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03-09-2009, 07:26 PM   #1
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P-TTL problem

Hi everyone,

I ran into a unique problem this weekend and I wanted to see if someone could help me. I recently purchased a non-pentax flash gun. I was told it would work with the Pentax K20d. I decided to give this new flash a go-ahead at a gig on Friday. The flash worked great except for 1 hicup.

When I purchased the flash I was told it would communicate with the K20d via P-TTL with no problems. I put my Tamaron 28-200 lens on my camera and then the new flash gun and started up the camera. Everything worked fine except when I tried to take the lens out to 200 the flash would only zoom out to 58 mm. I checked the manual it the flash was designed to go out to 105 mm.

I tried changing lenses with the same result...when I extended any lens past 58mm the flash gun would only zoom out to 58 mm.

I took the flashgun off the shoe and tried manuplating it manually and it would zoom out to it's full length.

The next morning when i got home I tried the same thing with my spare k100d...using the Tamaron 28-200 lens...and I got the same exact result (the flash would only zoom out to 58 mm).

I thought it might be a problem with the flash itself so I took the flash back to the store where I bought it and showed them the problem. We attached a pentax 18-200 lens and the flash had the same problem. The store rep thought it might be a communication problem with between the flash and the specific k20d that I had. We then tried attaching a pentax flashgun (the 360) to the K20d and the same exact thing happened...the 360 flashgun would only zoom out to 58 mm. We then checked to see if it was a problem with my specific K20d and pulled another (display model) k20d off the shelves. We tried both the 360 flash and the off brand flash I picked up and got the same result (the flash would only extend out to 58 mm).

Now that I've done my long winded story, has anyone else run into this problem? Is there a solution? Could you walk me though what to do step-by-step?

Thanks again.

03-09-2009, 07:34 PM   #2
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Sounds like the lens is not communicating the focal length to the camera's flash any further than 58mm. Is the EXIF data showing correct focal lengths from your shots taken with this lens?
03-09-2009, 09:44 PM   #3
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Sorry if I ask a stupid question: What's the max tele setting of the flash? You said 105mm but in what format?

My Pentax 540 flash can go only from 16 to 58 mm (equiv. to 24 to 84mm in 35mm film format).

There is a setting on the flash to change the focal length display, either in APS-C format (16 - 58) or 35mm format (24 - 84).

Maybe this is the limitation of Pentax body. It's interesting to find out.
03-09-2009, 10:13 PM   #4
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Actually, I think your right - it's the same with mine (forgot all about that).
That's the limit of zoom on most flashes on APS-C cams.
Similar story on my Sigma 500 Super.

03-10-2009, 06:37 AM   #5
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Does anyone know how to correct the problem?
03-10-2009, 07:31 AM   #6
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QuoteOriginally posted by Hey Elwood Quote
Does anyone know how to correct the problem?
Are you sure that 105mm limit is correct ? I assume you've got the Sigma 530 super then? It's the only pentax compatible flash I found on google that had 105mm written in the specs.

Can't you run the flash in manual mode and choose manual zoom setting?

Most P-TTL flashes does not have any narrower beam than 85mm. Pentax 540fgz, Metz 36AF4, Soligor DG420Z all end up at 58mm crop/85mm full frame.

I've got three possible scenarios:

1. Manufacturer has mislabeled the flash / only 105mm on Canikon

2. Pentax only have binary codes for up to 85mm zoom in their P-TTL protocol.

3. Sigma (?) doesn't have a clue how to get a higher number from the P-TTL protocol since they've reverse engineered against a genuine Pentax that has no such setting.

Either way you're kind of stuck, and might have got a slightly less powerful flash than they're trying to sell you (if guide number is measured at 105mm). If that's the case, it's an interesting find indeed.

Other than possibly slightly less power at full zoom there really is no problem shooting with the flash at 58mm and the lens at 200, there is just more light spilled outside the frame.
03-10-2009, 02:18 PM   #7
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QuoteOriginally posted by sveinmb Quote
Are you sure that 105mm limit is correct ? I assume you've got the Sigma 530 super then? It's the only pentax compatible flash I found on google that had 105mm written in the specs.
Actually, most Metz flashes and some Promaster ones do too:

Pentax P-TTL Flash Comparison: Zoom Reflector
Pentax P-TTL Flash Comparison: Feature Tables

But, as far as I know, of these only the Metz flashes convert to the correct focal length for crop-sensor SLRs, which is where the 58 is coming from.
03-10-2009, 02:42 PM   #8
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QuoteOriginally posted by mattdm Quote
But, as far as I know, of these only the Metz flashes convert to the correct focal length for crop-sensor SLRs, which is where the 58 is coming from.
The Pentax 540 can display the head zoom settings in either format: APS-C sensor or 35mm full-frame.

