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02-15-2016, 11:41 AM   #1
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K5ii off camera flash non-exposure

I've been searching around the forum/web but have been unable to find anyone with the same issue, but maybe I'm using the wrong terms.

I have a K5ii with 55mm DA* and an AF540 flash and I'm starting to dabble with full manual off camera flash, using the built-in as an optical trigger.

I've been doing some test shots, setting an aperture/ISO/shutter combo that will give me a very under exposed ambient image, in-built flash set to control only.

When I turn on the AF540, set it to manual at 1/1 power and take a picture the flash fires but it does not register on the exposure. I keep dialing down the flash output with the same results until I get to 1/16 power and suddenly the exposure is perfect. As I go down 1/32 to 1/64 the image exposure 'goes down' as you would expect.

Is there some secret to off camera manual flash? It's as if at 1/1 the flash is too powerful or it's taking too long to fire and the shutter has already closed. I did try dialing the exposure down to 1/10 to make sure it was open for a good amount of time and still the same results at high flash outputs.

This isn't limited to the AF540, I have an older Jessops brand '360' flash and same results. Full power in slave mode, no exposure, get it down to 1/8 and 1/16 and I get proper exposures.

Anything obvious I'm missing?

02-15-2016, 11:58 AM - 1 Like   #2
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QuoteOriginally posted by chiefsilverback Quote
I've been searching around the forum/web but have been unable to find anyone with the same issue, but maybe I'm using the wrong terms.

I have a K5ii with 55mm DA* and an AF540 flash and I'm starting to dabble with full manual off camera flash, using the built-in as an optical trigger.

I've been doing some test shots, setting an aperture/ISO/shutter combo that will give me a very under exposed ambient image, in-built flash set to control only.

When I turn on the AF540, set it to manual at 1/1 power and take a picture the flash fires but it does not register on the exposure. I keep dialing down the flash output with the same results until I get to 1/16 power and suddenly the exposure is perfect. As I go down 1/32 to 1/64 the image exposure 'goes down' as you would expect.

Is there some secret to off camera manual flash? It's as if at 1/1 the flash is too powerful or it's taking too long to fire and the shutter has already closed. I did try dialing the exposure down to 1/10 to make sure it was open for a good amount of time and still the same results at high flash outputs.

This isn't limited to the AF540, I have an older Jessops brand '360' flash and same results. Full power in slave mode, no exposure, get it down to 1/8 and 1/16 and I get proper exposures.

Anything obvious I'm missing?
The 540 needs to be in SL1 mode, it sounds like it's firing with the pre-flash. The Jessops probably isn't P-TTL, so again is firing on the pre-flash.

Tuggie76
02-15-2016, 12:02 PM   #3
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^^ Page 52 ^^
02-15-2016, 12:05 PM   #4
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What your missing is you need to think of flash photography as two separate exposures. Your camera exposure to control the ambient light and the flash exposure to control the lighting of the subject. The flash power you use depends on the distance and how much of your subject you want lit.

02-15-2016, 12:37 PM   #5
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Your shutter speed is limited to 1/180 sec or slower when using flash. If you use a faster shutter speed the exposure won't sync with the flash.
02-15-2016, 01:17 PM   #6
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I don't think he could set anything shorter than 180th with the pop-up raised .... ?
02-15-2016, 01:32 PM   #7
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QuoteOriginally posted by mcgregni Quote
I don't think he could set anything shorter than 180th with the pop-up raised .... ?
Correct.

The 540 (and Jessops) is firing on the pre-flash. If he wants to trigger remotely with optical control then P-TTL is needed. If he wants all manual control then on the k-5II the only option is using radio triggers. Unless the 540 has an option to ignore the pre-flash. The k-3 has an option for a manual flash on the pop-up with no pre-flash and this can be used to trigger manual off-camera flashes, but k-5II does not.
02-15-2016, 01:44 PM   #8
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Thanks for all the rapid responses. The comments about pre-flash don't make sense...

K5ii is set to full manual with flash in 'wireless' mode and the menu option to command only (not assisting with the exposure). Does the in-built flash still pre-flash even in this scenario?

Also if they were firing on the pre-flash, why when I get the external flashes down to ~1/16 power does the exposure suddenly come good?

---------- Post added 02-15-16 at 03:45 PM ----------

QuoteOriginally posted by Not a Number Quote
Your shutter speed is limited to 1/180 sec or slower when using flash. If you use a faster shutter speed the exposure won't sync with the flash.
I've had the shutter as slow as 1/10!

