robert@shangri-la.gatech.edu (Robert Viduya) (11/26/89)
Has anyone advice or pointers to information on how to photograph video screens? I'm trying to shoot the screen of an SGI 4D/120GT. I experimented with a Canon AE-1 with shutter speeds of 1/15 sec and 1/8 sec and let it choose the aperature. I was also using ASA 400 film. The results left a bit to be desired. I lost a lot of red tints except where the color was solid red and then it stood out too much. A lot of fine detail was lost as well. I probably should've used a lower film speed like possibly ASA 200. I also suspect that the color balance was screwed up in the development process and I was wondering what I could do to prevent that in the future (I don't do my own development). Any help would be appreciated. robert -- Robert Viduya robert@shangri-la.gatech.edu Office of Computing Services Georgia Institute of Technology (404) 894-6296 Atlanta, Georgia 30332-0275
rsingh1@dahlia.waterloo.edu (11/27/89)
In article <3777@hydra.gatech.EDU> robert@shangri-la.gatech.edu (Robert Viduya) writes: >Has anyone advice or pointers to information on how to photograph video >screens? I did a bit of this not too long ago. I'm no ace with a camera though, but the following info might help: The film I had the best results with was Kodak Echtochrome 64 (sp?). It seems to bring out the blues a bit more, which seems to suit the monitor quite well. Shutter speed I used was, if I remember correctly, quite short. I guess you want a shutter speed faster than 1/60th of a second (ntsc). I played around with lots, so I might be wrong on this. Something that botched up some of my pictures was the monitor I was using. In the lower right corner, there was a definite darker region than the rest of the monitor. Playing with the contrast/brigtness helped a lot. It would be kind if you could forward any advice you get to me. Or summarize to the net if you get lots. Later
sow@cad.luth.se (Sven-Ove Westberg) (11/27/89)
In article <18678@watdragon.waterloo.edu> rsingh1@dahlia.waterloo.edu () writes: | |Shutter speed I used was, if I remember correctly, quite short. I guess |you want a shutter speed faster than 1/60th of a second (ntsc). I played |around with lots, so I might be wrong on this. | A short shutter speed couses a dark band over the image. Since beam have to trace the entire image atleast once. I use a stable tripoid and a shutter speed around 0.5 sec. You have to try out the exact exposure figures for the screen you use. Sven-Ove Westberg, CAD, University of Lulea, S-951 87 Lulea, Sweden. Internet: sow@cad.luth.se
bio_zwbb@jhunix.HCF.JHU.EDU (Dr. William B. Busa) (11/27/89)
A short but detailed discussion of tricks for photographing video monitors can be found in the book: Video Microscopy by Shinya Inoue Plenum Press, NY 1986 (see pp. 423-432) This work also cites an Eastman Kodak booklet (which I've not seen), entitled "Photographing Television Images" I've found it helpful to use a zoom telephoto lens (80 - 200 mm), thus setting the camera as far away from the monitor as possible, reducing the effects of screen curvature. -- Dr. William Busa, Dept. of Biology, The Johns Hopkins University, Charles & 34th Sts., Baltimore, MD 21218 (301) 338-8207 bio_zwbb@jhunix.hcf.jhu.edu uunet!mimsy!jhunix!bio_zwbb
dennisw@tekigm2.MEN.TEK.COM (Dennis Ward) (11/27/89)
Check out the Polaroid/hood offering from Tektronix. They have a good choice of film and PC-size hood. -- Dennis Ward dennisw@tekigm2.MEN.TEK.COM C1-820 (206)253-5428
thant@horus.sgi.com (Thant Tessman) (11/28/89)
Some things I've discovered that help make better off screen pictures: At least 1/30 exposure time (as someone else mentioned). Requires using a tripod. Minimize reflections off the screen. (Turn off the lights. Cover the windows.) The farther away from the screen you can get, the less the curvature of the screen warps the image, so if you have a zoom lens, use it. Make sure the monitor's brightness is adjusted correctly. The way I do it is to display solid black, turn up the contrast all the way, and turn down the brightness until I can't see any 'leaks' in the display. (I saw a guy who knew more about monitors do it differently, but I can't remember what he did.) Make sure the gamma is adjusted correctly. On SGI's there is an image at /usr/people/4Dgifts/iristools/images/gamcal.bw that is a bunch of alternating stripes of black/white dots and grey areas. The more correct the gamma, the harder it is to see the stripes. Use the 'gamma' command. Most important: Display a pattern of either solid 50% grey, or alternating black and white stripes. (If the gamma is adjusted correctly, they should be about the same brightness.) Use this to find the appropriate apperature for a good exposure for all the images. Don't let the camera try to compensate for large fields of black. This will just overexpose the bright parts. I haven't messed with color filters, so I don't know if it's worth it trying to compensate for the temperature of the monitors or the film. If you're spending someone else's money, there are color printers and cameras that do the right thing. Good shooting. thant
davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) (11/28/89)
There are several things which I have found help good pictures. The first is a long exposure from a tripod to eliminate retrace showing up. The second is to move the camera as far from the tube as you can and stil frame it. I use a telephoto zoom. This helps overcome the curvature of the screen. Best trick is a Zenith flat tension mask monitor, which has a true flat surface. Oh, and a dark room is the easiest way to kill reflections I've found. -- bill davidsen (davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen) "The world is filled with fools. They blindly follow their so-called 'reason' in the face of the church and common sense. Any fool can see that the world is flat!" - anon
shirley@m.cs.uiuc.edu (11/28/89)
We use 100 speed film for both prints and slides. We want a slow high quality film, and this is the slowest that we can get processed quickly. We want a slow shudder speed to avoid electron gun visiblity, but not too slow to avoid nonlinearity problems in the film. For our monitor we usually use an f8 apature for about half a second. We get as far from the screen as we can to avoid distortions near the corners of the image. If you have a zoom lens it helps. We usually use slides because it seems to give the lab less of a chance to "correct" (screw up) the colors. Taking some shots of color bars at the beginning of the roll seems to help. Like monitors, films have their own gamma. We've found that with Ektachrome 100 the whites are white, the blacks are black, and the greys are too dark. Our monitor's gamma is around 2.3. We've found that using a gamma of about 3.0-3.2 we get better results with Ektachrome. The image looks crummy on the screen (washed out) but the photos look much better. You may find that even with a 24-bit monitor you see contouring. This can be especially true in photos. To avoid this we often dither in the 24 bit image (I think Roy Hall's book suggests this). When you've found an intensity between 0 and 1 and are about to output this as a byte, use "byte = floor (254.99999 * I + random_from_0_to_1)". If you don't have the ability to gamma correct your monitor, then you might want to first raise I to an exponent: I = I**(1.0/gamma). peter shirley shirley@m.cs.uiuc.edu
Classic_-_Concepts@cup.portal.com (11/28/89)
Re: request for help on photographing screens
I've done a lot of this. From experience, here's what I recommend:
1. Ektachrome 100 or Kodachrome 64 (or similar low ASA color slide
film). Fujicolor 100 is also good for prints.
2. Approximately 1/2 second exposure but BEWARE, the amount of
exposure can vary WIDELY with the amount of light and color
values present in the image being photographed. Meter for the
image, then always bracket two extra exposures (take a +1 and a
-1 exposure). Slight underexposure yields more saturated color.
Too fast a shutter speed results in diagonal scan lines showing.
3. ALWAYS shoot a TEST screen first. This has two benefits:
a) the processing lab can set slide mount in the right spot,
and adjust colors correctly for prints
b) you can set up your camera on the tripod more accurately
The test picture should consist of a SYMMETRIC image (or nearly
so, this helps you and the photo lab) with primary colors in
large blocks, some secondary colors and black and white, plus
a large cross hair and border AND a rectangle and/or circle in
the center which approximates what you seen through the lens
of your camera. If you line up only on the outer borders of the
screen, it's not necessarily lined up--you'll find it can look
'right' and the center might still be way off.
4. Always shoot in a darkened room; you may not see the glare, but
the film will record it. I shoot in the evenings. I also cut
out a black mask, from construction paper for the monitor, so
the light monitor doesn't glare onto the screen. You can buy
monitor hoods, but personally, I think they're overpriced.
5. Use a small monitor, if possible, less curvature and more satu-
rated color.
