1/25 th shutter in 50i ? at DVinfo.net

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Sony HVR-Z1 / HDR-FX1
Pro and consumer versions of this Sony 3-CCD HDV camcorder.


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Old January 17th, 2005, 02:28 AM   #1
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1/25 th shutter in 50i ?

Can the PAL FX1 shoot with 1/25th shutter speed in 50i ?

If so, iterpreted deinteralcing 50i footage to 25p should give a correct motion blur no ?

Thanks !

Frank
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Old January 17th, 2005, 05:35 AM   #2
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Yes it can do 1/25 shutter, but that is usually considered slow shutter.
I believe that 1/50 shutter corresponds to a 180 degree shutter like in most film cameras. 1/25 shutter corresponds to a 360 degrees shutter that is impossible on a film camera.
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Old January 17th, 2005, 06:16 AM   #3
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in my opinion in this case - 1/25 - the picture is blurred too much.

it looks artificially. but maybe it's just subjective. i will not use this settings. rather 1/50.

just my two cents. (or 1/50th of euro :))


filip
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Old January 17th, 2005, 11:02 AM   #4
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Frank,

Bear in mind that when the shutter speed drops below the field rate, your resolution is cut in half. This doesn't mean that slow shutter speeds cannot be used. Just that there will be a loss of vertical resolution. So for shots that require the utmost detail, it may be better to refrain from a shutter speed slower than the 1/50th.

Jon
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Old January 17th, 2005, 11:48 AM   #5
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<<<-- Originally posted by Jon Fordham : Frank,
Bear in mind that when the shutter speed drops below the field rate, your resolution is cut in half. -->>>

Jon, bear in mind that so far nobody has cared to measure the real resolution with slow shutter. ;->
Some even think that resolution does not decrease noticeably...
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Old January 17th, 2005, 03:30 PM   #6
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Toke,

This is not a camera specific issue. Anytime a video camera's shutter speed drops below the field rate, an interpolation must take place in order to create a full screen image. The exception would be if the CCD is progressively scanning at a rate slower than the recording system's field rate and a pulldown cadence is being used to fill up the remaining fields.

You are correct that no one has yet to report to this board a test that proves that the FX1 functions in the exact same manner as every other video camera in existence. So I will refrain from saying that my statement is 100% accurate. Though I would doubt that the FX1's CCD's and recording system is doing anything different than every other Sony camera when it comes to slow shutter speeds.

I understand the argument that has been presented here regarding the MPEG2 compression scheme playing a factor in the possibility of slow shutter speeds maintaining resolution. But unless the FX1 is functioning in a completely new and different manner, the drop in resolution and interpolation is taking place before the information reaches the recording stage.

Regardless you bring up a very valid point. The key word here is "noticeable". A drop in vertical resolution doesn't mean the slow shutter speeds can't used to great effect. I've used slow shutter speeds on many DV cameras on many projects over the years. In fact the FX1's slow shutter speed was the first option that excited me. For DV projects that need to shoot with slow shutter speeds but are concerned with resolution, the FX1's slow shutter would allow that project to shoot their slow shutter shots and not take near the resolution hit that it would in DV.

For anyone interested in a film that used DV slow shutter to great effect, I recommend checking out Hal Hartley's "Book of Life". This entire film was shot with the VX1000's slow shutter and I think it's one of the best DV film's I've ever seen.

I am currently in pre production on a film that will shoot with the FX1 starting mid February. I will make some time to put the FX1 in front of my 7A9 chart in the next week and test a 1/30th slow shutter speed compared to a 1/60th shutter speed and report back to this board what I find.

Jon
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Old January 17th, 2005, 05:04 PM   #7
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<<<-- Originally posted by Jon Fordham: I will make some time to put the FX1 in front of my 7A9 chart in the next week and test a 1/30th slow shutter speed compared to a 1/60th shutter speed and report back to this board what I find. -->>>

Great!
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Old January 17th, 2005, 09:42 PM   #8
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The main reason why I ask is the following.

I want to shoot using 50i (PAL) with the Z1 and then deinterlace to 25p with interpolation. This gives me a clean motion blur of one of the two fields (not blended) . The problem is , the shutter speed of 180 degrees in 50i using 1/50 th speed is actually half of 1/50th second, which comes down to an actuall motion blur of 1/100 ths shutter speed in a full frame.

That's why the question.

I was trying to use deinterlaced interpolate 50i footage to go to 25p and then dpeed down to 24P.

BTW: I then also understand Cineframe 25 in the Z1 will loose vertical resolution, correct ?

Thanks for the input !

Frank
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Old January 18th, 2005, 12:33 AM   #9
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Quote:
The problem is , the shutter speed of 180 degrees in 50i using 1/50 th speed is actually half of 1/50th second, which comes down to an actuall motion blur of 1/100 ths shutter speed in a full frame.
No, the shutter speed for each field is 1/50th. When recording 50i, the camera's eye is always open, and each field is recorded for 1/50th of a second.

