Nikon TTL question?

sk66

sk66

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Steven
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I found an odd peculiarity and I'm not sure why I'm getting the results I am.

Setup: Aperture priority, spot metering, Auto ISO with min SS set to max faster (2x FL) and max ISO set to 1000, X-sync set to auto FP, Flash: SB800, -2/3 FEC, TTL. I can also use CW/Matrix metering and TTL/BL with the same results.

With the D4 I get the results I expect, a lower SS at a lower ISO and a good exposure (say 1/30th ISO 400).
But with the D810 I get a high SS (1/3200 w/ 800mm) at max ISO (1000) and underexposure (flash in HSS inadequate).

There's at least 3 different ways to avoid the D810 issue, that's not the problem. My problem is that I do not understand why I am getting different behaviors/results from the two cameras. Is there maybe a setting I'm missing that isn't the same between them? Or maybe there was a logic/behavior change between the two generations and I just never realized it before?

Any ideas?
 
Out of my depth here but I can offer one thought.

With my D7000 I never get consistent flash exposure when auto iso is on.
 
The first time I used my D7000 with my studio lights, I got constantly under exposed images. Was using manual settings and couldnt figure out what the heck was going on. I had auto iso on, but didn't realise that it was still on even when the camera was on manual.
 
Bobsyeruncle said:
The first time I used my D7000 with my studio lights, I got constantly under exposed images. Was using manual settings and couldnt figure out what the heck was going on. I had auto iso on, but didn't realise that it was still on even when the camera was on manual.
Click to expand...
Yeah, auto ISO will fight you to keep the exposure the same... not a good choice for the studio...
 
Hi Steven - we're you shooting at 800mm on both cameras? I'm just wondering how the D4 decided that 1/30th was good shutter speed at 800mm with 2xFL set :/. The D810 outcome would be what I would expect from those parameters - although you might expect 1/1600 to be the shutter speed. Is the light mounted on the camera? Aperture choice the same ?
 
Scooter said:
Hi Steven - we're you shooting at 800mm on both cameras? I'm just wondering how the D4 decided that 1/30th was good shutter speed at 800mm with 2xFL set :/. The D810 outcome would be what I would expect from those parameters - although you might expect 1/1600 to be the shutter speed. Is the light mounted on the camera? Aperture choice the same ?
Click to expand...
Everything the same on both that I can tell/think of.

1/30 was the "minimum SS w/ flash" set on the D4... it's 1/60th (default) on the D810. Flash on camera, TTL/BL/FP. 800mm f/8 on both.

The D4, and every other DSLR I've ever used, first tries to get a proper exposure w/o flash when in a priority mode. It will use the highest ISO allowed (i.e. 1000) and the lowest SS (the min flash SS setting, 1/30 in this case) and then "fill in" with TTL flash. Once the ambient exposure maxes out (max ISO/min SS) then the flash starts to become more the "primary exposure."

Normally, to get the flash to go into HSS when in Aperture priority you have to be shooting into very bright light (the ambient exposure requires min ISO and high SS), or you have to switch to another mode. The D4 did what I expect as *normal*... the D810 didn't try to get a proper exposure before adding flash, letting it underexpose badly in favor of the min SS (auto ISO) setting.
 
I think the D810 is prioritizing a minimum shutter speed based on the focal length. I just tested this on my D810 and with auto-ISO on in aperture priority, it selects 1/f (or closest 3rd of a stop) as he shutter speed. If it hits the max ISO, it then starts to lower the shutter speed. With auto -ISO off, it varies the shutter speed to achieve the exposure at the set ISO. I don't know why your D810 is going for 1/3200 (as opposed to 1/800th ) though, but the rest of the problems stem from this (ISO 1000 is not enough to get the proper exposure at 1/3200, and the flash will now be in HSS and it won;t be powerful enough either...). I'll play around with a flash attached as well to see if that makes any difference to the behaviour.
 
Scooter said:
I don't know why your D810 is going for 1/3200 (as opposed to 1/800th )
Click to expand...
Because I have min SS set to auto "fastest" (2x FL). With a TTL flash attached, every other DSLR I've used ignores the auto ISO min SS setting and uses the "min SS with flash" setting instead... my D4 does.
Even w/o that, the normal behavior is to go below the min SS once the max ISO has been reached in order to get a proper exposure (as you described). My D810 does that w/o a flash attached... but not *with* a flash attached. It seems to be applying the auto ISO min SS setting, ignoring the min SS w/ flash setting, and relying on flash to make up the exposure w/o any consideration as to if it can (that last bit is normal as well).

There's several fairly easy ways to avoid the issue now that I've noticed it... I just have to remember/retrain when using the D810. But I'm not certain if this is now a "normal behavior" for newer models, or if my D810 has a glitch. As far as I can tell everything is communicating/syncing as it should.
 
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•


My Nikon experience thought me that their system is
pretty reliable whatever the body it is implemented into.

From what I read and understand from your preamble,
Spot metering is NOT the metering option sit is contra
productive. I would choose and set ponderate central to
20mm prior to selecting it or go matrix and forget about it.

Remember, the inverse square law is working for you!
 
Kodiak Qc said:
•


My Nikon experience thought me that their system is
pretty reliable whatever the body it is implemented into.

From what I read and understand from your preamble,
Spot metering is NOT the metering option sit is contra
productive. I would choose and set ponderate central to
20mm prior to selecting it or go matrix and forget about it.

