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Old 18th October 2017
RobEW RobEW is offline
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Olympus Flash RC mode – occasional dramatic underexposure

I’ve not tried RC seriously until a few days ago, and am getting very erratic results from it, including a large number of shots which are dramatically underexposed.

I’ve mainly been using the E-M1 with the accessory flash (FL-LM2) mounted on the hot shoe as master, and one or more Metz slaves (I have a 50 AF-1 for general use and two 26 AF-2s mainly for macro use mounted on a flexible non-electrical twin arm.)

I’ve also tried switching from E-M1 / FL-LM2 to E-M5 II / FL-LM3 (as I sometimes wondered if there was some kind of timing fault with my E-M1).

Camera has usually been in aperture priority mode, but occasionally manual.

For the sake of simplicity, on the camera RC menu I’ve been using just group A, set to TTL with no flash exposure compensation. The Master has also been set to OFF in the RC menu, meaning I don’t want it to contribute to the exposure. The RC menu also has an option to specify high, medium or low intensity for the master’s pre-flash sequence. I selected High as I can see no downside to this.

On the Metz 50 I’ve been using Slave mode, group A (without “servo” which is their term for a dumb slave). On Metz 26 I just press the “slave” button (which is acknowledged by a LED). The Metz 26 manual piece on Oly RC mode says “For slave flash unit 26AF-2, slave group A as well as all channels 1, 2, 3 & 4 are always set”.

As my title suggests, I’m sometimes getting great exposure, but sometimes – rather unpredictably – dramatic under-exposure. I’m unclear what factors are causing this and what remedies if any are appropriate.

A bit of research with Google finds hits on various forums showing that lots of people have similar problems, and lots of causes and possible remedies are hypothesised. I get the overall impression that remote flash is a bit of a black art, a bit hit and miss, that a lot of experience and judgement – and sometimes extra equipment such as radio triggers – is required to get it to work reliably, (and of course even more experience and judgement to get great lighting setup). Some of the experts seem to ignore RC mode and TTL and instead use multiple flashes in manual mode, dialling in settings to each flash individually and using dumb slave mode to trigger or radio triggers.

The “Strobehacker” blog ( https://strobehacker.tumblr.com/post...know-about-the ) has a lot of apparently sound information about how RC works. Briefly the commander flash send a series of low intensity signal flashes to convey the instructions on the camera’s RC menu to any TTL slaves. The TTL slaves (and possibly master) then issue a brief low intensity pre-flash and the sensor measures the received light. It then calculates the required flash settings and sends out more code pulses to instruct the slaves about strength required for the main flash. Finally (presumably after the shutter has opened) the master sends a pulse to trigger the actual exposure flashes.

Strobehacker also says, inter alia:

“Like other manufacturers’ optical wireless systems, this works great at short distances and under subdued light – but gets janky at longer ranges, in bright sunlight, or if there isn’t a clear line of sight between the control flash and the receiver flash.”

Gary Ayton also has useful insights his slightly dated wiki, e.g. here http://www.ayton.id.au/wiki/doku.php...mote_ttl_flash

Various web forum discussions have identified other possible causes and remedies for erratic dramatic underexposure:

- the master flash is somehow over-represented in the calibration pre-flash, and thus the distorts the exposure calculation
- bright reflective items in the foreground of a shot can fool the calibration pre-flash because of the way it extrapolates from low intensity light to high intensity.
- having Master OFF in RC menus is blamed by some people, as (they say) the Master ought to be part of the illumination


Suggested remedies:

• Some say we should (in a sort of moral obligation kind of way) have Master ON in RC menus. (I’m not comfortable with that; partly because you may not want light from that direction and partly because TTL sampling and calculations should be based on what equipment you’ve chosen to enable.) It does seem to solve the underexposure problem for some people.
• Some have suggested a FL-600 on hot shoe as master, pointed at ceiling so the light reaches all slaves but has minimal impact on subject. Seems an expensive option …
• Various people have suggested different kinds of purchased or homespun infrared filter over the front of the accessory flash, so it still sends signals to the slaves but doesn’t send visible light into the image.
• As ever with cameras, there’s an expensive tech fix – purchase radio triggers of various sorts. Few support RC mode though.
• I’ve not seen this recommended, but I wonder – depending on scene layout – whether sometimes a hot shoe cable to the master might make it easier to point it at slaves but not into the scene.

Is anyone else experiencing this, or has solved it, or is interested?

