NX70U ND Filter Behavior

[Andy Lewicky]

I've been working with Sony Support to verify that my camera's behavior is normal. Because of communications issues with Sony, I ended up creating a video, which is probably the easiest way to explain what I'm seeing. Can anyone else out there with an NX70U verify that their camera does the same?

Test Video for Lou at Sony on Vimeo

For the record, this only happens in bright sunlight. Pointing your camera at a lightbulb won't trigger the effect, probably because the EV isn't high enough...

Thanks!

[Warren Eagleton]

Hi Andy, well I can tell you my NX70P (New Zealand model) has not got your problem. Changing to manual either shutter or Iris with the camera pointing at the same scene causes no change in the opposite setting. I wish you luck with SONY support.

[Matt Sharp]

Very interesting. This could finally put the ND filter debate to bed.

I'll test it on mine in the sunlight later today.

[Tom Hardwick]

Andy, your NX70 will most certainly have internal (generally undocumented) ND filtration if there's no manual ND filter switch on the outside of the camera. This is done because the camera uses tiny chips, chips so small and focal lengths so short that shooting at apertures smaller than f/4.5 start to show the damaging effects of diffraction.

I don't have an NX70 but I'm pretty sure this is the case. The next thing to say is that the side-screen image is taken directly from the chips, and it's a WYSIWYG situation. If the screen's exposure looks correct then that combination of gain, s/speed, iris and ND are all working in perfect harmony.

Next, Sony camcorders are only in manual when all the little As have disappeared from the iris, s/speed, gain, w/bal. So although you've locked the aperture on your cam, all the other disciplines are still in auto as you've noticed.

Camcorders that use variable internal ND (such as yours and some of mine) invariably give unreliable aperture readouts. I say unreliable but I mean 'untrue'. The f/9.5 figure is an extrapolation of the internal ND and the actual aperture, and is a figure that you, as a photographer, will understand and relate to. Of course it's not shooting at such a small aperture, it would reduce the image sharpness quite noticeably if it was.

As I say, I don't have an NX70 (I have an NX5) but your display setting suggest that yes, when you lock the iris the ND is instantly removed from the optical axis, necessitating the increase in the shutter speed to compensate. Why Sony do this I've no idea, but it sure looks like this is happening.

More interesting points. 1/125th is not a shutter speed you want to use when shooting smooth movies, yet this camera has deemed it necessary because it's 'run out' of internal ND, and doesn't want you to shoot at apertures smaller than f/4 (understandably). Buying screw-on ND would be a good idea.

As you say, it only happens in bright light, correct. And you realise in your little movie you interpose auto and manual when you talk of the shutter speed?

I'd be very surprised if Warren's camera isn't exactly the same, though different firmware versions could well induce the internal ND to interject at different times. BTW, there's no electronic ND, it's always slivers of ND placed completely out of focus at the iris blade position.

Don't worry - your camera's fine. Just remember that the aperture readout is lying. Way back in PDX10 days Sony were doing this - on a 'professional' camcorder, too.

tom.

[Andy Lewicky]

Tom,

Yeah, I'm misspeaking when it comes to 'automate' in the video, but I figured it's clear enough given the context.

I'm almost certain the NX70U is not misrepresenting the aperture. I did some tests on the same scene, just moving through the various f-stops and then looking at them on my screen. You can clearly see picture degradation as each stop grows smaller (ie, the number gets bigger).

I also compared picture with the phantom ND filter (in full auto) versus the same indicated aperture in an assisted manual-mode (no ND, presumably). The manual image looks slightly better, albeit not as significantly as during the aperture test.

I could be wrong about this, but my strong suspicion is that the camera shows shutter and aperture values correctly at all times, and that there is a physical ND filter that is only active for the highest EV values when all three of gain, shutter, and aperture are automated (controlled by the camera).

Obviously this issue is a concern for a number of reasons, but the primary one as you note is my desire to have the option of shooting in bright daylight with a film-standard shutter speed, which would be 1/48 in 24p or 1/60 in 60p. Hence my attempt to get Sony to talk about what's happening, and my post here...

