[egordon99]

it's not an interpretation, it's how it works. see that meter/guide in the manual? the mirror picture (shooting into it) is proper. no clipping, proper exposure. bouncing is under exposed with clipping.
i think i'm done trying to get you guys to understand how you're misusing things.

Well then you've exceeded the dynamic range the sensor is capable of recording.

[egordon99]

Page 35: Wireless Mode (P-TTL Photography). How does P-TTL wireless work with an external flash (with on-camera flash serving as control only, i.e., not firing) if only the subject to lens distance matters? If I put the flash close to the subject you'd need a different illumination than if the flash was further away?



--KYC

Good point with the wireless. I can have my flash OFF THE FREAKIN' CAMERA SHOOTING THROUGH AN UMBRELLA and E-TTL works!

[Ash]

All right all...
This bounce flash photography technique thread posted by the OP had quickly turned into a discussion about whether P-TTL works or not off-axis, and never left it. Apologies to the OP - I hope at least you may have gotten something out of the thread before it was railroaded.

Jason may not be back to reply, but his reasoning for bounced P-TTL failure is flawed and he remains fixated on this reasoning. It should be made clear to beginners in flash photography that Pentax's P-TTL system is a fully automatic flash exposure calculating system that requires a 'pre-flash' (prior to the shutter opening) to calculate the required flash intensity the camera tells the flash to use during the actual exposure (when the shutter is open).

This function is NOT influenced by flash head orientation - the flash head could be pointing anywhere and the flash remains in P-TTL 'bounced' mode (indicated by the bounce icon on the flash), and pre-flash occurs which again is used to calculate flash intensity for the shot.

What will influence results is the distance from the flash to reflective surface to subject, the nature of the reflective surface (flat white surfaces giving incident angles towards the subject are best but other colours, shapes and angles can be used creatively), and the scene content (bright highlights typically cause underexposure).

As a result of Pentax dSLRs furiously trying to preserve highlight detail, P-TTL flash exposures are notoriously under-exposed at EV 0, FEC 0. Underexposure is not always bad, but does tend to lose important shadow detail and not produce brilliant highlights, so it's always advisable to start at FEC +0.7 or +1.0 - this can be set once and for all on the camera (Fn + down, then rear e-dial forward to adjust FEC). You'd be surprised how well P-TTL works with that minor adjustment done once only - e.g. https://www.pentaxforums.com/forums/general-photography-techniques-styles/455...-tutorial.html

[Ben_Edict]

All right all...
This bounce flash photography technique thread posted by the OP had quickly turned into a discussion about whether P-TTL works or not off-axis, and never left it. Apologies to the OP - I hope at least you may have gotten something out of the thread before it was railroaded.

Jason may not be back to reply, but his reasoning for bounced P-TTL failure is flawed and he remains fixated on this reasoning. It should be made clear to beginners in flash photography that Pentax's P-TTL system is a fully automatic flash exposure calculating system that requires a 'pre-flash' (prior to the shutter opening) to calculate the required flash intensity the camera tells the flash to use during the actual exposure (when the shutter is open).

This function is NOT influenced by flash head orientation - the flash head could be pointing anywhere and the flash remains in P-TTL 'bounced' mode (indicated by the bounce icon on the flash), and pre-flash occurs which again is used to calculate flash intensity for the shot.

What will influence results is the distance from the flash to reflective surface to subject, the nature of the reflective surface (flat white surfaces giving incident angles towards the subject are best but other colours, shapes and angles can be used creatively), and the scene content (bright highlights typically cause underexposure).

As a result of Pentax dSLRs furiously trying to preserve highlight detail, P-TTL flash exposures are notoriously under-exposed at EV 0, FEC 0. Underexposure is not always bad, but does tend to lose important shadow detail and not produce brilliant highlights, so it's always advisable to start at FEC +0.7 or +1.0 - this can be set once and for all on the camera (Fn + down, then rear e-dial forward to adjust FEC). You'd be surprised how well P-TTL works with that minor adjustment done once only - e.g. https://www.pentaxforums.com/forums/general-photography-techniques-styles/455...-tutorial.html

Very good summary. The camera doe not need to "know" much, because it will simply use a really existing pre-flash to actually meter the required amount of flash light.

Ben

[kyc]

All right all...
This bounce flash photography technique thread posted by the OP had quickly turned into a discussion about whether P-TTL works or not off-axis, and never left it. Apologies to the OP - I hope at least you may have gotten something out of the thread before it was railroaded.

Yes, let's try to get this discussion back on track.

As a result of Pentax dSLRs furiously trying to preserve highlight detail, P-TTL flash exposures are notoriously under-exposed at EV 0, FEC 0. Underexposure is not always bad, but does tend to lose important shadow detail and not produce brilliant highlights, so it's always advisable to start at FEC +0.7 or +1.0 - this can be set once and for all on the camera (Fn + down, then rear e-dial forward to adjust FEC). You'd be surprised how well P-TTL works with that minor adjustment done once only - e.g. https://www.pentaxforums.com/forums/general-photography-techniques-styles/455...-tutorial.html

Having upgraded from K100D to K-7, I find the metering to be less conservative (probably because it has 77 metering segments so one or two spurious highlights don't overwhelm the metering). Perhaps the FEC is not as necessary for the K-7.

