TECHNOLOGY: FILL-IN, FLASHGUNS and FP SHUTTERS ============================================== Olivier Jadot, oj@info.ucl.ac.be July 1995 1. What is fill-in? 2. What is the synch speed of a camera body? 3. What is the effect of the body synch speed on flash range? 4. What is the effect of the film speed (sensibility) on flash range? 5. Is it possible to use flash at a speed higher than synch speed? 6. Isn't the "effective GN" reduced when the shutter speed increases? 7. So, the range would be reduced. 8. What about normal operation versus FP operation? 9. At 7, we have seen the range isn't reduced. Could it even be increased? 10. Does it operate automatically? 11. Which combos are (have been) available on the market? 12. Which combos operate automatically? 13. Could I use a SB-25 (for instance) in FP mode on any boody? 14. Wich are the various effective GN? 15. What should I remember? 1. What is fill-in? Fill-in designates the use of flash in daylight. It allows to make shadows less harsh. 2. What is the synch speed of a camera body? It's the highest speed (shortest exposure time) at which you can use a flash. On most 24x36 SLRs (and also M6s and G1s but not Hexars), there is a focal plane shutter. It's made of 2 curtains. Its synch speed is about the time for one curtain to travel through the exposure window. When taking a picture, the first curtain leaves restplace and unveils the film. After a time equal to the exposure time, the second one leaves restplace, covering the film again. So, if the exposure time is shorter than the time needed for the first curtain to reach destination, there ain't any single point in time between the arrival of the first curtain and the departure of the second curtain, at which the whole filmframe would be unveiled. Thus, a short flashburst would reach some parts ot the film only and would be stopped by the shutter at some others parts. So, for flash-photography, the exposure time should be longer than the synch-speed. (The flashburst duration is shorter than 1/1000s for Canon 200E, 1/700s for Canon 420EZ, 1/400 for bigger Sunpacks. The fastest focal plane shutter on a 24x36 SLR has 1/300s synch. speed.) SEE ALSO 5. 3. What is the effect of the body synch speed on flash range? If you use flash at daylight, for a certain ambient light level, you'll want to keep the same exposure for the background. If you can reach a higher speed (thanks to higher synch speed), the aperture will be wider and so the range will be increased. 4. What is the effect of the film speed (sensibility) on flash range? If you use flash at daylight, for a certain ambient light level, you'll want to keep the same exposure for the background. If the film is faster, the aperture will be narrower but the GN of the flash will be bigger. As a result, the range will be the same! For instance, from f/11 @ 100ISO with a flashgun of GN 32m @ 100ISO to f/22 @ 400 ISO with the same flashgun whose GN is 64m @ 400ISO. Take care you may need an aperture so narrow that your lens doesn't allow it, if the day is too sunny or the film too fast or the synch speed too slow. 5. Is it possible to use flash at a speed higher than synch speed? With some combinations of flashguns and bodies, it is. Here is the way it works. As soon as the first curtain leaves restplace, the flashguns starts to emit many flashburst at a very high frequency (for instance 50kHz), as long as the second shutter doesn't reach arrival. This way, every part of the film will receive about the same number of flashbursts (from about 10 to about 100) during the same time (the exposure time) (but the "beginning" of the film frame will receive the flashburst numbers 1 trough 10 while the end of the film frame will receive the flashbursts numbers 78 through 87 for instance). We will call this mode of operation FP mode (FP as Focal Plane). WARNING: From now on, we will mainly talk about FP mode !!!!!!! 6. Isn't the "effective GN" reduced when the shutter speed increases? Yes it is. The time during which the flashgun has to emit flashbursts is the time between the departure of the first curtain and the arrival of the second. It equals the exposure time plus the time needed for one curtain to go from departure to arrival. For instance 1/4000s + ~1/200s or 1/250s + ~1/200s. It's always about the same (factor 2). But the time during wich a given part of the film receives light is far shorter at 1/4000s than at 1/250 (factor 16!) and a shorter time means less individual flashbursts, and less useful light for that part of the film, and a smaller part of the total energy given by the flashgun. So roughly, if the exposure time is 4 times shorter, the effective energy is decreased by 4 and the GN (range) is decreased by 2. 