Quote:
BTW: I then also understand Cineframe 25 in the Z1 will loose vertical resolution, correct ?
Yes, but not as much as you might think. In interlaced mode the camera does roughly 775 lines, but in CF25 it'll deliver about 575 lines -- a loss, but nowhere near half, which is what you might expect from a straight field-doubling. It appears that CF25 must be bypassing the interline field blurring process that helps reduce flicker on interlaced displays, and is thus outputting the raw resolution of one field (which would give it a theoretical maximum of 540 lines, which is close enough to the observed 575 to say that it falls within the margin of error when shooting a res chart).
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Old January 18th, 2005, 06:15 AM   #10
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<<<-- Originally posted by Barry Green : No, the shutter speed for each field is 1/50th. When recording 50i, the camera's eye is always open, and each field is recorded for 1/50th of a second. -->>>

Is it really? Doesn't ccd need any time to transfer the image forward?
"Normal" shutter speed with XL2 in 25p mode is 1/25.
So if one wants to imitate 180 shutter, then one should put it to 1/50?
My experience by quickly testing xl2 was that motion seemed quite stuttering with 1/50@25p. Not like with film and 180.
But then again with 1/25@25p motion blur seemed too long.
(I haven't shot anything real with xl2, but used a lot slow shutters with vx1000 and pd150.)

I've been a little bit confused about these shutter speeds vs. real exposure time per field/frame, so this would be very nice to get cleared.

With bigger cameras, I've noticed that you get brighter picture if you set shutter "off" than eg. 1/60. So I've believed that off means that eye is always open and 1/60 means time for both fields.
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Old January 18th, 2005, 08:05 AM   #11
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Hi Toke,

This is a great point you raise, and I can understand the confusion. I have to admit it has had me stumped for a while !

I think with 1/25 shutter speed each field is derived by combining both lines from the CCD (call it Field line A + Field line B), so you in effect get the same 1/25 of a second 'slice' shown on both fields (1/50 of a second). Therefore, discarding one field (to get the CF look) simply leaves you with the same 1/25 motion that is then repeated every 1/50 second to fill the second field.

In this respect shooting with 1/25 in 50i should render the same results as shooting with 1/25 in CF25 mode.

But, if the 180 shutter angle is needed, then you need to capture 1/50 motion, which can only be done at 1/50 shutter.
Where the first 1/50sec is captured by Field line A followed by the next 1/50 captured by Field line B, and so on..., it is then up to the de-interlacer as to how much of the second field is replaced by the first. But the resultant motion cadence should resemble the desired 180 shutter angle as that is what is captured by the CCD for each field.

Remember that an electronic shutter is not the same as the film equivalent - so the rules are not the same.

I hope this makes some sense :0)

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Old January 18th, 2005, 11:10 PM   #12
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Quote:
"Normal" shutter speed with XL2 in 25p mode is 1/25.
So if one wants to imitate 180 shutter, then one should put it to 1/50?
Yes, a 180-degree shutter in 25p would correspond to a 1/50 shutter speed. 1/25 would be a stop faster in exposure, but much blurrier.

Quote:
My experience by quickly testing xl2 was that motion seemed quite stuttering with 1/50@25p. Not like with film and 180.
The DVX at 1/48 at 24p delivers motion that looks *exactly* like film motion, as tested by shooting side-by-side with film. The XL2 should deliver exactly the same motion signature. I certainly haven't noticed the XL2 looking any strobier than a DVX. It should have an identical motion signature.

Quote:
I've been a little bit confused about these shutter speeds vs. real exposure time per field/frame, so this would be very nice to get cleared.
If you're shooting interlaced, and shooting at a shutter speed slower than the frame rate (i.e., shooting 1/25th with 50i) then the CCD should be dropping fields. I've never seen an interlaced camera that performs differently than that. With progressive scan, you can retain full resolution, but you get fewer distinct frames per second. The DVX can shoot at 1/6 of a second in 24P, and still deliver full frame resolution, but what happens is it prints duplicate frames to tape, so you get an effective 6 frames per second, each frame recorded four times. So the CCD buffers up the frame for output, and continually accumulates the existing frame. I didn't test the XL2 specifically for this, but I can't imagine why it would be different.

With bigger cameras, I've noticed that you get brighter picture if you set shutter "off" than eg. 1/60. So I've believed that off means that eye is always open and 1/60 means time for both fields. -->>>
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Old January 19th, 2005, 03:26 AM   #13
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You were trying to compare video shutter speeds to film cameras Joonas. I'd say that PAL video at the default 1/50th sec is like having a 360 degree shutter in film camera terms ~ as if everything that happens in front of the camera is recorded. Move your hand in front of the lens as you film at 1/50th and on replay you'll see that the blured images 'match up'. In other words, as soon as one blur stops, the next one in the next frame begins.

A film camera with a 180 degree shutter only records half of all the action that happens in front of it, the same as shooting at 1/100th in video.

tom.
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Old January 24th, 2005, 01:24 AM   #14
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Well Tom, I think what you're saying is true from a certain perspective, if you're shooting 50i video.
If you shoot 50i video, the motion is sampled 50 times per second, and if the shutter is 1/50, then the shutter stays open during the recording of one field, and "everything that happens in front of the camera is recorded".

But. I'm ofcourse talking about shooting 25p, cineframe25, or deinterlacing, which have the same motion, and the same amount of motion blur. In this case the motion is sampled 25 times per second, just as if you were shooting film with 25 frames per second. 1/50 shutter then gives you light to one frame. Only half of the things that happens in front of the camera is recorded. This is just like on film.

I'm only talking about 25 motion samples per second, because I never use interlaced footage without deinterlacing, that gets rid of the unwanted motion.

50 samples = 50i -> 1/50 shutter = 360 degrees
50 samples = slow motion on film -> 1/100 shutter = 180 degrees.
25 samples = 25p -> 1/25 shutter = 360 degrees, slow shutter.
25 samples = 25p -> 1/50 shutter = 180 degrees, just like in film.


I think you'll agree?
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Old January 24th, 2005, 02:18 AM   #15
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I do agree Joonas. You mean you never shoot 50i?
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