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Forums Lobby MASTER YOUR TOOLS - Hardware & Software Nikon Speedlights & Lighting topic #52958
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Subject: "D40 hot shoe" Previous topic | Next topic
Capt Slog Registered since 21st Feb 2011Mon 21-Feb-11 03:11 PM
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"D40 hot shoe"


GB
          

Hi,

I've been looking up some information about flash isolators, as I have access to some studio flash equipment and know I can't connect it directly to my camera.

I've found the Wein units and also various DIY solutions that use opto-isolators. It seems that most of these use the camera to switch around 6v, which in turn is used to switch the flash which could be in the region of 100's of volts.

OK so far, I think I understand.

Here's what's puzzling me. I connected a digital storage osciloscope to the flash hot shoe of my D40, using the outer connection and the main centre pin. On shutter release, I see a peak of around 560 mV (sorry, didn't make a note of the duration). Now that's around 0.5V coming from* of the camera, anyone know why or what it's for?

It has me worried because anything I buy or make will put voltage onto this circuit which is evidently logic based rather than a passive switch.

(* I say it's coming from the camera, but in true electrical sense it isn't, it's a potential of 0.5volts with no current flowing.)

  

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CharlieS Silver Member Nikonian since 29th Aug 2007Mon 21-Feb-11 03:55 PM
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#1. "RE: D40 hot shoe"
In response to Reply # 0


US
          

I'm not an expert in the electronics such as in a camera, nor do i have an oscilloscope available to do any testing, but I have a strong background in electrical engineering. I suspect what your seeing is stray voltage leaking into those circuits.
Think of it this way, shoe mount flash's, infrared triggers, or rf triggers commercially available all have worked on uncountable numbers of nikons with no problems.
If you doubt the reliability of the wein sync safe, go with a flash activated optical trigger on your flash heads, or rf triggers. As others besides myself will testify, they work without problems.

____________________________________________________________________
When no one is looking, Pigs can walk on they're hind legs

  

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MEMcD Moderator In depth knowledge in various areas Nikonian since 24th Dec 2007Tue 22-Feb-11 01:50 AM
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#2. "RE: D40 hot shoe"
In response to Reply # 0


US
          

Hi Dave,

Welcome to Nikonians!
You might want to check out Photo Strobe Triggering Voltages.
Like Charlie, I use RF triggeres with my strobes. They are available in a very wide price range from about $35.00 for Cleons to $295.99 for a Pocket Wizard MultiMax. You can also combine RF and optical triggers.
Good Luck and Enjoy your Nikons!

Best Regards,
Marty

  

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Arkayem Moderator Awarded for his high level skills in flash photography Charter MemberThu 24-Feb-11 02:31 AM
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#3. "RE: D40 hot shoe"
In response to Reply # 0


Richmond Hill, GA (Savannah), US
          

>Hi,
>
>I've been looking up some information about flash isolators,
>as I have access to some studio flash equipment and know I
>can't connect it directly to my camera.
>
>I've found the Wein units and also various DIY solutions that
>use opto-isolators. It seems that most of these use the
>camera to switch around 6v, which in turn is used to switch
>the flash which could be in the region of 100's of volts.
>
>OK so far, I think I understand.
>
>Here's what's puzzling me. I connected a digital storage
>osciloscope to the flash hot shoe of my D40, using the outer
>connection and the main centre pin. On shutter release, I see
>a peak of around 560 mV (sorry, didn't make a note of the
>duration). Now that's around 0.5V coming from* of the camera,
>anyone know why or what it's for?
>
>It has me worried because anything I buy or make will put
>voltage onto this circuit which is evidently logic based
>rather than a passive switch.
>
>(* I say it's coming from the camera, but in true electrical
>sense it isn't, it's a potential of 0.5volts with no current
>flowing.)

Your last comment is key.

When the center pin is not loaded and no current is flowing, there is no telling what Voltage it will float to. It all depends on leakage in the device and its surrounding components. The center pin typically grounds the flash to the case of the camera which completes the circuit from the center pin to the outside pin. This is done with a fairly tough device (either a MOSFET or J-FET) that will fire all modern shoe flashes.

The punch-through voltage of the oxide layer in the camera output device is typically somewhere around 20 volts. Therefore, if your studio strobes have 100's of volts in their circuitry, that may have to be blocked by the camera device, and that can punch the oxide in the camera device. You would normally only see that voltage if you measure the center pin steady state with the strobe attached and turned on. The voltage would be there all the time before the flash fired, being blocked by the output device in the camera. There would be no significant transient spike in voltage when the flash was fired. The voltage will simply go to zero referenced to the camera case as it completes the circuit. The currents that flow are typically quite low and will not damage the output device. It is before the flash is fired that the stress is put on that output device in the camera by blocking the high voltage.

Russ
Nikonian Team Member
Russell MacDonald Photography
Nikon CLS Practical Guide

  

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