Flash overexposure with new K5

dh87 · 08-03-2011, 01:21 PM

I now have the Pentax 16-50 2.8 for testing. I haven't tested carefully, but the first couple of flash pictures seem to be better with the Pentax than with the Sigma. Trouble is, a couple of the Sigma shots seemed to be better than they were when I took them a couple of days ago. I will have a further report tomorrow.

philbaum, the internal flash does overexpose less than the 540. The K5 is brand new. If it really doesn't work, Pentax should replace it with one that does. And, yes, this is a PITA.

**Ash** · 08-03-2011, 01:28 PM

Originally posted by dh87

I think that the FEC is additive, although I didn't test it carefully, and there is a -3 adjustment on the 540. Auto works pretty well for the 540, but there is no auto on the built-in. Isn't there auto on the Metz 58? Also, Metz remembers previous settings when you turn it off; Pentax forgets (according to the reviews). So, every time I start up the flash I can set it to FEC -2. That's not ideal.

Yes, Camera FEC + Flash EV is additive, and yes Metz flashes have A modes just like Pentax flashes. But why not set your FEC on the camera, since it will need to consistently be there? The camera will remember this setting after being switched off, so you won't need to do it on the flash at all. Just keep it as normal (EV 0) and adjust only as necessary as you shoot.

dh87 · 08-04-2011, 12:43 AM

I did some tests comparing the Sigma 17-50 2.8 and the Pentax 16-50 f2.8. In flash exposures, the Pentax lens is better. I tried with direct (not bounced) flash from the 540, and it comes out OK with the Pentax lens. With the Sigma lens, the photo is >1 stop overexposed. In another photo, both are overexposed, but the Pentax is a bit closer. The overexposure might be because there are 2 black objects in the field. In a fill flash photo, the Pentax also had a lower exposure and did not require as much compensation.

I took a couple of photos outside, and the Pentax has terrible chromatic aberration. I have not seen anything like this with the Sigma.

Class A · 08-04-2011, 06:25 AM

dh87, note that the metering is done by the camera. The lens (Pentax vs Sigma) shouldn't really play a role.

One reason why you could see exposure differences is that one of the lenses' aperture size is a bit off, i.e., does not precisely stop to the f-ratio you specify. However, you should then also see the same exposure differences in normal (i.e., no flash) shooting.

To the best of my knowledge the K-5 flash overexposure bug manifests itself the most with bounced flash. Direct flash seems to be mostly OK.

asp1880 · 08-04-2011, 07:05 AM

Originally posted by Class A

One reason why you could see exposure differences is that one of the lenses' aperture size is a bit off, i.e., does not precisely stop to the f-ratio you specify. However, you should then also see the same exposure differences in normal (i.e., no flash) shooting.

Could be. To verify, try shooting wide open in aperture priority. If it exposes correctly, it's most likely to be a sticky aperture.

Originally posted by Class A

To the best of my knowledge the K-5 flash overexposure bug manifests itself the most with bounced flash. Direct flash seems to be mostly OK.

There's also a wireless flash underexposure bug actually. Close and midrange focus gives correct wireless exposure, distant focus ( > ~2m) gives 3-4 stop underexposure. Easy to verify using manual focus. Focus close, it's OK, focus the same scene distant, it's underexposed. I see it with K-5 and the AF540 flash. It's also reported on the other forum.

Sincerely,
--Anders.

dh87 · 08-05-2011, 03:01 PM

Class A and asp1880:

The Sigma lens works correctly without flash. I don't see a difference in overall exposure going from f2.8 to f16 with intermediate values. I think that it's stopping down correctly in these cases. I will test the flash with different f stops. The flash overexposure is worse with the 540 than with the built-in flash.

