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Longcove
30th December 2010, 04:02 PM
Hi: My first post and slightly weird! I've custom built a ring flash for my 12-60. Six 1 watt white leds. Overdrive them and they give a huge amount of light To trigger it I've just been using an opto sensor and the built in flash but the stray light is a nuisance. Otherwise it works well for my ring flash is on for the same duration as the camera flash so I get TTL control. Very simple. Also made some gels to change colour temperature to match daylight. The simple solution for stray light is to mask the camera flash head but a wired control would be elegant. I happen to have a spare flash connector cable.
So the question. Does anyone know the connections for an Olympus camera? I haven't had time to work out whether the centre contact is merely a trigger and actual flash duration is controlled by one of the other contacts.
It is not a question I've ever had to ask myself before, but does anyone know?
Thanks.
Donald

theMusicMan
30th December 2010, 04:07 PM
Hi Donald

Welcome to the forum by the way... :)

I picked up an extension cable for my FL-50 from eBay, I believe it's the same as a Canon cable... I'm sure this is what you could use.

Longcove
30th December 2010, 04:24 PM
Hi John: Thanks for reply but I'm really asking about the connections. What does each one do. I think I will probably have to sit down with the oscilloscope and work it out. Then again why give myself the hassle, it works TTL at the moment.
Thanks.
Donald

Wreckdiver
30th December 2010, 04:48 PM
The centre contact is the trigger, which fires when shorted to ground. I haven't sussed the other 3 but they would be for the TTL.

Steve

photo_owl
30th December 2010, 04:56 PM
I think you are confusing (or in danger of confusing others) with you use of TTL in this context.

What I believe you are doing is triggering a fixed flash output and your camera is then operating in either A or S mode for the exposure in the same way that it would with any other light source - it will be successful over a particular range of circumstances relating to camera settings and ambient lighting based on the output level.

This is not TTL flash - there is no camera control of the flash output level.

I did have the flash connections somewhere - if I can find them I will post or link.

Not sure that you need more than centre 'fire' though - all the rest are about TTL control and would require an Olympus dedicated TTL module at the other end.

Edit - I see Steve typed faster!

Longcove
30th December 2010, 06:22 PM
Hi Photo_Owl: It is TTL! The camera is fooled into believing that the light hitting the subject is from the built in flash. But the camera flash is blanked off by the ring flash. So the only light hitting the subject is from the ring + a bit of ambient. The trick is to trigger the ring from the camera flash. TTL flashes work by varying the time the flash is emitting. When the camera senses that sufficient light has hit the subject for correct exposure it fires an SCR or transistor which bypasses the flash tube so the arc stops. So my simple ring flash just uses a photo sensor insensitive to ambient light but sensitive to the camera flash. When the flash is emitting the ring turns on. When the flash stops the ring stops. This is the dead simple way to control a ring flash.
However, I have an Olympus FL-CB02 flash cord designed to go from camera to the external flash gun off-camera support and thought that it would be more elegant to use this. The centre pin only initiates the flash and one of the other pins will control the cutoff. In fact I wouldn't be surprised if the flash on/off was controlled by another pin and that Olympus flashes ignore the centre pin. Not sure about this though! Another pin will be used for serial data so that the flashgun talks to the camera - info about zoom, camera on/off, and so on. At least that is how I imagine it will work otherwise we don't need so many pins! The centre pin has to be there to control third party non-TTL flashes - this is the convention among flash gun manufacturers. The arrangement of the extra pins forces you to buy dedicated flashguns thus increasing profits! Also the serial data will probably vary by manufacturer.
The reason for thinking about using a wired connection is that the stray light from the camera flash is a nuisance. It may be easiest to made a 'do-dad' to slip over the flash tube to only emit a narrow beam towards the photo receptor on my ring flash. It probably isn't worth the effort to find out about the pin arrangements and I should stick with what works.
As a matter of interest my ring flash is powered by two BLS1 batteries in series - just made a plastic box to house them. These drive a DC-DC converter to give me about 35 volts. I have a constant current source to drive the LEDs. The constant current sources is controlled to give various currents to control light output. The LEDs are switched by a MOSFET controlled by the opto sensor removed from an old Vivitar flashgun. Total cost $20 and elbow grease. The hard part is actually making the ring which slips onto a 72mm Cokin style adaptor.
It doesn't look like much but it works as well as the 'real' ones which cost a little more.
Donald

Graham_of_Rainham
30th December 2010, 09:08 PM
Any chance of some images of this thing... As a DIYer I too have built some "interesting" lighting rigs.