Hamid's tutorial on bounce flash is interesting. However, I don't quite get it, so perhaps someone can explain what I'm missing. The suggestion is to meter for ambient light, okay so far. Then he stops down a bit by changing shutter speed. The final exposure (with P-TTL bounced flash) would be the sum of (1) the stopped down ambient light exposure, plus (2) the P-TTL exposure in dark. So if I subtract out #1, which is quite dark to begin with, I don't imagine it would look too different from the final exposure. Therefore, wouldn't any short enough shutter speed at F/4 with P-TTL be the same as long as it was longer than the flash duration?

Another concern I have with the example is the shutter speed of 1/13 could result in motion blur on the stopped down ambient light exposure. This gets "added" to the flash-lit part of the exposure so it potentially could add slight motion blur to the final exposure. Am I missing something here?

Perhaps my approach is too simplistic, but I find that if ambient light is quite even then I just set my aperture (or use program line) and bounce away, no need for manual metering. However, if there is a brightly lit background (e.g., backlit window) that I want to expose properly then I meter for the backlighting, turn on the flash and let the P-TTL calculate the exposure for the subject.

--KYC

[ma318]

Hamid's tutorial on bounce flash is interesting. However, I don't quite get it, so perhaps someone can explain what I'm missing. The suggestion is to meter for ambient light, okay so far. Then he stops down a bit by changing shutter speed. The final exposure (with P-TTL bounced flash) would be the sum of (1) the stopped down ambient light exposure, plus (2) the P-TTL exposure in dark. So if I subtract out #1, which is quite dark to begin with, I don't imagine it would look too different from the final exposure. Therefore, wouldn't any short enough shutter speed at F/4 with P-TTL be the same as long as it was longer than the flash duration?

Another concern I have with the example is the shutter speed of 1/13 could result in motion blur on the stopped down ambient light exposure. This gets "added" to the flash-lit part of the exposure so it potentially could add slight motion blur to the final exposure. Am I missing something here?



--KYC

Metering for the ambient would be a good idea if the flash is at 90d and there is a relatively large distance between the subject and the background (e.g. the subject is 10 feet from the camera and there is a wall in the background 30 feet from the camera). If you don't meter for the ambient, then the wall will be really underexposed. The brightness of the flash hitting the wall is only 1/9 of that hitting the subject due to inverse square law for light intensity fall-off.

Also if the background is really far away (e.g. a sunset), then you should meter for the ambient as well and use the flash to fill the subject. Otherwise the sunset background may turn out too underexposed.

If the background is relatively close to your subject and it is not too reflective or bright then you should be able to get away without metering for the ambient or the background.

[Ash]

The suggestion is to meter for ambient light, okay so far. Then he stops down a bit by changing shutter speed. The final exposure (with P-TTL bounced flash) would be the sum of (1) the stopped down ambient light exposure, plus (2) the P-TTL exposure in dark. So if I subtract out #1, which is quite dark to begin with, I don't imagine it would look too different from the final exposure. Therefore, wouldn't any short enough shutter speed at F/4 with P-TTL be the same as long as it was longer than the flash duration?

ma318's explained it good - there probably would be a small different the shutter speed would make going from 1/13 to 1/180 (flash-sync speed), but still significant - this is typically 'dragging the shutter'.

Another concern I have with the example is the shutter speed of 1/13 could result in motion blur on the stopped down ambient light exposure. This gets "added" to the flash-lit part of the exposure so it potentially could add slight motion blur to the final exposure. Am I missing something here?

There may be some motion blur with such a slow shutter speed but generally for most stationary subjects this shutter speed would be quite acceptable. So in this case there would be little to worry about other than camera shake, which at 1/13 should also be OK with a 31mm lens with SR on.

Perhaps my approach is too simplistic, but I find that if ambient light is quite even then I just set my aperture (or use program line) and bounce away, no need for manual metering. However, if there is a brightly lit background (e.g., backlit window) that I want to expose properly then I meter for the backlighting, turn on the flash and let the P-TTL calculate the exposure for the subject.

--KYC

You could use P-TTL in both circumstances. If the backlighting is overwhelming for the camera at 1/180sec, then there is where you would consider HSS flash, also handled reasonably well by the flash in P-TTL mode - just choose your shutter speed accordingly.

[attack11]

Ash, my flash is usually off axis. That doesn't change the camra/flash distance to subject. If there was Pentax literature supporting a bounce method, i think it'd be in the 360/540 manuals.

Well then you've exceeded the dynamic range the sensor is capable of recording.

um, no. the room is a control.

[egordon99]

um, no. the room is a control.

