Max flash sync speed 1/500. Anything to do with sensor?

Discussion in 'Mirrorless Digital Cameras' started by jemini_joseph, Jan 29, 2004.

  1. May be a stupid question. Does anybody know if the flash sync speed has something to do with CCD/CMOS/LBCAST? I've noticed that all the professional film cameras and any digital cameras other than CCD sensor has only 1/250s flash speed. Latest Canon 1D II is an example. Ne camera has only 1/250 and older version had 1/500. Nikon's D2H went down in speed too. Does it has something to do with the speed of the sensor? Is there any article explaning this?
    Thanks

    Color-pictures.com
     
  2. Yes. Some sensors are capable of "electronic shutter" operation, others are not. If the sensor has this capability, you get 1/500 sec x-sync, like D1X, D1H, 1D, or D70. If it doesn't, you get whatever sync speed the mechanical shutter on the camera is capable of: 1/250 for the F100 shutter in the D2H or the EOS-1V shutter in the 1D II, 1/180 for the N80 shutter in the D100.

    Currently no CMOS sensors have electronic shutter capability, which is why Canon lost this capability when they moved from CCD on 1D to CMOS in 1D II.

    Some CCD sensors don't have it, either. Supposedly, the Fuji Super CCD has it, but Fuji didn't choose to use the capability in S2. The Sony ICX413AQ sensor used in Nikon D100 and Pentax *ist D didn't have it, but the design of the sensor should have permitted it. The D70 appears to use a new version of ICX413AQ that does have electronic shutter, so you get a 1/500 sec electronic shutter x-sync, instead of the 1/90 that the N75 shutter in D70 is capable of.
     
  3. the CCD equipped Nikon D70 has a 1/500th top sync speed.
     
  4. jbq

    jbq

    Yes, it's the sensor technology. CCDs have an "electronic shutter" feature, which not all sensor technologies have as far as I know. Notice that a D1H or D1x can actually sync at any speed, the limiting factor becoming the flash and not the camera (typical flash duration at full power can be over 1/1000s).
     
  5. Thanks Joseph, Ellis and Jean-baptiste <br>
    Then I do have another question to add to this. Is this same as the high speed flash (that allows sync upto maximum shutter speed)? <br>

    I'm not much worried about technical note about it. I know if you use HP flash you will limit the guide number. The battery will drain faster too. Is that the case with this 1/500 flash sync too? Or it just take the battery life? Or there's no difference from normal flash at all from a user perspective? <br>
    Thanks again guys. Ellis, I notice that the D70 has this too. This is very usefull for bird photographers not to lose shutter speed when using fill flash. I'm considering D70. That's one of the reason I've noticed this...<br>
    Cheers
     
  6. jbq

    jbq

    Jemini: no, "high-speed flash" is the opposite:

    Regular 1st curtain flash (with no CCD tricks): start opening 1st curtain. end opening 1nd curtain. start firing flash. end firing flash. wait according to the exposure time. start closing 2nd curtain. end closing 2nd curtain.

    The flash sync speed is primarily limited by how long it takes to open/close the shutter.

    The flash sync speed is the shutter speed at which the "wait according to exposure time" is zero. If we assume that the time between "start firing flash" and "end firing flash" is 1/500s, it means that in order to be able to reach a 1/250s flash sync each curtain must be able to entirely physically move in less then 1/500s (that's about 30 miles per hour on average, i.e. 0 to 60 in 1/1000s and 60 to 0 in 1/1000s).

    Now, with a CCD trick:
    start opening 1st shutter, end opening 1st shutter, start recording, start firing flash, end firing flash, end recording, start closing 2nd shutter, end closing 2nd shutter.

    Notice that the speed at which the shutter moves is entirely factored out, and that you could actually do the same thing without a shutter. The limiting factor is purely the duration of the flash. By using a flash below its maximum power, the duration is very short (shorter than specified), and it might be possible to use even faster shutter speeds (I'm extrapolating here, I don't have the kind of hardware ot experiment, my DSLR is a 10D).

    High speed flash works this way:
    start firing flash. start opening 1st curtain. start closing 2nd curtain. end opening 1st curtain. end opening 2nd curtain. end firing flash.

    If we assume the same curtains as above, the flash needs to be able to continually fire for about 1/125s (for 1/250 "high-speed" sync) to 1/500s (for 1/8000s "high-speed" sync). In the first case the flash "hits" the shutter curtains half the time, so it loses half its power like that. In the second case the flash "hits" the shutter curtain 97.5% of the time and loses that much power like that. Add to that that the flash needs to be brought up to a steady light before starting to open the first curtain, and you'll understand why high-speed sync results in those lower GN numbers.
     
  7. I strongly doubt 1/500th is a sensor-shuttered sync speed. The two cameras I know
    of that use sensor shuttering can sync at ALL speeds--my antique 1.4mp Sony DSC
    -770 syncs all the way to 1/2000th, and the E-20 in progressive (eg sensor
    shuttered) mode syncs all the way to 1/4000th. Also worth noting is that the E-20 can
    only deliver 2.5mp in progressive mode, HALF what it can deliver in mechanically-
    shuttered mode. And, of course, these speeds are faster than most flash's full-power
    duration. You can actually use these cameras to test flash duration.
     
  8. jbq

    jbq

    Roger: Ken Rockwell reports http://www.kenrockwell.com/nikon/d1xperf.htm that the D1 series can sync at all speeds (up to 1/16000) through the PC terminal, but only to 1/500s through the shoe, goes on to explain that this is possible thanks to an electronic shutter, and explain that the sync is limited to 1/500s because some powerful strobes have a duration longer than 1/1000s. It's veyr possible that Nikon used the same techniques on the D70, with the same reson to artificially limit the sync speed to 1/500s. All that is pure speculation, of course.
     
  9. Jean Baptiste: The scenario you lay out makes perfect sense to me. I'm VERY willing to
    believe 1/500th as an idiot-proofed max sync speed, just not as a "real" limit. I
    apologize for not considering idiot-proofing as a cause of mischief.

    What I'm then left wondering about is why Oly had to cut resolution to enable sensor-
    shuttering, but Nikon didn't?
     
  10. Thanks Jean-Baptiste, Roger. <br>
    This is kida tough for me to digest, but I understand this enough to answer my question. So in effect I can use my flash with full GN at 1/500. I'm considering D70 for naturephotography. Having high sync speed is usefull for outdoor fill flash photography without affecting the shutterspeed...
     
  11. I may be missing something but I thought the sync speed was limited by the mechanical shutter, which DSLR still have. The shutter has to be fully open when the flash goes off and 1/250 used to be the limit. Now, 1/500 is possible because of the smaller sensor, because the shutter can be fully open for a shorter period. That's how I understand it. Actually, I wonder why the D2h syncs at 1/250 only.

    If my memory is correct, High-speed sync is achived by emiting small bursts of flash during the whole exposure period. For example, if the slit created by both curtain is 6mm wide and travels over 24mm, you'd need 4 equal bursts of flash to cover the whole frame.
     

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