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05/21/2009 08:07:11 PM · #1 |
Hi,
I have a Canon 400D, Sigma 17-70mm f2.8-4.5 and Sigma EM-140DG Ringflash. I need the ring flash for medical photography but I am having problems getting it to work as I expect.
I am trying to shoot in aperture priority mode with the smallest aperture at 70mm (f36) but the camera does not seem to be taking the flash into account when it is metering the shot and I end up with the camera using very high shutter speeds. (>10 seconds) The flash works fine as far as I can tell.
Does anyone know what I am doing wrong?? Do you think there is something wrong with the flash?
Any ideas would be much appreciated, thanks,
Stephen |
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05/21/2009 08:11:35 PM · #2 |
I am assuming a ringflash will work the same as any flash.
What is your shutter speed? If it is higher than 1/250, then its to fast for the flash. Its not syncing. Bring your shutter down to 1/250 then adjust your aperature or your ringflash to get desired exposure.
hope this helps
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05/21/2009 08:19:14 PM · #3 |
| Try taking it out of Aperture Priority. That's what's causing the really long exposure. In Manual mode, set the desired aperture, at f/36 ambient light won't even come into play, most likely, so set your shutter speed to 1/250 (I think that's the 400d's x-sync). The flash will still work in E-TTL, setting flash power for proper exposure. |
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05/21/2009 09:57:06 PM · #4 |
Is the flash itself set in manual mode or ETTL?
When you take the photo (with the >10 second exposure) is it properly exposed?
Oh yeah.... Another thing- what kind of working distance do you have? That flash has a pretty low guide number... so you may just be underpowered.
Message edited by author 2009-05-21 21:59:05. |
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05/22/2009 05:09:23 AM · #5 |
Many thanks for your replies.
Nick, you have it spot on, it's the Aperture Priority Mode on my Canon. I can get things to work OK in Manual and full auto mode now.
I also had a dig around in the menus and custom functions and found the crux of the problem - there is an option for to have fixed shutter speed (1/200)when using flash in aperture priority mode - with this option enabled it all works.
I think spiritualspatula you are right about the power of the flash, I may need to up the ISO or slightly drop the aperture to get bright images in some circumstances. Usually I'll be at a working distance of around 20-30cm. I'm geting a sigma 105mm f2.8 macro soon but was a little concerned that there is something up with the flash.
Thanks again for the help. |
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05/22/2009 08:39:13 AM · #6 |
| If it is power, you may want to consider a ringflash adapter (if you have another higher power strobe). It turns ordinary strobes into ringlights. There are currently two manufactured models available, the Rayflash and the Orbis. Both take about a step of light away from your flash. The Rayflash is flash specific whereas the Orbis is one size fits almost all. I have the orbis and use it with an SB-900 with pretty good results, though you can't control lighting ratios as with the Sigma you have (well. I guess you COULD if you DIY'd it...). |
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05/22/2009 07:12:25 PM · #7 |
Originally posted by stegga1000000:
I can get things to work OK in Manual and full auto mode now.
I also had a dig around in the menus and custom functions and found the crux of the problem - there is an option for to have fixed shutter speed (1/200)when using flash in aperture priority mode - with this option enabled it all works. |
Glad I could help. One tip, though. If you use full auto (green rectangle) mode, the camera will lock your shutter speed at 1/60, I think. This is fine if all of your light is coming from the flash, which I believe is likely in your case, but if flash and ambient are mixing, it could cause ghosting. Especially at a telephoto focal length, where camera shake can be seen. (>60 or so mm. in this case). I would recommend, for your purpose, to stick to full Manual mode or Aperture Priority mode with the shutter speed locked to 1/200 by custom function 03. |
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05/27/2009 05:38:41 AM · #8 |
Yeah, I don't find the auto mode particularly helpful at all. I do get ghosting and find the metering quite hit and miss. Also for medical photography you need to ensure that a small aperture is used to retain large depth of field which is the opposite of what full auto seems to want to do!!
Once again thanks for your help, Stephen
P.s should have the sigma 105mm macro by the end of the week, looking forward to it coming!
Message edited by author 2009-05-27 05:41:50. |
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