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04-25-2007, 08:24 PM   #1
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P-TTL flash issues

I have a Digital Concepts 736AF flash, which claims to be P-TTL with pentax dSLRs. I agree to a certain extent - direct flash comes out well exposed when shooting at a distance recommended by the guide. But I bought the flash for its bounce capability, and I've not quite worked that part out yet:

All of my bounce shots have been quite under-exposed at Flash Exposure Compensation (FEC) 0.0. So I bumped it up to +1.0 (K100D doesn't go to +2.0!). It was worse! Very poor exposure.

After a while of putting up with this, I experimented going the other way (FEC -2.0). Lo and behold, it actually increased flash intensity and made the images much brighter. Is there any logic in this?

Unfortunately, the flash unit has no functions other than first and second-curtain slow sync. Can't play around with the flash much - not even a manual setting!

Anyone else had P-TTL flash problems with bounce? I'd like to be able to master this skill and any input would be greatly appreciated!

04-25-2007, 09:20 PM   #2
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No offense, but it sounds like you bought a POS. I would return it to place of purchase and put the money toward a Pentax or Sigma flash unit.

I can't find much info on this unit on the net. No reviews, even for other camera brands. Not a good sign.
04-26-2007, 01:56 AM   #3
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I'd say "you get what you pay for" but sadly that sometimes isn't true. I've paid for things that deliver far less than I paid for! It sounds like you may be in the same bucket with your new "P-TTL" flash. For what it's worth, I have the AF-360FGZ and the AF-540FGZ and they both do very well at bounce exposures.

If buying only one flash, I'd recommend the AF-540FGZ. I know it's pricey, but it's absolutely the most feature-packed Pentax flash I've ever owned. It's a terrific piece of engineering.
04-26-2007, 03:54 AM   #4
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With the 540, does the flash automatically adjust its intensity for flash photography, or do you need to manually adjust the FEC? I understood P-TTL to be able to automatically adjust everything, but it's sounding like not all P-TTLs are equal.

Although the Digital concepts flash is nowhere near the price range of the 360 or 540 (at US$60 from an eBay vendor), it was really all I wanted to pay for a reasonable bounce flash - I'm not sure for my amateur purposes it warrants spending a small fortune for a 540.

A Pentaxian reviewing one of the Digital Concepts flash said this:

I recently bought this flash unit (Digital Concepts 952AF/PEN), and it works well with my K100D. It is P-TTL, judging by the ability to see the pre-flash in the viewfinder before the mirror rises. It works well as long as the flash is strong enough to produce a good exposure, but underexposes more than needed when flash intensity is less then optimal. I compared the P-TTL result against a manual 1/1 charge over a range of apertures. As long as the full charge manual shots are overexposed, the P-TTL produces consistently good exposures. But when I close the aperture to a point where the manual full charge is exposed correctly, the P-TTL underexposes. For some reason, the P-TTL doesn't deliver a full charge. This is not a big problem, because if the shot is underexposed, you can safely turn the flash to manual mode (a single push of a button), without fear of overexposing.

The unit has a switch for first curtain / second curtain sync, so you can use slow sync flash. It does not support high sync flash. Curiously, when the flash is set to first curtain sync, the flash icon in the viewfinder stays lit even if the flash is not ready, causing me to sometimes shoot before the flash is charged. This does not happen in second curtain sync mode - the flash icon blinks while the flash is charging.

The unit supports the anti-red-eye pre flash, if this mode is set by the camera.
The 270 degree swivel and 90 degree bounce are very good - you can bounce directly up off the ceiling even if you point your camera at an angle downward.

The built-in diffuser and reflector plate are very handy and improve picture quality.

It can be used in principle as a wireless slave, but not with the built in camera flash - it fires on the built-in flash's pre-flash. If you have another non-P-TTL flash unit, you can use it as a master to trigger the slave.

The manual says it should produce only 80 flashes on a set of fresh alkaline batteries. I used a set of 2000mAh NiMH, shot 250 flash pictures, and they are still going strong.

Overall, I'm very happy with this unit, even though it has a few quirks, mentioned above. Looking at the specs, I believe it is identical to the Soligor DG-420 Z mentioned above.

Granted, the unit he's referring to is quite a step above my 736AF without swivel, but bounce functionality from the same manufacturers (Sakar) should surely be similar...

04-26-2007, 01:00 PM   #5
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Well, from reading your post about how FEC works (or doesn't work) with your flash, it sounds to me like your flash is seriously borked. There is no reason I can think of that dialing in negative FEC should make the resulting image brighter. It sounds like a pretty major problem in the way they implemented their version of P-TTL.

It also sounds like their P-TTL might not be "real" P-TTL at all from your description of how it handle (or doesn't handle) wireless usage with the K10D. With the Pentax flashes, you just clip them on and start shooting. If the flash has enough power to light the scene, you get a well exposed shot. There are the occasional problems with shiny reflective things in the scene, but overall they do extremely well either straight on or bounced.