Thanks!

[Andy Lewicky]

I should also ask -- If your camera doesn't do this in bright light, can you note your shutter/aperture settings?

That would be interesting information...

[Tom Hardwick]

Andy - interesting observations you post. Why not zoom to telephoto, put the camera in manual and look down into the lens with an LED torch to watch what the aperture blades and ND filters (if any) are doing as you vary the aperture.

If I do this on my SD900 Panasonic I notice that the camera shoots at maximum aperture for as long as it has ND to add. When all the NDs in place and it continues to get brighter, only then will it physically start to stop down the lens. So when it reads f/5.6 it's actually shooting wide open at full tele (f/2.8) and when shooting one stop down from max (f.4) the readout says it's f/8 - and so on.

When you switch the 900 to shoot stills, the internal ND is not used and the aperture readout is correct. Clever programming.

I agree with you that in AUTO the NX70 does appear to use the internal ND, but allows you (the creative, manual exposure photographer) to choose lots of dof and lose sharpness if you consider that a fair trade. But as movies are ruined by fluctuating exposure it does seem odd that Sony insist that you fit external ND just so that you can shoot at the default s/speed yet go no smaller than f/4.

I do dislike internal ND. It's great for the couldn't care less auto-shooter, but for the rest of us it clouds the issue. I've watched your film again, and sure enough, as you lock the iris the ND is instantly removed. The s/speed has to be shortened to compensate. The camera's still in the fully auto exposure mode, note.

Same when you lock the s/speed - then (with the ND completely removed) the iris has to stop right down to compensate. Still fully auto exposure of course.

Very odd firmware, Sony.

tom.

[Matt Sharp]

I had a chance to test it out on mine and acts just like yours Andy.

Originally Posted by Tom Hardwick

Andy - interesting observations you post. Why not zoom to telephoto, put the camera in manual and look down into the lens with an LED torch to watch what the aperture blades and ND filters (if any) are doing as you vary the aperture.

Tom I did exactly that, the aperture stops down along with the indicated iris all the way to closed. I didn't see an internal ND though. Not saying it's not there, but I wasn't able to see it.

[Tom Hardwick]

Switch it to auto then Matt, and you should see those NDs dancing about.

This sort of discussion makes me wish that Sony were more open about what was happening - especially so for folk who are buying this camera for professional applications. This is hardly a casual picnic-cam, so the NX70's pdf should (at the very least) tell prospective purchasers what to expect.

As photographers they'd buy some serious screw-in NDs before they left the shop. Yet using filters in front of such very short focal lengths is always to be frowned upon. Not only do they reduce the hood's efficiency but they're a constant hassle to keep spotless. Which is why, Sony, you fit internal ND. Why deny us access to this simply because we want to lock the exposure?

Warren's camera response still surprises me, though it might suggest there are some 70s out there that behave. And that your cameras (Matt and Andy) need to go beck to Sony for a fix.

Andy - have you thought about posting your findings as a review on Sony's Style pages?
Like this one:

http://store.sony.com/webapp/wcs/sto...376733#reviews

tom.

[Andy Lewicky]

Matt, thanks for the confirmation.

Unfortunately, even in full-auto (with the presumed ND active), the NX70U still can't expose a normal scene under daylight with a 1/48 or 1/60 shutter. And in manual mode, trying to use these shutter speeds forces you up into diffraction-affected f-stops, with visible picture degradation.

Being forced to carry external filters and swap them out really undermines the camera's appeal as a run-n-gun docu shooter. Baffling--and very disappointing.

Tom, I'm still trying to work with a Sony pro support rep to get an admission that this is in fact the default behavior of the camera, rather than a service issue. My past experiences with Sony don't leave me feeling encouraged that they will admit a problem exists until after they've fixed it, and even then maybe not... :)

[Matt Sharp]

Originally Posted by Tom Hardwick

Switch it to auto then Matt, and you should see those NDs dancing about.

With it in auto I was able to see something. You can't exactly see the filter but you can see it's leading edge go from the bottom of the iris to the top, and then the reflection of the LEDs in the iris is a bit stronger.