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Photo Forum / Film Photography / Medium format / May 2007How does TLR's shutter work?
hi, i want to check my Rolleiflex TLR's shutter condition. i am sure the 1/60 is slower than 1/125 and 1/30 is shlower than 1/60. by these evidences, can i ensure that some of most often used shutter speed ( 1/8, 1/15, 1/30, 1/60, 1/125 ) are accurate? thanks. Recently, Steven Woody <narkewoody@gmail.com> posted: > hi, i want to check my Rolleiflex TLR's shutter condition. i am sure > the 1/60 is slower than 1/125 and 1/30 is shlower than 1/60. by these > evidences, can i ensure that some of most often used shutter speed > ( 1/8, 1/15, 1/30, 1/60, 1/125 ) are accurate? An easy way to check this without test equipment would be to shoot a roll using a gray card. Fill the frame with the card, then use equivalent settings, e.g. 1/125 @ f16, 1/60 @ f8, etc. When developed, the frames should all look the same. Neil > Recently, Steven Woody <narkewoody@gmail.com> posted: > [quoted text clipped - 7 lines] > settings, e.g. 1/125 @ f16, 1/60 @ f8, etc. When developed, the frames > should all look the same. In that case use slide film. And include near white and near black in the image. Some color too. I use a digital osciliscope and a IR photo sensor with an IR source outside ... on the 500 C/M I pre-fire the mirror and body shutter and hold the sensor inside the body. Then fire the lens shutter. At wide aperture. (could do it stopped down too I suppose).  Signature-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm -- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm -- [SI] gallery & rulz: http://www.pbase.com/shootin -- e-meil: Remove FreeLunch. Recently, Neil Gould <neil@myplaceofwork.com> posted: > An easy way to check this without test equipment would be to shoot a > roll using a gray card. Fill the frame with the card, then use > equivalent settings, e.g. 1/125 @ f16, 1/60 @ f8, etc. When > developed, the frames should all look the same. To correct my pre-coffee response, equivalent settings should be "... 1/125 @ f8, 1/60 @ f16, etc.", but I hope you got the general idea. Neil > Recently, Neil Gould <neil@myplaceofwork.com> posted: > [quoted text clipped - 7 lines] > > Neil Forgot about f 11 huh?? Recently, Dave <dsmith5@optonline.net> posted: >> Recently, Neil Gould <neil@myplaceofwork.com> posted: >> [quoted text clipped - 9 lines] >> > Forgot about f 11 huh?? Damn... I need more coffee!!!! Neil > hi, i want to check my Rolleiflex TLR's shutter condition. i am sure > the 1/60 is slower than 1/125 and 1/30 is shlower than 1/60. by these > evidences, can i ensure that some of most often used shutter speed > ( 1/8, 1/15, 1/30, 1/60, 1/125 ) are accurate? > > thanks. No. You can assume that if the speeds are not accurate, they are all out of timing to about the same extent, at least withon the following groups: 1 - 1/15; 1/30 - 1/250; and 1/500. Depending on your model of Rollei, the shutter speeds within these groups are probably governed by the same mechanisms. The exposure comparison tests others have described will tell you whether each speed is or is not consistently out of timing with others, but that will not tell you whether any speed is accurately timed. You would need to test the actual timing of each shutter speed to judge its accuracy. You can usually get this done at a camera store for free or low cost, assuming you have one remaining in your area. Years ago, there as descibed an easy way to test such timing with a recortd turntable, by photographing a white line on a black record to see how far it turns during the exposure, then do the math. If you don't have a turntable or a head for the math, that's out. A current Google search will pull up a number of DIY home built shutter speed testing devices which are cheap and easy to build, if you have any experience with DIY electronics. Lacking an ability to test absolute speeds, you can get by if the exposures are relatively consistent, if not necessaily accurate. If so, you can adjust your film speed rating to accomodate a shutter which runs about the same amount slow at all commonly used speeds, using the exposure techniques which several other replies have described. > You would need to test the actual timing of each shutter speed to judge its > accuracy. You can usually get this done at a camera store for free or low [quoted text clipped - 5 lines] > home built shutter speed testing devices which are cheap and easy to build, > if you have any experience with DIY electronics. TV signals are made up of two interlaced fields to produce one frame. Each field is half a frame and is displayed for 1/2 of the time. For the U.S., that's 525 lines divided by 2 or 262.5 (the first line starts in the middle of the screen) every 60th of a second. In PAL/SECAM countries except Brazil, it's 625/2 (312.5) every 50th of a second. If you photograph the entire TV screen with enough resolution on the film to count the lines you can test the shutter speed from 1/60th up. For the U.S.: 1/60 = 262 lines (or so) 1/125 = 131 lines. 1/250 = 65 lines. 