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Old Aug 20, 2002, 4:04 PM   #1
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Default Flash Interface MFI-2 Repost

This is what I posted in the old Steve Forum . For the benefit of whom who are interested ( here and in other forums) I repost it now.
Note that I made this device in the context of months ago , when the D7i and the D7 upgrade are not available yet , meaning the D7 ( prior to firmware 122 ) was not able to fire single flash.
I did this to use my Metz connected via D7 hot shoe in manual and auto-aperture ( or auto-thyristor) mode. Rear curtain sync is also possible in slave at second flash triggering ( I couldn't use the camera signal in rear curtain mode) .
With the arrival of the upgraded D7 and the D7i , this circuit is more or less useful ; Though, with D5 and D7 original ( prior to 122 firmware) , it still make sense.
The slave-counter feature is useful if you have a camera which can't have the preflash disabled , this device frees you from sticking with the few choices of slave flash on the market.

==============================

The MFI-2

I called it " MFI-2 " (Metz Flash Interface 2) because it was my main goal
( the #1 was for my 35mm Nikon SLR with 45CT-1).
It's kind of black box (in fact , it is a black box ) which has these features:


1) Input:
- Minolta D7 ( D5 & D7i as well) , Nikon, or any camera hot shoe contacts, presenting to the camera's hot shoe contacts a safe voltage level of 3 volts and a max possible current of around 5 micro-Amps ;
- A standard dumb slave cell;
- Any electronic/mechanical contact;
- What ever electric/electro-mechanic/electronic circuit you could imagine to trigger the flash ( by sounds ...)

2) Output:
Any external flash that has trigger voltage up to 400 volts (limited to the internal opto-isolator only; in my case , my Metz 45CT-1 has the highest trigger voltage , 225 volts)
If you need a higher voltage drive, just choose the right opto-isolator .

3) Modes:
- Direct normal flash;
- Fire the external flash at the second detected flash ( or signal)
(D7 fill flash and Rear-Sync modes for example);
- Fire the external flash at the third detected flash ( D7 red eyes reduction mode for example).

*** Rear-Sync direct mode ( directly hot shoe connected, use no slave cell ) : I did not success to use the input signal yet
( seems that the D7 signal drops after the curtain close . So, this is for later ...

4) Limitation:
This is just a dumb flash "firer" , no TTL of course. I use this with my Metz flashes on manual or Auto aperture modes.
This does not bother me because, most of the time , I have to impose the shutter speed to preserve background .
More technical infos are included in the schematic.

Original color schematic (output from Orcad)

B&W (gray shade, light background ) schematic , more practical for printing purpose


Description of the circuit:

The input contact (from hot camera hot shoe or slave cell) trigger the counter (via clock line) to advance one count.
At the pre-selected value ( 1, 2 or 3) , the counter trigger the monostable circuit to produce an output pulse ,
and the same time , reset the counter to zero to be immediately ready for the next cycle. The monostable circuit is necessary to have a reliable signal for the opto-isolator.
The external flash is then triggered by the opto-isolator , giving complete electric isolation with the circuit.
The choice of opto-isolator depends on the need ( voltage, SRC or Triac output ...etc, there is no limit, go to kV range if you like )

The start-up reset circuit insure that the circuit is properly reseted at power on.
This circuit is not an absolute necessity ; without it, you just have to check ( with the led) that the counter is zero first time you turn on , if needed, push the reset button. Also, you can leave the device on for days , battery consumption is ridiculous .

The manual " [[ reset/temporary disable ]] " pushbutton is used to reset the circuit ( and disable it as long as you hold it)
in case a not desired flash got caught by the counter
(you could also prevent this by optically shield the slave cell and the on board flash coupling) .

Construction:

This may not a $$ worth project. I did this because I like to. I bought the black box case ( several $$) ,
a battery holder that I did not use ( to save a quarter of inch in the box space ) , photo connecting wires
( which anyway , I got to buy for general use).

All electronic parts , chips, leds, pushbuttons, selector, hardware ... came from junk box. ( if you notice the chip's legend, you could see that they dated some decades ago )
The main tools are all sort of files, big, small, round, square , etc ... to make presentable holes in the plastic, drill , hot glue gun, super glue
and of course , a minimum of electronic instrumentations (meters, logic probe ...) ; a scope is always welcome.
Last, lot of patience and passion are necessary , if not, go get a Minolta dedicated flash at store .


Photos coming :

MFI2 mounted on Metz bracket

MFI2 mounted on Metz bracket, Rear view

Slave cell mounted on a temporary bracket (old flash bracket for Coolpix 950)
Slave cell
Slave cell
Slave cell

Settings and led display

Exterior view
Exterior view
Exterior view
Exterior view
Exterior view

Construction details

Inside View
Everything's inside , ready to close the cover ...
The last circuit is not planed at the beginning, so I had to .. squeeze it a bit

MFI2 bracket for the Metz 45 side slot (fiberglass laminate)
4011 and opto-isolator
The counter with the selector
pre-mounted Leds
Home made for pin 1 and pin 4 contact on D7 hot shoe


All pics are at:
http://www.pbase.com/kcan/


... The End


NHL suggested me to use processor , but I am not equipped to do that ( anymore)
Thanks again to NHL and many others for interesting discussions we had way back in the old post on this subject!
I still use this on my D7i , until I get my Metz adapter which offer ADI mode also.