7. So, the range would be reduced. No, it wouldn't. Whenever you use this possibility with an exposure time of 1/500s or 1/2000s for instance, the range would stay the same. The effective GN would be twice smaller but remember the ambient light: you would open 2 stops, making the aperture number twice smaller too. So the range would stay the same. Note that if you can only choose frome n powerlevels on the flash, this means that for a given ambient light level, there are only n distances between flash and subject allowing proper flash exposure and proper background exposure! 8. What about normal operation versus FP operation? With today's technology, the range of the flash is far higher for normal operations: for instance 42m @ 1/250s, normal ops vs. 20m @ 1/250s, FP ops (Remember 7). Whatever the technology, if we agree that the amount of energy delivered would be the same in both case, the range and the GN would be higher in normal operations. Remember that with the FP mode of operation, the flashgun begins to release energy as soon as the first curtain leaves restplace. As long as that curtain hasn't reached home, the "end" of the filmframe won't "see the light". So, if the exposure time is about synch speed, since the travel time of the curtain is also about synch speed, there will be about half wasted energy. So the GN would be at least SQR2 lower for FP operation. 9. At 7, we have seen the range isn't reduced. Could it even be increased? Yes, maybe. Our computation of the decrease of the effective GN was based on the assumption that the flashgun operates exactly in the same way at 1/500s than at 1/2000s for instance. But if it does, the last flashbursts in the sequence would be completely useless when using a 1/2000s shutter speed: At 1/500s they would be needed to give light to the last part of the film but at 1/2000s, the second curtain would have already reach arrival! If the flash takes this into account and manages to release this energy at a time when it would be useful, the effective GN could decrease more slowly at faster speeds and the range would indeed be increased. To make this energy useful, the individual energy of every flashburst should be increased or the flashburst frequency should be increased. It seems that the Minolta 5400HS is able to modify the energy of every flashburst but it seems that it doesn't use this ability to 'improve' the GN at higher speeds. 10. Does it operate automatically? With normal TTL metering, the light energy is modulated by stopping the flashburst after the right amount of time. But with FP operation, the flashgun should behave the same way during the whole exposure cycle or some parts of the film wouldn't be exposed the same way. So, you have to determine the amount of light needed _before_ the beginning of the exposure! The flashgun could for instance send a few pre-flashes and the body could analyse the results. This would be 'Trough The Lens' metering but it wouldn't be 'Off The Film' but off the shutter blades instead. Once you know how much light you should give, you need a way to give more or less light. It could be done by changing the flashbursts frequency (Remenber you can't go down to low frequency or the exposure will be uneven) or you can change the power of individual flashbursts. It seems that the Minolta combo works that way. 11. Which combos are (have been) available on the market? The first one were the OM-4 Ti and OM-707 with the F-280 flashgun. Up to some extent, Olympus is still ahead with this feature built-in on the "cheap" IS-3000 (IS 3 DLX in the states IMO). They also offer the OM-3T with this feature when used with F-280. Nikon had the F-90 plus SB-25 and now F-90X + SB-26. Minolta has the 700si and 600si bodies with the 5400HS flashgun. Sigma has the SA-300N plus EF-430 super flash! It seems that Metz flashguns (MZ-40, MZ-50) don't allow FP flash. 12. Which combos operate automatically? As far as I know, the only one is the Minolta. Moreover, it is TTL! With Nikons, you have to manually choose between 2 power levels. 