I understand the desire to save money. I fix meals at home and save the cost of eating out. I walk or bicycle to work in nice weather to save car expense. But when I'm buying stuff for my hobby, I spend the money I saved in other pursuits and get stuff I really like. I spent nearly $1000 for my camera and I like to take flash pics, so buying a name-brand flash tailor made for my camera was an easy choice for me. (Had I wanted to save money, I may have opted for the Sigma flash.)
04-26-2007, 01:19 PM   #6
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Its a regular TTL. It says on the specs. I don't know much about either because I shoot with a manual flash.

But I'm guessing the problem is not with the flash. Your flash guide is for direct flash only it looks like. So when you bounce, the light intensity is reduced by the time it reaches your subject. Therefore, drop the shutter speed/open up the aperture to compensate. Or boost the ISO to 400.

Another solution is to keep the settings suggested by the chart but go to the dollar store and buy some velcro + one of those hard plastic sports card sleeves and make yourself a removable bounce card.

Btw, my manual (not TTL or P-TTL) bounce flash cost me $17 so you don't need to break the bank for good lighting.
04-26-2007, 06:05 PM   #7
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Ah. Well, that explains a lot.

It isn't compatible with the P-TTL system of the K10D and K100D. It should work on the ist-D or ist-DS, however.
04-26-2007, 06:40 PM   #8
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Well K10D or not, really all you need is a bounce flash with one central sync pin to fire off the flash and the max sync speed for *Ist dSlrs is 1/160th. (Probably the same for K series, no?)

What benefits do TTL and P-TTL give you when you are bouncing the light/using diffusers? I mean the flash doesn't really "know" what angle you chose or what type of diffuser you have on right?

04-26-2007, 08:09 PM   #9
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QuoteOriginally posted by FotoPete Quote

What benefits do TTL and P-TTL give you when you are bouncing the light/using diffusers? I mean the flash doesn't really "know" what angle you chose or what type of diffuser you have on right?
The camera still measures the light Through the Lens(TTL); during the exposure w/TTL and during preflash w/P-TTL. So, the flash doesn't know, but the camera does.
04-26-2007, 08:26 PM   #10
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You're right. It's well worth getting a good flash - I'll attest to that now. I'm more critical now about a manfuacturer's claims with regards to P-TTL so I'll look out for the Sigma/Pentax flash when the time's right.

Unfortunately I bought this funny flash from a US vendor for Sakar that offers 1yr warranty but only 1wk money back returns. It took me longer than that to work out things weren't quite right.
04-26-2007, 09:53 PM   #11
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QuoteOriginally posted by Ash Quote
You're right. It's well worth getting a good flash - I'll attest to that now. I'm more critical now about a manfuacturer's claims with regards to P-TTL so I'll look out for the Sigma/Pentax flash when the time's right.

Unfortunately I bought this funny flash from a US vendor for Sakar that offers 1yr warranty but only 1wk money back returns. It took me longer than that to work out things weren't quite right.
This Digital Concepts flash is supposed to work...maybe your was mis-represented. That would change the 5 day condition on a legal level I would guess..
eBay: Auto Focus TTL Bounce Flash for Pentax Digital SLR NEW (item 300104829542 end time Apr-30-07 16:23:09 PDT)
.................P-TTL & TTL Operation
The flash performs pre-flash for cameras to calculate the intensity of light output. Therefore the flash light output is controlled automatically.
..............................
Maybe i'm not following your story very well. Seems like someone elses fault, not yours......
04-27-2007, 03:08 AM   #12
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Hi jeffkrol,

I certainly wished this was the case. At least that was the promise given to me by the seller prior to me buying it - definitely P-TTL. If so, then yes, there should be a pre-flash to calculate intensity. But no matter what setting I have on the camera - no pre-flash.

I wonder then how it manages to calculate its intensity. I'm afraid it may indeed be only auto, just sensing ambient light and filling in with flash as deemed necessary by the flash - and no communication between the flash and the camera.

I haven't found any evidence to disprove this yet - so that's my loss. I'll just save up now for the 540 and close my eyes when the price comes up on screen...
04-28-2007, 01:49 AM   #13
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File a complaint through eBay. Sounds like the item was misrepresented.
04-28-2007, 08:21 AM   #14
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Not sure if it is misrepresentation. It does sound like the flash has some form of pre-flashes. So it could just be the P-TTL wasn't fully compatible or wasn't implemented very well.

All 3rd party do P-TTL by reverse engineering, including Sigma. It is not at all a trivial task, and it is hard to get it 100% right. That's why Pentax flashes can work flawlessly while others may not.
04-28-2007, 10:30 PM   #15
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If it says "P-TTL" then it means it is for PENTAX. P-TTL is a Pentax trademark, it is not a generic term. Other camera makers have different monikers for their preflash TTL schemes. The seller can't claim it is P-TTL but it just doesn't work with Pentax -- that is a contridiction. P-TTL means Pentax, and only Pentax, compatibility. If it doesn't work on a Pentax camera, it is NOT P-TTL no matter what they say.
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