6. If there is more than one graphics mode, set it on the highest
resolution (e.g., Setlace on an Amiga will double scan lines
producing more saturated colors).
7. Try, if possible, not to create images that go right to the edges
of the screen. Unless you have very high depth of field, you
won't be able to focus both on the outer edges and the inner part
of the image, again because of curvature.
8. Remember to hide your cursor. Sigh--I know this sounds obvious,
but you'd be amazed how many people forget, they're so busy getting
everything else perfect. A cursor in the middle of a great graphic
is an unpleasant surprise when you get your pictures back.
9. I've gotten best results with a telephoto lens or macro lens.
70 mm seems good. In the early days I shot with 50 & 55 mm and got
too much distortion on the edges.
10. ALWAYS use a tripod and a cable release is a good idea too.
11. After every 3 or 4 shots, you should redisplay your test
screen and recheck the viewfinder to see if you're still
lined up.
Even with all this preparation, you can expect uneven results. I get
photos that range from above average to good (for excellent, you need a
direct film recording process). Some of them even look film recorded, de-
pending on the resolution and structure of the picture being photographed.
Screen shots are good for meeting deadlines and creating proofs. For really
high quality, send your diskettes to a service bureau, but get a sample first
I've found service bureaus that produce images ranging from very bad to
superb with a variance of only about 20% in price.
\_
)\_ _/
`/)\_ __ //
__ _____________________________________________ `\\)\_ / '~//
/// Julie Petersen (LadyHawke@cup.portal.com `\\//\\/|'//'
/// Classic_-_Concepts@cup.portal.com) (\/Yyyy/'
__ /// The things he said have never been disproved, /Yyyy/'
\\\ /// only dismissed. --Peter Reich //\\ LadyHawke
\\/// ______________________________________________ ///\\\ John.Mood@p110.f12.n376.z1.FIDONET.ORG (John Mood) (11/28/89)
In an article of <25 Nov 89 17:42:23 GMT>, robert@shangri-la.gatech.edu (Robert
Viduya) writes:
RV> From: robert@shangri-la.gatech.edu (Robert Viduya)
RV> Date: 25 Nov 89 17:42:23 GMT
RV> Organization: Office of Computing Services, Georgia Tech
RV> Message-ID: <3777@hydra.gatech.EDU>
RV> Newsgroups: comp.graphics
RV>
RV> Has anyone advice or pointers to information on how to photograph
RV> video
RV> screens? I'm trying to shoot the screen of an SGI 4D/120GT. I
RV> experimented with a Canon AE-1 with shutter speeds of 1/15 sec and 1/8
RV> sec and let it choose the aperature. I was also using ASA 400 film.
Take and lock your shutter speed at 1/15 then bracket DOWN (smaller
f-stops) from the camera's choices for aperture. I think this may help you
prevent washout of the colors in the brighter areas. You will need to operate
the camera manually.
RV> balance was screwed up in the development process and I was wondering
RV> what I could do to prevent that in the future (I don't do my own
RV> development). Any help would be appreciated.
You might want to go to a custom lab, and tell them that the first frame
is a greyscale card (available at your local custom printing labs). Tell them
to balance for color on that, then lock the settings for color balance. Most
labs will automatically evaluate the color balance on each frame, based on an
average of what appears in 'most' frames. This is obviously not worth a toot
for screen photos... It's there on the film, and not screwed up in development.
It's the color balance on the photo printer.
John Mood
P.O. Box 12352
Columbia, S.C. 29211-2352
Disclaimer: Hell, I ain't even responsible for what I do!
