K-5 Over-Exposure with flash

I'll pop my toe in the water here as an inexperienced user of flash on a new K-5.

I use manual mode on the camera, and P-TTL on the flash. I stick more or less to MattMatic's suggested camera and flash settings in his flash guide.

Providing that of course one doesn't get too close to the subject (in which case there's not much of a cure), it works as advertised. I use a Pentax 540 flash with a Stofen diffuser, and generally pointing up at 45 degrees. The flash is mounted on the camera itself.

So no K-5 issues in this respect for me...

I'm not using a Metz, I'm using a Pentax AF360FGZ

I'm hardly going to be happy spending £200 on a flash to have it stuck on manual mode. Not much use when trying to grab a snapshot at an event.

Clearly not in many users experiences. My GX20 works perfectly using the same flash.

I've occasionally encountered this bug too, although only a few times. I don't use flash much so I just switched to manual and took another shot, but if I used it a lot this would be very annoying.

There is also another flash bug on the K5 which has been discussed here before. It's even weirder, the flash overexposes when you focus on something further than 2m away and are using wireless PTTL.

The one saving grace is that you see the problem on the camera's rear screen. At least we dont have to pay for ruined films.

I take note of John's comments and greatly respect the experiences of the professionals on here. However there is somewhere an issue that needs Pentax to address. I agree with the thoughts that why would anyone buy a Pentax gun or any other with so much automation only to use it in manual mode?

I hope Pentax are taking note of forum comments, the camera will be getting a tarnished reputation as whispers spread. I will be the first to praise them when a solution is found but right now I'm feeling like many on the other forum that the camera could have been released before it was ready.

Manual focus, manual exposure adjustment and manual flash adds up to the ultimate in creativity. I'd still keep my K5 and would hate to let it go back for checking. The images are the best I've ever had on digital and I'm still learning.

FWIW, the K10D & K20D had extremely aggressive action when using flash. Even the slightest highlight would slug the flash so that often images would be severely underexposed.

The K7 & K5 flash control is (IMHO) generally better, especially given the fact that the K5 has astonishingly good dynamic range (esp in RAW).

I'm sure there's a rational explanation to the situation you have shown...
...I'd really like to examine the full EXIF (i.e. from exiftool) information from the shots you show at f/3.5. You see the EXIF contains the ambient light levels, the preflash levels and the slave flash levels across all 77 segments. That data may well help explain.

Failing that, I'll try and find a little time to setup the same kind of test (I have the AF360, AF540 & Metz 50MZ5). At the moment I still have the K7 and *ist-D as well (and a newly acquired semi-dud K10D) so I can compare across a wide range of situations

Matt

Excellent Matt, can I send you some test shots so you can look at the EXIF?

Okay dokay...

I strongly suspect you've hit the minimum flash distance
Looking at the EXIF data I can see that the metering is similar between the two - in some areas the second image is about 1.5Ev higher on the flash-metered readings, but overall there's not much in it.

What I do notice is that you've got the camera on f/3.5, ISO200, 1/180s

Actually, for flash exposure the shutter speed is completely irrelevant! (This is a key piece of understanding for flash work )
The ISO & aperture are what matters.

I haven't got my AF360 to hand, but checking the manual I reckon at ISO200 you have an effective guide number of between 45 and 50. At aperture f/3.5 that's around 13-14.5m maximum distance. The minimum distance is about one tenth - so 1.3 to 1.45m minimum.

You're probably 'on the edge' - where the granularity of flash output is causing you issues. At such a short distance the flash can only control itself so much.

Think of it like putting sugar cubes in your coffee. If you have half a cup of coffee then one cube might be too much, but none is too little.

With all flash systems you'll need to give it some room to work. You can control the effective distance by reducing the aperture (higher f-number), increasing the physical distance, or slugging the output (by using a diffuser that typically cuts output in half). Even a piece of tissue paper over the flash head will do wonders!

The AF360 does show the min & max distances on the LCD display - but, of course, when you angle the flash that disappears (because it doesn't know how high the ceiling/bounce is).


I'd suggest you try exactly the same test:
* With a piece of tissue paper over the flash head
* At f/8 instead of f/3.5
* At double the distance

Once you within the flash range you should get consistently good exposure.

HTH!
Matt

I'll try that later Matt and post the images, thanks. But that wouldn't explain why the shots came out perfectly on my GX20 (K20D)

My problem looks to be that my Metz gun has developed a fault during the last 2 weeks. It worked fine on my KX, then with deteriorating results on the K5 and now just as bad on the KX.

The good folk of SRS have offered to have it checked by Metz.

I hope this sorts it..and meanwhile I can still enjoy the K5 and will owe Pentax a huge apology!

I have exactly the same over exposure problems as Daydreamjay. I generally set ev to -1 when using bounce flash on the K5 but this is not always enough (sometimes is, sometimes isn't - not consistent). Because of this problem I tend to use my old K10d for flash work (which is usually right at ev +1). Hardly an ideal situation though.

Well, as Daydreamjay hasn't replied to my suggestions and his further tests how can you know for sure?

Looking at his images, as I said, his problems were likely down to being closer than the minimum distance and hitting the granularity of flash power control at low level (which could, as Rataegeoff mentioned, even be a power control issue failure in the flash itself).

If you want me to examine EXIF too, then feel free to email me an overexposed image and I'll run my eye over it


IMO, I've found the K7 & K5 to be significantly better at flash exposure compared to K10D/K20D

Matt

Thanks Matt. Unfortunately I think I have deleted all the duds. I don't think it's flash unit failure though, as I have both the 540 and 360 and get the same problem. I'll try your suggestions and see how I get on.

Hi Matt, I'll be back on thus when I have resolved my much bigger problem on the other thread lol.

Mmm....just been pondering on this whilst ironing a couple of shirts.

I am one of those people for whom flash photography is a bit of a 'black art' - I am much more confident with available light. Because of this when using flash I tend to put the camera on 'P' setting and the unit to PTTL, on the assumption that I should then get correct exposure most of the time for the sort of shots that I use flash for - mostly family and friends at functions. I generally use bounce flash with a stofen diffuser.

Am I using the best default settings, I wonder?

Probably not for functions
One of the main arts of flash usage is balancing the light between ambient and flash. Often this is where my expectation of the balance is quite different to the camera's idea

There are really simple ways of telling the camera what you want to accomplish... but using P on everything isn't one of them .

I've written plenty of threads on the topic here...

Aha! Sorry I didn't link you with that problem! (Must read more carefully! LOL!) Hope you get it sorted soon
Matt