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Author Topic: Nikon D3s - Uneven Exposures  (Read 4697 times)

jvora

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Nikon D3s - Uneven Exposures
« on: July 21, 2013, 08:06:46 AM »

Hello :

Am slightly stomped with this issue -

While shooting a 18% Kodak Grey Card ( was trying to calibrate my Light Meter to the D3s's Sensor at Base ISO ) using my Nikon D3s, the Test seems to reveal un-evenness in the results.

Attached please find the Test Result.

This was shot using 2 Strobes on either side of the Grey Card with the camera on a Tripod. The Strobes were set to an approx 45 Degress Angle with no obstruction in the light's path to have caused this issue.

Image shot at X-Sync Speed at f/13.0 using a Nikon 85mm F/1.8 D lens.

I get a similar result when using the 50mm F/1.8 D lens as well.

Any thoughts why the exposure is uneven and that too only on one side ??

Remain worried : (


Jai

ps : This question has been cross-posted on another Forum as well.
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opgr

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Re: Nikon D3s - Uneven Exposures
« Reply #1 on: July 21, 2013, 08:18:49 AM »

1. make sure the card is absolutely flat. Can be tested quite easily: turn is on its side, shoot again, if the unevenness has also turned sideways, then the card is most likely bend.

2. might be reflectivity of a black stand, exacerbated by the lights positioned slightly high, and possibly a processing that exaggerates (auto) contrast. Same test as above: if the unevenness remains at the bottom of the picture, then this is the most likely cause...
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FranciscoDisilvestro

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Re: Nikon D3s - Uneven Exposures
« Reply #2 on: July 21, 2013, 09:16:17 AM »

Hi,

How is your camera set up for X-sync speed, 1/250 or 1/320? Sometimes if you use 1/320 with external strobes you get that result.

You might try slower speeds too

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BartvanderWolf

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Re: Nikon D3s - Uneven Exposures
« Reply #3 on: July 21, 2013, 09:46:52 AM »

Hi,

How is your camera set up for X-sync speed, 1/250 or 1/320? Sometimes if you use 1/320 with external strobes you get that result.

You might try slower speeds too

I would have suggested the same, try with a slower speed, but Francisco beat me to it. You could even try using a long exposure time in a darkened room, and manually trigger the flashes. That should help ferret out a possible synchronization issue.

Another possibility is that the shutter-curtains move at different speeds, but that should become evident in regular outdoors exposure situations as well. Try shooting the sky at the same shutter-speed.

Cheers,
Bart
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jvora

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Re: Nikon D3s - Uneven Exposures
« Reply #4 on: July 21, 2013, 10:02:34 AM »

Hello :

Yes ! Setting the camera to the max sync ( 1/250th )for strobes could be the reason for the unevenness - Seems logical - Will try shooting at a lower speed - 1/125th or even 1/60th.


Thanks,

Jai
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jvora

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Re: Nikon D3s - Uneven Exposures
« Reply #5 on: July 21, 2013, 10:06:57 AM »

Hello :

Thats a good suggestion - WIll shoot the Sky at 1/250th and higher speeds and note if there is un-evenness !


Thanks,

Jai
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TMARK

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Re: Nikon D3s - Uneven Exposures
« Reply #6 on: July 22, 2013, 03:20:01 PM »

How are you syncing the strobes?  My older Nikons did this (D2x, D200) when using Pocket Wizards at X-Sync.  My Canons did not (5D, 1ds, 1ds2, 1ds3, 5D2).

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opgr

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Re: Nikon D3s - Uneven Exposures
« Reply #7 on: July 22, 2013, 03:51:36 PM »

How are you syncing the strobes?  My older Nikons did this (D2x, D200) when using Pocket Wizards at X-Sync.  My Canons did not (5D, 1ds, 1ds2, 1ds3, 5D2).