1/500th = 32 lines. Geoff. SignatureGeoffrey S. Mendelson, Jerusalem, Israel gsm@mendelson.com N3OWJ/4X1GM IL Voice: (07)-7424-1667 Fax ONLY: 972-2-648-1443 U.S. Voice: 1-215-821-1838 Visit my 'blog at http://geoffstechno.livejournal.com/ > TV signals are made up of two interlaced fields to produce one frame. > Each field is half a frame and is displayed for 1/2 of the time. [quoted text clipped - 13 lines] > 1/250 = 65 lines. > 1/500th = 32 lines Good in theory, might be a little challenging in practice. For NTSC, the horizontal line rate is 15750, so each horizontal line takes 63.492uS. I believe this means the table is more like: 1/60: 262 lines (or so, as you point out) 1/125: 126 lines 1/250: 63 lines 1/500: 31.5 lines (might want to call this 31 lines) If the shutter remains open longer than 1/60th of a second, you may start to see additional lines in the vertical gap between the lines. This just means you're seeing the "other" set of lines that make up a complete frame. If you're unlucky enough to include a vertical retrace period in your exposure, there will be lines at the bottom or top of the screen, or both. Some of the lines are used to send non-video content and may not be visible, and the blanking interval itself may vary somewhat in length, but it's around 800-1300uS. So you may want to take several exposures at each shutter speed if you try this. The real gotcha is that it's actually quite difficult to count lines with much precision due to the persistence of the CRT. The phosphors in the CRT continue to emit light for quite a while after being scanned by the electron beam. It's true that phosphors scanned while shutter is open will be brightest, but it can be hard to tell in practice, especially when the content on the screen isn't one homogeneous intensity. I don't know how long real CRTs will be commonly found, though. Certainly, I haven't given in to the temptation (yet) of LCD and plasma TVs, but I know that LCD changes the rules and plasma might as well. With all that said, this is a pretty useful technique and an excellent way to find out if your shutter is grossly out of whack. I tried this experiment with an SLR set to 1/500th of second, and was surprised how often I caught the vertical retrace (or couldn't be sure). Longer shutter speeds will be more likely to catch the retrace. The persistence of the phosphors was quite evident; it could add 2-3 lines to a count if not really careful. At least once, I caught the faint ghost of a new line beginning, too. No film was harmed in this experiment; I did count 31 lines, but I could be off a line either way. Cheers, Dana <...> > The real gotcha is that it's actually quite difficult to count lines with > much precision due to the persistence of the CRT. The phosphors in the [quoted text clipped - 3 lines] > brightest, but it can be hard to tell in practice, especially when the > content on the screen isn't one homogeneous intensity. There's also another gotcha. The blades of a leaf shutter move at finite speed. The opening and closing phases are not sudden but gradual. How much so depends on aperture. If you see fading lines at the edges, part of them is caused by the shutter. The 1/500 mark means "1/500-equivalent amount of light at full aperture". IIRC, the official speed at 1/500 is only 1/380, when measured at f/32. The longer time compensates the slowness of the blades. -- Lassi > <...> >> The real gotcha is that it's actually quite difficult to count lines with [quoted text clipped - 9 lines] > so depends on aperture. If you see fading lines at the edges, part of them > is caused by the shutter. Good point; I haven't done such a test with a leaf shutter but it makes complete sense. The brief test I did was with an SLR with a curtain shutter, so I wouldn't expect to see the same exact effect. However, I would expect that a curtain shutter would have a similar problem; assuming that the shutter curtains open down, in the same direction the electron beam moves, the shutter will "chase" the beam, perhaps at a rate far slower than the effective shutter speed (which, I believe, really represents the delay between two curtains falling). While I do not know how fast shutter curtains actually move, it's easy to imagine a shutter could move slowly enough to skew a measurement. > The 1/500 mark means "1/500-equivalent amount of light at full aperture". > IIRC, the official speed at 1/500 is only 1/380, when measured at f/32. The > longer time compensates the slowness of the blades. Ah, right. Fascinating. Dana > > <...> > >> The real gotcha is that it's actually quite difficult to count lines with [quoted text clipped - 30 lines] > > Dana did you both ment to say that a leaf shutter will exposure different amount of light for the same 1/500 in different appertures? my shutter is a leaf shutter. - woody > did you both ment to say that a leaf shutter will exposure different > amount of light for the same 1/500 in different appertures? my shutter > is a leaf shutter. Yes, a well known fact. I just wouldn't expect to see the difference with anything but a slow color chrome filme like Velvia 50. Martin > > You would need to test the actual timing of each shutter speed to judge its > > accuracy. You can usually get this done at a camera store for free or low [quoted text clipped - 30 lines] > IL Voice: (07)-7424-1667 Fax ONLY: 972-2-648-1443 U.S. Voice: 1-215-821-1838 > Visit my 'blog athttp://geoffstechno.livejournal.com/ thank you. ensure the exposures are relatively consistent rather than all the way accurate is my real intent. thank you Randy, i've got the idea. one question left: it seems you think 1/8 is not with the same group of 1/15, 1/30, does it? - woody |
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