Tricking your camera for higher synch speed - split from Sunpak thread

[RonFrank]

Thanks Ron.

My D70 also only syncs to 1/500 but with the controllers I can go much higher. There are other ways to "trick" the camera by shimming the hotshoe.

Hey Mike,

Can you explain this? How can you go much higher with *controllers*, and how can you *trick* the camera by shimming the hotshoe?

I'm aware that camera manufactures can sync flash with their camera's at up to 1/8000, but it takes some doing as a Mirror only gets out of the way of the sensor so fast. Strobe durations also very widely, and based on settings, so as Bob (I think) pointed out, your going to clip the stobe if it has a duration of 1/1000 (which is right in the range), and you are shooting at 1/2000.

So Ikelite flashes can somehow sync at 1/2000?

I'm hardly new to photography, but I AM rather new to UW photography. Frankly, I've found the lack of stardardization between manufactures of strobes, brackets, arm systems, and cables rather frustrating.

While I think there is some solid quality UW strobes out there, getting information on these products without actually calling a dealer (no one in Denver carries anything on beyond Sea&Sea or the LOWEST model of ikelite) is also difficult.

Thanks

 

[Tortuga Roja]

Ron,

All I am talking about is tricking the camera so that it is unaware that you are shooting with a strobe. It really has nothing to do with the strobe. If I connect the strobe via the sync cord and bulkhead, directly to the hotshoe, the camera "knows" I have a strobe attached and will not allow me to set my shutter faster than 1/500. If I hook my strobe to the bulkhead thru the Ike manual controllers, the wiring is such that the camera doesn't "see" the strobe even tho it will trigger it to fire with the shutter release.

The alternative, if you don't have a controller, is to not slide the hotshoe connector all the way into the hotshoe. The idea here is to allow one element to make contact but not the other giving the same effect. That is, camera does not "see" the strobe but will still fire it. In order to keep the hotshoe connector at the right place (not quite fully engaged) others have used a shim to keep it from sliding too far forward. I have never done this since I have the controller.

Keep in mind that I have a pre-iTTL housing. I have been told that the iTTL circutry will do the same thing as the controllers, thus allowing you to set the shutter speed just as you can when the strobe is not being used by the camera.

Bob is right in that if the shutter is faster than the strobe burn time, the strobe is clipped energy is wasted and the exposure will not be as expected. I'll leave the math to Bob and the links he suggested since that's all way above my pay grade. I'm more of the "shoot, review, adjust, shoot again" type of guy.

HTH

 

[vkalia]

Ok, now I have a question.

The max sync speed is determined by the shutter curtain movement across the film/sensor plane. There are actually 2 curtains - the first one "opens" the shutter, allowing light to fall on the sensor, and the second one "closes" the shutter, stopping further exposure of the sensor. When you press the shutter, the first curtain moves across the sensor, exposing it, followed by the rear curtain, blocking additional exposure. The gap between the two curtains is dictated by your shutter speed.

[This is a very non-technical explanation, I am afraid]

The reason cameras dont sync at higher speeds is that at those speeds, the rear curtain is so close to the front curtain that only part of the sensor is exposed at any given time. So a flash at these speeds only illuminates that part of the sensor which is exposed at any given time. This results in uneven illumination across the frame.

That, incidentally, is why non-SLR digicams can sync at any speed (they dont have the manual shutter curtains). That is also why high-speed syncs involve a pulsing flash (atleast with Canon).

Fooling the sync times may work, but it risks causing banding. At least, that is how the theory goes. Now, if this doesnt happen in practice, that would be interesting to know.

I am not an expert on flash, incidentally, so I'd be keen to hear from someone else if I am missing anything here.

Vandit

 

[Tortuga Roja]

Well done explanation Vandit!

Here's the way I understand it (and I admit I am over my head here): Manual and electronic shutters are not necessarily separated by whether the camera is an dSLR or not. My Canon G2 (non dSLR) had an manual shutter and could not sync higher than 1/250 while my Oly 5050 (non dSLR) had an electronic shutter which would allow much higher sync speeds. My D70 has combined mechanical and CCD electronic shutter. How this works is something I don't know. I have seen examples of the banding you are talking about but never from my 5050 or my D70. I assume I would have had that problem with the G2 but I never had a way to "trick" it as I needed the onboard flash to be on to fire my strobe.

 

[vkalia]

Heya Mike - thanks for that tidbit. I didnt realize that some digicams also have mechanical shutters (I have a G6 for over a year, and didnt realize that. Doh ). Time to do some digging.

Vandit

 

[RonFrank]

Vkalia,

You are exactly correct. This is one reason that the copal shutters (they looke like the irus of an aperture, and open all at once) allows sync speeds at any shutter setting (Zeiss Hasselblad lenses for example).

Focal plane shutters travel exactly as you describe even if there is really not *two* shutters in some implementations.

This is why I can not understand how people are using flash at sync speed above the camera's X-Sync speed.

 

[RonFrank]

On the D70 all shutter speeds up to 1/250 are handled mechanically, all faster shutter speeds are handled electronically (e.g., the shutter opens for 1/250 and the sensor turns on and off to create the shutter speed effect). This arrangement first appeared on the D1 and provides one very useful side effect: flash sync speeds are increased substantially (arbitrarily limited to 1/500 on the D70, just like the D1 series).

So the shutter is really open for 1/250 for all speeds beyond that and the sensor controls the exposure. The resulting sync speed at 1/500 must be because it just happens to work out, and Nikon could exploit that. I guess at faster speeds the sensor timing is *off* and does not sync.

The bottom line appears to be if you are triggering a flash at shutter speeds beyond the X-Sync settings, either the flash is not going to record, or you are going to end up with a strip in the frame somewhere that did get flash exposure. I'd suggest that the latter could result in problems.