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06-04-2012, 03:45 PM   #1
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Flash fires twice in Trailing curtain sync mode

I just bought a AF 360 FGZ to use with my K-7. While using it in Trailing curtain sync mode the flash fires twice- once at the begining of the exposure and one at the end.

I assume (as i read in other posts) that the first one is just the pre-flash, but i was wondering if there's any way to use the flash without it pre-flashing?
I tried to change the flash mode from P-TTl to A or M, but it seems that in Trailing curtain sync it's always going back to P-TTL. Is that realy so? And why does the flash needs the pre-flash anyway?

I'll be happy if someone could help me understand this a bit better...

06-04-2012, 04:02 PM   #2
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QuoteOriginally posted by manuido Quote
I just bought a AF 360 FGZ to use with my K-7. While using it in Trailing curtain sync mode the flash fires twice- once at the begining of the exposure and one at the end.

I assume (as i read in other posts) that the first one is just the pre-flash, but i was wondering if there's any way to use the flash without it pre-flashing?
I tried to change the flash mode from P-TTl to A or M, but it seems that in Trailing curtain sync it's always going back to P-TTL. Is that realy so? And why does the flash needs the pre-flash anyway?

I'll be happy if someone could help me understand this a bit better...
I am no flash expert, nor do i have any pentax flashes, but the pre-flash I believe is to get the exposure information so it can get the right settings for the shot.

Alternatively do you have red eye reduction on? I think that also fires a pre flash too.
06-04-2012, 04:29 PM   #3
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Just flipped to page 65 of the AF 540 FGZ manual and it indicates that trailing curtain sync is not available in A or M setting.
06-04-2012, 04:33 PM   #4
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Yep, preflash. Normally it happens fast enough on First Curtain shooting that you many people simply do not notice it.
But with second curtain you have quite a lag between first and second curtains that it becomes very obvious.

And sadly with Pentax flashes... no way to turn off pre-flash.

06-04-2012, 04:35 PM   #5
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QuoteOriginally posted by amoringello Quote
And sadly with Pentax flashes... no way to turn off pre-flash.
To be more specific... no easy way.
If you get a sync adapter that has only the center firing pin, or if you use remote flash gear, the flash and camera cannot communicate using PTTL, so the flash reverts to being pretty much the same as any manual flash.

But as long as you're shooting with a 5pin connector or with PTTL wireless signaling, you're stuck with pre-flash.
06-04-2012, 05:20 PM   #6
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Can't do trailing curtain sync with a fully manual flash at all (at least I can't with mine).

Actually, the above statement isn't quite true. I can configure my manual flash (a Lumopro LP160) to be an optical slave so that it's triggered by my on-board flash going off (this isn't the same as P-TTL because there's no exchange of information). I can additionally configure it to ignore the first flash. With flash compensation on the on-board flash dialed right down I can effectively get my manual flash to do rear curtain. However, I'm not able to do this with the radio triggers - I just get first curtain then.

Don't know why Pentax don't allow manual trailing curtain sync. It does seem like a silly restriction.

Basically, this means that you're going to get a pre-flash or you're not going to use trailing curtain sync. It has to be said that the pre-flash doesn't do any active harm so no biggie.
06-04-2012, 11:15 PM   #7
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You can determine if it's the pre-flash by using the 2 second timer; the pre-flash will happen before the mirror goes up, the 'normal' flash will happen while the photo is taken.

06-05-2012, 03:32 AM   #8
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Thanks everybody for the answers. Thanks Mattt: i missed this part in the manueal... Probably because the German version i got (buying it in Switzerland) uses for some reason two different terms for trailing curtain sync.
06-05-2012, 04:44 AM   #9
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You can do manual trailing sync if you have a metz58 II oncam (or connected with PTTL) master controlling 540s/360s slaves, wirelessly. It's how I do my stuff.
06-05-2012, 05:53 AM   #10
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the question, i believe has been answered, it is the preflash, but there should be some mention here I feel about how P-TTL works.

