I absolutely agree.
There's no light loss concerning the dynamic range (signal/noise assuming a white-noise signal) when switching from interlaced to progressive in a low-light situation (actually the dynamic range of progressive is higher than the dynamic range of interlaced in bright situations). In interlaced-mode there's an operation before interlacing from 60p to 30i happending which accumulates every two successive lines (so the pixel-values of line(y) of the output is line(y)+line(y-1) of the input, in other words filtering each frame with the kernel [1, 1]^T), probably to cope with that interlaced-flickering without decreasing the noise-level (to artificially degrade the value of the camera?). Of course you could in principle (when ignoring/compensating that non-linear gamma stuff) apply that operation to the "darker" progressive shots in post to get the same result, but of course the temporal resolution is gone.
So to conclude: When switching from progressive to interlaced (in low-light situations, when reasonable gain-settings would differ by 6dB between interlaced and progressive assuming aperture and shutter speed are fixed), the dynamic range stays the same, the light-sensitivity increases at the expense of vertical resolution and of course the temporal resolution increases (with costs of additional vertical resolution drop+aliasing while movement).

Bottom line:
If you need 30p/25p and it gets dark, don't play with the interlaced-mode, but increase the gain value, because you will still capture more picture information than in interlaced-mode.

Hey guys, Doug is a guy you should all take some advise from. He has been at this for a long time and is an expert in his field. I agree impliedly with his call here. Unless you're shooting in an ambient light situation where there's no lighting other than a couple of 60 watt bulbs for light, That's about the only time to turn the shutter off. Exposure is a combination of , iris, ND filter and shutter speed and gain if absolutely necessary.

It's not a good sign if even simple things in life like shutter-speeds already leads to delegation of judgement.
That's an improper rule of thumb. The question is not, if the shutter should be off or on, but which is the shutter-speed I want to use. Shutter off effectively just means, to select the slowest possible shutter-speed, which is 1 divided by the framerate.
My experience is that a shutter-speed of 1/50s or 1/60 looks in general most natural/inconspicuous. So when shooting with 50 or 60fps, turn the shutter off, if you want to get natural looking motion blur. If you shoot with 24 or 25fps, use a 180°-shutter.
It gets interesting if you shoot with 24 or 25fps and have a low-light situation. My rule of thumb for that situation would be: If there's just very little motion and you would need a lot of gain to get the exposure right, turn the shutter off. If there's a lot of motion or you would just need a small amount of gain, leave the shutter on.

Definitely shutter-off for groundglass 35mm adaptor work. My personal preference for direct-to-camera imaging.

Didn't mean to appear judgmental, just agreeing with Doug. Yes, I turn the shutter off on occasion when shooting in dark situations where there's not much in the way of motion. Sounds like you have the same convictions. But yes, the question is not whether to turn the shutter on or off. It's choosing a shutter speed optimal to the shooting conditions and as a creative choice. I guess if your shooting in the dark most of the time you're going to need to use the lowest shutter speed most of the time, which is off. The irony here is, this thread wouldn't even exit if the shutter function had no off and simply started with the lowest scan rate possible for the selected frame rate.

Yes, I like that Sony gives me some technical insight by not abstracting the shutter controls just into selecting resulting shutter speeds, but also let me turn it on and off. But I guess Sony overrated the technical comprehension of some of its customers when sourcing this control out.

Interesting that people are expressing such strong views on this question. I wonder how many have actually given the matter any serious assessment. The correct answer is that which you find by your own testing and evaluation. I've run my own tests for a variety of situations (including passing traffic) and find that shooting 24/25P shutter "off" does not give strange effects and I prefer the greater motion blur for its impression of smooth motion. However if shooting at higher frame rates or need to process with stabilisation routines, it is a different matter. I have no problems with people disagreeing, but I am interested in their evaluation criteria. Might be some correlation with complaints about jerky motion at 24fps.

Besides that I don't like the heavy motion blur with 1/24s shutter speeds, what do you think about the finding that almost every hollywood movie is shot with a 180° shutter?

That isn't a persuasive argument, and anyway not entirely true (shutter angle is varied as required). However a film camera cannot have 360 shutter (the shutter must be closed while the film is advanced). I've shot a lot of film, so I'm aware of the related issues. The golden rule is test and assess. What other people (including highly experienced DOPs) suggest is your starting point, not your commandment. Your conclusion is that "off" results in too much blur; that's right for your use.

Sometimes they use faster shutter-speeds to make a scene look more stressful, but (almost) never slower. Could you give me one example of a hollywood production which uses in any scene a slower shutter-speed than 1/48s (@24fps)?
Why don't they shoot digitally? Do you think that some esoteric arguments regarding picture quality are more important to them than price performance ratio and less restrictions on workflows and shutter-speeds? I'm not an insider, but I guess that most major productions today are shot digitally.
That's right, but my personal experience regarding shutter-speeds perfectly matches with what I find in todays big commercial productions. I have no problem with your preference for slow shutter-speeds, but you have to put up with that I think your opinion is an outlier.

Since shutter speed is set for a specific shot you cannot make a statement that a film is shot at a particular shutter speed. Obviously 180 shutter is the most common opening for a film camera, and you specifically have no idea what shutter settings are used for any digitally photographed feature film. That most features are shot digitally is incorrect, as you could have easily determined. But this is quite pointless and irrelevant. I leave you to hold your views.

Yes, I can. Shutter speeds are easily recognizable (at least for me). I watched many movies (like many of us) and they are in most cases very near to 1/48s (of course I can't differenciate between something like 1/46s and 1/50s).
Again, yes I do. Give me any random scene of any random movie, and I bet that it was recorded with an 180°-shutter. (Btw., it's very easy to measure the shutter-speed of a shot afterwards if there's enough motion and resolution.)
I'm sorry, I edited my last post while you wrote your last. But again: What's the argument for shooting in film? And no, it's not pointless: If most movies would be shot digitally, restrictions concerned with celluloid-shooting would have a low relevance concerning this discussion.

The basis of 180 shutter is in film, not video. But I'm pleased you spend your time trying to measure shutter speeds of feature films; keep it up wasting your time. You have rather lost the plot.

You go around my question: Why would todays hollywood prefer shooting 180° film over 360° digital, if 360° would look better than 180° to the majority?
I don't have to measure it, because I can see it. But if you doubt it, we can measure it.

Sorry I have to disagree with this, IMO when shooting in interlace mode there is no need for shutter most of the time it's only when shooting progressive that shutter becomes more useful and even then I wouldn't use it 99.9% of the time.