Vivitar 285 on Rebel T1i - disaster or not?

[bill_todd]

<p>I have an old (over 20 years) Vivitar 285 Zoom Thyristor flash that works perfectly. Can I use it safely on my Rebel T1i or is the voltage too high?<br>

I understand the many advantages of a current E-TTL flash and also the advantages of not spending $300 or more on something I will use very very rarely.:) Thanks.</p>

[Farkle-Mpls]

<p>Likely the voltage is too high. I have a 283 of the same vintage and the voltage measured >200 volts (I think) ... way more than the recommended 6v. The newer 285HV flashes are around $90 at B & H are those have safe trigger voltages. I've used them without issue on my 40D.</p>

<p>Measuring the trigger voltage yourself is pretty easy. Google for the procedure and test it yourself (assuming you have a volt meter).</p>

[Michael R Freeman]

<p>285 or 285<strong>HV</strong>?</p>

<p>The distinction is important, as the earlier 285 can have a <strong>very high</strong> sync voltage, while the more modern 285HV has a low sync voltage. The 285HV that I used to own (circa 1985) had a sync voltage under 6V, but the only way to determine the sync voltage on the unit that you have with absolute certainty is to measure the potential between the center contact and the ground with a multimeter / voltmeter.</p>

[bill_todd]

<p>I have a cheap voltmeter. On the 500V scale nothing happens. On the 150V scale the the needle just barely moves. On the 15V scale the meter has so little resistance that the flash fires. It may be safe but before I use it I will try to find someone with a better voltmeter. Thanks for your help.</p>

[Mike Gammill]

<p>A cheap voltmeter typically has 1000 ohms/volt sensitivity which means that you may not get an accurate reading from a high voltage low current source such as a flash contact. Meters of this type have such low resitance that the voltage drops when you connect the meter and it may even fire the flash. You need a meter that is rated at 20,000 ohms/volt in order to get a meaningful reading (YMMV). I have a ten year old Radio Shack digital multitester which has 20,000 ohms/volt sensitivity and have never had any trouble measuring sync voltage. Of course, you could get a Wein Safe Sync which reduced sync voltage to 6 volts.</p>

[garymoncur]

http://www.botzilla.com/photo/strobeVolts.html

[nick roberts]

<p>Your camera will tolerate a trigger voltage up to 250V, not 6V - however, some 285s can still be higher than that.</p>