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06-17-2020, 01:25 PM   #16
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A very interesting thread! Thanks to all the contributors so far who have made so many great points.....

For me, in my own limited experience with the AF280T and M series lenses, the most significant distinction between 'Auto' mode flash and P-TTL is control over the balance of flash and ambient exposures.

P-TTL provides a direct and functional workflow for independently controlling the ambient and flash exposures.... (flash exposure controlled by flash compensation, and ambient controlled by the 3 key settings of ISO, Aperture and time value).

So long as you choose an appropriate camera mode, such as M, to exert direct control over your ambient exposure, and you are working within the distance range that your P-TTL flash can correctly expose for, then you have tools to finely tune your flash and 'background' balance, in half or even third stop increments.

Try that in Auto mode! The flash output in auto mode does not self adjust to compensate for any changes to the ISO or aperture settings on the camera, so trying to achieve a specific balance will quickly become an act of contortion and will prove impossible in many configurations and lighting conditions. Each change to ISO and Aperture on the camera will affect the flash exposure recorded making any light balancing attempts futile.

A member earlier wrote about P-TTL flash exposures using the camera metering modes..... I'm not sure about that? I have not been aware of such fineries on our Pentax cameras and had thought that P-TTL only used the Matrix mode. This could be a reason that A type lenses are not always reliable as they cannot utilise the matrix system. However it stands as something to be tested more thoroughly and I would be pleased to be corrected.

06-17-2020, 03:01 PM   #17
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QuoteOriginally posted by mcgregni Quote
Try that in Auto mode!
I learned to do that back-in-the-day. As with fully manual flash, one simply uses a different aperture setting than suggested, just like in the old days. It can be a bit limiting in that most auto-thyristor models only provide two aperture choices, but not much worse than coming up against the limits of P-TTL attenuation or range with some subjects.

Where things get complicated is when using a vintage dedicated Pentax flash (e.g. AF280T) in auto mode with a modern dSLR in exposure modes where the flash may override the camera's choice for aperture.* Yes, the new cameras still obey the will of the original analog dedication, something that the photographer should be aware of when working in other than M or Av modes. Auto ISO is particularly evil when doing auto flash (duh).

As for P-TTL and metering modes...all three work with P-TTL, even with A-series lenses, the same as for non-flash photography. The difference between A-series and auto-focus lenses is that the camera always does the pre-flash at full intensity with fail-over to full intensity main flash if the pre-flash metering is out of range. As a result, high ISO, wide-aperture, and close subject P-TTL with A-series lenses often results in gross overexposure.


Steve

* Yes, the aperture chosen for auto flash is appropriate to the set ISO. I suspect that flash identifies its guide number when signalling its mode.

Last edited by stevebrot; 06-17-2020 at 03:14 PM. Reason: style
06-17-2020, 05:22 PM   #18
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I can't imagine how Auto can cope with one or more off camera flashes.

We need the metering of what the camera's seeing, not from a flash on a stand off to the side or bounced off a wall or whatever. P-TTL does work in those situations.

Auto you're trapped with the flash on your hotshoe.

Last edited by clackers; 06-17-2020 at 06:33 PM.
06-17-2020, 05:40 PM   #19
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QuoteOriginally posted by mcgregni Quote
that P-TTL only used the Matrix mode
I'm pretty sure that is the case, because highly reflective surfaces like mirrors and windows completely throw off P-TTL metering. A dedicated flash meter is an advantage because it can do spot meteriing. Or you can chimp and keep changing manual settings until you get the results you want. In my experience it all comes down to how much time you have to experiment and adjust your flash, if you need to take spur of the moment photos with flash, P-TTL is your best bet with a Pentax camera. Whether or not P-TTL is as capable as flash metering and control systems from Canon and Nikon is another subject; and isn't an option if you want to use your Pentax camera.

06-17-2020, 10:46 PM   #20
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QuoteOriginally posted by RGlasel Quote
I'm pretty sure that is the case
I am quite certain that I took photos a few hours ago using matrix, center-weighted, and spot using my K-3. As with regular metering, each mode has its strengths.


Steve
06-17-2020, 11:20 PM - 1 Like   #21
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QuoteOriginally posted by RGlasel Quote
Whether or not P-TTL is as capable as flash metering and control systems from Canon and Nikon is another subject
They pretty much use the same algorithms. Very similar to Canon's approach, IIRC.
08-25-2020, 06:57 PM   #22
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QuoteOriginally posted by clackers Quote
I can't imagine how Auto can cope with one or more off camera flashes
this was an experiment i did last xmas......wanted to see how consistent auto flash could be just bounced off the ceiling....surprisingly it seems so.....af360fgz on a cactus v6 (set to manual so a 'dumb' trigger) off camera and remained in the same spot for the 3 frames to make this "pano" .....K-50 with mamiya/sekor 55/f1.8......

not that i have done it but think i could use 2 fgz's off camera set to different iso/fstop....granted it would all be bare flash....but main light and a rim/hairlight i believe would work as the sensors would be focused on completely different things......but that's only a guess and nothing to back it up with

08-25-2020, 09:37 PM   #23
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QuoteOriginally posted by clackers Quote
Auto you're trapped with the flash on your hotshoe.
Unless you aren't. Auto flash attenuates based on signal to its detector. It is a bit of an art to configure, but each flash "sees" its own work along with contribution from its partners that happens its way. A single off-camera flash is fairly easy, two a bit harder. That said, it is probably easier to simply do such set-ups manually and determine aperture with a flash meter. There are even workarounds to allow use of softboxes and such.

I have a small project in mind using auto-flash for a balanced on-off camera rig for running-and-gunning. I have the bits and pieces at present to make it work and just need to figure out a fun way to demonstrate it.

More recently, I have been doing direct comparison of on-camera P-TTL with the Sigma EF-610 DG Super* vs. Auto with the Vivitar 283. Which wins depends a lot on the subject and ambient light. Where P-TTL fails badly is with "A" series lenses and close distance, higher ISO, and/or wider apertures. I also discovered that having a window looking out on a brightly lit landscape behind and to the side of a sky-lit interior will totally fool P-TTL into damping the ambient out of existence, something that Auto handles easily. It is the global contrast in the frame that gums the works.

Fun, eh?

I think I will title the thread, "Advantages of Auto Over P-TTL Flash".


Steve

* Yes, I really should pick up a AF540FGZ for this sort of thing. The Sigma can be a pain.

08-26-2020, 03:34 PM   #24
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came across another example of 'auto' off camera using 'dumb' wansen radio trigger with aperture blocked K-50.....

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