Remember, the inverse square law is working for you!
Click to expand...
Yeah, the system has been very consistent between bodies over the years... that's why I was caught so off guard. But now that I think of it, I'm not sure this is the first time it's bitten me w/ the D810. It might be the first time I didn't catch it early and that I've studied the settings/differences after the fact (the D810 is not usually the camera I use for low light/TTL flash).

Spot metering wasn't used and wouldn't really help the issue overall... spot metering also disables the BL (balanced/back lighting) feature.
 
sk66 said:
Because I have min SS set to auto "fastest" (2x FL). With a TTL flash attached, every other DSLR I've used ignores the auto ISO min SS setting and uses the "min SS with flash" setting instead... my D4 does.
Even w/o that, the normal behavior is to go below the min SS once the max ISO has been reached in order to get a proper exposure (as you described). My D810 does that w/o a flash attached... but not *with* a flash attached. It seems to be applying the auto ISO min SS setting, ignoring the min SS w/ flash setting, and relying on flash to make up the exposure w/o any consideration as to if it can (that last bit is normal as well).

There's several fairly easy ways to avoid the issue now that I've noticed it... I just have to remember/retrain when using the D810. But I'm not certain if this is now a "normal behavior" for newer models, or if my D810 has a glitch. As far as I can tell everything is communicating/syncing as it should.
Click to expand...


Ok, here's what I found with the this setup:-

Nikon D810
Nikkor 85mm AF/D 85mm f/1.8 - at f/1.8 as there isn't a lot of light in here now.
Aperture priority
EC 0.0
FEC 0.0
Auto ISO - Min shutter speed Auto - fastest.
Base ISO - 64
Max ISO 12800
X-Sync speed set to 1/250th with auto FP
Min flash shutter speed 1/60th
Matrix metering

Flash mounted on camera - SB900 TTL.

In a well lit bit of the room:-
With flash turned off - Shutter speed 1/400th. ISO 250
With flash turned on - Shutter speed 1/400th ISO 250

In a dark part of the room:-
With flash turned off - Shutter speed 1/400th. ISO 12800
With flash turned on - Shutter speed 1/20th ISO 250

In a well lit part of the room, with MAX ISO 1000
With flash turned off - Shutter speed 1/400th. ISO 250
With flash turned on - Shutter speed 1/400th ISO 250

It only seems to change the exposure if there is relatively low ambient light. With enough ambient, it makes no difference whether the flash is on or not. In a dark corner though, my D810 seems to behave like your D4 - it drops the shutter speed for a 4 stop increase (and there's more flash than ambient now so the flash will freeze the action). It drops the ISO by roughly 5.5 stops for an effective 1.5 stops lower exposure - and I assume the thinking is that the flash then adds this back in. Interesting that when it's dark it not only abandons the auto ISO min shutter speed, but ignores the flash min shutter speed too. There's more than enough ISO headroom for 1/60th after all but it seems to "like" ISO 250. I would guess there's a 3rd scenario between the two where there's a reasonable but minority amount of ambient where it obeys flash min SS, and reduces ISO.

One other thing that occurs to me: at 800mm your subject is maybe quite far away, and so flash on camera will play a lesser part in the exposure, hence the camera deciding to obey auto ISO min SS - "fastest" as it think most of the light will still be ambient.
 
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arrgh - I think I have the answer. Your D4 has Slow sync enabled, and your D810 does not. If I turn this off on my D810 - it behaves like yours - ie maintains the high shutter speed even with the flash on. Doh!
 
Scooter said:
arrgh - I think I have the answer. Your D4 has Slow sync enabled, and your D810 does not. If I turn this off on my D810 - it behaves like yours - ie maintains the high shutter speed even with the flash on. Doh!
Click to expand...
Close!
My D4 was set to rear curtain and the D810 was set to front. If I set the D810 to slow or rear curtain it behaves as I expected.
Now I'll have to try and wrap my head around why it behaves differently in front curtain sync... The good news is my D4 behaves the same, so at least it seems to be consistent across the line.
Thanks!
 
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sk66 said:
Close!
My D4 was set to rear curtain and the D810 was set to front. If I set the D810 to slow or rear curtain it behaves as I expected.
Now I'll have to try and wrap my head around why it behaves differently in front curtain sync... The good news is my D4 behaves the same, so at least it seems to be consistent across the line.
Thanks!
Click to expand...


Ah yes - rear also enables "slow" :) Rear assumes you want a slower SS for some ambient blur (at a fast shutter speed it won't make too much difference if it's front or rear). You can think of the options as "Front - fast" Ie obeys min SS limits, "Front - slow" and "Rear - slow" (and there is no "Rear - fast" as this wouldn't be much use).
 
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The manual is no help... it (basically) says that it will use the minimum SS w/ flash setting. It also says that in slow sync the ISO may be automatically raised preventing a lower SS (something I've never seen). Apparently this change came about around the time of the D7000 and I've never noticed (I have a habit of generally using rear curtain).

I can see some minor benefit... I.e. use front curtain with a higher min SS setting in auto ISO to allow you to force it into HSS. But really, just turning on/off auto ISO is easier than switching flash sync modes... at least it involves larger buttons (or leaving auto ISO off and using easy ISO instead).

Crap, another thing to remember... especially because front curtain has distinct advantages in certain situations.
 
sk66 said:
Crap, another thing to remember... especially because front curtain has distinct advantages in certain situations.
Click to expand...

Yep - must remember to undo all the stuff I just changed or I'm going to be scratching my head at the next indoor event :)
 
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