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FORUMS General Gear Talk Flash and Studio Lighting
Thread started 20 Nov 2017 (Monday) 10:41
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Flash Sync Issue

 
Temma
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Joined Sep 2009
Rocky River, Ohio
Nov 20, 2017 10:41 |  #1

For a couple of months, I've been using 2-3 Amazon Basics manual flashes with Neewer radio triggers on my Canon T4i for focus stacking.

I periodically see the shutter at the bottom of images in the stacks.

When this started I was shooting on Manual at 1/250.

I went down to 1/200 and it became less frequent, but was still there.

I went down to 1/160 and it became less frequent still, but was still there.

I haven't tried to go lower yet, since I needed to recharge the tablet that I use to control my focus rail last night.

This appears to happen regardless of whether the batteries have been freshly charged or not. I already extended the pause time from five to eight seconds for a different reason. Do I need to make it longer still?

Does anyone have any suggestions?




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Numenorean
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Nov 20, 2017 10:49 |  #2

The maximum sync speed for that camera is 1/200. So you either need to use high speed sync or use a slower shutter. Technically it shouldn't be there at 1/200 but you aren't using a Canon flash so all bets are off.


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Chet
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Nov 20, 2017 10:52 |  #3

What are the triggers rated at? I've had cheap triggers that 1/160 was about it.


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Temma
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Nov 20, 2017 11:07 |  #4

Chet wrote in post #18500411 (external link)
What are the triggers rated at? I've had cheap triggers that 1/160 was about it.

I don't know. I'll have to see if Amazon lists that in their online specs.

Thanks.




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Temma
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Nov 20, 2017 11:10 |  #5

Chet wrote in post #18500411 (external link)
What are the triggers rated at? I've had cheap triggers that 1/160 was about it.

From Amazon's page for the triggers:

Sync speed: 1/250s




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OceanRipple*
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Nov 20, 2017 11:23 |  #6

Temma wrote in post #18500425 (external link)
From Amazon's page for the triggers:

Even if they claim 1/250th (optimistically) for the triggers, your camera cannot offer that.

I would suggest 1/160th too.




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Chet
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Nov 20, 2017 11:29 |  #7

Temma wrote in post #18500425 (external link)
From Amazon's page for the triggers:


So did the Pro Master triggers I had. Says 1/250, but only reliable at about 1/160. I read lots of poor reviews for the Neewer radio triggers just now on Amazon. Cheap triggers are a great introduction into off camera flash but will quickly leave you wanting more. I currently use Radio Popper Jr. and they cost me 3 times more and are also just average. I've had to take 2 apart and repair broken wires already. Folks in the reviews really seem to like the Yongnuo triggers, seem to be a better bang for the buck.


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Temma
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Nov 20, 2017 11:46 |  #8

Chet wrote in post #18500438 (external link)
So did the Pro Master triggers I had. Says 1/250, but only reliable at about 1/160. I read lots of poor reviews for the Neewer radio triggers just now on Amazon. Cheap triggers are a great introduction into off camera flash but will quickly leave you wanting more. I currently use Radio Popper Jr. and they cost me 3 times more and are also just average. I've had to take 2 apart and repair broken wires already. Folks in the reviews really seem to like the Yongnuo triggers, seem to be a better bang for the buck.

When I was starting out in focus stacking, I had the Yongnuo YN560 flashes recommended to me.

Very quickly, I found an abundance of bad review of them.

Paradoxically, I don't think I ever saw a bad review of the Yongnuo triggers.




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Wilt
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Nov 20, 2017 19:14 |  #9

Your camera is, at best, good for X-sync at 1/200...and then when you add the signal propogation delay of a radio trigger and receiver, it can slow down another fraction of an EV.


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dmward
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Nov 21, 2017 08:24 |  #10

What most photographers forget is that the rated X sync speed for a camera's shutter is with a hard wire connection between the camera sync port and the flash.

