the pictures. If you take tranparencies you will have no trouble. If you take prints you may have a fight with the processing lab (or more to the point their brain dead colour correction computer). 1 hour, corner shop places are the worst, but the cheapest. They will happily ruin the colour balance of a lot of pictures because they assume that you have taken nice pictures on your holidays not of a red sphere against a black background. This will come back as an amber sphere against a grainy light blue-grey background. What is worse is that these places often cannot turn off the compensation. Professional labs, will charge a lot more, but understand (and deliver). 9. Write down what worked. So you can use it again. Hope this is of some use to someone. Dept of Computer Science Francis Vaughan University of Adelaide francis@cs.ua.oz.au South Australia