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01-28-2011, 06:58 AM   #1
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External Flash K-7 vs K10d

It's me again with my new K-7 - sorry.

I have a Cobra 450AF flash, marked 'For Pentax'

Obviously it's an old one that expects TTL, but it was no bother on the K10 - I just put the camera in manual mode, adjusted the shutter and aperture with a few test exposures - although I got good at guessing in the end - and shot away. The flash appeared to operate on full power all the time, but, hey, it was only 5 or something. In fact it cost me less than that - my dad bought it at a junk sale and gave it to me. Bargain.

I digress.

With the K-7 it seems that it tries to meter - certainly the little green 'Auto' light comes on briefly after firing, which I am pretty sure it didn't on the K10d.

This means that I have no control over how powerful the flash is - sometimes it gets it right, and more often than not it doesn't.

I've just done some tests of the same subject, with the same settings, with the camera on a tripod, but using M and X modes.

The X mode picture is definitely darker. (show in RAW by mistake, but both just opened and cropped in PS. Both under exposed, but first one (X) is definitely darker.
Both 1600 ISO 1/180 f5.6. With the k10d I was generally shooting 200 ISO, 1/45, f5.6 or thereabouts in the same room) There isn't much difference in these as the subjct is so close I presume, but you can still see there is a difference.

Any ideas what is going on, or if there is some setting I can change (or contact on the flash I can blank off) that will mean it just fires at full power?

Thanks.

X mode


M mode


01-28-2011, 07:20 AM   #2
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what I have noticed is that from time to time, when wantong to shoot my AF540FGZ with a manual aperture lens, the flash tries to operate in TTL mode on the K7.

I have not looked into what is hapening here but there seems to be a little bit of a bug in terms of the flash with the K7.

Usually with the K7 I use the flash in P-TTL mode.
01-28-2011, 08:10 AM   #3
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Thanks - my flash pre-dates P-TTL so I have no choices that way - it used to be fully manual on the K10 and fire at what I assumed to be full power.

It now seems to be firing at less than full power on the K-7 - but the power it uses is different between X mode and M mode, I guess because it's trying to work.

It'd just be nice to be able to get it to fire on full power and let me deal with the exposure!
01-28-2011, 12:43 PM   #4
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That is interesting. In term of flash control, I haven't notice any difference between K7 and K10D (except for some improvement in p-TTL exposure). Can you please post photos of the flash (both back and front). I'm curious. Thanks.

01-28-2011, 01:46 PM   #5
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These two shots are taken of the same sofa, with the same flash, with the same room lights and with the same camera settings (ISO 200, 1/45, f4.5)

The k10d was clearly triggering the flash at full power - or at least with way more power than the k-7 is.

(Not a fully controlled experiment as the k10 doesn't work any more, hence the k-7. You'll spot that the model is in bed at the moment so I had to use a stand in!)

k-7


k10d
01-28-2011, 02:17 PM   #6
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Several questions:

1. What modes does the Cobra has? TTL? Manual? Auto?

2. Please try K7 + Cobra in manual (full power mode) and post the result.

3. Is there a way to use K7 + Cobra but the Cobra is NOT attached to the K7 hotshoe (e.g. via a PC cord)? I wonder if the data pins on the K7 hotshoe confuses the Cobra.
01-28-2011, 02:26 PM   #7
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Here's the flash itself. It is the same size on both sides, I just knocked the tripod when I was turning the flash around :-)


Last edited by Northern Soul; 01-29-2011 at 03:09 AM.
01-28-2011, 02:30 PM   #8
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QuoteOriginally posted by SOldBear Quote
Several questions:

1. What modes does the Cobra has? TTL? Manual? Auto?

2. Please try K7 + Cobra in manual (full power mode) and post the result.

3. Is there a way to use K7 + Cobra but the Cobra is NOT attached to the K7 hotshoe (e.g. via a PC cord)? I wonder if the data pins on the K7 hotshoe confuses the Cobra.
Hi - sorry, was resizing the images of the flash as you posted.

