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03-05-2009, 03:16 PM   #1
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Vivtar 550FD Auto Thyristor with K20D

Hey all--

I have never used a flash before, with any camera, but recently got a Vivtar 550FD for free with some other stuff on eBay. It seems like a good flash, with a TTL mode, and it is indeed the M/P/O version, designed to work with the Pentax cameras of its day.

It fires on the K20D and didn't fry anything, so that's good. But could anyone give me a little primer on how to use it with my camera?

It's exactly like this one, except says M/P/O instead of C/R:



03-05-2009, 03:34 PM   #2
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BTW, it's putting out 5.7 volts, according to my multimeter.
03-05-2009, 03:44 PM   #3
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For the auto, I believe you just dial in your iso, and match your aperture to what either auto setting tells you. One of the auto modes should give more reach, but will require larger apertures and may blow out close subjects (as the range it lists will show). The other auto will allow smaller apertures, but won't give you the reach. I don't know off hand the max allowable shutter speed for your camera.
03-05-2009, 05:17 PM   #4
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QuoteOriginally posted by unkabin Quote
For the auto, I believe you just dial in your iso, and match your aperture to what either auto setting tells you. One of the auto modes should give more reach, but will require larger apertures and may blow out close subjects (as the range it lists will show). The other auto will allow smaller apertures, but won't give you the reach. I don't know off hand the max allowable shutter speed for your camera.
I don't know either, offhand. In any event, the aperture setting is dictated by distance from the subject? When I say I'm a newb at this I mean that I really understand nothing...

03-05-2009, 06:22 PM   #5
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QuoteOriginally posted by mabelsound Quote
I don't know either, offhand. In any event, the aperture setting is dictated by distance from the subject? When I say I'm a newb at this I mean that I really understand nothing...
I have one of those and I have a book (somewhere). You can buy manuals (reprints)all over the place but in some respects there pricey ($10-20)... especially considering most of what you are paying for is the reproduction of foreign languages. The books are multilingual.
Will see if I can find mine.
Oh TTL will not work on your camera. Either manual or one of the 2 auto modes do work
03-05-2009, 06:35 PM   #6
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QuoteOriginally posted by jeffkrol Quote
I have one of those and I have a book (somewhere). You can buy manuals (reprints)all over the place but in some respects there pricey ($10-20)... especially considering most of what you are paying for is the reproduction of foreign languages. The books are multilingual.
Will see if I can find mine.
Oh TTL will not work on your camera. Either manual or one of the 2 auto modes do work
OK, great, thanks! I did try TTL mode...it fired, but the exposures were all over the place. If you can check for me and see more specifically how to use the two auto modes, I'd be grateful. If not I'll just fool around until I figure it out.
03-05-2009, 06:35 PM   #7
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The manual is online here:

http://www.cameramanuals.org/flashes_meters/vivitar_550_fd_n.pdf
03-06-2009, 02:26 AM   #8
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Not Safe

The TTL won't work anyway. As for the trigger voltage, different units produce different ones:-

Photo Strobe Trigger Voltages

Moreover, the trigger voltage is not all that could tell if it will fry your DSLR body or not, there is also the current!

Still, my advice is to use only Pentax original flash units, preferably current P-TTL ones. My old Pentax TTL flash measures only 2.8V (very stable, regardless of battery used and its level), so if yours measures 5.7V, the discharge current can still be much higher.

QuoteOriginally posted by mabelsound Quote
Hey all--

I have never used a flash before, with any camera, but recently got a Vivtar 550FD for free with some other stuff on eBay. It seems like a good flash, with a TTL mode, and it is indeed the M/P/O version, designed to work with the Pentax cameras of its day.

It fires on the K20D and didn't fry anything, so that's good. But could anyone give me a little primer on how to use it with my camera?

It's exactly like this one, except says M/P/O instead of C/R:



03-06-2009, 08:04 AM   #9
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QuoteOriginally posted by mabelsound Quote
OK, great, thanks! I did try TTL mode...it fired, but the exposures were all over the place. If you can check for me and see more specifically how to use the two auto modes, I'd be grateful. If not I'll just fool around until I figure it out.
Sorry, didn't get a chance to look yet but Dave found a "free" copy...
QuoteOriginally posted by alohadave Quote
Thanks for finding that.
03-06-2009, 08:18 AM   #10
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QuoteOriginally posted by alohadave Quote
Excellent, thanks a lot! I checked Butkus but somehow failed to notice it.
03-06-2009, 08:34 AM   #11
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TTL mode won't work on a K20D

TTL mode requires that the camera have a sensor in the mirror box to read the light from the flash, usually bounced off the film/sensor. Film cameras had these sensors, as did the early Pentax dslrs, such as the *istD.

In current Pentax dslrs, there is no such sensor. They use their P-TTL system, in which the flash unit fires at low-power prior to capturing the image. The mirror is still down, so the light is reflected up into the viewfinder and is read by the same light sensors used for ambient light exposures. The camera then tells the flash to fire again, at a specified intensity/duration. This time, the mirror is up and the shutter is open. This all happens in a small fraction of a second. Many people can't even discern the two seperate flashes.

Older flashes can only be used on a K20D (assuming safe voltage) if they have a manual or "auto" mode. The latter mode requires that the flash unit have a sensor to measure the light reflected from the subject. A TTL-only flash unit is just about worthless on a modern dslr.

I believe that the fastest flash sync shutter speed is 1/180 second, just like my K10D. So-called "High-speed" flash requires that the flash unit be capable of firing several flashes as the focal plane shutter moves across the image sensor. At 1/180 and slower, there is a brief period of time in which the entire shutter is open. Above that speed, the second shutter curtain begns closing before the first curtain is fully open, resulting in a moving slit that travereses the image sensor.
03-06-2009, 11:02 AM   #12
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Yes, this flash has two auto modes and its own built-in sensor.

Can I use it in Av mode, or is it necessary to use X?
03-06-2009, 11:56 AM   #13
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QuoteOriginally posted by mabelsound Quote
Yes, this flash has two auto modes and its own built-in sensor.

Can I use it in Av mode, or is it necessary to use X?
This subject is too broad... Here is the "flash primer" I have an easy to get to link to.... The D could do regular TTL as well as the new modern-ish p-ttl.
Just read about manual and automatic.
jr-worldwi.de: Photography: Technic
Your aperture and iso should match that set on the flash. Speed should set itself..
03-06-2009, 12:39 PM   #14
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I have used this flash on my DS without ruining the camera. I had it from my film days. As mentioned, the M/P/O version never had TTL to start with. The flash-charged indicator works in the viewfinder; that's about all the communication there is between flash and camera. The flash works best with the lens set around 30-40mm. Wider than that and you'll have vignetting (dark areas around the edges where the flash didn't reach). If you zoom in more, the flash power might not be enough to fully light the scene.
03-06-2009, 01:01 PM   #15
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QuoteOriginally posted by Just1MoreDave Quote
I have used this flash on my DS without ruining the camera. I had it from my film days. As mentioned, the M/P/O version never had TTL to start with. The flash-charged indicator works in the viewfinder; that's about all the communication there is between flash and camera. The flash works best with the lens set around 30-40mm. Wider than that and you'll have vignetting (dark areas around the edges where the flash didn't reach). If you zoom in more, the flash power might not be enough to fully light the scene.
you got me confused.. The 550 M/P/O is TTL capable just not p-TTL capable.
The D and I'm pretty sure DS should do TTL and p-TTL..
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