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01-13-2014, 01:12 PM   #1
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TTL metering with Metz flash

Sorry if this is a dumb question, but can someone please help me understand why my K-30 and K-01 are both under-exposing when I bounce my Metz?

Longer version of my question: I haven't owned an external flash since my film days many eons ago, but Santa was good to me this year and now I'm the proud owner of a Metz Mecablitz 36 AF-5. It seems like a very well built unit and TTL metering seems to work fine when the flash is pointed directly at the subject. Exposure is perfect (well, as perfect as can be expected with a $100 consumer flash) and the images are pleasing. But when I try to bounce the flash off the ceiling, the subject is very under-exposed. Of course I realize that the amount of light is less when reflected off a ceiling, but I thought TTL metering would compensate for this?

Or am I doing something wrong? Any guidelines for using TTL flashes on Pentax?

Thanks in advance!

01-13-2014, 01:58 PM   #2
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What was your aperture and ISO? How high is the ceiling?
01-13-2014, 01:58 PM   #3
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There are several threads about this, with different solutions. A search should find several threads.
Personally I use a Metz Mecablitz 50 AF-1 flash on a K-5 II and when using straight on it works pretty good. When bouncing the flash I first take a test shot, and usually end up increasing the flash output about two stops. It also depends on the distance needed and if using a diffuser.‎‎. To compensate I adjust on the flash unit, instead of camera. I also shoot raw for better development of over-exposure & under-exposure areas of the photo.

Here is two links to a album where I used the Metz flash mostly bounced at 45 degrees.
http://wingincamera.zenfolio.com/c3-info-meeting-12-06-2013
http://wingincamera.zenfolio.com/c3-prayer-meeting-11-16

Last edited by Wingincamera; 01-13-2014 at 02:08 PM.
01-13-2014, 04:58 PM   #4
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QuoteOriginally posted by pericombobulation Quote
I thought TTL metering would compensate for this?
Only until the maximum light output for the flash is reached. Not only does bounce flash increase the distance that light spreads out over (reducing its power by the square of the distance) but ceilings only reflect a fraction of the light shining on them. One other thing to check is that your shutter speed isn't faster than the length of time your flash fires at maximum output. For maximum output on a 52 AF-1 (which I have, so I found this in the manual) the flash fires for 1/125 of a second. If my shutter speed is faster than that, I'll miss out on some of the flash's light output. I assume you left any exposure compensation settings alone when you switched from direct flash to bounce flash. Also increase your ISO (if set to Auto, increase the upper limit if possible), which has the same effect as enlarging the aperture. That way you give your camera more leeway when its program tries to control your flash.

01-13-2014, 05:46 PM   #5
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I'm not trying to be a killjoy, but your use of 'TTL' triggered the thought - - Your Pentax cameras use 'P-TTL' technology .... the 36 AF-5 comes in 5 versions, only one of which supports Pentax P-TTL. Can you confirm you do in fact have a Pentax compatible version?
01-13-2014, 08:12 PM   #6
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Tilting the head up and bouncing off the ceiling is really only part of the solution. This can result in shadowed "raccoon eyes" which is okay if you like the zombie look.

I'd try bouncing some of the light forward with a bounce card. Just attach anything from a business card to a full sheet of heavyweight paper to the tilted up head with a rubber band. This will reflect some of the flash straight forward on your subject relatively softly. You might want to experiment with different sized bounce cards to give the most pleasing effect. If you bend and angle the flash card forward, you can vary the ratio of light bounced off the card vs the light that bounces off the ceiling. Also, you can experiment with different size bounce cards.

There are commercial versions of this available, of course -- Probably the first was Lumiquest -- now there are lots of suppliers waiting to take your dollars for something you can make for pennies or less.

There are also many more sophisticated flash modifiers available that might be able to help you get good external flash results. Most of the designs could be duplicated pretty easily for DIY projects.

Scott
01-14-2014, 08:36 AM   #7
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Thanks for the advice everyone. I did confirm that the 36 AF-5 is the Pentax version. I'm realizing now that there is probably nothing wrong with the flash or the cameras - just my misunderstanding. I'll try a few more shots tonight, but I think I was doing several things wrong. For one thing, I think I was shooting with the diffuser on - reading through some posts it sounds like I should leave the diffuser off by default, unless shooting at short focal lengths.

RGlasel, I see your point about shutter speed. I think herein lies the source of my confusion - I thought that P-TTL would help the camera choose the appropriate shutter speed, based on available light and the flash's available synch speeds? I could see how I might have limited the camera's options in some shots, as I chose Av mode and set the ISO manually. But even in Auto, where the camera can pick ALL the settings as it sees fit, it still underexposes when I bounce it. My ceilings are 8-foot, so nothing unusual there.

Thanks again!
01-14-2014, 08:42 AM   #8
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One other question - I thought that P-TTL fires a pre-flash to help the camera determine proper exposure. I am not seeing any pre-flash. Does it happen so fast that I can't distinguish it from the main flash event? Or does the 36 AF-5 in fact use TTL and not P-TTL (as is listed on their website)? Or is the pre-flash not firing for some technical reason?

Thanks!

01-14-2014, 09:23 AM   #9
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The pre-flash is very fast. Many people cannot detect it in most instances. Unless you lock the shutter speed, the standard behavior for P-TTL is to attempt a fill flash situation. The shutter speed will go down to about 1/<focal length> if necessary to use as much available light as possible and as little flash as possible. If this is not the desired technique (it rarely is for me), use an exposure method that locks the shutter at 1/180.
01-14-2014, 09:42 AM   #10
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There have been numerous threads about exposure issues when bouncing. Consensus seems to be that the camera makes the mistakes; you can (as said earlier) compensate for it by 'increasing' the output power of the flash (flash ev compensation).

QuoteOriginally posted by pericombobulation Quote
ne other question - I thought that P-TTL fires a pre-flash to help the camera determine proper exposure.
Use the 2-second timer (for demonstration). You will see the pre-flash, next the mirror will go up and 2 seconds later (when the image is taken) you will see the main flash. This will prove that you're combo is using pTTL (or not if you only see the main flash).
01-14-2014, 09:48 AM   #11
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sterretje, thanks for the tip - I'll definitely try that.

Jim, sounds like a good rule of thumb, but why 1/180? Wouldn't 1/125 give slightly more balance toward ambient light if that's what the flash synch speed is?

Thanks!
01-14-2014, 05:10 PM   #12
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QuoteOriginally posted by pericombobulation Quote
in Auto, where the camera can pick ALL the settings as it sees fit, it still underexposes when I bounce it.
I'm not sure if you set exposure compensation on your flash (I can with the 52 AF-1), but even if you can't you can still play with exposure compensation for ambient light and your flash separately. To make it worse, your camera is programmed to select shutter speed, aperture and ISO that tends to balance out your EV settings in ways you may not want. Which is why many people on this board recommend manually setting your camera's exposure for ambient light, and let the P-TTL program determine how much flash to apply. Personally, I find setting the camera's exposure compensation to -1.0 EV and then the flash compensation to +1.0 EV gives me decent results, but every change will have an effect on how well lit your subject and background are. Your flash sends the same amount of light to the entire frame, so differences in how reflective objects are will throw it out as well.
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