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07-01-2012, 07:53 AM   #1
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Some insight into flash overexposure

I have a new K-5, with an AF 50mm f/1.4, and 360AF flash, and it often overexposes to pure white. I've narrowed it down to situations when I use a bounce flash, or fill flash when in Aperture priority mode. (I have done this using High Speed Sync for years with my K100D with great results). For my most common shot in Av at f/3.5, outdoors, with a fill flash in HSS, K100 looks great, K5 is pure white every shot. The flash appears to over expose, even when set to HSS.

I was surprised to see that the K5 manual had two references that don't make sense to me:
(1) page 182 In Av mode with a flash, the shutter is limited from1/180s and slower
(2) page 189 says high speed sync ONLY works in Tv or M.

Looking at my blown out examples, sure enough, in P or Av the K5 sets the shutter speed to 1/180s no matter how bright the scene is and how low the Aperture, whether HSS is on or not.

I suppose I could use it in Tv , but the feel of the image is dictated by the aperture, and I get sort of specific about that. Seems really weak to force it into Manual, for such a basic function. Anyone heard of Av fill flash support being addressed in later firmware? The strangest part is that it works so well on the K100D.

07-01-2012, 09:40 AM   #2
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I have a few options:

• use a lower ISO (maybe)
• try an ND filter
• use M mode to set a faster shutter speed with HSS set on the flash
• don't use the flash if the scene is plenty bright

I think the behavior you are describing sounds normal.

Here's an example with the ND filter:
Strobist: Using ND Filters to Kill Depth of Field
07-01-2012, 05:28 PM   #3
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QuoteOriginally posted by gpellegrinetti Quote
I have a new K-5, with an AF 50mm f/1.4, and 360AF flash, and it often overexposes to pure white. I've narrowed it down to situations when I use a bounce flash, or fill flash when in Aperture priority mode. (I have done this using High Speed Sync for years with my K100D with great results). For my most common shot in Av at f/3.5, outdoors, with a fill flash in HSS, K100 looks great, K5 is pure white every shot. The flash appears to over expose, even when set to HSS.

I was surprised to see that the K5 manual had two references that don't make sense to me:
(1) page 182 In Av mode with a flash, the shutter is limited from1/180s and slower
(2) page 189 says high speed sync ONLY works in Tv or M.

Looking at my blown out examples, sure enough, in P or Av the K5 sets the shutter speed to 1/180s no matter how bright the scene is and how low the Aperture, whether HSS is on or not.

I suppose I could use it in Tv , but the feel of the image is dictated by the aperture, and I get sort of specific about that. Seems really weak to force it into Manual, for such a basic function. Anyone heard of Av fill flash support being addressed in later firmware? The strangest part is that it works so well on the K100D.

#1 (page 182) is discussing the built-in flash. Since the built-in flash does not have HSS, it cannot set a shutter speed higher than 1/180 no matter what mode you choose.

#2 (page 189) does not say "only".

I just shot several images in my sunny/shady back yard with the AF540 and the K5, with the 540 set to HSS and the K5 set to AV f5.6, ISO 400. The camera selected shutter speeds above 1/180, and when I metered on the bright part of the scene, I was able to shoot at a shutter speed of 1/800 and the flash did fire and fill the shadow areas.

I have used AV and HSS on all of my Pentax bodies and the K5 seems to work similarly to the older bodies as far as I can tell.

I just wish the bounce over-exposure of the K5 would be addressed and that Pentax would publish a detailed description of exactly how the PTTL system works in various modes and how it interacts with the multi-segment metering system as PTTL flash results are often puzzling and sometimes down-right baffling.

Ray
07-01-2012, 05:31 PM   #4
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Helpful thread--thanks all!!

07-01-2012, 05:42 PM   #5
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Does the K-5 have exposure troubles when you use fixed ISO? Auto ISO produces whacky flash exposures on my older Pentaxes. I no longer have a K-5, so I can't check this.
07-01-2012, 09:21 PM   #6
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It's ok with fixed ISO.
With ISO AUTO the K5 sets highest Iso for ambient light. But the minimal distance is generally too far so all objects before this minimal distance are burned.