--
--
John Mood == ...!usceast!uscacm!12.110!John.Moodjwi@cbnewsj.ATT.COM (Jim Winer @ AT&T, Middletown, NJ) (11/28/89)
> Robert Viduya writes: > >Has anyone advice or pointers to information on how to photograph video > >screens? rsingh1@dahlia.waterloo.edu writes: > Shutter speed I used was, if I remember correctly, quite short. I guess > you want a shutter speed faster than 1/60th of a second (ntsc). I played > around with lots, so I might be wrong on this. (sorry if I got the attributions backwards). This information is WRONG! Your shutter must be open at least one full (and preferably two full) screen write cycles which are usually 1/30 second. Speeds of 1/30 to 1/15 should work for most screens. (The shutter is a traveling window. It is not all open at the same time -- the first curtain opens and the second follows to close it resulting in a traveling slit at high speed. To capture the screen, you must have the speed slow enough that the entire shutter is open at once long enough for the screen to write an image.) To avoid loss of detail, it is essential to use a very solid tripod or vibration (including the mirror movement in the camera) will cause blur. The speed of the film won't make that much difference between about 25 and 400 since the camera will adjust the f-stop. The finer grain of slower speed film is wasted when the monitor has a maximum resolution of around 72 dots/inch. Some types of *slide* film have a slightly different color balance, notably Ektachrome and Fujichrome -- but in general, this is a waste of time since the adjustment of the monitor will have much (several orders of magnitude) greater effect. I would suggest 100 speed slide or print film. Turn off the room lights or use a hood. Reflections will cause problems. See what arpeture the camera picks and then shoot additional picutres at -1, -2, +1 and +2 f-stops for slides or at -2 and +2 for prints. After a few test rolls, use the setting that works the best in the future. The slides will show you reasonably true colors. The prints are another story (see below). In both cases, you may want to use an ultraviolet filter over the lens to avoid color distortion be light you can't see. For slides, the colors are as they are taken (with any ultraviolet distortion). For prints, the colors are usually screwed up by the processing lab. The problem is that the automatic print making machines are set to balance the color to an average gray. Whenever you have a picture with a solid background that is not gray, you get what is called "subject failure." That means that the picture itself (unlike most snapshots) does not balance to average gray. For example, if the background is blue, the print will be too yellow to attempt to make it balance to average gray. Your best bet is to use a local lab and tell them that the roll of print film has "subject failure" and that they should lock the machine at the base setting for the film type when printing instead of letting it pick the color balance. (The base setting is the setting that would be used for an exactly average snapshot that already balances exactly to gray. The base setting does not cause distortion.) Good luck! Jim Winer ----------------------------------------------------------------- opinions not necessarily | "And remember, rebooting your brain and do not represent | can be tricky." -- Chris Miller any other sane person | especially not employer. |
klee@chico.pa.dec.com (Ken Lee) (11/29/89)
While we're on the subject, I've had excelent results with Polaroid slide film. Your boss will probably be really impressed when you have a slide show ready in 30 minutes. Of course, he/she may take advantage of your speed and make you "improve" it. Ken Lee DEC Western Software Laboratory, Palo Alto, Calif. Internet: klee@decwrl.dec.com uucp: uunet!decwrl!klee
nick@sunpix.UUCP ( Sun Visualization Products) (11/29/89)
Forgive me if this goes out twice - I got back some garbage and am trying from a different machine --------------------------------------------------------- In article <18678@watdragon.waterloo.edu>, rsingh1@dahlia.waterloo.edu writes: > In article <3777@hydra.gatech.EDU> robert@shangri-la.gatech.edu (Robert Viduya) writes: > >Has anyone advice or pointers to information on how to photograph video > >screens? > ..... > > Shutter speed I used was, if I remember correctly, quite short. I guess > you want a shutter speed faster than 1/60th of a second (ntsc). I played > around with lots, so I might be wrong on this. > Maybe everyone knows this, but here are some hints gained from long years of experience - some of my screen shots are in the first SIGGRAPH proceedings (1974). Your monitor is putting up a complete picture in 1/60 (noninterlaced displays) or 1/30 (interlaced) second. If you use a shorter exposure, you won't get the whole picture. Your best bet is to use 1/2 second or 1 sec - if you get 15.25 or 29.75 frames it won't matter too much - assuming you've got a still image on the screen!!! I find Ektachrome 100 or 200 does pretty well - stop down to f/8 or so and you'll have some depth of field to accomodate CRT curvature. Always bracket your exposures +/- a stop or two. Using up film is much less of a pain than going through the whole process all over again. If you use your meter to check