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06/29/2004 09:03:14 PM · #1 |
I ordered 550 flash and the specs are saying "can be used with lenses 24-105 mm.
Is that mean I can't use it with my 20 mm fixed lens?
Where is Kirbic or Adrian Tung when I need them ?
Message edited by author 2004-06-29 21:07:44. |
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06/29/2004 09:14:11 PM · #2 |
Sure you can, remember that 20mm on your rebel is equivalent o to 32mm. The 550EX has a little screen thingie at the top that you can pull out in front of the flash to increase the angle of coverage.
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06/29/2004 10:08:24 PM · #3 |
| So what happens if you use the flash in a true 20mm lens? Or a 200mm lens? |
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06/29/2004 10:18:57 PM · #4 |
That range simply refers to the "zoom" on the flash. It has the ability to respond to the focal length of the lens by "focusing" the flash. It will give a wider field of view for wide angle (around the 24mm end) and a narrower, more directed and I'm sure stronger flash when the lens has a longer focal length (all other things being equal like E-TTL or E-TTL2 measurement). It's pretty cool to zoom in or out and hear the flash keeping track. As doctornick stated, for wider angle shots the flash comes with a flip down diffuser that helps to disperse the flash for an even wider field of view. It isn't that the flash won't work outside that range, it just isn't constructed to physicallycompensate correctly beyond those limits. Guess that's where the manual settings come into play.
Hope that helps some.
Kev
EDITs are in italicized type.
Message edited by author 2004-06-29 22:21:45.
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06/29/2004 10:33:54 PM · #5 |
If you use a lens that has a wider angle of view that your flash unit's angle of coverage, you will see a falloff in the corners of the image where the light from the flash not as strong. In this case, a lens wider than 15mm would cause falloff.
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06/29/2004 10:36:08 PM · #6 |
| Very informative, guys! Thanks! |
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06/29/2004 11:19:31 PM · #7 |
| So,if i set at 17 mm mode and I'm using 20 mm lens,flash will be having stronger effect than normal? |
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06/29/2004 11:42:13 PM · #8 |
Kosta,
When you drop that diffuser panel down in front of the flash head the motor inside the flash unit seems to set the head so that its ready to give a flash for the widest field of view (at least I can hear the motor activating when I drop down the diffuser on mine). That doesn't mean that its stronger or weaker. Just that the flashtube is being moved in relation to the reflectors inside the flash head (I'm guessing) so that the resulting flash is dispersed as much as possible in hopes that when the flash hits the diffuser panel it will go even wider to cover the field of view from your 20mm lens. Now that's just conjecture based on how my 550EX sounds and seems to operate when I put the 17-40mm lens on, zoom as far out as I can and then drop the diffuser panel in front of the flash head. The flash seems to operate every time I pull out the diffuser panel and drop it (even if the flash isn't attached to a hot shoe).
I think its worth noting that E-TTL and E-TTL2 play a part in the strength of the flash. The motorized "zooming" of the flashtube within the 550EX seems to only play a part in the field of view across which the flash is expected to be dispersed. An example would be that given exactly the same scene with an 18% gray subject and no direct hot spots, if I put the 70-200 lens on and zoom up to 100mm I would hear the flash head zoom the flash tube. If I remove that lens and replace it with the 17-40mm and zoom it out to 17mm and then drop the diffuser over the flash head I would hear the 550EX trying to zoom the flash tube to keep up with the much wider field of view. Now at no time would the camera actually have tried to guage how strong the flash should be because I'd never depressed the shutter release button which would have caused the camera to try a preflash for E-TTL (or E-TTL2) evaluation.
This is just my best guess explanation based on the photonotes.org info and then being dumb enough to do this kind of thing and wonder what the hell all that sound is inside the 550EX (not that its loud but its pretty darned consistent when you zoom in and out).
Hope this clears this up. If not, I hope someone with more technical info can share it to enlighten (hehe) all of us.
Kev
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06/30/2004 12:01:50 AM · #9 |
Thanx kevin for in dept explanation:-)
I will get my 550 tomorrow and do the testing ! |
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