With my AF 540 i proceed like that :
- mode M
- Iso 400 or 800 max for ambient light

- sets aperture for the minimal distance (flash head at 90, see the range illumination)
- then i control exposure with shutter speed : -1 to -2IL to have ambient light slightly underexposed and subject well exposed with TTL flash.
- then i use the reflector with head nearly vertical (or hold the flash in wireless mode)

Last edited by pscl57; 07-01-2012 at 09:28 PM.
07-02-2012, 05:03 AM   #7
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Thanks Ray for the detailed response. Glad to know that the camera is designed to work in HSS. I'll have to do some more experiments. I wonder if there is a dirty contact or loose connection on my flash? The behavior seems like it is intermittently turning on and off the HSS.
07-02-2012, 06:12 PM   #8
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QuoteOriginally posted by gpellegrinetti Quote
Thanks Ray for the detailed response. Glad to know that the camera is designed to work in HSS. I'll have to do some more experiments. I wonder if there is a dirty contact or loose connection on my flash? The behavior seems like it is intermittently turning on and off the HSS.
I have had trouble with the flash not being seated all the way, especially with my Sigma flash. When it backs out a little or isn't seated fully, I often get blown out shots. In most cases the fact that the flash is not fully seated isn't obvious by just looking at it.

I have not seen this issue with my Pentax AF540 flash.

Ray

07-03-2012, 10:59 AM   #9
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I actually have same problem when using AF360 flash on K-5 and K-10, set at HSS to fill shadow. Most pictures were terribly overexposed. I thought it was because my k-10 had a split focus screen which might affect the PTTL metering; and my K-5 just had a bad contact. Thanks for posting your question here. so it seems not a single case of your or mine, nor a universal problem that affect every camera and flash. Very strange. The flash worked fine on K-X, but I have sold the camera.

And I have checked the shutter speed, it did go faster than 180, but still pictures got overexposed.

Haven't tried M or Tv though.

And I have tried F, AF and DA lenses. lens is not the answer here.

Any idea? I am looking into buying an AF540 and use 360 as a wireless slave flash.

Graham
07-04-2012, 06:49 AM   #10
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I tried Tv model on K-5 last night, still the same result, over-exposed.

Is there any other setting on the camera or flash that I don't know?

Thank you for any suggestions.
07-04-2012, 06:59 AM   #11
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QuoteOriginally posted by grahame Quote
I tried Tv model on K-5 last night, still the same result, over-exposed.

Is there any other setting on the camera or flash that I don't know?

Thank you for any suggestions.
Have you tried using manual ISO?
07-04-2012, 07:08 AM   #12
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Yes, I always set ISO manually.

To force the shutter speed faster than 180, I had to set ISO 800 last night.

Graham
07-04-2012, 04:33 PM   #13
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Personally, I've found that it works ok with ISO set manually.
It gets quirky with Auto ISO.
07-04-2012, 05:13 PM   #14
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QuoteOriginally posted by dadipentak Quote
Helpful thread--thanks all!!
+1

I own a AF540 but ever since I've had my AB strobes, I use the Vagabond lithum batteries therefore use my strobes even on location.

I really need to learn how to use my AF540 more fully.
07-06-2012, 09:54 AM - 1 Like   #15
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I just got off the phone with Pentax support. He indicated that "Pentax Japan is aware of the issues" and that there is no firmware updates, past or planned, to address it. Nor did he have any suggestions for how to remedy, or mitigate the problem, only said that it is apparently a "limitation" of the hardware and circuitry. This is extremely disappointing. It means that the K5 cannot be used with a fill flash in high speed sync mode. That is the most common scenario in which I shoot portraits, which is the foundation of my work. I guess I should have gone with the big boys.
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