P-TTL is a predictive flash exposure process. The camera takes the ambient light reading, and also the impact from the preflash, to judge the contribution to exposure that the preflash makes, and then calculates the flash duration required for the exposure settings. as a result, it is not possible to simply eliminate the preflash because it is an integral part of the metering system.

the older TTL flash, that was available on the *istD series, simply looked at the light being reflected off the sensor and terminated the flash when the exposure requirements (based on ISO) were met. The problem with TTL is that in some cases, the shutter could remain open long after the flash ended, continuing the exposure and leading to over exposure.
06-05-2012, 07:28 AM   #11
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QuoteOriginally posted by Lowell Goudge Quote

the older TTL flash, that was available on the *istD series, simply looked at the light being reflected off the sensor and terminated the flash when the exposure requirements (based on ISO) were met. The problem with TTL is that in some cases, the shutter could remain open long after the flash ended, continuing the exposure and leading to over exposure.
Thanks Lowell I didn't actually know until now how TTL worked and the shortcoming of it.

So how come many people around here lament (if thats the word) the loss of TTL and dislike P-TTL.? Other than that P-TTL can often be inaccurate and inconsistent I mean?
06-05-2012, 04:44 PM   #12
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QuoteOriginally posted by steve1307 Quote
So how come many people around here lament (if thats the word) the loss of TTL and dislike P-TTL.? Other than that P-TTL can often be inaccurate and inconsistent I mean?
If they are like me, probably because they have at least one perfectly fine Pentax TTL flash in their inventory (I had 3). We lament the loss of functionality ... and to regain that functionality, I spent a goodly amount for a decent P-TTL flash.

It isn't so much that I dislike P-TTL, but I could easily mix TTL & manual flashes (halo or background lighting). It is more difficult to mix P-TLL & manual flashes because of the pre-flash.
06-06-2012, 07:39 AM   #13
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QuoteOriginally posted by steve1307 Quote
Thanks Lowell I didn't actually know until now how TTL worked and the shortcoming of it.

So how come many people around here lament (if thats the word) the loss of TTL and dislike P-TTL.? Other than that P-TTL can often be inaccurate and inconsistent I mean?
QuoteOriginally posted by JimJohnson Quote
If they are like me, probably because they have at least one perfectly fine Pentax TTL flash in their inventory (I had 3). We lament the loss of functionality ... and to regain that functionality, I spent a goodly amount for a decent P-TTL flash.

It isn't so much that I dislike P-TTL, but I could easily mix TTL & manual flashes (halo or background lighting). It is more difficult to mix P-TLL & manual flashes because of the pre-flash.
For me there are good and bad with all designs,

Many people tout that P-TTL solved an issue with the difference in flash metering between taking the light reflected off the film emulsion, and that off the sensor which was more reflective, although I personally think this is BS. My *istD metered just as well with a TTL flash as my PZ-1. the issue, I think came down to cost. TTL requires an additional sensor and required real time metering during exposure, P-TTL uses the normal metering sensors and is a predictive mode that simply tells the flash how long to fire, with no real time metering involved.

For me, I liked TTL for a number of reasons, (yes I did have a TTL flash (AN AF500FTZ) which I think has a much shorter full power duration than the AF540FGZ because it was designed to be used with the PZ-1 which had 1/250 sync on a full frame, and therefore had a much shorter 100% frame open time.)
- TTL is usable with legacy lenses, because it meters the actual flash illumination during exposure, and therefore does not car whether there is an M42, K or KA/later mount lens attached
- it only flashes once, and the preflash can be disturbing, there are lots of threads on this
- it can be used using specific nikon flashes as remote slaves, because some nikon flashes in slave mode turn off when the master flash turns off allowing multi flash setup with metering. There are slave units that can do this also.
- pre flash on P-TTL is also used as a focus aid, and if you are constantly pointing and aiming, you can fire the preflash a ton of times, not just for focus but also for metering, that cause the batteries to go down quickly or to overheat the flash unit

Both TTL and P-TTL have their issues, and regardless of which someone likes or dislikes, i think all the complaints about inconsistencies are the result of a lack of understanding how the systems work.

P-TTL solved a lot of problems that were real, and allowed for more intelligent slave flash control, but at a cost for some users.

I personally think pentax would be very smart, at least on the flagship camera to offer both again, like it did on the *istD
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