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03-11-2013, 10:20 PM   #1
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TAv with flash

Pentaxians,

Does the K30 still use highest ISO of the Auto ISO range in TAv Mode with flash on ?
Is there any way for us to use TAv with flash and the camera uses proper ISO to make correct exposure, without getting the image way overexposed with too high ISO ?

Would somebody sheds some lights for me please. Thanks.

03-11-2013, 10:51 PM   #2
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I rarely use Auto ISO, but an alternative might be to set a lower upper bound for the Auto ISO range when using flash.

Personally, I'd be using M mode if I want to control both shutter speed and aperture while using flash. Otherwise, usually use Av and keep an eye on shutter speed to confirm it was broadly in an appropriate range, and change either aperture or ISO if not.
03-12-2013, 06:47 AM   #3
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QuoteOriginally posted by Ken T Quote
Pentaxians,

Does the K30 still use highest ISO of the Auto ISO range in TAv Mode with flash on ?
Is there any way for us to use TAv with flash and the camera uses proper ISO to make correct exposure, without getting the image way overexposed with too high ISO ?

Would somebody sheds some lights for me please. Thanks.
From what I can tell, the only logical mode for flash photography on the K-30 (all models?) is Av. I just did a test using the built-in flash:

No flash - Av mode
F 5.6
1/40
ISO 6400

With flash - Av mode
F 5.6
1/40
ISO 400

I say "logical" but there are random times when I've seen the shutter speed go higher without flash than with. Seems that's when you allow the ISO to float to 12,800.

If I switch to TAv mode, I get the same ISO setting both with and without flash so this is why I don't think Pentax has set up their cameras to work correctly in TAv mode under flash power. All I get are the same speed and shutter (expected) but the ISO doesn't auto-adjust downward to compensate for the extra flash lighting -- over exposed as a result.

Haven't tried it with the 360FGZ external flash but I may do that later.


Edit: repeated with 360FGZ


Essentially the same result as the built-in flash. In Av mode, the ISO adjusts downward to compensate for the addition of strobe lighting. In TAv mode, the ISO remains the same with or without flash resulting in major overexposure with the flash.

Additionally, in Av mode I had to dial in +1.0 FEC for the 360FGZ to get the image correctly exposed and the same as with the built-in flash. One more reason why us folks don't think Pentax has done enough to sort out all of the flash issues on their equipment.

Last edited by IchabodCrane; 03-12-2013 at 07:27 AM. Reason: Added new info
03-12-2013, 07:09 AM   #4
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QuoteOriginally posted by southlander Quote
I rarely use Auto ISO, but an alternative might be to set a lower upper bound for the Auto ISO range when using flash.

Personally, I'd be using M mode if I want to control both shutter speed and aperture while using flash. Otherwise, usually use Av and keep an eye on shutter speed to confirm it was broadly in an appropriate range, and change either aperture or ISO if not.
Agreed, I decrease the upper limit of the ISO to 800, have the camera on M mode, set the shutter speed to 1/160 and pick an aperture and let the flash do the rest. In P-TTL mode, the flash should adjust itself.

