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07-31-2011, 10:10 AM   #1
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Flash overexposure with new K5

I just bought a K5 with a Sigma 17-50 f2.8 lens. Flash pictures seem to me to be overexposed, both with the built-in flash and with the 540 that I bought. The mode (Av, P, auto) doesn't seem to affect this problem. The problem can be fixed by adjusting the flash compensation to -1.0 either on the camera or on the 540 (I haven't read its manual yet, so who knows what I really did). I really don't like this as a solution because it limits how far down flash illumination can be used for fill since there's only one more compensation stop. I don't have any other lenses to test (I think that Pentax M lenses can't be used), and the Sigma seems to be communicating correctly with the camera.

I should say that I know nothing about digital photography. The K5 is replacing my ME Super. I haven't read far enough in the manual to learn how to transfer pictures to my computer, and I am judging on the camera monitor. Other photos appear more or less correctly exposed, I think, although I prefer the underexposed versions of some photos that I took outdoors.

Am I doing something wrong with the flash? Is this normal behavior? Thanks for any help.

07-31-2011, 11:54 AM   #2
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If you leave ISO setting on auto it will use a high ISO and try to fill-in with the flash, but in low light it instead over-exposes. Manually set the ISO to 100 or so when using flash, and the results should be MUCH better.
Welcome to digital. I still prefer film (MX, LX, ME) in many ways - digital is an entirely different beast; but the K-5 can give lovely images.
07-31-2011, 12:11 PM   #3
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Thank your for your response. In auto, it does select high ISOs (1600 and 3200), but I reset it to 100. Maybe the 100's are better, but they're not right. I think that the room I took these in is reasonably illuminated, and I'm not sure that it's low light. I also tried X mode, but I still am not getting good results. I am going to figure out if my 540 has Auto, or I'll try my old Sunpak flash on Auto, just for comparison.
07-31-2011, 02:30 PM   #4
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I already heard about such problem from several users. Are all the settings in default? Is the metering mode on zone? Isn't there high key adjusted in image settings? All that can affect exposure. When I had this problem it was because my AF point selection was set to auto and I had AE linked to AF point.
Also, for some users the flash overexposure was solved by FW1.11.

07-31-2011, 02:38 PM   #5
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Take care in using the old flash. Do a search to find safe voltage ratings so you don't damage the k-5.
07-31-2011, 04:12 PM   #6
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QuoteOriginally posted by dh87 Quote
Thank your for your response. In auto, it does select high ISOs (1600 and 3200), but I reset it to 100.
That's not such a great idea. Do that in manual mode and you're forcing the flash to dump 5 stops of light, that wont look very good as it will give you the black tunnel look. Do that in a Av mode and you'll pay for it in far too slow of a shutter speed.


You are on the right track though, here's a cut and paste from a post I made on a similair issue.

=============================================================
Yes that is typical, the camera is exposing for purely ambient light in auto or semi-auto modes, and does not take flash exposure into account in that mode. So, do not shot in auto or semi-auto modes whilst using pTTL on the flash unless you are only doing subtle fill flash. Indoors is not for fill flash.

So, put the camera in manual mode, ISO ~400 to 800, shutter ~1/100, aperture to taste. You want the meter to be saying you are under exposing by 1 to 3 stops. The flash should be in pTTL mode. Aim the flash preferably at a wall so light will bounce off that and illuminate your subject. Push the shutter. The camera will then instruct the flash to achieve overall correct exposure which it will do by adding the stops of light via flash that you are underexposing with your shutter/ISO/aperture settings. Then chimp and if your subject looks to bright or dim after this then use the FEC compensation on the flash to adjust. Typcially I end up dialing in -0.3 or -0.7 FEC. If ambient is too dark or bright then use ISO, aperture or shutter to adjust, this will alter the mix between ambient and flash but not the total overall exposure (only FEC will do this).

Remember, in pTTL mode the camera will use the flash output to achieve overall correct exposure. The more negative the meter says the scene is, the more light will have to be dumped by the flash to achieve correct exposure (hence the greater the ratio of flash to ambient). The less negative, the less flash will be dumped and the brighter the more the ambient light will show up.

All this sounds complex but is actually very easy once you try it and get the hang of it. The results are fantastic so it's worth mastering.

The best site I've found on using TTL mode on the web is this one http://neilvn.com/tangents/. The think "the strobist" is the best site for off camera manual flash photography if you don't want to use pTTL.

Good luck and have fun experiementing

Last edited by twitch; 07-31-2011 at 04:33 PM.
07-31-2011, 09:09 PM   #7
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Thanks to all for your answers. On my old camera, flash exposure was reasonably reliable, but I had to set the flash and the aperture manually. I thought that my new camera could do that without my manual intervention.

