Minimum power for Speedotron 102 flash head (MW8QVC tube)

I have a pair of Speedotron Blackline power packs and 3 102 flash heads with MW8QVC flash tubes. The tubes are rated at 3200ws maximum. I've been using these for wet plate collodion and direct-paper exposures.

Recently I've been fooling around with traditional Tri-X 400 135 film and have found that getting the flash power to three heads down to an acceptable level to be a bit of a problem.

I was wondering if anyone knew the MINIMUM power that the MW8QVC Speedotron tube will reliably flash at? My power packs have three 1200/800/400 channels, each with two sockets. One of the packs further has a power reduction dial calibrated in f/stops. Using the 400 watt channel and dialed down 3 stops, I figure this to be 400/2/2/2 = 50ws. I am assuming the f/stop control simply reduces output power and assumes light output reduction from the tube is linear.

I do get flash output from one tube on the channel at this very low setting, but have no idea if the tube will flash reliably at that low power level.

The Speedotron site and Google were not any help.

Any thoughts?

Best,

Don

Speedotron were(are?) made in Chicago. They have an address in Bartlett. Phone is: (630)246-5001

I have not run into a 'minimum power' level on studio flash tubes. Speedlight tubes are limited by the control circuitry to about 1/256 power, and your flash tubes are limted by the lowest power level on the pack, divided among the number of heads plugged into the same channel.

My Dynalite M500 one (of two) channel goes down to 62 w-s, plus there is additional variator to permit 31 w-s, and there are two connectors in that channel so each head gets only 15 w-s. Switch settings permit 1/4 power, the variator gets the pack to 1/8 power, and dividing it into two heads puts 1/16 power into each tube...far more than the 1/256 power level that speedlights can achieve.

wiltw said:

I have not run into a 'minimum power' level on studio flash tubes. Speedlight tubes are limited by the control circuitry to about 1/256 power, and your flash tubes are limted by the lowest power level on the pack, divided among the number of heads plugged into the same channel.

My Dynalite M500 one (of two) channel goes down to 62 w-s, plus there is additional variator to permit 31 w-s, and there are two connectors in that channel so each head gets only 15 w-s. Switch settings permit 1/4 power, the variator gets the pack to 1/8 power, and dividing it into two heads puts 1/16 power into each tube...far more than the 1/256 power level that speedlights can achieve.

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I think you are right. Each of the 2400ws Speedo packs has a 1200, 800. and 400 ws channel that can be ganged or isolated in some limited ways. Assuming they are set to isolated channels, the lowest power level is 400ws. That channel has two connectors, so if two 102 heads are connected, each gets 200ws. The pack with the variator allows up to a 3 f/stop reduction, further reducing the power in all the channels by up to a factor of 2^3 or 8 or 200/8 = 25ws per tube.

I guess the fact I am getting flashing at these low powers indicates that things are ok. I was most worried about flash-to-flash consistency of the light output.

Regards,

Don

Why are you asking us instead of dialing the pack you have down like you're asking about, and pressing the button a few times to see what happens? If you are functioning at the margins of the equipment as you think you are (I am not sure this is the case) then the results may be inconsistent, depending on the kit in front of you, and only your case should matter to you.

My money would be on them not designing the equipment to be set to a setting that did not work.

DonF said:

I guess the fact I am getting flashing at these low powers indicates that things are ok. I was most worried about flash-to-flash consistency of the light output.

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It is unfortunately true that one brand of less-expensive monolight has been known to shift to the pink (Red) direction as its power levels are dropped to its two lowest power levels. The community griped so much about that, that the same company later introduced a new monolight that did not exhibit such color shift at lowest power settings.

mdarnton said:

Why are you asking us instead of dialing the pack you have down like you're asking about, and pressing the button a few times to see what happens? If you are functioning at the margins of the equipment as you think you are (I am not sure this is the case) then the results may be inconsistent, depending on the kit in front of you, and only your case should matter to you.

My money would be on them not designing the equipment to be set to a setting that did not work.

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I have, of course, tried dialing down to the minimum on the 400ws channel with two heads connected and firing off some tests. The output seems consistent.

I am asking the plural "you" for the same reason anyone asks a question here....to get the wisdom of others' experience.

Don

I still run Speedo Blackline and have successfully only gone down to 400w/s with your setup.

I would suggest getting some ND filters for your lights or I have an associate that painted his spare reflector flat black
and it took out 1.5 stops and added a more dramatic flair to the nudes he was shooting....

