Bounce type flashgun

Indeed.

And presumably, the flash-sensor cuts off the flash when it's measured a total amount of reflected light, returning to it from whatever its field of view happens to be.

If there's a significant amount of light returning to the flash sensor from an area outside the camera's angle of view, is it not possible that what remains inside the camera's angle of view will be therefore be underexposed?

If so, then

cannot be true, since it's the focal length of the lens and camera sensor size that determine the camera's angle of view.

Incidentally, I realise that using a shorter focal length won't change the duration of the flash in this instance, and therefore the part of the frame that looked dark before won't get any more light.

But with more of what comes back to the flash sensor now contributing to the picture, the bright bits from the previously cut off part will look bright, and presumably appropriately so in relation to the dark bit that was in the frame before.

I suppose the only way to fix this is the way they do with more sophisticated guns - focus the beam from the flash more, so that it comes back from a smaller area.

I do take your point that if the illumination is uneven, then the sensor and the lens could be picking up different intensities of light. My point was that, in general, the focal length and image frame are immaterial.

G

The whole point about TTL is that the light meter sees the same light as the image frame. Usually, it works fine, but my own experience with TTL and P-TTL on the *ist D and K10D is that the old auto-guns produce good results more consistently than the TTL and P-TTL guns.

Best of all, by far, is full manual, where you do test shots to determine precisely the right exposure. However, in a dynamic situation, this isn't always practicable.

G

And this seems to be a consistent theme from others too - there's a worrying amount of "dud results on auto" out there. Particularly since I'm thinking of investing in something that's supposed to be able to give me good results on auto.

Actually... I disagree

I have a very high hit rate in P-TTL... but I understand what's happening and I'm just about to outline a number of pertinent thoughts in Pete's thread...

Matt

Splendid. This is the sort of wrong I like to be

Looking forward to your thoughts

To put it into perspective, I do use (wireless) P-TTL where full manual isn't practicable, and the results are usually OK. However, there are sometimes duds which I can't explain. I find I get more consistent results with my old AF240Z, but there are other reasons, like lack of power and the necessity of using a slave trigger, that make the modern gun more convenient to use.

I am contemplating the purchase of a 540, so the occasional problems with P-TTL aren't sufficient to put me off the technology.

I mean to try some tests with and without a diffuser. It is possible that very bright reflections from an un-diffused flash may be the root of the
difficulty. It would be interesting to hear what Matt uses.

G

Let me just change that to "I think I understand what's happening..."

As George says, there is the occasional dud, but in difficult situations like weddings I've found it right 9/10 times. And shooting in RAW I've never had a shot that wasn't perfectly usable even with the "dud" situation.

(But there were several times that I should've thought a little more carefully about the settings before taking the shot )

Matt

Topic written (phew!):
https://www.pentaxuser.com/forum/viewtopic.php?t=4916

I'm trying an experiment this weekend.

I'm shooting a wedding for a local businessman (who's business has recieved international attention (even the Jay Leno mentioned it on the Tonite Show)).
(Sorry can't say more....).
Will be shooting at a Euro Styled fine food restaruant, with impossible lighting...dark as a cave on one side (candle light) and a two story wall of windows on the other, exposed to sunlight. (even sounds impossible! even if I get bright overcast daylight in the restaruant, there will be dimmed light and candles in the art gallery enclave.). no usable cielings, reflective surfaces everywhere. VERY demanding clients! The restaraunt owners also own a magazine, that caters to very upscale clientele, and some of my biggest competitors are regular contributars! (make you or break you type job...no pressure! lol).

Gerri will be shooting the k10 with 50mm 2.8 macro and 28-70 f4 af 360 flash....with the ds2 and 10-17 fisheye.

I'll be setting up 2 video cameras, and using a canon g5 with the canon 420ex flash (similar spec to the 360 pentax, tried and ture....) as well as the pro one.

My proxcimity to the vid cams (one with shotgun mic, and one lavalier set up) means the mic might pick up the noises from the slrs, hence the reason for using the nearly silent canons).

I'll let you know the percentage of duds we get on each system, and if the pentax fairs noticibly different than a camera/flash combo I know from experience can handle tough lighting scenerios!

Yikes Don!
That sounds mighty lot of fun

Be interesting to hear what happens... but my guess is that having the K10D on Auto ISO and Av should be good. (I have mine setup with the front dial to adjust the ISO and the rear to change Av. That way I can manually adjust ISO rating, and press the Green button to switch into 100-1600 auto. I just love the K10D for that )

BTW, I've updated the info and made it sticky:
https://www.pentaxuser.com/forum/viewtopic.php?t=4950

Matt