The Pentax lens definitely has more CA, and some of the CA is in the middle of the field, not at the edges. The Sigma has CA as well, but there's less, and the CA is at the edges of the field.

philbaum · 08-05-2011, 04:12 PM

Originally posted by asp1880

There's also a wireless flash underexposure bug actually. Close and midrange focus gives correct wireless exposure, distant focus ( > ~2m) gives 3-4 stop underexposure. Easy to verify using manual focus. Focus close, it's OK, focus the same scene distant, it's underexposed. I see it with K-5 and the AF540 flash. It's also reported on the other forum.

Sincerely,
--Anders.

Is it a bug or is it a design limitation?

As i understand it, pttl increases or decreases the power of the flash dependent on what light the sensor is experiencing. I could be wrong, but i don't think pttl knows what distance the remote wireless flash is from the camera. But flash power increases/decreases are not linear with regard to the distance of said flash from the camera, square root reduction i believe. If the camera cannot compute the distance to the remote flash, then a reduction of power that would have worked on a close wireless flash, will result in excessive underexposure in a more distant flash.

I remember in my K20 or K10 manual, there was a warning in there that wireless flashes should be within 10' of the body, but i can't check it since i'm on the road. So i'm wondering if this isn't a design limitation of wireless flash usage in general.

I do know that a Metz flash on my camera body in direct orientation, can compute the distance from the flash to the subject. But in any other flash orientation than direct, or in off-camera, that data area is left blank on the flash LCD.

Off topic - i was watching a training video on using fill flash recently, and the well-known pro, Nikon equipment, was going around adjusting the remote flashes manually rather than using his radio trigger controls.

For the remote flash work i've done recently, up to 35 feet away and out of view behind concrete walls, I've used manual adjustments and got there within 1 or 2 iterations.

Last edited by philbaum; 08-05-2011 at 04:18 PM.

08-04-2011, 07:05 AM	#35
asp1880 Veteran Member Join Date: Jul 2010 Location: Lyngby, Copenhagen Photos: Albums Posts: 742	The wireless flash underexposure bug Originally posted by Class A One reason why you could see exposure differences is that one of the lenses' aperture size is a bit off, i.e., does not precisely stop to the f-ratio you specify. However, you should then also see the same exposure differences in normal (i.e., no flash) shooting. Could be. To verify, try shooting wide open in aperture priority. If it exposes correctly, it's most likely to be a sticky aperture. Originally posted by Class A To the best of my knowledge the K-5 flash overexposure bug manifests itself the most with bounced flash. Direct flash seems to be mostly OK. There's also a wireless flash underexposure bug actually. Close and midrange focus gives correct wireless exposure, distant focus ( > ~2m) gives 3-4 stop underexposure. Easy to verify using manual focus. Focus close, it's OK, focus the same scene distant, it's underexposed. I see it with K-5 and the AF540 flash. It's also reported on the other forum. Sincerely, --Anders.

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08-03-2011, 01:21 PM	#31
dh87 Junior Member Join Date: Jul 2011 Location: Maryland Posts: 25 Original Poster	I now have the Pentax 16-50 2.8 for testing. I haven't tested carefully, but the first couple of flash pictures seem to be better with the Pentax than with the Sigma. Trouble is, a couple of the Sigma shots seemed to be better than they were when I took them a couple of days ago. I will have a further report tomorrow. philbaum, the internal flash does overexpose less than the 540. The K5 is brand new. If it really doesn't work, Pentax should replace it with one that does. And, yes, this is a PITA.

08-03-2011, 01:28 PM	#32
Ash Loyal Site Supporter Join Date: Mar 2007 Location: Toowoomba, Queensland Photos: Gallery \| Albums Posts: 23,920	Originally posted by dh87 I think that the FEC is additive, although I didn't test it carefully, and there is a -3 adjustment on the 540. Auto works pretty well for the 540, but there is no auto on the built-in. Isn't there auto on the Metz 58? Also, Metz remembers previous settings when you turn it off; Pentax forgets (according to the reviews). So, every time I start up the flash I can set it to FEC -2. That's not ideal. Yes, Camera FEC + Flash EV is additive, and yes Metz flashes have A modes just like Pentax flashes. But why not set your FEC on the camera, since it will need to consistently be there? The camera will remember this setting after being switched off, so you won't need to do it on the flash at all. Just keep it as normal (EV 0) and adjust only as necessary as you shoot.