exposure, remember to consider your total image - if you meter a small white area (text) on a big black background, you'll get the wrong answer - by a couple of stops !! Think of it this way - your camera meter will give you a great exposure of a grey object. If what you meter is mostly black, then the camera will try to make that grey - close down to make it black again. If you are shooting black text on a white background, then open up a few stops. Record what you shoot - look at the results and write them down for future use - assuming you don't fiddle with the brightness and contrast in the meantime. Another hint is to use a longer than normal lens (for a 35mm camera, don't use the 50mm lens, use 85mm or 105mm or so). This'll put you further away from the screen, but will help with the perspective distortion. Always use a tripod of course. And if you don't have a cable release, try using the self-timer on your camera. That way you'll have your big shaky hand off the camera when the shutter opens. On some cameras, there is an added bonus as the SLR mirror will swing up at the start of the self-timer period, vibrations will dampen down, and then the shutter will open. Much harder to do, but better is to build a gadget that'll blank video, open your camera shutter, unblank video for exactly one (or N) frames(s) and then blank the video again. If you don't know how to build such a gadget, find someone who does. Use in a dark room of course !! Finally, if possible forget all this stuff and use a machine made for the job (Matrix Instruments or whoever) if you've got the $$$$. Nick England Director, Visualization Technology Sun Microsystems Inc nengland@sun.com
3ksnn64@pur-ee.UUCP (Joe Cychosz) (11/29/89)
In article <3777@hydra.gatech.EDU> robert@shangri-la.gatech.edu (Robert Viduya) writes: >Has anyone advice or pointers to information on how to photograph video >screens? I'm trying to shoot the screen of an SGI 4D/120GT. I have a SGI here, and shoot most of my slides/prints from it. >experimented with a Canon AE-1 with shutter speeds of 1/15 sec and 1/8 >sec and let it choose the aperature. I was also using ASA 400 film. I don't know how you have configured your Canon (I assume AE means some form of automatic). I would set the speed and aperature manually as described below. Also, get rid of the 400 speed film, it is too grainy and has poor color properties for this application. Use 100. >The results left a bit to be desired. I lost a lot of red tints >except where the color was solid red and then it stood out too much. >A lot of fine detail was lost as well. I probably should've used a >lower film speed like possibly ASA 200. These are all properties of using 400 speed film and printing problems. > I also suspect that the color >balance was screwed up in the development process and I was wondering >what I could do to prevent that in the future (I don't do my own >development). I think you mean printing and not the developing of the film. This is probably the most crutial step. The expose time and aperature settings are fairly forgiving for ASA 100 film. It is in the printing where the color is realy determined. Below discusses printing on comercial machines. Since you are doing your own work, I can't help much other than suggesting that you determining what is the equivalent of density in your printing process. Here is my guide to photographing computer graphics displays. This was posted a while ago in comp.graphics. I have updated it some to discuss the problems of the Nikon 70-210mm lens and some printing info on specific machines. ---------------------------------------------------------------------- Film: I use Kodak ASA 100 print film for prints and Ektachrome ASA 100 (Ektachrome 64 is no longer available) for slides. Setup: This is the longest and most crucial step. It is important to get the lens as perpendicular as possible to the screen. Things to watch for are monitors which tilt (like Suns or SGIs). I also try to get the lens as close as possible to the screen and still be able to focus. This helps reduce the effects of the curvature of the screen. For a 70-210mm Macro Nikon this is about 2 ft at 70mm. This contradicts what one might think in that one would expect the flattest photo to appear by getting as far away as possible and shooting with as long of a lens as possible. The problem is in the distoration in the lens system at 210mm. Keep in mind that a macro lens works on a series of approximations. What results is concave pillowing which is oppisite of the convex pillowing caused by the curvature of the screen. The optimal flat picture occurs when the convexed pillowing of the screen is balanced with the concaved pillowing of the distortion in the lens system. Since I do not have a straight 200mm lens, I have not been able to study and measure the distortion in the macro. One final note: I tend to shoot images that are either 640x480 or 512x 512 off of the SGI. I have shot full screen images, but the curvature of the screen gets a bit difficult to control, especially with the 70-210 lens problems. Exposure: I use a 1/2 second exposure at f8 with half a stop added in. To bracket the exposure I also shoot a f5.6 and a f11 exposure. With ASA 100 speed film the exposure can be fairly forgiving. That is to