Radio triggers, by their nature introduce delay. There are three elements to the delay. A) processing delay. It takes time for the trigger firmware to read the electrical signal, convert it to a radio pulse and then send the pulse to the transmitter. B) propagation delay. The radio signal has to go from one place to another. The distance may not be too far but it still takes time. There are also radiation patterns that may influence the signal as it passes through the atmosphere. In some cases having the transmitter and receiver too close together is problematic. Antenna position can also influence transmission efficiency. C) when the receiver "hears" the fire radio message it has to translate it, via firmware, into an electrical fire pulse that is sent to the flash control circuit.

We complain about having to slow the shutter from x sync speed to to one or so EV slower. With a predominately flash lit shot the shutter is irrelevant.

Once an engineer explained to me all of the engineering it takes to build a wireless trigger system, what's amazing is that they work as reliably as they do.


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Wilt
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Post has been edited 1 month ago by Wilt.
Nov 21, 2017 11:47 |  #11

'propogation delay' can be subject to interpretation as to the 'start point' vs. the 'finish point' used for the delay calculation. dmward's apt description treats 'propogation' delay as the time it takes for the radio signal from tranmitter to receiver, an infinitesimal amount of time at the speed of light.

In a communications system, the propagation delay refers to the time lag between the departure of a signal from the source and the arrival of the signal at the destination. So if you consider the departure of the signal from the 'source' (the camera shutter contacts) to the 'destination' at the flash contacts, what propogation delay wrote applies to the entire A-B-C sequence added by the use of a radio transmitter+receiver in between the camera and the flash, and points A and C are responsible for probably 99.5% of the entire delay in signal arriving at the flash. That is why some transmitters and receivers are less handicapped in preserving the original sync speed capability than other transmitters and receivers...yet point B 'delay; is identical for both sets.


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Temma
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Nov 21, 2017 13:14 |  #12

I've got it down to 1/125, and the shutter problem seems to have gone away.

Incidentally, none of the components is more than a foot from the transmitter, less actually.




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OceanRipple*
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Nov 21, 2017 13:43 |  #13

Temma wrote in post #18501207 (external link)
Incidentally, none of the components is more than a foot from the transmitter, less actually.

Paradoxically, having the Rx less than 2 feet from the Tx can sometimes exacerbate communication problems.

But the 1/125 is good.




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dmward
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Nov 21, 2017 16:46 |  #14

Wilt wrote in post #18501155 (external link)
'propogation delay' can be subject to interpretation as to the 'start point' vs. the 'finish point' used for the delay calculation. dmward's apt description treats 'propogation' delay as the time it takes for the radio signal from tranmitter to receiver, an infinitesimal amount of time at the speed of light.

In a communications system, the propagation delay refers to the time lag between the departure of a signal from the source and the arrival of the signal at the destination. So if you consider the departure of the signal from the 'source' (the camera shutter contacts) to the 'destination' at the flash contacts, what propogation delay wrote applies to the entire A-B-C sequence added by the use of a radio transmitter+receiver in between the camera and the flash, and points A and C are responsible for probably 99.5% of the entire delay in signal arriving at the flash. That is why some transmitters and receivers are less handicapped in preserving the original sync speed capability than other transmitters and receivers...yet point B 'delay; is identical for both sets.

Wilt, in the real world B is more likely to be the most variable. Partly because of interference that may cause retransmission, if that's built into the radio protocol. It shouldn't be, according to engineers with whom I've discussed this. And, sadly, the radio wave travel less than their theoretical best speed. All that aside, the total delay is quite small. Its usually some design influence that causes a repeatable delay requiring a slower shutter speed.


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Wilt
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Post has been last edited 1 month ago by Wilt. 5 edits done in total.
Nov 21, 2017 16:58 as a reply to dmward's post |  #15

It has to be admitted that if light goes 186000 miles/sec. that changing distance from 10' to 1' is only the matter of 1/1,000,000,000 th of a second vs. 1/100,000,000 the of a second. Even increasing distance to 100' means that it still needs only 1/10,000,000 th of a second for the signal to travel between transmitter and receiver.
If there is an issue caused by short distance, it is most likely the fact that the increase of signal strength overwhelmed the receivers' dynamic range, and the receiver has gone into saturation.

So needing to slow down shutter from 1/200 to 1/160 or 1/125 is caused by A + C, not B.


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Flash Sync Issue
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