louk@tslwat.UUCP (Lou Kates) (02/21/90)
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
michiel@idca.tds.PHILIPS.nl (Michiel Fierst van Wijnandsbergen) (02/22/90)
In article <146@tslwat.UUCP> louk@tslwat.UUCP (Lou Kates) writes: >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 My original Follow-up failed I believe. Here it is again. Sorry if I posted it twice now. I did it a few times. Here's how: Put up your tripod to have the display full in your finder. Measure the time you need. Choose an exposure time/aperture that is 1 of 2 stops over what you measured (+1 or +2). I would take two pictures; one at +1 and one at +2. If your screen has bright text on a dark background that is. If your screen is reverse use -1 and -2 instead. If the image is full color or a normal tv set, don't correct the time at all. Make sure your exposure time is at least twice as long as the screen refreshing frequency. Usually this is 1/30 for 60Hz screens, or longer. The longer the the, then better it is up to a time of about 1 second. Don't use longer times. Good luck. -- # Michiel Fierst van Wijnandsbergen Internet fierst@idca.tds.philips.nl # # Philips Telecomm. and Data Systems UUCP ...!mcvax!philapd!fierst # -- # Michiel Fierst van Wijnandsbergen Internet fierst@idca.tds.philips.nl # # Philips Telecomm. and Data Systems UUCP ...!mcvax!philapd!fierst #
jsivier@ux1.cso.uiuc.edu (Jonathon Sivier ) (02/23/90)
In article <146@tslwat.UUCP> louk@tslwat.UUCP (Lou Kates) writes: >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. I have done this many time and gotten very good results. Make sure you take the picture in a darkened room so you don't get any glare off the glass front of the CRT. Use a tripod and a shutter speed of at least 4 times the refresh rate of the monitor (i.e. if the monitor is 60 Hz your shutter speed should be a minimum of 1/15 sec.). This is to reduce the effect of the black banding you would get at a higher shutter speed. In general the longer the exposure the better. Take your exposure reading directly off the screen with no other light sources and I would recommend bracketing your exposure, take several shots with some above the "correct" exposure and some below. For example if the correct exposure was f4 at 1/4 second take three shots, one at this setting and one each at a half a stop over- and underexposed. Good Luck. Jonathan Sivier jsivier@ux1.cso.uiuc.edu
kevin@msa3b.UUCP (Kevin P. Kleinfelter) (02/23/90)
louk@tslwat.UUCP (Lou Kates) writes: >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 Years ago, when I was using a TRS-80 Model I (see...I SAID it was years ago), I played with this just for grins. I was using black-and-white print film, and I never made prints (just developed the negatives). Use a tripod, and FILL the frame (I hope you are using a SLR, otherwise filling the frame can be tough). Use a shutter speed no faster than 1/30 of a second to avoid problems with the scan rate on your terminal (these problems are similar to flash sync). Be sure to note exactly where the brightness and contrast knobs on your monitor are set. It would be meaningless for me to tell you what f-stop and film speed to use, because I do not know how bright your monitor (and image) are. Try a relatively slow film, to reduce granularity (about an ASA 200 or an ASA 64). Then get a 12 or 24 exposure roll, and shoot some test shots, bracketing widely (i.e. try each full stop from F-4 through F-22). If you use print film, don't bother printing this test roll, you just want to examine the negatives under a magnifying glass, to see what works. (Uhh, hmmm... you DID note which frames had which settings, didn't you?) Actually, putting the settings on the screen can be a good reminder. I found that black-and-white was easier to get right, because a lab will do really strange stuff to your colors if you use color film. -- Kevin Kleinfelter @ Management Science America, Inc (404) 239-2347 gatech!nanovx!msa3b!kevin
adb@alice.UUCP (Alan Berenbaum) (02/27/90)
From the brochure "KODAK Scientific Imaging Products", pages 26 and 27:
Photographing TV and Computer Screen Images
It is a relatively simple task to record a color or monochrome image
displayed on a television set, monitor, or computer screen. Although
a 35 mm single-lens-relfex (SLR) camera is recommended for ease of
focusing and framing the image, any automatic or adjustable camera will
yield good resutls. Close focusing capability is a must if the screen
image is to fill the film frame.