KCan
August 2002, repost
( original posting : May 2002)
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Old Aug 20, 2002, 5:02 PM   #2
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Default The next phase

Ages ago I wondered why a slave unit couldn't be made to control flash output based on the duration of the original TTL controlled flash. Someone has done that. Ikelite has a digicam compatible underwater flash system that maintains TTL control without a physical connection to the camera inside the housing. The slaved flash mimics the output of the built in flash which essentially completes the feedback loop. Non-dedicated flash with full TTL control. I wonder what it would take to do the same with a Metz.
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Old Aug 20, 2002, 7:58 PM   #3
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This is interesting , I never heard of this b4.
But in the case of camera using a preflash to compute TTL ( our case), should it preflash also the slave? or disable the slave for preflash computing , and just flash it after ? It may not work since after the preflash, the TTL data was already computed, based on the duration of the main flash only .

Could it be the reason why Metz can't integrate TTL in the SCA ?

[Edited on 8-21-2002 by KCan]
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Old Aug 20, 2002, 9:12 PM   #4
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The slave flash would have to duplicate each pulse of the main flash in equal duration. Say for example the main flash is covered by the slave unit as the Ikelite does. None of that light is reflected back to the lens. The CCD senses the returned flash from the slave only. The slave will of course have more power but this doesn't matter. The camera sets the main flash duration based on the returned light from the pre-flash and compensates just as it would for an unusually reflective or close subject.
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Old Aug 20, 2002, 9:33 PM   #5
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In theory it could have worked, and if flashes stay simple as they should...

Minolta in their wisdom (as well as Canon) also sends low-power digital control pulses through their flash's head to control remote slaves wirelessly, both before and after the main pulse. Just as we discussed before in the old forum this is where a low cost microprocessor like a PIC would come into play (KCan circuit would pass them right through)... It's unclear wether theses pulses are disabled or not when the wireless remote is disabled in the main menu. If they are then it could be done...
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Old Aug 21, 2002, 1:03 AM   #6
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... more and more interesting , but I guess it's Mission Impossible to obtain full specs of flash control from Minolta ( or other makes) , isn't it ?
On the D7 , signal on pin1 and 4 seems to be pure "curtain" signal , no pulse , unless my too aged 10 Mhz scope miss them.

BTW, do you think/know if the the Dimage's flash use multiple pulse flash , or just 1 pulse ( variable duration as the classics ) ?
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Old Aug 21, 2002, 5:43 AM   #7
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KCan

In the 7/9xi film days, the wireless slaves can be controlled through the built-in flash, a 3500/5200/5400, or an optional IR controller (The IR controller now automatically turns off when the D7(i) is turned on!). Can you check the same pin with the wireless flash enabled on the D7i? if the control pins pulses then we are in good shape (since we all know how to turn it off), and it is a variable duration as the classics in the non-wireless mode. You can also verify this with a scope on the slave eye sensor rather than the camera pins...

BTW this is exactly what you guys all wanted, and Minolta already has the control for wireless slave built-in! Not only it control multiple flashes, but also with different ratios and 4 independent users can shoot @ the same time on different codes...(Hey may be I should hook a slave eye to the logic analyzer... but I don't have a D7i, Duh)

[Edited on 8-21-2002 by NHL]
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Old Aug 21, 2002, 9:46 AM   #8
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I wasn't thinking D7/wireless specific. No need to analyze logic, just need to emulate what the main flash does in real time. Ikelite has done if for a not unreasonable cost, about $425 which is not bad for underwater, and it works with any camera.

[Edited on 8-21-2002 by padeye]
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Old Aug 21, 2002, 12:52 PM   #9
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Hey colonel NHL, I just notice that you are promoted to senior grade

I will see about the signal .
About slave eye , I guess it's better to hook an analyzer to the sensor alone , b/c I suspect some primary debouncing circuit in the packed slave eye ( that's also what I did on purpose inside my MFI's)

Padeye,
The ideal for me would be Metz wireless receiver emulating a Minolta D flash , and take advantage of all D7i wireless feature .
But, must be more logical and more economic to go with a Minolta system in this case ...

How come that the Ikelite principle has not be more "popular" ?
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Old Aug 21, 2002, 1:23 PM   #10
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I guess I got promote while debating 'hot-air' with smjs over the merit of the microdrive... and found out that we both work on the same airplane!

The Ikelite was done out of necessity because of the difficulty making the various sync wire sea-waterproof. I think it'll will work for through the lens TTL, but I doubt its effectiveness with the pre-flash TTL or ADI; However, it should not be hard to make a circuit track the ON time of a flash pulse. The problem would be more how to turn the Metz OFF once it's triggered... Metz must have a way since they just did the cable!

[Edited on 8-21-2002 by NHL]
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