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03-28-2010, 06:05 PM   #1
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Why won't Pentax flash PTTL work?

I have both the 360 and 540 flash and neither of them will function at all in PTTL mode. If I use Auto mode I get good exposures (but auto zoom doesn't work on the 540). What is up with these rediculously underexposed images? I am very frustrated with these flashes, enough that selling everything to buy a Nikon and one lens sounds like a good move.

If I buy a Metz or a Sigma flash will this problem resolve or is it the camera?

Using a Pentax K20D but it was the same with my K10D and is the same with my Samsung GX-10.

Examples below. First shot is on Auto mode using a Gary Fong Lightsphere, ISO 200 F4.0 1/30 second. Second photo is exactly the same except PTTL. The lightsphere is pointed up like it is supposed to be.

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03-28-2010, 07:38 PM   #2
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back away from the ledge! It should work but we would need more info. First off, what lens are you using? Also take the lightsphere off and try it. Bounce and PTTL don't play well together.
03-28-2010, 08:21 PM   #3
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QuoteOriginally posted by mtroute Quote
back away from the ledge! It should work but we would need more info. First off, what lens are you using? Also take the lightsphere off and try it. Bounce and PTTL don't play well together.
What lenses are you using
are they in A mode
03-28-2010, 08:42 PM   #4
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I'm using a Sigma 18-50 f2.8 EX glass (great glass). There is no "auto" selection on this lens.

These next two shots are the same as before, but no lightsphere and straight on to the target (obvious heavy flash in the first).

Fist shot - Manual - ISO 200 - f4.0 - T1/30 - flash on AUTO w/ matching iso and f stop

Second shot is exactly the same except PTTL.

This has been my experience with these flashes for a year and a half (the 540 has been back to the factory twice). All the adjustments on these shots below are zeroed (flash and camera +/- = 0). To use the flash I usually have to bump the flash to +1.0 and the camera to +2.0, even then it is marginal for anything further away than 6 feet. In software it usually requires one more F stop push to get a good exposure for a total of four full stops underexposed..... sigh.. If I didn't have such a good arsenal of lenses already, I really would consider the big "N" switch.... the ledge... there it is...

Thanks, folks.

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03-28-2010, 09:01 PM   #5
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P-TTL will only work with lenses that allow the camera to control the aperture. If your lens has an aperture ring, but no "A" setting, then it would seem to be a manual lens.

Is it an auto-focus lens? P-TTL can work with A-series (or equivalent) lenses, so it doesn't have to be AF. All AF lenses allow the camera to control the aperture. A-series lenses (or equivalent) also allow this. M-series or older lenses, which are manual focus, manual aperture lenses, have no electronic communication between the lens and camera body. This communication is necessary for P-TTL to work.

Do you have a kit lens, or any AF lens? Try it with that lens. It should work.

If your Sigma lens is manual aperture, then the answer to your second question is no, a Metz or other brand of flash won't be able to use p-ttl, either. Its the lens, not the flash that is the limiting factor.
03-29-2010, 01:26 AM   #6
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QuoteOriginally posted by jshram Quote
I'm using a Sigma 18-50 f2.8 EX glass (great glass). There is no "auto" selection on this lens.
That's because it doesn't have an aperture ring, as it an auto lens.
http://www.sigmaphoto.com/shop/18-50mm-f28-ex-dc-macro-sigma
03-29-2010, 01:46 AM   #7
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Something's not quite right with your P-TTL results.
They both look like there's no flash component to the exposures, just ambient light.
I've personally never had such issues in P-TTL, direct or bounced with the 540 flash.
I keep my FEC at +0.7, and exposures are almost always spot on.
Is there anything else you can report on the flash mode? Can you see P-TTL on the flash unit when in the mode?
03-29-2010, 03:04 AM   #8
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Exif? I don't mean just the settings, but the real exif, with all the information. Maybe theres some obscure setting you forgot about.

03-29-2010, 04:07 AM   #9
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Reflections...

Hi, it is all about metering and not flash itself. In first example camera tried to avoid overexposure from windows- here I guess spot metering would do a great job as matrix/CW ones "see" the windows and dramatically lower the flash output despite of fact that flash will not make them brighter- camera just can not analyze the content of frame. In second example a step to the right would cure it all as metering underexposes due to the reflection from the background glass-covered reflective image. With auto flash no such precise decisions are made. IMHO shooting with flash is very creative and it takes a lot of learning to understand its behavior :-) but once You get the idea it is pure fun.
Best and happy flashing, JR
03-29-2010, 04:49 AM   #10
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QuoteOriginally posted by jshram Quote
What is up with these rediculously underexposed images? I am very frustrated with these flashes, enough that selling everything to buy a Nikon and one lens sounds like a good move.
Does PTTL not working at all or is it producing underexposure? In later case, it is a well known issue and I am equally frustrated with it. I found some info here

RiceHigh's Pentax Blog: P-TTL Reliability

Hope it helps
03-29-2010, 06:16 AM   #11
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QuoteOriginally posted by mtroute Quote
Bounce and PTTL don't play well together.
To the contrary -- I find my Metz 48 AF-1, at least, is far more predictable (and correct) with bounced flash. (I suppose because direct reflections are less of an issue.)
03-29-2010, 06:25 AM   #12
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QuoteOriginally posted by yusuf Quote
Does PTTL not working at all or is it producing underexposure? In later case, it is a well known issue and I am equally frustrated with it. I found some info here

RiceHigh's Pentax Blog: P-TTL Reliability

Hope it helps
Rice Low doesn't know his a$$ from a hot rock.
03-29-2010, 06:31 AM   #13
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QuoteOriginally posted by Blue Quote
Rice Low doesn't know his a$$ from a hot rock.
I don't care what he do & don't know, just checkout the article, it points to many forum post where users are having the same issues and it's my personal experience too - PTTL is certainly disappointing.
03-29-2010, 06:45 AM   #14
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QuoteOriginally posted by yusuf Quote
I don't care what he do & don't know, just checkout the article, it points to many forum post where users are having the same issues and it's my personal experience too - PTTL is certainly disappointing.
I agree that Pentax should have kept the ttl option available for their cameras given that there are a lot of us that use legacy glass etc. The point I should have made is that RH is a collection of Pentax negativity and sometimes it is better to look for what works i.e. articles on the flash camera combination and reviews. I have more problems with AF lenses and p-ttl causing people to close there eyes during pre-flash.

There are a lot of controls on the flash and body which sometimes over complicates things in my opinion.
03-29-2010, 06:50 AM   #15
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QuoteOriginally posted by Reps Quote
In second example a step to the right would cure it all as metering underexposes due to the reflection from the background glass-covered reflective image.
Ditto that. And FWIW, Nikon systems will do exactly the same thing. I was trying a friend's D300 w/ SB800 setup at a x-mas party and taking pictures of their kids. One kid stood next to her toy box while I took the photo and the glossy cardboard reflected light straight back. The end result was massive underexposure. And Nikon has the best i/p/e-TTL (this double flash technique) system too

I personally still prefer Auto-Thyristor mode...

p.s., RiceHigh should know this since he claims he run Canon as well but he never mentions it...
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