03-12-2013, 10:26 AM   #5
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Thank you all friends. I've been using M mode with flash since I got K-20D when it came out, now I just got a K30 and did not see Pentax got any improvement in that area after few generations, and I was just wondering that I might be missing something. The main push to make me opened this thread is I like using TAv so much but been frustrated whenever turn on the flash in that mode. Anyway, thanks to all of you did spend your precious time to try to help me out..
03-12-2013, 10:48 AM   #6
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QuoteOriginally posted by Ken T Quote
Thank you all friends. I've been using M mode with flash since I got K-20D when it came out, now I just got a K30 and did not see Pentax got any improvement in that area after few generations, and I was just wondering that I might be missing something. The main push to make me opened this thread is I like using TAv so much but been frustrated whenever turn on the flash in that mode. Anyway, thanks to all of you did spend your precious time to try to help me out..
I understand your frustration. Probably the simplest thing you can do is move the mode dial from TAv to Av or Tv when using the flash. Not perfectly what you want but you'll find it to work reasonably well enough.
03-12-2013, 11:21 AM   #7
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QuoteOriginally posted by Ken T Quote
Thank you all friends. I've been using M mode with flash since I got K-20D when it came out, now I just got a K30 and did not see Pentax got any improvement in that area after few generations, and I was just wondering that I might be missing something. The main push to make me opened this thread is I like using TAv so much but been frustrated whenever turn on the flash in that mode. Anyway, thanks to all of you did spend your precious time to try to help me out..
Not good idea to use TAv mode with flash...metering with TAv mode takes the entire frame into consideration; use M mode only on camera with PTTL flash.
03-12-2013, 02:48 PM   #8
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I am rest assured now that K30s are not any better than K-20D in TAv with flash. This cleared my mind that I might have gotten a defective unit. Thanks guys.

03-14-2013, 03:37 AM   #9
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Wow, that explains it!
I use Av as TAv as proposed by OP on this forum so I don't get caught out anymore. TAv will not handle bright to dark extremes and I often got caught out and as I don't chimp it can be a disappointment when the shot is lost (especially birding etc).
Use Av and set front dial to ISO and it works exactly like TAv.
And since then I haven't had a bad flash shot and it never dawned on me its the Av ability.
Thks for that.
03-14-2013, 04:14 AM   #10
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Following up my earlier post, IMO, the issue in using TAv and flash is that the camera has no idea what the photographer is trying to achieve when using flash with TAv.

Specifically, in allowing ISO to roam with TAv while locking in shutter speed and aperture, how is the camera to know what balance of ambient light vs flash is intended by the user? Digital cameras are computers and computers need programming by humans. The software needs to come up with an answer to the question of "What ISO" when using TAv and flash. It has to have some answer or the program fails to continue executing. Not a good result. Without knowing the user's intentions, a reasonable answer to program in is the lower of "ISO needed to broadly balance flash and ambient light" and "Maximum ISO as specified by the user in setting up the Auto ISO range". So in low light, a high ISO is specified if the Auto ISO range is widely defined by the user. Two possible downsides here: (1) reduced dynamic range increases prospect of burnt out highlights (2) close subjects in conjunction with high sensitivity may mean the flash cannot quench its output quick enough to avoid blowing out the scene.

While the above is speculative on my part, it seems a reasonable explanation of the OP's experience.
03-14-2013, 06:20 AM   #11
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QuoteOriginally posted by southlander Quote
Following up my earlier post, IMO, the issue in using TAv and flash is that the camera has no idea what the photographer is trying to achieve when using flash with TAv.

Specifically, in allowing ISO to roam with TAv while locking in shutter speed and aperture, how is the camera to know what balance of ambient light vs flash is intended by the user? Digital cameras are computers and computers need programming by humans. The software needs to come up with an answer to the question of "What ISO" when using TAv and flash. It has to have some answer or the program fails to continue executing. Not a good result. Without knowing the user's intentions, a reasonable answer to program in is the lower of "ISO needed to broadly balance flash and ambient light" and "Maximum ISO as specified by the user in setting up the Auto ISO range". So in low light, a high ISO is specified if the Auto ISO range is widely defined by the user. Two possible downsides here: (1) reduced dynamic range increases prospect of burnt out highlights (2) close subjects in conjunction with high sensitivity may mean the flash cannot quench its output quick enough to avoid blowing out the scene.

While the above is speculative on my part, it seems a reasonable explanation of the OP's experience.
I understand your point about the camera (the programmers in reality) not know what the user is trying to achieve. However, it doesn't make sense for the camera to select the same ISO under TAv for both non-flash and flash operation. The one exception to this is perhaps an assumption that TAv with flash would be used for fill-flash under strong ambient lighting. There I could see that you would want the ISO to not change when turning on the flash. Of course there's no documentation in the manual about this.
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