QuoteOriginally posted by elho_cid Quote
I already heard about such problem from several users. Are all the settings in default? Is the metering mode on zone? Isn't there high key adjusted in image settings? All that can affect exposure. When I had this problem it was because my AF point selection was set to auto and I had AE linked to AF point.
Also, for some users the flash overexposure was solved by FW1.11.
I believe that everything is set to default. The metering is zone. I am not sure what a high key is. AF point selection is set to auto, but I don't think that AF and AE are linked?

I bought the camera on Tuesday from B&H, and I am surprised to see that it's firmware version is 1.01. One of the reasons that I had waited to buy the camera was to wait for any new production issues to be resolved. I am going to try to update the FW...

QuoteOriginally posted by crewl1 Quote
Take care in using the old flash. Do a search to find safe voltage ratings so you don't damage the k-5.
OK, I won't try the old flash.

QuoteOriginally posted by twitch Quote
That's not such a great idea. Do that in manual mode and you're forcing the flash to dump 5 stops of light, that wont look very good as it will give you the black tunnel look. Do that in a Av mode and you'll pay for it in far too slow of a shutter speed.


You are on the right track though, here's a cut and paste from a post I made on a similair issue.
...
Even at ISO 100, the camera was able to get enough light at f2.8.

I can get the flash photos to look OK by using FEC of -1.0. I'm not really eager to have to adjust anything in manual for flash pictures. I don't understand why the manual method that you're suggesting is different from setting the EC to -1 to -3 and shooting in an automatic mode.

I also tried to take a flash fill picture outside. I needed to adjust the FEC to -2.0. This is certainly a problem because some fill pictures would need less fill than the one that I took.

QuoteOriginally posted by philbaum Quote
PF member Twitch provided this recount of how to use a Pentax flash system:

https://www.pentaxforums.com/forums/pentax-k-5-forum/152004-auto-iso-ext-flas...ml#post1593282

with the final recommendation to use Manual exposure mode and avoid auto ISO, which as you observed will provide a high iso. One post reported that the over exposures with pttl were associated with iso's over 800 iso. I don't know that personally, just that when i normally use 100-800, i don't have any more than 1/2 EV overexposure, which i use FEV to correct or PP.

Others have reported the latest firmware update, 1.11 as solving some bugs with their overexposure concerns, so that may be worth trying for you.

best wishes,
I am going to work on the firmware update. I did try X mode and still got overexposed pictures. I will try some more pictures tonight.

Thanks.
08-01-2011, 10:27 AM   #8
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I tried using the 540 on Auto instead of PTTL, and it works perfectly. I called Pentax, and they say that maybe the Sigma lens is the problem. I have no idea if that's possible. The lens does seem to send information to the camera and the flash about zoom length and exposures without flash seem to be accurate. Does anyone know? Thanks.

08-01-2011, 11:35 AM   #9
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Maybe the lens is just too slow with aperture diaphragm action...
08-01-2011, 12:02 PM   #10
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QuoteOriginally posted by elho_cid Quote
Maybe the lens is just too slow with aperture diaphragm action...
I tried taking flash picture at different apertures including wide open, and they're all overexposed. I don't know if this addresses this issue. I still haven't updated the firmware.
08-01-2011, 01:36 PM   #11
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If shooting wide open take care that the picture is not overexposed even normally without flash (f2,8 1/180 ISO100 may be too much for a sunny day). Try the FW upgrade it only takes a minute and it could help.
08-02-2011, 12:03 AM   #12
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I applied the firmware update. No effect, I am sorry to report.

I also transferred the photos to my computer. On the computer the look a bit less overexposed, but they're still not right. The AF540 shots still look awful; for comparison with the built-in flash, I took these with the flash pointed straight at the scene, and the photos seem to me two or three stops overexposed.
08-02-2011, 12:38 AM   #13
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This has been discussed a lot here: K-5 with flash - PentaxForums.com

I still have 2 stop overexposure with P-TTL external flash (AF540 or Sigma EF500) but it is consistent.
08-02-2011, 02:07 AM   #14
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QuoteOriginally posted by Ash Quote
This has been discussed a lot here: K-5 with flash - PentaxForums.com

I still have 2 stop overexposure with P-TTL external flash (AF540 or Sigma EF500) but it is consistent.
Maybe I have unrealistic expectations about the camera getting this right and about the quality of images with the built-in flash. My major concern at the moment is whether my Sigma 17-50 lens is failing to communicate properly with the camera (and hence should be replaced with the Pentax 16-50). What all these other threads seem to say is no.

Consistent with your experience the AF540 is much worse than the built-in. I can't say that this is a good thing.
08-02-2011, 02:40 AM   #15
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By consistent I mean that if I set FEC to -2.0 I can go ahead and shoot P-TTL under different lighting conditions and get well exposed flash shots most of the time.
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