I don't know what that sentence is supposed to mean.

Anyway, IF P-TTL doesn't work when bouncing, then HOW is the flash output calculated? It's not firing at full power. It's not firing at the minimum power. Does the flash just randomly select a power?

Or does the flash fire a pre-flash of known power, and then the meter in the body evaluates the reflected light and based on the ISO/f-stop, determines what power is needed for proper exposure? (hint, that's what it does, and that explains roughly WHAT P-TTL is )

[kyc]

Ash, my flash is usually off axis. That doesn't change the camra/flash distance to subject. If there was Pentax literature supporting a bounce method, i think it'd be in the 360/540 manuals.

But it is in the manuals (I posted on this above)!

Page 53 (AF360FGZ manual): Bounce Flash. With the AF360FGZ you can tilt the flash head... this function is effective when photographing in P-TTL or TTL mode...

Page 35 (AF360FGZ manual): Wireless Mode (P-TTL Photography).


So here you have Pentax literature explicitly stating that P-TTL is available with bounce flash (page 53) and also in wireless mode (page 35). In wireless, the distance from flash to subject can be very different to the distance from camera to subject.

Moreover, the manual references to using P-TTL with bounce or wireless are much more unambiguous than the manual reference you had provided indicating "distance" was calculated (from which you concluded could only be taken from the AF lens reading). Others have pointed out many different ways of calculating a "distance" by metering pre-flash vs ambient.

[egordon99]

But it is in the manuals (I posted on this above)!

Page 53 (AF360FGZ manual): Bounce Flash. With the AF360FGZ you can tilt the flash head... this function is effective when photographing in P-TTL or TTL mode...

Page 35 (AF360FGZ manual): Wireless Mode (P-TTL Photography).

He won't believe you unless you rip out the page from the manual and mail it to him

[kyc]

But it is in the manuals (I posted on this above)!

Page 53 (AF360FGZ manual): Bounce Flash. With the AF360FGZ you can tilt the flash head... this function is effective when photographing in P-TTL or TTL mode...

Page 35 (AF360FGZ manual): Wireless Mode (P-TTL Photography).


So here you have Pentax literature explicitly stating that P-TTL is available with bounce flash (page 53) and also in wireless mode (page 35). In wireless, the distance from flash to subject can be very different to the distance from camera to subject.

He won't believe you unless you rip out the page from the manual and mail it to him

Sadly, I think you are right. However, given that it looks like his misinformation has gained some sort of following I think other users could benefit from learning that P-TTL works with bounce.

Certainly, attack11's method for bounce flash usage (full manual mode with fine tuning) works well. But the opportunity could be lost during the time it took to fine tune manual flash (or else the user would follow attack11's advice of using full on flash with P-TTL and not get as good a result as P-TTL bounced).

Ultimately, photography is all about capturing the moment so any advantage is good. That's why I use matrix metering (if I'm confident it works) if there isn't enough time to meter manually and make adjustments using test shots.

[Ash]

Ash, my flash is usually off axis. That doesn't change the camra/flash distance to subject. If there was Pentax literature supporting a bounce method, i think it'd be in the 360/540 manuals.

Jason, a change in flash-head axis will change the flash-to-subject distance - because the distance is not calculated as the most direct route from the flash to the subject, it is rather the distance from the flash to the reflective surface in the direction of the axis of the flash head, and back to the subject at the incident angle the light hits the reflective surface. This does not take into account the opacity and colour of the reflective surface, which considerably alters the reflected light intensity and hue.



Furthermore, the flash light direction varies with the size and reflective nature of a flashcard used to point the direction of the light forwards:


But none of this means P-TTL doesn't work in bounce mode - I've said enough about this in previous posts, so I think we can lay this issue to rest or we'd be just flogging another dead horse.

[jpzk]

I have no problems using P-TTL and bounce flash with my cameras. One thing that helps is to use the wide panel on the flash when bouncing.

Just got the AF-540FGZ and I have one question if you wouldn't mind:
(a true beginner's question).

You said you use the wide angle panel, that would be the thicker piece of translucent plastic which you pull out of the head of the flash?
And the "Catch Light Panel", the translucent, bigger one, what would you use that for?
Thanks.

JP

[flyer]

Just got the AF-540FGZ and I have one question if you wouldn't mind:
(a true beginner's question).

You said you use the wide angle panel, that would be the thicker piece of translucent plastic which you pull out of the head of the flash?
And the "Catch Light Panel", the translucent, bigger one, what would you use that for?
Thanks.

JP

Using the wide angle panel will reflect the light off a larger area, thus creating a more evenly lit room. Unfortunately, it also reduces the flash range, but, generally, room sizes in homes are not so large as to prevent proper exposure.

As for the catch light panel, it will reflect some of the light forward, thus avoiding harsh shadows under the eyebrows, nose and chin. It will also allow you to have a "catchlight" in your model's eye. On the Sigma flashes, there is no catch light panel, so I use a piece of white card held with a rubber band.