say, you'll get a reasonable picture as long as the exposure and f-stop are within reason. Never shoot faster than the refresh rate of the monitor, 1/60th. A wide black bar will appear on the screen. This even goes for taking pictures of monitors sitting in rooms. If you do you will endup with black bars on the screen. For room shots I use 1/8 second or longer. I have shot 1 second exposures at f8 and have had similar results out of a sugestion of Craig Good at Pixar. Again, ASA 100 speed film is pretty forgiving. I have found the exposue metering systems in cameras to unreliable when determining the exposue. This is especially true when shooting vector displays. Also, you want to avoid full white areas such as menu areas and the like. Change them to a 70 - 80% grey. The pictures will look much nicer when printed. Processing: For prints I usually tell the people that process my film that the roll contains computer graphics. Many film printers are computered controlled and are setup for printing people, sky, grass, trees and other things which you would find in normal photos. These printers usually lose it when the get a picture with lots of black and fully saturated colors. Vectors are the hardest to process. I use a Noritsu and a Fuji machine for my processing. Usually one or two units of density must be added (i.e., +1, +2) for computer graphics shots. The process you are going through is to balance the quality of the color with the quality of black. If you don't do this you will end up with brown instead of black. The Noritsu and Fuji will will print on the back of the photo what settings were used. So if you do reprints bring the old photo in so the processor can see what settings they used last time. Examples follow below: Noritsu: 896 45 N N N 6 2 896 = Sequence number 45 = Film code (45 = Kodak 100) N N N = Yellow, Magenta, Cyan print levels. N = neutral, there will be numbers -1, +1, etc. for non-neutral settings. 6 = Density setting. 2 = Ignore. Fuji: 79 010005 28 +01 +0 -01+02 NN -5 0 79 = Sequence number. 010005= Film/vendor/speed code (Kodak 100) 28 = Daily density setting, results from calibration. +01 = Density setting. +0 -01+02 = Cyan, Magenta, Yellow print leves. +0 = neutral. NN = Ignore. -5 0 = Ignore. One other problem the film processing machines have is alignment. Lets say you are shooting pictures of some square 512x512 images. The film processor will more than likely assume that the left edge of the image is the left edge of the picture. I will not center it for you. This will also happen with slides. To solve this problem two things can be done. One: shoot a few fully exposed pictures at the beginning of the roll so the machine can set where the left edge is for the rest of the roll. Or two: us an alignment background pattern like I do. This looks something like this: ---------------------------------- ! ! ! ! ! ! ! ----------------- ! ! ! ! ! ! ! ! ! !-------! Image ! ! ! ! ! ! ! ! !--------! ! ! ! ! ! ----------------- ! ! ! ! ---------------------------------- I am in the process of working on a calibration image which will help the process people make there settings. I am also working on reducing the yellow edges which appear (especially at red and green boundries). I don't expect to have any of this done sometime soon though.
3ksnn64@pur-ee.UUCP (Joe Cychosz) (11/29/89)
In article <1788@crdos1.crd.ge.COM> davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) writes: > There are several things which I have found help good pictures. The ... > > Oh, and a dark room is the easiest way to kill reflections I've found. But be aware of nearby monitors. Joe
rusty@fe2o3.UUCP (Rusty Haddock) (11/29/89)
In article <24526@cup.portal.com> Classic_-_Concepts@cup.portal.com writes: > Re: request for help on photographing screens > > I've done a lot of this. From experience, here's what I recommend: > > 2. Approximately 1/2 second exposure but BEWARE, the amount of > exposure can vary WIDELY with the amount of light and color > values present in the image being photographed. Meter for the How 'bout checking the reciprocity correction for ``long'' (< 1/15-sec) exposures? Sure, it'll vary from film to film but I haven't seen anyone mention this yet. Still, it might be a good idea to verify that you may or may not need to increase the exposure or add a filter here and there. Then again, I've been out of photography for a while. Please correct me if this is no longer needed with the ``modern'' films. -Rusty- -- Rusty Haddock o {uunet,att,rutgers}!mimsy.umd.edu!fe2o3!rusty Laurel, Maryland o "IBM sucks silicon!" -- PC Banana Jr, "Bloom County"
jh34607@suntc.UUCP (john howell) (11/29/89)
In article <2172@bacchus.dec.com>, klee@chico.pa.dec.com (Ken Lee) writes: > While we're on the subject, I've had excelent results with Polaroid > slide film. Not me ... when the polaroid 35mm slide film first came out around 1983 I tried using it for just this purpose, but could never get very good color saturation or contrast. True, it was good in a pinch, but I could never mix 'real' slides in the presentation since that showed how bad the polaroid ones were. Of course ... there probably is a better film stock available today, but unless it comes in comparable quality to ektachrome, the same problems would still be there.