As you can see the Cobra has very few controls. The green 'Auto' light flicks on after the shot with the k-7. As far as I can recall, it didn't do that on the K10.

The little ISO slider at the top is purely for reference as far as I can tell. It doesn't feel like it is attached to anything, if you know what I mean, and certainly it had no effect with the K10.

01-28-2011, 02:37 PM   #9
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So the flash is fully TTL, no auto, not even manual.

If the camera does not support TTL, the flash should fire full power. But based on your description, that doesn't happen.

You need to test if the data pins on the camera messing up the flash's power.

Do you have an adapter to fire the flash via the K7's PC port? Or can you block the data pins on the flash's foot with a piece of electrical tape (leaving the center pin for sync signal)?

If not, try this: remove the flash from the camera, in a dark room (so ambient light does not mess up the experiment), set the camera on a tripod, 1/4 sec shutter speed (slower if you can't catch it), hit the camera's shutter release, then immediately hit the test button on the flash. You can tell if the flash fires at full power.
01-28-2011, 05:18 PM   #10
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Thanks for your interest and help in this - I'd assumed that it would just fire on full power if it couldn't meter too - as it did on the K10.

I don't have a sync cable so I fired it manually with a .5second exposure in a very dark room (still ISO 200, f4.5) - this shows that the K-7 is definitely firing it with less power. As I've typed that it's occurred to me it may be interesting to see what exposure it comes up with if I put the flash on the hotshoe in a dark room. I will find out! Anyway - here's the same scene as above with the flash fired via the test button.


Last edited by Northern Soul; 01-28-2011 at 05:47 PM.
01-29-2011, 03:06 AM   #11
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Edit to add that it was only when double checking the EXIF from the shots I took with the K10 using the Cobra flash that I realised how ridiculous it was that I had to use ISO 1600 to get anywhere near a correct exposure of something no more than 2 foot from the flash (with a light path for the flash light of no more than 12 feet)
01-29-2011, 03:38 AM   #12
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A few more (very rough and ready) test shots.

This is an ambient light shot ISO 200, 1/45, f4.5


Same pots, with the flash, same exposure


Same pots, with the flash with all but the centre contact taped over. Same exposure


So the K-7 is definitely trying to do something with this TTL only flash. I guess I just have to work out which pins it uses for AF assist and which are for exposure - although I guess the K-7 won't need the focus assist as it has it's own lamp.

White balance is all over the place too. Is this usual?
02-03-2011, 02:16 PM   #13
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After a bit more digging I have a little more to add to this.

The flash was operating on full power with all but the centre contact covered, but all the shots had a blue colour cast, and I also noticed the 'flash ready' symbol wasn't appearing in the viewfinder. Neither of these problems occurred with the K10.

I found (via google which sent me to a thread here which linked to it) this diagram of what the pins actually do and after some experimentation found that the flash fires on full power, with the correct white balance, if you cover just the 'digital pin.

I presumed the cool cast was because the camera didn't know there was a flash, but I'm not so sure - there is still no 'flash ready' light on the camera, but it seems to make a white balance altertation, which it wasn't before.
02-03-2011, 02:28 PM   #14
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QuoteOriginally posted by Northern Soul Quote
I found (via google which sent me to a thread here which linked to it) this diagram of what the pins actually do and after some experimentation found that the flash fires on full power, with the correct white balance, if you cover just the 'digital pin.
That is very interesting, the most being the different behaviors of the K10D vs K7. I was not aware of any flash protocol difference from the K10D to the K7.

Now that you've identified the pin that needs to be masked off, you can dissemble the foot of the flash, and disconnect that pin. I think it's a pretty simple operation.
02-18-2011, 10:56 AM   #15
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I've updated the firmware on the K-7 since I first tried it with the flash (was on v1.0, now on 1.11)

Made no difference to this problem though - just thought I'd post for completeness.
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