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Sony TRV950 / PDX10 Companion
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Old September 14th, 2004, 01:32 PM   #1
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Some 950 operation Questions

I have just purchased a new TRV950 and am learning it's features but some are not very clearly explained in the manual.
1.Auto Shutter - in the setup menu's you can turn it off, but no explanation what happens when you do.
2. When I turn off "Auto Hold" it seems I can only change 1 option. So if I adjust shutter speed, is the apeture automatically adjusted ? Also are all other options that I dont touch left on Auto ?
When do I use the Zebra bars at 100 and when at 70?
I have seen the affects of fast shutter speed, but if I set a speed below 1/30 is the picture "smeared" across multiple frames seeing as the frame rate is 29.97?
I'm sure I'll find more as I go along , but hopefully some advanced users can give some guideance
Thanks in advance to those who reply.
Samuel Birkan is offline   Reply With Quote
Old September 14th, 2004, 04:45 PM   #2
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Welcome Samuel!

I will try to answer based on my experience with the PDX-10 which should be the same.

1. I don't shoot in automatic mode, so I can't confirm this but I assume turning auto shutter off will prevent the camera from changing shutter speeds. I set mine to "off" when I got the camera and left it there....

2. You can adjust both shutter and iris, but with one "gotcha". When you go into manual mode the default will be to control the iris opening with the wheel. To change the shutter speed you need to release the iris setting by pressing the exposure button. Then press the shutter button and you can select any desired speed, which will show in the viewfinder. Now press the exposure button again and it will lock shutter speed as shown in the viewfinder. You will now be able to set any desired iris opening by turning the wheel. The "gotcha" is that you need to do things in this order - pick your shutter speed first, then set the iris. If you pick an iris opening first and then change the shutter, the iris is automatically set by the camera. Why? Ask Sony.... Also, it gets a little more complicated "behind the scenes" because your camera has several tiny neutral density filters in the optical path behind the lens. When it "feels like it" the camera will insert these filters in response to your turning the iris wheel. The purpose is to force you to keep the iris opening within certain tolerances that Sony has determined produce the best image. The strange thing is that none of this has ever been documented in an official Sony publication.

3. At 100 IRE the zebra bars will indicate maximum exposure on pure white areas of the image. At 70 IRE they do the same thing with a neutral grey roughly comparable to Caucasian skin tone.

4. Actually you will see the shutter "smear" as you call it using any speeds below 1/60. This is due to the fact that interlaced video captures 60 fields per second. When you set the shutter at 1/30 the same data is written to both the odd and even fields. Some people like this effect since it roughly mimics the motion blur and feeling of film, however since the both fields of the image are identical you have greatly reduced your vertical resolution. Each field would normally consist of 240 lines for a total of 480 lines per frame. But at 1/30 sec shutter speed you get 240 pairs of identical lines. In point of fact, the resolution loss may not be quite so bad however since for other reasons the camera only has about 360 lines of vertical resolution. As you select even slower shutter speeds this same data is written to more than one frame. So at 1/15 sec you would be writing the same data to both fields of two frames, and the motion blur would be even more pronounced.

Have fun with the new camera! You'll learn a lot along the way.
Boyd Ostroff is offline   Reply With Quote
Old September 15th, 2004, 09:10 AM   #3
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Thanks for all the info - wow this is a great forum. Your answer and the previous post about ND filters really cleared up some questions I had.
I am a bit mystified though by your comment, {"since for other reasons the camera only has about 360 lines of vertical resolution. "} .
Could you explain ?
Samuel Birkan is offline   Reply With Quote
Old September 15th, 2004, 10:18 AM   #4
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This isn't a limitation specific to the TRV-950, but it's the case with just about any interlaced camera. As you know, interlaced video consists of two fields each of which contain every other line of the image. So first we display the odd field which contains lines 1, 3, 5, 7, 9....479. Then 1/60 second later we see the even field with lines 2, 4, 6, 8...480.

Now imagine a very thin horizonal line in your image - like a clothesline maybe - that only is 1 pixel wide. It might appear as line 31 in the odd field of the image. Now when the even field is displayed the line is so thin that it doesn't appear on line 30. Or an alternate scenario might be that it's sort of between those two lines, so it shows on line 31 in the odd field and line 30 in the even field.

In either of these cases, you would get sort of a flickering effect. These problems can occur with any high contrast nearly horizontal lines and edges in the image. To reduce the flickering caused by this, the camera does some sort of averaging of the vertical lines. This results in a vertical resolution that's less than the theoretical maximum of 480.

You can verify this for yourself by shooting a resolutin chart like I did. This image is taken from one of the little "targets" in the upper left-hand corner of the EIA 1956 resolution chart. I took a jpeg of the chart and down-rezzed it to 720x480, so the following image shows the theoretical maximum resolution you could expect: http://greenmist.com/dv/res/x-a1.JPG. You can read the vertical resolution by looking at the converging horizontal lines in the 9 o'clock position. Notice they become blurry somewhere between the 400 and 500 line bullseye rings.

Now look at the following image of the same chart as photographed by the PDX-10, which uses the same chips as your 950: http://greenmist.com/dv/res/x-c1.JPG. You can see that the lines blur out within the 300 to 400 line range somewhere. For more info see http://greenmist.com/dv/res
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