Good morning, Edimilson;
The Vivitar 2800 has a thyristor flash control circuit operated by a light sensor on the front of the flash. I think the light sensor is a small round eye. If you are using the 2800 flash in the normal Automatic Mode, the light sensor must be looking at the subject you are trying to photograph. If the light sensor can see the subject, then it can "meter" or measure the light falling on the subject to decide when to stop the flash.
If the light sensor is also facing the wall when you take the picture, the light sensor will very accurately measure the light falling on the wall, and not the light falling on the subject. That will give you a very dark picture of the subject.
If the light sensor cannot see the subject, try putting the 2800 into Manual Mode and do the old fashioned calculations for the flash to bounce surface to subject distance, and see if you get better results in Manual Mode.
Last edited by Ralph Javins; 01-10-2009 at 09:06 PM. Click to view previous post history.
Ralph Javins, Latte Land, Washington
When they ask you; "How many Mega Pixels you got in your camera?"
just tell them; "I use activated silver bromide crystals tor my image storage media."
What Ralph said.
If you are using the auto function on the flash, the sensor on the flash needs to point toward the subject, in order to ensure that the subject is properly exposed.
It might be possible to use a mirror or reflector to allow you to leave the sensor facing forward, while re-directing the light toward the wall.
Matt & Ralph,
The 2800 has a tilting bounce head, and a sensor that always points in the same direction as the lens, i.e. always at the subject, and not at the wall or ceiling used for bounce. See the manual I linked to. You're warning about a problem that can't occur unless the flash is taken off the hot shoe, a configuration the OP isn't using.
I think I (and Ralph) probably misunderstood Edimilson when he referred to "holding the camera sideways". After thinking further I assume now he meant holding the camera in a way that results in a vertically oriented photo.
Reviewing again his description, I wonder if Edimilson is right and he had the bounce angle set wrong, so that the light is missing the subject. The distances (1/2 meter, and then 1 meter) are quite short, so the tolerances are probably narrow.
Hope we can help.
It's possible that the flash sensor is seeing the reflection off the wall and quenching the flash output when the wall is properly exposed, leaving the sofa/subject underexposed by 2-3 stops;
try shielding the sensor from the wall with a bit of masking tape and a small cut piece of exposed and developed in roomlight photopaper(completely black side toward sensor eye, matte surface best, but glossy works), so the sensor can only "see" the subject.
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I think you are probably right about the flash bouncing beyond the subject, especially at such a close distance. He should probably be tilting the flash head to 75 degrees minimum, and likely 90 degrees at that distance.
Originally Posted by MattKing
On the other note mentioned, I haven't seen any of these flashes have a problem reading the subject rather than the bounce wall. The sensor is inset a little. A small piece of cardboard for a "gobo" can't hurt, but it's likely unnecessary.
So a sketch being worth at least 10 words, I'll attach one showing how to aim the flash so that the light hits about halfway along the wall to the subject, the green line, rather than putting it so far along the wall that the light falls behind the subject, as with the red line.
For the distance that Edimilson was using, I'd start at 90 degrees, the flash head tilted to go straight at the wall, so that the bounce is in front of the subject.
Like other have pointed out, your problem relates to the fact that in trying to orient the flash you have the sensor pointing not at the subject but to the wall. You can use the flash in manual mode, estimate exposure and bracket. You can use a flash meter but that costs money. If you have a digital camera that can fire the flash you can use it to take test shots to determine exposure.
I am not sure about this. You see, I have just tested the same thing with another flash, a Vivitar 285HV I bought for my newest film cameras. I bounced it off the same wall as mentioned and also off a white board. The results were very satisfactory (have a look: http://www.apug.org/gallery/showphot...=40916&limit=1). I guess the older Vivitar 2800 didn't work either because:
1) I the flash didn't properly hit the subject, or
2) I should have opened up a stop or two on the camera, or
3) The thrystor thing on the Vivitar 2800 does not work so well as the one on the 285 HV (which worked very well)
I will try to sort this out next time I use the 2800.
Thank you everyone!