I do faintly recall a syncing issue with Canons on these forums years ago, though the images had a distinct darker top or bottom half, not a graduated result.
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jvora

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Re: Nikon D3s - Uneven Exposures
« Reply #8 on: July 22, 2013, 09:09:59 PM »

How are you syncing the strobes?  My older Nikons did this (D2x, D200) when using Pocket Wizards at X-Sync.  My Canons did not (5D, 1ds, 1ds2, 1ds3, 5D2).




Yet to perform the TEST - A-prior, the Sync is performed with the regular Sync Cord connecting the camera to the Strobe directly.


Jai
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TMARK

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Re: Nikon D3s - Uneven Exposures
« Reply #9 on: July 23, 2013, 09:42:52 AM »


Yet to perform the TEST - A-prior, the Sync is performed with the regular Sync Cord connecting the camera to the Strobe directly.


Jai

What kind of flash duration are you getting? 

These problems are frustrating but at least with digital you can experiment and find the issue.  A sync cord should rule out a sync problem in the trigger.  That leaves shutter times being off or other camera sync issues, or flash duration being too long, such that teh shutter closes before the strobe dumps all its power.
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langier

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Re: Nikon D3s - Uneven Exposures
« Reply #10 on: July 23, 2013, 11:28:19 AM »

Looks to me as though the flash duration is a bit too long for the camera sync. Slowing down to 1/180th or 1/125th will probably fix the issue. The flash must have a fairly long pulse duration.

Another possible solution is to lower the power of the flash to say 1/2 power. The flash duration may be a little faster.

In any case, this is a good example of why one should always test equipment and technique so that there are no surprises or issues when working in real life! In the heat of battle with a paying client especially is not the time to find out about issues such as these!
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LKaven

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Re: Nikon D3s - Uneven Exposures
« Reply #11 on: July 25, 2013, 01:14:02 AM »

Using a straight-wire PC-sync will not necessarily solve the problem.  Some strobes, even when hard-wired, induce enough delay to make using the Nikon at X-sync speed (1/250 in this case) unworkable.  Optical and radio sync can induce even more delay of course.  The OP's problem is almost certainly due to this, and will be solved by using a lower shutter-speed. 

jvora

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Re: Nikon D3s - Uneven Exposures
« Reply #12 on: July 26, 2013, 07:33:55 AM »

Hello :

Ok - I FINALLY had the chance to perform the TEST - This time around, I shot at 1/125th and the results are what one would expect - Pretty even - There is some small amount of variation and could be attributed to the age of the Grey Card, ( even though it looks even to the eye ).

I thank each of you for helping me resolve the issue - Shooting at of 1/250th of a second with the strobes ( Elinchrom ) was the issue.



Thanks again !!



Jai
« Last Edit: July 26, 2013, 11:32:18 AM by jvora »
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BobDavid

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Re: Nikon D3s - Uneven Exposures
« Reply #13 on: July 26, 2013, 10:51:48 AM »

Yep, I discovered this problem too. d800/Pocket Wizard/Elinchrom RX 1200s.  I wonder if Elinchrom's Skyport system improves sync speed. I am able to get even results with the Nikon at 1/125 or slower. My Sony a900 worked fine at 1/250.
« Last Edit: July 26, 2013, 10:55:14 AM by BobDavid »
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Ellis Vener

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Re: Nikon D3s - Uneven Exposures
« Reply #14 on: July 26, 2013, 12:11:30 PM »

A: Which Pocketwizard system? ControlTL, MultiMAX, Plus II, Plus III?

B); Flash duration isn't the issue here unless it is very short flash duration - which isn't the case with most Elinchrom. Flash triggering timing is. As Mr. Kaven points out that could be inherent to the flashes or it could be in the camera's programming.

What may be happening ais that at X-Sync speed (with the D3s that is in the 1/250 to 1/320 second range) what is likely happening is that rear curtain is starting to move a little prematurely for your flash. Using 1/200th or longer should solve the problem - as BobDavid and Jai have discovered The Pocketwizard ControlTL and MultiMAX units have an advance mode feature allowing you to finetune the timing for your specific camera and light set up . I've never needed to use it but I know that it is there.
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