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02-04-2011, 02:21 PM   #1
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K-x with FA-50 and Metz 48 Overexposes

Hi..I recently bought the Fa-50 from e-bay at excelent condition..But i was trying to shoot some portrait pics at Av mode with Metz at P-TTL at wide aperature..F1.4-F2.2 and with auto iso 100-1600..The camera overexposes extremely..I have added a pic to see the problem..At other modes the cam closes the aperature and everything works fine...And with my other lens DA 18-135 i have no issues so far...What should i do?Should i worry about something faulty?



02-04-2011, 02:49 PM   #2
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f/1.4 or f/2 and ISO 1600 is waayy too bright for a flash. If you want to use f/1.4 or another really wide aperture, set your ISO to 100 or 200 and leave it. Don't use auto.
02-04-2011, 02:59 PM   #3
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Shouldn't the camera determine faster shutter or lower iso itself?
02-04-2011, 03:03 PM   #4
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Sometimes the exposure is so beyond the meter that the camera just guesses. I see it a lot with my K20D and K 50mm f/1.4 -- set to f/1.4, ISO 1600 and meter off the sun...the camera will recommend something like 1/3 sec shutter speed. I think it just comes down to a limitation of the light meter. Other brands will likely do the same thing.

02-04-2011, 03:08 PM   #5
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So i don't have to visit service? Is it normal? One last info. I tested with onboard flash and auto iso 100-12800. It chooses 12800 and burns the whole pic.. It's like it's not counting flash..Also i m taking all the pics in low-light envirorment..I just noticed that when my object is well lit and the iso is already low(100-400) the pics look just fine but when in darkness the iso goes as high as it gets..

Last edited by Dionisis_K; 02-04-2011 at 03:15 PM.
02-04-2011, 06:50 PM   #6
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It's quite likely that the camera isn't taking the flash into account when it is setting ISO for the scene, and so in a dark environment it is setting the ISO as high as it can, and then is unable to quench the flash to provide correct exposure.
Best bet is to limit the auto ISO to something more reasonable, or just go to a discreet ISO setting when using flash.
02-05-2011, 02:47 AM   #7
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Thanks guys for your answers..I know how to come over this with manual settings..But my question is that the purpose of ttl is the camera to adjust the settings to the pre-flash.. Why does it fail so dramaticaly?Maybe algorithm needs improvements..
02-05-2011, 09:01 AM   #8
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QuoteOriginally posted by Dionisis_K Quote
Thanks guys for your answers..I know how to come over this with manual settings..But my question is that the purpose of ttl is the camera to adjust the settings to the pre-flash.. Why does it fail so dramaticaly?Maybe algorithm needs improvements..
Think of it this way:

At a safe exposure settings, the camera pre-flashes to check out the exposure, then using p-ttl, it sets the flash exposure. Lets say you were underexposed at 50% gray. The camera uses the flash and tries to make it 18% gray and all it good.

So, during the pre-flash it looked at your 50% gray scene and calculated what to do to get it to 18% gray

If the camera sees 50% gray, it fixes it
If the camera sees 35% gray, it fixes it
If the camera sees 18% gray, it doesn't have to do anything and will try to flash at its lowest power
If the camera sees 7% gray, its already over exposed, and even using its lowest power, still over exposed
If the camera sees white, it could be 1 or 2 or 10 stops over exposed. There is no difference between shades of white. How would it know how what to do?

02-05-2011, 10:11 AM   #9
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That makes sense..Anyway,my biggest concern was if something was faulty..I guess i don't have to worry anymore..Thanks a lot for your answers..
02-05-2011, 10:29 AM   #10
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Solution is simple Don't use auto ISO when using flash.

The camera only 'adjusts' the flash when using P-TTL. The other settings are determined before the pre-flash is fired. The camera uses the pre-flash to determine the required duration of the flash.

While the picture is taken, the camera will tell the flash to stop at the moment that that duration is reached. However flashes have a minimum duration; if the camera tells the flash to stop after 1/50000 sec but the minimum of the flash is 1/20000 sec, you will have over exposure.

From your shutter speed comment, it sounds like you have some reading to do why there is something called X-sync
02-05-2011, 10:44 AM   #11
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Yep, nothing wrong with your equipment, you just selected initial settings that were beyond the PTTL capability to adjust to.
02-05-2011, 02:19 PM   #12
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Thanks guys!!After that i realised that p-ttl adjusts flash and not camera settings!!
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