Good Luck or get a 400w/s blackline pack on Ebay which you can scale down to 100w//s using your heads.
Been there done that....Those smaller blackline packs are reasonable cost $ (if you can find them).


Good Luck
Harlequin

mdarnton said:

...If you are functioning at the margins of the equipment as you think you are (I am not sure this is the case) then the results may be inconsistent, depending on the kit in front of you, and only your case should matter to you. My money would be on them not designing the equipment to be set to a setting that did not work.

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I've shoot Speedotron for decades. If you can dial the pack down to any level (via the knob, channel switching and channel choice), you'll get consistent light. If there's an available outlet on the channel you're using, sticking another head on it and pointing it off into another room will reduce that channel to half (that's called a "bleed head". Just don't lie it face down on the floor!) Someone used to make an in-line power reducer for speedo, haven't seen one of those in years though.

You can use ND gel, or you can chop up some metal window screen, which won't fade over time. Screen doesn't come in reliable "1 stop" levels and so on (unless you buy professional wire scrims), so testing or metering is in order. With softboxes, ND is tougher. You can get some black bridal net and glue it to velcro and use it like a fabric grid; might take a couple layers, but it's cheap and freakishly handy. Amazed this isn't a standard manufactured item.

Matthews-style black net flags are handy too, but require a c-stand optimally. Those are better for things like "her face looks great but her boobs are too bright" as you can feather the light down without fully blocking it.

You can hunt down a 400ws pack - they're awesome, they're tiny, they're great for wide DOF and so on - and they're pretty dang rare. 805 packs are more regularly found, they do dial down, but they're not much less than a 1000 head. They are nicely portable though, pretty small size. Speedo also made monolights for about a minute, the Force 5 and Force 10. The 5 is 500 WS. They have full dial-down on the back. Didn't catch on as they were mostly plastic I recall, but never used one.

I bought a beater head on eBay with no tube for fifty bucks, took some parts from it and made a mount that will hold an on-camera style strobe - it's a cool location light; I love the 11" grid for female faces. I use a Vivitar 285 in it and a radio slave. Battery powered, manual light levels - makes a fast light for clamping to a ceiling or something with no cables needed. Got this shot with it, used a tungsten full-CTO gel on the head; shot this at happy hour so there was no good way to use packs and heads and stands:

Awesome post and shot. Thanks for all of the great info. I have tried the bleeder head, and it seems to work as-expected. The light falloff with the stop reduction dial seems pretty accurate, even if the 400ws channel is split across the two outlets. I think I will scout around for a lower power pack, as the two 2400ws units require too much playing around and Rube Goldberg techniques.. Or maybe just get a few modern monolights.

Regards,

Don

Don, your post #4 is correct. Dial down the adjustment knob, plug 2 heads into the lowest output bank, switch that bank to "isolate". This is the minimum energy output configuration that can be delivered to one head.

To get a less light on the subject, M Carter gave good suggestions. I would also add that moving the light farther from the subject, and using a significantly larger modifier can help, albeit with a different quality (more or less directionality, more or less enveloping character).

There are always speedlights...

DonF said:

Awesome post and shot. Thanks for all of the great info. I have tried the bleeder head, and it seems to work as-expected. The light falloff with the stop reduction dial seems pretty accurate, even if the 400ws channel is split across the two outlets. I think I will scout around for a lower power pack, as the two 2400ws units require too much playing around and Rube Goldberg techniques.. Or maybe just get a few modern monolights.

Regards,

Don

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Did my usual "not ready for bed, let's dig around on ebay" the other night - I think there were at least 2 1205 (modern, dial down) packs, - those are great - and an 812 (older, no dial down, lowest 1-head output is 100 ws, worth a couple hundred if you just need more packs). I have one of those and a 1201A (lowest 1 head output is 200 ws, no dial down). With the non-dial-down packs, I often use one of those for my key, and then between dial down (I have 2 805's and a 1205), I can finesse other lights in the scene to align with the key (like get my key at 5.6 and then use a dial down for rim or hair or BG lighting). The 805 is really one of the best things Speedo ever made - really tiny and light, almost the same kick as the bigger 1205, uses a standar computer-style power cable, 1/4" sync and a built-in slave.

Funny, all those years of shooting 4x5 product and I was cramming extra heads into the softbox, never enough light. Now it's "how the hell do I tone this all down??"