13. Could I use a SB-25 (for instance) in FP mode on any boody? Since this flashgun operates manually, you may think you could but you couldn't. The only thing needed is the trigger but the flash has to be triggered before first curtain departure, unlike conventional flashguns. This kind of trigger wouldn't be available on any body! Just like second curtain flash is not available on many bodies. 14. Wich are the various effective GN? For OLYMPUS: For the OM-4Ti/OM-4T (?x-synch of 1/60s) with F-280: Shutter speed: 1/60s 1/125s 1/250s 1/500s 1/1000s 1/2000s GN(m) : 14.7 10.4 7.3 5.2 3.7 2.6 The numbers for the OM3-T should be the same! For the OM-707/OM-77AF (?x-synch of 1/100s) with F-280: Shutter speed: 1/100s 1/125s 1/250s 1/500s 1/1000s 1/2000s GN(m) : 15.6 12.4 8.8 6.2 4.3 3.1 The better shutter of the OM-707 allows better GN (less wasted light!). The flashburst duration in FP mode is between 1/50s and 1/25s with the OM-4 and between 1/70s and 1/30s with the OM-707 For the IS-3000 (?IS-3 DLX in the US) with its built-in flash: Shutter speed: 1/125s 1/250s 1/500s 1/1000s 1/2000s GN(m) : 16 11 8 5.6 4 These numbers are computed from a graph. They shouldn't be very accurate: for instance 16 is computed from 1m range at f/16. BTW "4" is not obvious from the Olympus booklet. One may think of 4.5 instead ogf 4 but if you look at the whole Olympus graph, the 4.5 seems to be very inaccurate! Anyway, thanks to Joe Clark and to the belgian branch of Olympus. For NIKON combos, F-90 or F-90x (x-synch of 1/250s) with SB-26 or SB-25), there are two settings: FP1, full power or FP2, half power: FP 1 Guide Number (at ASA 100; for meters/feet) Shutter Zoom-Head Position speed 24mm 28mm 35mm 50mm 70mm 85mm ------------------------------------------------------------------ 1/250 14/46 15/50 17/56 20/65 23/74 24/77 1/500 10/33 11/36 12/39 14/46 16/52 17/56 1/1000 7/23 7.5/25 8.5/28 10/33 11/36 12/39 1/2000 5/16 5.3/17 6/20 7/23 8/26 8.5/28 1/4000 3.5/11 3/7/12 4.2/14 5/16 5.6/18 6/20 FP 2 Guide Number (at ASA 100; for meters/feet) Shutter Zoom-Head Position speed 24mm 28mm 35mm 50mm 70mm 85mm ------------------------------------------------------------------ 1/250 10/33 11/36 12/39 14/46 16/52 17/56 1/500 7/23 7.5/25 8.5/28 10/33 11/36 12/39 1/1000 5/16 5.3/17 6/20 7/23 8/26 8.5/28 1/2000 3.5/11 3/7/12 4.2/14 5/16 5.6/18 6/20 1/4000 2.5/8.2 2.6/8.5 3/10 3.5/11 4/13 4.2/14 Thanks to Ed Yost ! For the MINOLTA combos, 700si or 600si (x-synch of 1/200s) with 5400HS, in meters: mm 24 28 35 50 70 85 105 speed 1/250 11 12 13 16 17.4 17.4 19 1/500 8 8.7 9.7 11 12 12 13 1/1000 5.6 6.1 6.7 8 8.7 8.7 9.5 1/2000 4 4.4 4.8 5.6 6.1 6.1 6.7 1/4000 2.8 3.1 3.4 4 4.4 4.4 4.8 1/8000 2. 2.2 2.4 2.8 3.1 3.1 3.4 Thanks to Francis Tinseng ! The 70 and 85mm colums are not typos (or typos in the flash manual then !) Note that the GN may have been higher if the synch speed of the bodies had been faster! (Because the ratio of wasted light would have been lower.) For SIGMA: SA-300N (?x synch of 1/125s) + EF-430 Super Guide numbers in meters at ISO/ASA 100. Two FP modes: FP1 and FP2. FP2 is in brackets. 28mm 35mm 50mm 70mm 80mm --------------------------------------------------------------- 1/250 15(10) 16(10.6) 18(12) 20(13.4) 21(14) 1/500 10.6(7) 11(7.5) 12.6(8.4) 14(9.5) 15(10) 1/1000 7.5(5) 8(5.3) 9(6) 10(6.7) 10.5(7) 1/2000 5.3(3.5) 5.6(3.7) 6.3(4.2) 7(4.7) 7.5(5) 1/4000 3.7(2.5) 4(2.7) 4.5(3) 5(3.4) 5.3(3.5) Thanks to Boon Li Ong ! Since, the synch-speed of the camera is only 1/125s, these numbers are outstanding, from an engineer point-of-view ;-) (More wasted energy at 1/250s if the synch is 1/125s than if the synch speed is 1/250s!) 15. What should I remember? Remember that FP operation is nice, as nice at 1/2000s or 1/8000s than at 1/500s but that the range would be decreased compared with normal operation. BTW, most of the informations in those tables are redundant. If you know the numbers for a given shutter speed, you can compute the GN for others shutter speed. You just need to remember that with each of those combos, multiplying the speed by 2 means dividing the GN by SQRT 2. Moreover, don't worry about those GN, compute the range for the given speed for which you remembered the GN, according to the relevant aperture for ambient light and then choose whatever speed-aperture you want. I hope you could understand the FAQ and you learned something. Have a good day. Olivier Jadot