If I get time I’m hoping to try some more careful experiments to see what factors affect my manifestation of this problem. What are the most important controlled varuiables and independent variables I wonder?
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Old 18th October 2017
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Re: Olympus Flash RC mode – occasional dramatic underexposure

Quote:
Originally Posted by RobEW View Post
On the Metz 50 I’ve been using Slave mode, group A (without “servo” which is their term for a dumb slave). On Metz 26 I just press the “slave” button (which is acknowledged by a LED). The Metz 26 manual piece on Oly RC mode says “For slave flash unit 26AF-2, slave group A as well as all channels 1, 2, 3 & 4 are always set”.
The Olympus RC mode only works with guns that are RC mode compatible. Having the Metz guns in "Slave" mode means they will fire as soon as they see any flash. If they see the pre-flash from the command unit, they will fire and when the main trigger flash is emitted, they will not have had time to recharge to full capacity, hence you get an under exposed image.

I only use RC mode with FL50Rs & FL36Rs, but have had the same underexposure, when I have forgotten to switch them back to RC mode, having used them as slaves.

I tend to only use Manual mode exposure with the shutter at 200 and Aperture at about f/4 adjusting ISO a little to get the exposure I want, and using the RC to adjust the lighting ratios of each gun.
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Old 18th October 2017
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Re: Olympus Flash RC mode – occasional dramatic underexposure

Thanks for that information.

My understanding of the Metz terminolgy is a bit different but I might be wrong. The Metz manuals seem to have been translated into English by someone who isn't a native English speaker and who also doesn't use the same terminology as the Olympus manuals. But I think Metz uses the term "Servo Mode" to mean dumb slave (i.e. Metz unit flashes as soon as anything else around it flashes, and it uses whatever settings have been applied to the slave unit, rather than what the camera body might want). If you select "Slave Mode" rather than "Servo Mode" on the Metz, it then asks you specify which group (A, B or C) you want to be in and which channel you want to use, which implies it's planning to fully obey the Oly RC protocols.

Last edited by RobEW; 20th October 2017 at 07:33 AM. Reason: typo
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Old 18th October 2017
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Re: Olympus Flash RC mode – occasional dramatic underexposure

Reading pages 91-94 confirms what you say:

http://www.metz-mecatech.de/index.ph...e304e876f6994b

So in Metz speak "Slave" mode, it's back to the techniques to get that control flash sequence to the remote guns in as clear a path as possible. I did once use a small mirror to turn the light around a corner.

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Old 23rd October 2017
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Re: Olympus Flash RC mode – occasional dramatic underexposure

I'm wondering if my little FL-LM2 is a bit erratic. I don't have a spare to test this, nor a more powerful master such as FL-600R or Metz 52. Or maybe it's as simple as poor hot shoe contacts ...

I seem to get similar erratic outcomes with E-M5 II and FL-LM3 but I haven't tried often enough to be sure.
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Old 23rd October 2017
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Re: Olympus Flash RC mode – occasional dramatic underexposure

Try using 2nd curtain flash setting "Sync2" That gives fractions of a second more time for the system to work in. It's clutching at straws, but something I use most of the time even at shutter speeds of 250.

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Old 25th October 2017
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Re: Olympus Flash RC mode – occasional dramatic underexposure

Someone suggested changing metering mode too. I stuck it on the intelligent setting when I first got camera and haven't touched it since. I'm old school, brought up on film cameras, so quite happy to look at what I'm being offered in viewfinder and then use focus and recompose or exposure compensation if needed. But for flash photoraphy maybe that's not appropriate. I'll check out spot metering.
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Old 25th October 2017
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Re: Olympus Flash RC mode – occasional dramatic underexposure

I've been to a couple of Damien McGillicuddy's talks on studio lighting and he is pretty dismissive of RC mode (and more generally of optical signaling used to control slave devices). His advice is really two fold:

- Use radio controlled flashes from a proper trigger on the camera

- Buy a flash meter and set flash power manually.
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Old 25th October 2017
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Re: Olympus Flash RC mode – occasional dramatic underexposure

The Godox system seems to have some merits, combining (if I understand correctly) the functions of master flash and radio trigger in a single device, and slave flash and radio receiver in another single device.
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Old 28th October 2017
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Re: Olympus Flash RC mode – occasional dramatic underexposure

One thing which would help a lot would be for slave units to have as much flexibility in being able to adjust the orientation of the light / infrared detector as they provide for adjusting the flash head. Or have detectors all round instead of just in one spot. For instace on my little Metz 26-AF-2 https://www.metz-mecatech.de/index.p...36a8ebc1bdd575 , the "slave sensor" (which I take to be the part which detects light signals) seems to be in the front, so that if the Metz is between camera and subject and pointing towards the subject, then it is unable to receive a direct light signal. The sensor should surely be on the back of the unit for this application. Yes, I suppose it's possible to start using mirrors and the like to get the signal round corners, but it seems cludgy and labour-intensive and error prone.
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Old 3rd November 2017
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Re: Olympus Flash RC mode – occasional dramatic underexposure

I use a similar setup for macro but with two FL-300Rs and mostly in camera manual mode. When I get similar exposure problems is mostly when the 300R batteries are close to exhausted and take longer to recharge. However, if the pop-up master has been knocked and is down, that leaves the exposure to ambient.

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