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01-02-2009, 10:56 AM   #1
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Under exposing bounce flash?

Has anyone had problems with bounce flash being occasionally seriously underexposed? I'm using a 360 flash and a K20D in 'X' exposure mode. The flash was purchased used with some damage to the neck that I repaired. I am wondering if there is further electronic damage or if this is a known problem.

01-02-2009, 11:27 AM   #2
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If you are using P-TTL, the system could still be fooled by reflecting surfaces, or the flash may lack power to expose correctly at your set aperture and ISO.
By bouncing, you reduce the amount of light hitting the target quite seriously, both by the increasing traveling distance, and the roof, which absorbs some light, and, naturally, spread the light some more.
01-02-2009, 01:19 PM   #3
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I've found the problem with bouncing of the ceiling and with a ring flash adapter. I wondered if the flash was not powerful enough, but when I switch to manual mode, I get overexposure, so the flash has the power. If I use direct flash, I seem to get good exposure.
01-02-2009, 01:24 PM   #4
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What aperture were you using? If you were using anything like f:8 or smaller (I mean aperture, not numbers), then you might not have enough power to expose properly. Could you post a picture with EXIF, it would help find out what went wrong.

01-03-2009, 10:10 AM   #5
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It looks like the problem may be with the flash overall.

All ISO 200 + DR expansion.

Here is a natural light shot (no flash)


Here is direct flash f4.5 1/60


Bounce flash f4.5 1/60


Manual bounce flash at full power


Wireless bounce flash with flash very close to on shoe position


The manual flash shows the flash gun has enough power. I've played around with lots of other apertures and distances and the flash always seems to underexpose by about the same level. Using flash EV compensation helps a little, but only gives +1 EV.
01-03-2009, 11:53 AM   #6
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It seems that this is a general problem with the Pentax flashes

https://www.pentaxforums.com/forums/pentax-camera-accessories/7355-underexpos...-ttl-mode.html

RiceHigh's Pentax Blog: P-TTL Reliability

I will open a new thread with a better title - https://www.pentaxforums.com/forums/pentax-dslr-discussion/45696-pentax-flash...-problems.html
01-03-2009, 01:41 PM   #7
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QuoteOriginally posted by jfsavage Quote
Has anyone had problems with bounce flash being occasionally seriously underexposed? I'm using a 360 flash and a K20D in 'X' exposure mode. The flash was purchased used with some damage to the neck that I repaired. I am wondering if there is further electronic damage or if this is a known problem.
X-flash does not use Auto ISO, it automatically selects the minimum allowed sensitivity. Try a shot with the ISO set to 800 or even 1600 and see if that corrects the lighting level. I find I have to bump the ISO a couple of stops when I bounce. I don't know why this is, the Sigma 530 is a very powerfiul flash.
01-03-2009, 04:24 PM   #8
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I also use Sigma flashes and found out I have better results when I bounce with the wide angle panel extended over the flash head. Don't know if it would help with the Pentax units, but it's worth a try.

01-03-2009, 04:32 PM   #9
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QuoteOriginally posted by flyer Quote
I also use Sigma flashes and found out I have better results when I bounce with the wide angle panel extended over the flash head.
Yes, I've found that as well.
01-03-2009, 09:19 PM   #10
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QuoteOriginally posted by flyer Quote
I also use Sigma flashes and found out I have better results when I bounce with the wide angle panel extended over the flash head. Don't know if it would help with the Pentax units, but it's worth a try.

I also always use the wide angle panel on the Pentax flash head when bouncing.
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