Several options are available: use a camera with a close-focusing
(macro) lens, use a lens with a fixed focal length of about 100 mm,
use "tele-extenders' to increase the focal length of a normal lens, or
use a supplementary close-up lens on a normal 50 mm lens. A lens of longer
focal length, (e.g., one of 100 mm), minimizes the effect of screen
curvature. You also need a stable tripod or platform because exposure
times are too long to permit hand-holding the camera.
Shutter Speed
Becuase images on a television or computer screen are formed line-by-line
by a rapidly moving electron beam, you can obtain a complete picture of the
screen only if the camera shutter speed is slow enough to allow the moving
beam to complete its scan. To avoid photographs with dark or light "banding,"
the beam should complete many scans.
TV images typically are composed of 525 horizontal scan lines (U.S.
standard) or 625 scan lines (the standard adopted by other countries).
For the U.S. standard, a complete scan takes 1/30 second (1/60th for the
odd- and 1/60 for the even-numbered lines). Theoretically you should use
a shutter speed no faster than 1/30 second, or 1/25 second for a 625-line
picture. These times are for a camera with a leaf shutter; for cameras
with a focal-plane shutter, reduce shutter speed to 1/8 second in order
to avoid getting a dark band across your picture and to stop TV action
scenes.
For computer screens, however, the subject is not moving and the
resolution requirements are much higher. Also, photographs are frequently
made of charts or graphs with light-colored backgrounds, and which show up
dark bands particularly well. When photographing computer screens, you can
obtain the best results with exposure times of 1/2 to 1 second. This exposure
puts many images of the screen on the film to minimize the effect of
"banding"--a film speed of ISO 100 is ideal.
Adjusting The Screen Image
Reduce the contrast of the screen image to slightly below the setting for
normal viewing. For a black-and-white image, adjust the brightness control so
that there is detail in the highlights and also in the shadows. For a color
image, adjust the color controls so the image is visually pleasing.
If your TV, monitor, or computer has an automatic brightness control--
one that varies image brightness in response to changing levels of room
lighting--turn the control off and adjust the brightness manually. For
computer screens, reduce the brightness so there are no scan lines visible on a
black screen.
Room Lighting
Darken the room completely if possible, or to a practical level to reduce
ambient illumination. Doing so helps make the area around the screen image
appear black in your pictures. A black surround is usually more pleasing than
a lighter one or one reflecting part of the room. If you photograph screen
images frequently, consider using a specially devised black "tent" or cone that
fits tightly around the screen.
Do not use flash or other lighting to illuminate the screen; it will
overpower the screen image. If you camera is equipped with automatic flash,
disable it or cover the flash with a piece of cardboard or other opaque material.
Film Recommendations
Use daylight color film to photgraph images on color screens. Color pictures of
color screen images may have a blue-green appearance because the sensitivity of
the film is different from that of the eye. Use a slow film, e.g., KODAK
EKTACHROME 100 Profressional Film. This film speed will call for a 1-second
exposure at f-8 to f-11. A 400-speed film may be too fast; you will not be
able to stop down to near f-11. Excellent photographs of computer screens are
made using small f-stops (to account for screen curvature) _and_ long shutter
speeds. KODACHROME 25 Professional Film has produced very good results.
To improve color rendition with KODACHROME and EKTACHROME Professional Films,
you may need to use a KODAK Color Compensating Filter CC10 or 20R over the
camera lens and to increase the exposure by 1/3 stop. Use a CC20B filter with
a color negative film such as KODAK VERICOLOR III Professional Film, which
provides brighter colors than and increased color contrast over the "conventional"
100-speed film. Experiment with this film, becasue it works better with some
phosphors than others.
