y4m4
Cal Graham
Got an old auto flash that isn't of much use to you anymore? Wanna manually control its output? Good news it will cost less than $10 at RadioShack! It turns out that if you put a variable resistor(potentiometer) in place of the little light-sensing cell you can manually control practically any flash.
So to do this you have to open the flash up. You'll need some small screw drivers and will probably need to take off a decal or two. Once its open cut the wires that connect to the photo cell. Make sure you leave enough wire on each side to strip and solder.
If you want to eliminate the photocell all together and go full manual just hook the potentiometer in place of it. On my potentiometer you use the left and middle terminals. Test it out! You'll need a potentiometer that goes to about 200k ohms if you are planning on taking the cell out or use a switch to bypass the potentiometer.
Now the way I'm doing it is as follows. I am hooking the potentiometer and photo cell in parrallel with a switch so I can have full use of my original auto modes. Take a look at the attached image for circuit diagram. The other plus is that I can have full power without buying another potentiometer, mine is only 100k ohms, not enough to fire the flash at full.
The way my vesion works is that you need to have your flash set on 'Manual,' or full power with the switch in the On position. Now you can control the output. Turn the switch Off and it reverts to its original factory settings.
I recommend you mock this up using alligator clips to make sure it works on your particular flash before soldering anything.
The idea came from this guy who has a some great information on his site about the Vivitar 283: http://www.krebsmicro.com/VIV283/index.html I'm not sure why he has a small capacitor connected in his setup but mine works fine without it.
Take it easy on me and my symbols. I'm a Mechanical Engineering Technology student so I have little training in electronics(or anything for that matter since I'm jsut finishing up my second year).
Please, be careful! Flashes have pretty large capacitors and can hurt you. Make sure you discharge your flash prior to taking it apart and remove the batteries. Please don't blame me if you mess anything up or hurt yourself. I didn't make you take your flash apart.
Now that you have a full manual flash make sure you check out the Strobist site for some stellar information.(No affiliation!)
So to do this you have to open the flash up. You'll need some small screw drivers and will probably need to take off a decal or two. Once its open cut the wires that connect to the photo cell. Make sure you leave enough wire on each side to strip and solder.
If you want to eliminate the photocell all together and go full manual just hook the potentiometer in place of it. On my potentiometer you use the left and middle terminals. Test it out! You'll need a potentiometer that goes to about 200k ohms if you are planning on taking the cell out or use a switch to bypass the potentiometer.
Now the way I'm doing it is as follows. I am hooking the potentiometer and photo cell in parrallel with a switch so I can have full use of my original auto modes. Take a look at the attached image for circuit diagram. The other plus is that I can have full power without buying another potentiometer, mine is only 100k ohms, not enough to fire the flash at full.
The way my vesion works is that you need to have your flash set on 'Manual,' or full power with the switch in the On position. Now you can control the output. Turn the switch Off and it reverts to its original factory settings.
I recommend you mock this up using alligator clips to make sure it works on your particular flash before soldering anything.
The idea came from this guy who has a some great information on his site about the Vivitar 283: http://www.krebsmicro.com/VIV283/index.html I'm not sure why he has a small capacitor connected in his setup but mine works fine without it.
Take it easy on me and my symbols. I'm a Mechanical Engineering Technology student so I have little training in electronics(or anything for that matter since I'm jsut finishing up my second year).
Please, be careful! Flashes have pretty large capacitors and can hurt you. Make sure you discharge your flash prior to taking it apart and remove the batteries. Please don't blame me if you mess anything up or hurt yourself. I didn't make you take your flash apart.
Now that you have a full manual flash make sure you check out the Strobist site for some stellar information.(No affiliation!)
Attachments
Wimpler
Established
Thank you for posting this. I am a mechanical engineer student as well 
Will certainly give it a try this summer.
For those interested: another interesting possibility is to make your own slave flash triggers. Several circuit diagrams are available online.
Those auto flash light sensors can also be interesting for other things. If you have some old broken flashes you can use these photocells to make your own light meter or for a shutter speed tester, just to give some examples. Good luck and be carefull.
Will certainly give it a try this summer.For those interested: another interesting possibility is to make your own slave flash triggers. Several circuit diagrams are available online.
Those auto flash light sensors can also be interesting for other things. If you have some old broken flashes you can use these photocells to make your own light meter or for a shutter speed tester, just to give some examples. Good luck and be carefull.
Silvio
Newbie
It sounds useless to me as long you don't know exactly your GN for each of your manual settings. By the time you'll figure it out, you gonna end up messing some photo opportunities just because you want to use an auto flash in manual. It makes no sense to me. But hey, it doesn't matter as long as you're happy with it.
Silvio
Silvio
y4m4
Cal Graham
Yeah, this guy used a $1 solar caclulator to make an optical slave trigger: http://home.rochester.rr.com/carlvogt/Strobe.htm
Make a Safe Sync type adapter for your High Voltage flashes: http://www.carlmcmillan.com/Optoisolated_Adapter.htm
Find out if your flash is safe for modern cameras: http://www.botzilla.com/photo/strobeVolts.html
If you solder a mono mini jack into the hot shoe contacts I'm sure you'd have yourself a sync port on practically any flash.
Maybe I should change the name of the thread to DIY Flash Mods?
Eh, I'm a cheap SOB and besides, its fun. If you have a meter you can find the various settings in stop increments and corresponding resistances. If you shoot a DSLR well you can tweak the exposure to your liking if you are in a home-studio-type setting. If your doing a serious studio shoot where it isn't efficient to tweak your exposure like this well this modification isn't for you.
I just like building things.
Make a Safe Sync type adapter for your High Voltage flashes: http://www.carlmcmillan.com/Optoisolated_Adapter.htm
Find out if your flash is safe for modern cameras: http://www.botzilla.com/photo/strobeVolts.html
If you solder a mono mini jack into the hot shoe contacts I'm sure you'd have yourself a sync port on practically any flash.
Maybe I should change the name of the thread to DIY Flash Mods?
Silvio said:
Eh, I'm a cheap SOB and besides, its fun.
If you have a meter you can find the various settings in stop increments and corresponding resistances. If you shoot a DSLR well you can tweak the exposure to your liking if you are in a home-studio-type setting. If your doing a serious studio shoot where it isn't efficient to tweak your exposure like this well this modification isn't for you. I just like building things.
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Silvio
Newbie
If you're doing a serious studio shoot you need serious studio strobes, not $25 vivitar, achiever or sunpak. And if you shoot a dslr, you might have enough money left to buy a better flash. BTW I just like shooting photos despite the fact that I build workstations and servers. Congratulations for your time lost in a $25 flash mod project.
Silvio
Silvio
y4m4
Cal Graham
$25 Vivitar? You have overestimated me sir; $10 is all I spent on the flash in question. Thanks for your input though. I'm pretty sure that anyone who is unfortunate enough to click on my thread and read my ramblings would know that this isn't for serious work of any kind.