08-04-2011, 12:43 AM	#33
dh87 Junior Member Join Date: Jul 2011 Location: Maryland Posts: 25 Original Poster	I did some tests comparing the Sigma 17-50 2.8 and the Pentax 16-50 f2.8. In flash exposures, the Pentax lens is better. I tried with direct (not bounced) flash from the 540, and it comes out OK with the Pentax lens. With the Sigma lens, the photo is >1 stop overexposed. In another photo, both are overexposed, but the Pentax is a bit closer. The overexposure might be because there are 2 black objects in the field. In a fill flash photo, the Pentax also had a lower exposure and did not require as much compensation. I took a couple of photos outside, and the Pentax has terrible chromatic aberration. I have not seen anything like this with the Sigma.

08-04-2011, 06:25 AM	#34
Class A Pentaxian Join Date: Aug 2008 Location: Wellington, New Zealand Posts: 11,251	dh87, note that the metering is done by the camera. The lens (Pentax vs Sigma) shouldn't really play a role. One reason why you could see exposure differences is that one of the lenses' aperture size is a bit off, i.e., does not precisely stop to the f-ratio you specify. However, you should then also see the same exposure differences in normal (i.e., no flash) shooting. To the best of my knowledge the K-5 flash overexposure bug manifests itself the most with bounced flash. Direct flash seems to be mostly OK.

08-05-2011, 03:01 PM	#36
dh87 Junior Member Join Date: Jul 2011 Location: Maryland Posts: 25 Original Poster	Class A and asp1880: The Sigma lens works correctly without flash. I don't see a difference in overall exposure going from f2.8 to f16 with intermediate values. I think that it's stopping down correctly in these cases. I will test the flash with different f stops. The flash overexposure is worse with the 540 than with the built-in flash. The Pentax lens definitely has more CA, and some of the CA is in the middle of the field, not at the edges. The Sigma has CA as well, but there's less, and the CA is at the edges of the field.

08-05-2011, 04:12 PM	#37
philbaum Veteran Member Join Date: Oct 2007 Location: Port Townsend, Washington State, USA Posts: 3,659	Originally posted by asp1880 There's also a wireless flash underexposure bug actually. Close and midrange focus gives correct wireless exposure, distant focus ( > ~2m) gives 3-4 stop underexposure. Easy to verify using manual focus. Focus close, it's OK, focus the same scene distant, it's underexposed. I see it with K-5 and the AF540 flash. It's also reported on the other forum. Sincerely, --Anders. Is it a bug or is it a design limitation? As i understand it, pttl increases or decreases the power of the flash dependent on what light the sensor is experiencing. I could be wrong, but i don't think pttl knows what distance the remote wireless flash is from the camera. But flash power increases/decreases are not linear with regard to the distance of said flash from the camera, square root reduction i believe. If the camera cannot compute the distance to the remote flash, then a reduction of power that would have worked on a close wireless flash, will result in excessive underexposure in a more distant flash. I remember in my K20 or K10 manual, there was a warning in there that wireless flashes should be within 10' of the body, but i can't check it since i'm on the road. So i'm wondering if this isn't a design limitation of wireless flash usage in general. I do know that a Metz flash on my camera body in direct orientation, can compute the distance from the flash to the subject. But in any other flash orientation than direct, or in off-camera, that data area is left blank on the flash LCD. Off topic - i was watching a training video on using fill flash recently, and the well-known pro, Nikon equipment, was going around adjusting the remote flashes manually rather than using his radio trigger controls. For the remote flash work i've done recently, up to 35 feet away and out of view behind concrete walls, I've used manual adjustments and got there within 1 or 2 iterations. Last edited by philbaum; 08-05-2011 at 04:18 PM.