jwi@cbnewsj.ATT.COM (Jim Winer @ AT&T, Middletown, NJ) (11/29/89)
Rusty Haddock writes: > How 'bout checking the reciprocity correction for ``long'' > (< 1/15-sec) exposures? Sure, it'll vary from film to film > but I haven't seen anyone mention this yet. Still, it might > be a good idea to verify that you may or may not need to > increase the exposure or add a filter here and there. Reciprocity corrections depend on knowing what the correct exposure is to start with. When you are using trial and error to determine the best exposure, there's no point in worring about reciprocity. Jim Winer ----------------------------------------------------------------- opinions not necessarily | "And remember, rebooting your brain and do not represent | can be tricky." -- Chris Miller any other sane person | especially not employer. |
tmurphy@wpi.wpi.edu (Tom [Chris] Murphy) (11/30/89)
In article <140@suntc.UUCP> jh34607@suntc.UUCP (john howell) writes: >In article <2172@bacchus.dec.com>, klee@chico.pa.dec.com (Ken Lee) writes: >> While we're on the subject, I've had excelent results with Polaroid >> slide film. > >Not me ... when the polaroid 35mm slide film first came out around 1983 >I tried using it for just this purpose, but could never get very good >color saturation or contrast. True, it was good in a pinch, but I could >never mix 'real' slides in the presentation since that showed how bad >the polaroid ones were. > >Of course ... there probably is a better film stock available today, but Well, sorry to say it seems no better. We do a lot of slides here from a Presentation Technologies Imagemaker (a neat box that eats HPGL) and have occasionally used Polaroid slide film. Our graphics art person often complains about contrast and color problems with the film. ------------------------------------------------------------------------------- Thomas C. Murphy Worcester Polytechnic Institute CAD Lab Internet: tmurphy@wpi.wpi.edu tmurphy@zaphod.wpi.edu BITNET: TMURPHY@WPI BIX: tmurphy CompuServe: 73766,130 If the Universe is constantly expanding, why can't I ever find a parking space?
m_rhoten@portia.Stanford.EDU (matt rhoten) (11/30/89)
I haven't had much problem with failure of exposure due to lack of reciprocicity (sp?) with exposures shorter than 1/8 second. Perhaps this was due to the film I was using (Kodak 100). But in most cases a camera store will have information on how much to correct for the exposure. -Matt Rhoten -- ------- Internet: m_rhoten@portia.stanford.edu
dave@imax.com (Dave Martindale) (12/01/89)
In article <264@fe2o3.UUCP> rusty@fe2o3.UUCP (Rusty Haddock) writes: > >How 'bout checking the reciprocity correction for ``long'' >(< 1/15-sec) exposures? Sure, it'll vary from film to film >but I haven't seen anyone mention this yet. Still, it might >be a good idea to verify that you may or may not need to >increase the exposure or add a filter here and there. The reciprocity data for films assumes a constant exposure level during the exposure time. If you're making a 1 second exposure of a normally-lit scene, the light reaching the film is pretty dim, and reciprocity compensation is needed. But if you are shooting a CRT, the light actually reaches the film as 60-70 short pulses of light each second, each of which is considerably brighter than the average light level. I would expect that little or no reciprocity compensation is needed. (I've never used any). The limiting case of this effect happens with digital film recorders. The entire exposure may take 5 minutes, but each point on the film is exposed to light of each colour exactly once, with an "exposure time" that is determined mostly by the decay time of the CRT phosphor - somewhere in the microsecond to millisecond range. If reciprocity compensation is needed, it's due to very short exposure time, not long exposure. About using spot meters: If you have a spot meter that will reliably meter a flickering source (the Pentax digital will not, the Minolta digital will, and any analog one should), measure a full-intensity white area in the middle of the screen, then give about 2.5 stops more exposure than that. Or, if you meter understands making highlight readings, do that, and it will make the 2.5 stop compenstation internally. Either way, you ensure that the highest intensity that your CRT can produce will fall at the upper edge of the linear portion of a slide film's response curve, guaranteeing a good exposure with maximum shadow detail. (Negative films have a longer range, and you might be able to get better results with more than 2.5 stops increase). This method is actually better than measuring an "18% grey" patch. The actual brightness of an "18% grey" patch depends on how accurately you do "gamma correction" for the monitor, while white is white no matter how messed up your gamma correction is.