You can also use the above color films to record the white, green, or amber
images from monochrome computer screens (without the use of color compensating
filters), or use black-and-white films if you do not need to retain the green or
amber colors in the picture.
[herein are listed a number of KODAK films. It is, after all, a KODAK document.]
Exposure Determination
Choose the correct shutter speed (1/2 to 1 second for computer screens and
1/4 to 1/8 second for TV images), and leave the f-stop stetting to be determined.
Consult your camera manual to determine how to set exposures with an essentially
fixed shutter speed.
Cameras equipped with a built-in exposure meter are useful, but the TV or
computer screen should fill the image area when the reading is taken. For
typical displays of "average" color and brightness content, you meter should
yield correctly exposed slides. For predominantly bright displays, bracket
exposures on the "overexpose" side; for predominantly dark screen displays,
bracket on the "underexposure" side. If you have through-the-lens metering
and you are using a color film with a color compensating filter over the camera
lens, your camera should automatically increase exposure to compensate for
attenuation by the filter.
To be sure of getting a properly exposed picture, bracket your exposures.
In 1/3-stop increments, overexpose or underexpose 1 full stop from any
calculated exposure.
Selected Reference
Eastman Kodak Company 1986. Photographing Television and Computer Screen
Images (AC-10).
To order publications from KODAK, write to:
Eastman Kodak Company
Dept 412-SP
343 State Street
Rochester, New York 14650-0608
Copied without permission, but then, it was a free catalogue, so I don't
think they'll mind.
Alan Berenbaum adb@research.att.com
AT&T Bell Labs
Murray Hill, NJfrancis@chook.ua.oz (Francis Vaughan) (02/27/90)
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
gords@cognos.UUCP (Gord Smith) (03/01/90)
In article <1255@msa3b.UUCP> kevin@msa3b.UUCP (Kevin P. Kleinfelter) writes: >louk@tslwat.UUCP (Lou Kates) writes: >>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. >[Many good tips] I've never done it myself, but I've been told that in order to avoid funny curving of the ouline of the screen in the corners, you should place the camera as far as possible from the screen use a zoom lens to fill the picture with the screen. This 'flattens' out the picture. Hope this helps. -- D. Gordon Smith Voice: (613) 738-1338 ext 6118 P.O. Box 9707 Cognos Incorporated FAX: (613) 738-0002 3755 Riverside Dr. uucp: gords@cognos.uucp || uunet!mitel!sce!cognos!gords Ottawa, Ontario "Very clever, Worf. Eaten any good books lately?" - Q CANADA K1G 3Z4
djb@bbt.UUCP (beauvais) (03/01/90)
In article <146@tslwat.UUCP> louk@tslwat.UUCP (Lou Kates) writes: >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. > I have several suggestions: Use a longer focal length lens - 100 mm or above. Telephoto lenses compress depth, minimizing the effect of the curved CRT screen. Stop down the lens for greater depth of field. This is necessary because of the curved CRT screen. Use a tripod. That way, you only have to align and focus once, and you can do it all with the lights on! (More on that later) Make sure your lens axis is at a right angle to the screen. Lighting is simple - NONE!!!! Shut off ALL lights or completely shade the screen or you will get reflections, or at a minimum, a washed out screen. Don't use a flash! The image on the screen provides all the light the exposuer needs! Your shutter speed should be 1/30 of a second or slower (1/15, 1/8.....). Otherwise, part of the screen will be much brighter than the rest because the shutter wasn't opened long enought for a full retrace of the CRT image. I determined my exposures by writing a program which flooded the screen with a gray color - assumed to be halfway between all black and all white. I made a meter reading from it. If this is not possible, I would try flooding the screen with characters, meter off this screen as a starting point, then bracket your exposures a couple of stops in either direction. Use a slower, finer grained film. Kodachrome 25 or 64, or Fujichrome 50 for slides, T-Max 100 or Tech Pan for B&W, Kodacolor 100 for prints. E-mail if I can help any further. Good luck!