Can we see some results as well please

*chr

photo_owl
30th December 2010, 09:57 PM
Hi Photo_Owl: It is TTL! The camera is fooled into believing that the light hitting the subject is from the built in flash. But the camera flash is blanked off by the ring flash. So the only light hitting the subject is from the ring + a bit of ambient. The trick is to trigger the ring from the camera flash. TTL flashes work by varying the time the flash is emitting. When the camera senses that sufficient light has hit the subject for correct exposure it fires an SCR or transistor which bypasses the flash tube so the arc stops. So my simple ring flash just uses a photo sensor insensitive to ambient light but sensitive to the camera flash. When the flash is emitting the ring turns on. When the flash stops the ring stops.

I hate to disagree with anyone, especially someone as knowledgeable as you, but what you have operating isn't TTL Auto flash mode.

As you point out for normal (non-FP) operation flash power is a function of the duration of a fixed intensity. In TTL Auto on the E's and most digital cameras (actually most cameras - the OM2 being slightly different by reading it from the actual film surface if my memory serves) the camera will control this output by presetting it based on a pre flash around 1/1000th of a sec before the shutter and main flash.

In Auto mode the flash output is actively monitored by either a thyristor on the flash or the camera's metering system for the on-board unit in the manner you describe. Nothing wrong with that (and much that's better in many ways than TTL Auto mode)




The arrangement of the extra pins forces you to buy dedicated flashguns thus increasing profits! Also the serial data will probably vary by manufacturer.


Indeed it's the signaling protocols that are incompatible - I believe there have been a number of similar pin arrangements to functions over the but functionally falls down on the electronic side!


Welcome to the forum and I look forward to reading more.

Longcove
31st December 2010, 12:07 AM
Hi Photo Owl: Not that knowledgeable! I don't mind disagreement for we are having a discussion, not an argument. The reason I joined this group is because I'm fed up with people on the dpreview forum who constantly name call and too many behave like idiots. There if you disagree you are called fool, and it ain't conducive to learning.
What the ring is actually doing is mimicking the built in camera flash. The camera flash drives the ring so if it flashes then the ring flashes for the same duration. The only problem is to get the ring to emit similar amounts of light - hence the adjustable current through the LEDs. The camera thinks the light is coming from the built in flash.
Now, you seem to be questioning the TTL part of all of this - but I'm not sure? The built in flash doesn't have any built in monitoring so the flash duration is based on what is happening at the camera sensor - dunno whether it off the image sensor or off a special sensor, I thought I read somewhere that there is a separate sensor but the location is unimportant - this is TTL operation. It doesn't sound right to have a second sensor but I'm not sure, perhaps I'm confused with diagrams of the E-330 when it first appeared
You can use off camera flashguns in a different way. The FL-36s and 50s or the Vivitar 285HVs or whatever has a built in sensor. The 36 and 50 in Auto mode get information from the camera as well as from the flash. The flashgun then computes the flash duration based on this info and the input to its sensor. Basically this replaces all the calculations done in the old days when one had to be able to count! The Vivitar is a little cruder in that it doesn't talk to the camera so you have to tell it how the camera is set. I mention the Vivitar for it is a real workhorse and I run it off camera with a Peanut flash trigger.
Anyway , I now suspect that I've asked a question without an answer unless you find something.

Graham asked about images and I will post them when I find out how. It will not be for a while for the camera and the ring are a few thousand miles away.

There is an interesting website called Fuzzcraft - http://fuzzcraft.com/ringlight4-0.html - run by Joris. He has produced a number of rings and is into using fibre optics now. As far as I know no one else has used the camera flash output to trigger the ring as I have, but I haven't actually looked.
Donald

photo_owl
31st December 2010, 12:32 PM
Donald - I'm not questioning whether there is TTL metering going on at all; I was simply pointing out the risk of confusion between the E system TTL Auto functionality and what you had 'going on'.

Unfortunately all I have managed to do is make sure that confusion happens!