jordan@Morgan.COM (Jordan Hayes) (12/04/89)
Rusty Haddock asks: How 'bout checking the reciprocity correction for ``long'' (< 1/15-sec) exposures? Reciprocity tends to break down (``reciprocity failure'') at much longer times than those being reccomended for this kind of work. Especially for slower films. Ektachrome 100, for instance, would become a problem at around 4 seconds of exposure; at that point, i'd rather worry about vibration from your officemate slamming the door. /jordan
Leo.Waltz@f270.n106.z1.fidonet.org (Leo Waltz) (12/09/89)
I'm also wondering about proper focal length of lenses to use to minimize the corner distortion of some monitors. I assume that the greater the focal length the better. Any comments ?
Chris_F_Chiesa@cup.portal.com (12/10/89)
This seems to be an "old" topic, but what the heck, I don't get to the News very often... My father is a professional photographer and is occasionally called upon to photograph a computer display; as I recall, he usually puts the camera on a tripod, uses as "long" a lens, at as much of a distance, as is feas- ible (i.e. he can't, if there's no space to "move back"), then TURNS THE AMBIENT (room) LIGHTS DOWN OR OFF and uses an exposure anywhere from 1/30 to SEVERAL seconds, depending on the light level coming from the display. If the client wants also to show the computer itself, WITH display image, Dad will fire an electronic flash unit AFTER exposing for the display, thereby giving brief illumination to the surrounding objects...
3ksnn64@pur-ee.UUCP (Joe Cychosz) (12/12/89)
In article <5204.2581ACEC@urchin.fidonet.org> Leo.Waltz@f270.n106.z1.fidonet.org (Leo Waltz) writes: >I'm also wondering about proper focal length of lenses to use to minimize >the corner distortion of some monitors. I assume that the greater the >focal length the better. Any comments ? This is in general true. However when working with Macro-zoom lens such as the Nikon 70-210mm. The problem is in the distoraton in the lens system at 210mm. For a 70-210mm Macro Nikon I use about 2 ft at 70mm. This contradicts what one might think in that one would expect the flattest photo to appear by getting as far away as possible and shooting with as long of a lens as possible. The problem is in the distoration in the lens system at 210mm. Keep in mind that a macro lens works on a series of approximations. What results is concave pillowing which is oppisite of the convex pillowing caused by the curvature of the screen. The optimal flat picture occurs when the convexed pillowing of the screen is balanced with the concaved pillowing of the distortion in the lens system. Since I do not have a straight 200mm lens, I have not been able to study and measure the distortion in the macro. Joe
davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) (12/12/89)
In article <13793@pur-ee.UUCP> 3ksnn64@pur-ee.UUCP (Joe Cychosz) writes: | This is in general true. However when working with Macro-zoom lens such | as the Nikon 70-210mm. The problem is in the distoraton in the lens system | at 210mm. For a 70-210mm Macro Nikon I use about 2 ft at 70mm. | This contradicts what one might think | in that one would expect the flattest photo to appear by getting as far | away as possible and shooting with as long of a lens as possible. Certainly that's the technique I see most recommended and the one I have used. I never tried going very close, but I will probably try it over the holidays, since I'll have some shots at the end of a roll, no doubt. -- bill davidsen (davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen) "The world is filled with fools. They blindly follow their so-called 'reason' in the face of the church and common sense. Any fool can see that the world is flat!" - anon