Flash exposure issue

**Ash** · 07-10-2009, 05:57 AM

Great note there Matt.
Should have known to come to you in the first place with this question...

Makes more sense now, but then how can one boost flash output when bouncing in P-TTL mode if FEC and EV are not used?

GeneV · 07-10-2009, 10:31 AM

Originally posted by mattdm

This has been a pretty frequent topic. Point the flash up to bounce from the ceiling and you'll find the EV/FE compensation is no longer needed. Whatever it's doing, it's doing on purpose. The leading theory is that the P-TTL algorithm is too sensitive to bounced-back light caught by the matrix metering and is trying very hard to avoid the blown-out-flash look.

I'll have to experiment with my K-7. In theory, the much-better matrix metering should make this less of a problem.

Also in theory, it could be changed by a firmware update, but the fact that Pentax has kept it this way for so long seems to indicate that it's on purpose.

Note that if you have a Metz 58 AF-1, it will stay in A mode without jumping back to P-TTL.

Do the current crop of dedicated flashes automatically add EV compensation when the heads are in bounce position? Some of the old Vivitars did that.

SOldBear · 07-10-2009, 11:36 AM

Originally posted by GeneV

Do the current crop of dedicated flashes automatically add EV compensation when the heads are in bounce position? Some of the old Vivitars did that.

What do you mean by "add EV compensation when the heads are in bounce position"?

In P-TTL or TTL mode, the light output is determined by the light sensor in the camera body.

In A mode, the light output is determined by the light sensor in the flash body.

In P-TTL/TTL/A modes, if the head is in bouncing position, in order for the sensor (either in the camera or in the flash body) to receive the same amount of light, the light output of the flash will automatically increase.

In M mode, the light output is determined by the power ratio setting (by the user).

I'm not sure if I answered your question.

res3567 · 07-10-2009, 08:15 PM

Originally posted by mattdm

This has been a pretty frequent topic. Point the flash up to bounce from the ceiling and you'll find the EV/FE compensation is no longer needed. Whatever it's doing, it's doing on purpose. The leading theory is that the P-TTL algorithm is too sensitive to bounced-back light caught by the matrix metering and is trying very hard to avoid the blown-out-flash look.

I'll have to experiment with my K-7. In theory, the much-better matrix metering should make this less of a problem.

Also in theory, it could be changed by a firmware update, but the fact that Pentax has kept it this way for so long seems to indicate that it's on purpose.

Note that if you have a Metz 58 AF-1, it will stay in A mode without jumping back to P-TTL.

Just did another test and again the flash boosted its power when I adjusted FEC AND EV in the bounce position.

FLASH EXPERTS! Y'all tell me whats up!

F 4, 1/125, ISO 400,
0 FEC, 0 EV
Name: Macro 064.jpg
Views: 134
Size: 14.6 KB

Name: Macro 064.jpg
Views: 134
Size: 14.6 KB

+1 FEC, 0 EV
Name: Macro 065.jpg
Views: 135
Size: 19.5 KB

+1 FEC, +1 EV
Name: Macro 066.jpg
Views: 122
Size: 21.4 KB

+1 FEC, +2 EV
Name: Macro 067.jpg
Views: 137
Size: 24.9 KB

Last edited by res3567; 07-10-2009 at 08:34 PM.

slawek · 07-10-2009, 09:12 PM

Doesn't it show that both FEC and EV work the same way - determine flash output.

res3567 · 07-10-2009, 09:38 PM

Originally posted by slawek

Doesn't it show that both FEC and EV work the same way - determine flash output.

Yea. that is what I am getting at. I am new to this and there seems to be a descrepency here. That is why I posted the pics. EXIF data don't lie.

07-10-2009, 08:15 PM	#19
res3567 Veteran Member Join Date: Sep 2008 Location: Houston Tx. Photos: Gallery Posts: 1,876	Originally posted by mattdm This has been a pretty frequent topic. Point the flash up to bounce from the ceiling and you'll find the EV/FE compensation is no longer needed. Whatever it's doing, it's doing on purpose. The leading theory is that the P-TTL algorithm is too sensitive to bounced-back light caught by the matrix metering and is trying very hard to avoid the blown-out-flash look. I'll have to experiment with my K-7. In theory, the much-better matrix metering should make this less of a problem. Also in theory, it could be changed by a firmware update, but the fact that Pentax has kept it this way for so long seems to indicate that it's on purpose. Note that if you have a Metz 58 AF-1, it will stay in A mode without jumping back to P-TTL. Just did another test and again the flash boosted its power when I adjusted FEC AND EV in the bounce position. FLASH EXPERTS! Y'all tell me whats up! F 4, 1/125, ISO 400, 0 FEC, 0 EV +1 FEC, 0 EV +1 FEC, +1 EV +1 FEC, +2 EV Last edited by res3567; 07-10-2009 at 08:34 PM.

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07-10-2009, 05:57 AM	#16
Ash Loyal Site Supporter Join Date: Mar 2007 Location: Toowoomba, Queensland Photos: Gallery \| Albums Posts: 23,920	Great note there Matt. Should have known to come to you in the first place with this question... Makes more sense now, but then how can one boost flash output when bouncing in P-TTL mode if FEC and EV are not used?

07-10-2009, 10:31 AM	#17
GeneV Veteran Member Join Date: Oct 2008 Location: Albuquerque NM Photos: Albums Posts: 9,830	Originally posted by mattdm This has been a pretty frequent topic. Point the flash up to bounce from the ceiling and you'll find the EV/FE compensation is no longer needed. Whatever it's doing, it's doing on purpose. The leading theory is that the P-TTL algorithm is too sensitive to bounced-back light caught by the matrix metering and is trying very hard to avoid the blown-out-flash look. I'll have to experiment with my K-7. In theory, the much-better matrix metering should make this less of a problem. Also in theory, it could be changed by a firmware update, but the fact that Pentax has kept it this way for so long seems to indicate that it's on purpose. Note that if you have a Metz 58 AF-1, it will stay in A mode without jumping back to P-TTL. Do the current crop of dedicated flashes automatically add EV compensation when the heads are in bounce position? Some of the old Vivitars did that.

07-10-2009, 11:36 AM	#18
SOldBear Veteran Member Join Date: Feb 2009 Location: Alameda, CA Posts: 3,206	Originally posted by GeneV Do the current crop of dedicated flashes automatically add EV compensation when the heads are in bounce position? Some of the old Vivitars did that. What do you mean by "add EV compensation when the heads are in bounce position"? In P-TTL or TTL mode, the light output is determined by the light sensor in the camera body. In A mode, the light output is determined by the light sensor in the flash body. In P-TTL/TTL/A modes, if the head is in bouncing position, in order for the sensor (either in the camera or in the flash body) to receive the same amount of light, the light output of the flash will automatically increase. In M mode, the light output is determined by the power ratio setting (by the user). I'm not sure if I answered your question.

07-10-2009, 09:12 PM	#20
slawek Inactive Account Join Date: Nov 2008 Location: Canada Photos: Gallery Posts: 188 Original Poster	Doesn't it show that both FEC and EV work the same way - determine flash output.

07-10-2009, 09:38 PM	#21
res3567 Veteran Member Join Date: Sep 2008 Location: Houston Tx. Photos: Gallery Posts: 1,876	Originally posted by slawek Doesn't it show that both FEC and EV work the same way - determine flash output. Yea. that is what I am getting at. I am new to this and there seems to be a descrepency here. That is why I posted the pics. EXIF data don't lie.