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04-11-2016, 03:40 PM   #1
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Noob notes on off-camera flash.

Tools:

Pentax K-5 with the PC port cover unscrewed and VERY carefully set aside.
Pentax AF200Sa thyristor flash. This was an heirloom for me, but I'm sure e-bay can provide it or an equivalent.
Hotshoe adaptor with PC cable (i.e. for turning cold shoes into hot shoes) - again from ebay, I think it cost me CDN$16?
Male-female PC extension cord. This cost me AUD$10 on a recent trip and is easily 1.5m long, maybe 2m.

It started out with an experiment to provide illumination for my slide copier rig. This failed mostly because I was choosing lenses poorly, but I was certainly getting enough illumination. It's inconsistent, but read on for a potential solution.

The first thing I found out was that this arrangement lets me hold the camera and flash at arms' length and discharge from any direction I pleased, with (naturally) no need to maintain direct line of sight between the on-camera flash and the front of the now semi-remote unit. Naturally some tweaking of exposures, including some test shots, is required until experience is gained, primarily because the connection is a "dumb" one (it can only transmit a signal to fire) and because the flash is wired to behave as if it's always on the camera (and always the same distance from the film plane). When this assumption becomes incorrect, one is flying strictly on one's own.

The other thing I found out, and only realised afterwards, was that if you hold a finger or thumb over the thyristor sensor, you can trick it into always firing at full power. And while these AF200Sa's are certainly not the last word in raw luminance, when you bounce one off a fairly low ceiling at relatively close range, you can get some really impressive illumination.

Further experiments are of course necessary. But one thing that occurred to me is that once I have the appropriate lens setup back on the slide copier rig, I could stop all the way down to f/22, cover the thyristor sensor with something and let fly. This sort of slide copier work is just what a corded flash was made for.

04-11-2016, 05:24 PM   #2
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Not having ever done slide duplication, I am wondering why you use f/22 for that?
04-11-2016, 10:17 PM   #3
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I think it was because the flash is firing at full power, and that plus the small distances meant the small aperture was needed for correct exposure .....

It's good to hear that you've got it all working, and it seems an economical setup! I was wondering though, does the flash not have any manual power settings to allow a much lower output? This could certainly save you a lot of exhausted batteries .....
04-11-2016, 11:17 PM   #4
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...and a lof of diffraction as well...

04-12-2016, 03:40 AM   #5
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QuoteOriginally posted by mcgregni Quote
does the flash not have any manual power settings to allow a much lower output?
Not the AF200Sa, no. The AF200T did, and more importantly it had a manual mode with half, quarter and eighth powers. I may yet get one. As things stand, the discharge is much less powerful when the thyristor is running the show, but then the exposures are not necessarily constant. No doubt a bit of fooling around here and there will get results, but there just hasn't been the time recently - other things have taken over a little.

The obvious next step, I guess, is to try it with the AF540FGZ-II on the hotshoe instead of the 200Sa, with the discharge strength set to manual.
04-12-2016, 04:23 AM   #6
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...or what I consider to be the best manual flash for the money, Yongnuo YN560 mkIII or IV.
lots of power, fast recycle time, sturdy construction, easy to set up, mkIII has built-in RF receiver, mkIV both receiver and transmitter.
04-12-2016, 05:06 AM   #7
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If you're stuck with tricking them to fire at full power for consistency, you can get ND gels to reduce the flash power - make sure there's sufficient airflow between the flash head and the gel as full power may end up pretty hot. Regular ND filters on the camera would also work, or you could stick them between the flash and the slide (they'll be large enough to cover the slide up close)

You can also diffuse with copy paper or parchment paper or just about anything whitish, a few layers can really cut the power down and provide more even illumination, like a light table. Colour shifts can be an issue but if you're setting up something semi-permanent for slide copying you only have to sort it out once.

Finally, moving the flash back will also help, assuming you have space or are allowed to knock out a wall or two.

But yeah, auto-thyristor and copy work requiring consistent results can be a little piece of madness...

04-12-2016, 06:12 AM   #8
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<Inventor hat on>
You could try covering the thyristor with a cap and put a led in it, diffused with something inside the cap (opaque plastic etc) and hooked up to a dimmer.
That way you can illuminate the sensor on the flash with an adjustable amount of light.
It's something you can build in 5' or even buy ready-made.

The batteries, the flash, your eyes and the Planet will thank you ;-)
04-12-2016, 07:18 AM   #9
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I'm guessing you're using this corded method, apart from the fun and experimental aspect with an old flash, because you don't have line of sight for optical triggering between your K5 flash and AF-540FGZII ?

You may be surprised by how many corners the optical signal can get around, as it bounces and reflects off things. You can't use this method though with a non-A type lens (uncoupled aperture), as the trigger signal needs P-TTL to function. You might be able to use optical triggering with the 'dumb slave' (SL2) mode on your AF-540FGZ, with manual power control (down to 1/256 -) .... Just shade the built-jn flash from illuminating the subject if possible.
04-12-2016, 07:51 AM   #10
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QuoteOriginally posted by mcgregni Quote
I'm guessing you're using this corded method, apart from the fun and experimental aspect with an old flash, because you don't have line of sight for optical triggering between your K5 flash and AF-540FGZII ?
That's what I'm worried about, yes. However, in light of what you've said, I shall give the off-camera mode another go. The slide copier unit should be sufficiently light-sealed from the front. Any back-reflections from surfaces behind it should get lost in the main discharge. The lens I've found works best is my DA35 Limited Macro; the MFD is so short that I can simply fit the slide copier on and get sharp focus, although the problem is that it then crops the edges a little and I have to stand it off using a front filter and a screw-on rubber hood (that has long since lost its rubber). The first roll of B&W I developed, I was able to use brightly sunlit snow as the background lighting, and that worked exceptionally well since it was featureless and more or less evenly lit. However, with spring rolling in, other means will become necessary.

The other thing, of course, is that I'm looking towards the day when I won't have an on-camera flash any more (K-1).
04-12-2016, 08:44 AM   #11
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Ok, with the DA35 you have no issues with wireless P-TTL triggering. You can set the triggering mode to 'controller' in the camera custom menu, and this means that your built-in flash will not emit any light into the scene , it will just send a trigger flash. Keep your AF-540 in SL1 mode, and set 'wireless Slave' with M (manual power) mode. You have to set the power on the AF540 directly (flash compensation does not apply in Manual).
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