02-15-2016, 02:00 PM   #9
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QuoteOriginally posted by chiefsilverback Quote
K5ii is set to full manual with flash in 'wireless' mode and the menu option to command only (not assisting with the exposure). Does the in-built flash still pre-flash even in this scenario?
Yes. Command means it is going to communicate with the remote flash optically using the P-TTL protocol. The camera fires a pre-flash to measure exposure, then sends the info to the remote, then triggers everything. Sorry, but there is no way to do what you want to do with the k-5II. The k-3 does have a full manual flash setting and it will work as you want. The only way to do what you are trying to do on the k-5II is with radio triggers like the Cactus v5.
QuoteOriginally posted by chiefsilverback Quote
I've had the shutter as slow as 1/10!
That's fine. Anything UP TO 1/180 will work, but the camera will not fire the flash at all if you set a speed FASTER than 1/180th.

You might want to read through mcgregni's guide in post #6.

---------- Post added 02-15-16 at 01:03 PM ----------

You might also want to read up on manual flash and balancing ambient light with flash. I often shoot at 1/10th second with flash to balance the ambient. But the flash is going to come and go very quickly, far quicker than 1/10th. It might be 1/2000th at full power and 1/20,000th at low power, each flash will be different and I do not know the numbers for the 540, mcgegni's guide might have those. So you can use the flash to illuminate the subject and the slow shutter speed to illuminate the background. But you have to then calculate two different exposures. One for the flash and subject and another for the ambient and the background.

Last edited by jatrax; 02-15-2016 at 02:06 PM.
02-15-2016, 02:04 PM   #10
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QuoteOriginally posted by jatrax Quote
Yes. Command means it is going to communicate with the remote flash optically using the P-TTL protocol. The camera fires a pre-flash to measure exposure, then sends the info to the remote, then triggers everything. Sorry, but there is no way to do what you want to do with the k-5II. The k-3 does have a full manual flash setting and it will work as you want. The only way to do what you are trying to do on the k-5II is with radio triggers like the Cactus v5.
That's a kicker, it also makes it more strange that it works perfectly when the flashes are wound down to 1/16 power output, I'll take a couple of test shots to demonstrate...
02-15-2016, 02:11 PM   #11
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QuoteOriginally posted by chiefsilverback Quote
That's a kicker, it also makes it more strange that it works perfectly when the flashes are wound down to 1/16 power output, I'll take a couple of test shots to demonstrate...
If you really want to do manual off camera flash you need radio triggers. Or you can use wired and the PC-sync port. But you cannot do this with an optical command on the k-5II. Trust me I tried. I finally bought a set of Cactus v5 transceivers and all is good. For multiple flash setups I can trigger the main with the radio trigger and I have the rest set in slave mode to trigger optically. So they actually fire off of the flash from the main light, not the camera.

Now I have the k-3 and it is capable of doing what you want but since now I have the triggers there is no point.
02-15-2016, 02:21 PM   #12
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Like in another recent thread, it sounds like you are expecting 'M' camera exposure mode to also turn your built-in flash into a manual unit. It doesn't have any manual mode that will remove a P-TTL pre-flash.

Even though your slave flash is in wireless manual, the on-camera controller flash still functions using the P-TTL optical signals, and communicates some mode information to the slave prior to main flash. So the pre-flash will be an issue to any slave acting in 'dumb slave' mode. So the others above are right to point towards checking for 'S' mode settings.

Now, how this all relates to the main flash mode in wireless 'M' eludes my memory and brain power for now! Let me run some tests with my AF-540II (it's the MkII right?) and K7 (same as K5II for flash) and come back. I don't use Manual much on the Pentax flashes, I prefer P-TTL for my wireless work mostly.... But its nice to know its there and will work when needed!
02-15-2016, 02:51 PM   #13
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Here are some test images with the camera set at ISO100, f4 and 1/25 shutter speed:

1. No flash
2. Command flash only to show no impact to exposure
3. Both externals set to 1/4 power
4. Both externals set to 1/8 power
5. Both externals set to 1/16 power

---------- Post added 02-15-16 at 04:55 PM ----------

QuoteOriginally posted by mcgregni Quote
Let me run some tests with my AF-540II (it's the MkII right?)
It's mkI AF540. BTW - thank for the flash overview, I read through it yesterday.

---------- Post added 02-15-16 at 04:59 PM ----------

QuoteOriginally posted by jatrax Quote
If you really want to do manual off camera flash you need radio triggers. ... I finally bought a set of Cactus v5 transceivers and all is good.
I was planning on picking up a pair of Yongnuo YN560-IV flashes and a Cactus v6, but figured I'd play about with what I've got. I was going to get a basic moonlight kit but then read some articles on using speed lights and it seems to make far more sense to go the speed light route.
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02-15-2016, 03:01 PM   #14
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Wait a minute afaik, the AF540fgz most certainly will not fire on the preflash when set to SL2. At least my two won't.
02-15-2016, 03:14 PM   #15
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QuoteOriginally posted by Oldbayrunner Quote
Wait a minute afaik, the AF540fgz most certainly will not fire on the preflash when set to SL2. At least my two won't.
Yet more confusion! The pre-flash thing is definitely confusing because as you can see from my images at 1/8 and 1/16 power the flashes do work, but any higher and they have no impact on the exposure!?!?!
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