03-10-2009, 03:55 PM   #9
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you may be seeing an issue with field of view.

the pentax camera with the AF540 FGZ only zooms out to 58mm, yet on my PZ-1 it zooms to 85 or 90mm,

the flash compensates for field of view of the lenses, depending on the body. I imagine your flash does the same.

Note however, the flash does not zoom ion or out so to speak, it changes the angle ov ccoverage, now I know that people will say this is the same thing, BUT really the flash is covering the field of voiew of a 58 mm lens on an ASP sensor.

try the flash off camera in manual zoom mode and see what it does, it will probably assume it is on a film body and give you a "longer" focal length. this display does not impact power, but once at the longest length you will get the maximum flash power regardless of lens focal length.

If you want more get a better beamer, to focus the flash more on telephoto lenses
03-10-2009, 05:01 PM   #10
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QuoteOriginally posted by SOldBear Quote
The Pentax 540 can display the head zoom settings in either format: APS-C sensor or 35mm full-frame.
Sorry, I didn't mean to imply that it can't. (I was referring to 3rd-party flashes, since that was specified.) I actually have a page on my guide for this feature too:

Pentax P-TTL Flash Comparison: Camera Format Conversion

03-10-2009, 05:03 PM   #11
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QuoteOriginally posted by Hey Elwood Quote
Does anyone know how to correct the problem?
So, which flash do you have?

If it's Metz, my guess is that you've accidentally enabled the extended zoom mode, which automatically uses one step wider than required, to increase the amount of diffused/bounced light.

Turning this on or off is done differently on the different Metz models....
03-10-2009, 07:35 PM   #12
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The flash I have is called a promaster 7500dx digitalFlash. It's an off brand flash gun since I can't afford the big guns like Metz, Sigma or Pentax just yet. I actually contacted Pentax directly and after some trial and error we determined that a digital flash gun will only extend to 58 mm. Anything above that the flashgun and camera don't communicate since the flash thinks a film camera is being used.

I understand now that is wasn't my camera, the flash gun or something I was doing. I just don't understand why the a digital camera can't make a flash gun go further then 58 mm. This kind of makes owning a flashgun pointless since it's being used for wedding photography, portraits and such. Just a little dumb founded. All my pictures turn out under exposed if I'm a few feet away from the subject. Just frustrating.

I do have to say Pentax's customer service is awesome. Their people were very easy to communicate with and they really listened to your problems and frustrations and take your concerns to heart.
03-10-2009, 08:37 PM   #13
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QuoteOriginally posted by Hey Elwood Quote
All my pictures turn out under exposed if I'm a few feet away from the subject.
There must be something else, not the zoom setting on the flash.
03-11-2009, 04:57 AM   #14
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QuoteOriginally posted by Hey Elwood Quote
The flash I have is called a promaster 7500dx digitalFlash. It's an off brand flash gun since I can't afford the big guns like Metz, Sigma or Pentax just yet. I actually contacted Pentax directly and after some trial and error we determined that a digital flash gun will only extend to 58 mm. Anything above that the flashgun and camera don't communicate since the flash thinks a film camera is being used.
This isn't true in general; it works with the Sigma and Metz flashes. It may, however, be a problem with your particular unit — on Promaster's web site, they list the 7500EDF as compatible with the K20D and K10D, but not the 7500DX.

QuoteQuote:
I do have to say Pentax's customer service is awesome. Their people were very easy to communicate with and they really listened to your problems and frustrations and take your concerns to heart.
They have decent customer service, but sometimes you have to ask "are you sure? Could you double check that?" and sometimes the answer comes back differently.

When I had questions about 3rd-party flashes, they flat-out refused to answer them (even when the question was more about the K10D rather than really about the specific flash). If they did give you an answer, it's going to be from a Pentax perspective, and since 58mm is the actual limit of all of their flashes, that may be why you got the answer you did.

My suspicion is that either they're just speculating about how it might work, or else they're giving a garbled response about the APS-C/full-frame conversion. Or that they're right and the 7500DX really does have a communication problem.

Have you tried contacting Promaster? Their flash tech support is actually quite good — I've found they're better at responding to e-mail than Pentax, even.
03-14-2009, 05:42 AM   #15
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Well - even a quick Google search could tell you the 7500dx is no good. "Promaster 7500dx p-ttl" responds with a link to this forum: https://www.pentaxforums.com/forums/pentax-camera-accessories/10413-promaster-7500dx-k10d.html


In fact the 7500dx is really old, and probably based on a reverse-engineered p-ttl mode that does not comply with the standard. It can work with old cameras like the DL or DS, but not with any K-model. The 7500edf does however look like it should work with your camera.
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