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Sony TRV950 / PDX10 Companion
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Old October 30th, 2004, 11:28 PM   #1
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Focusing with a PDX10

Having worked for a long time with film or 2/3” video cameras I find only one problem with my PDX10: focusing. I think I will be more than willing to pay the price difference and have the very same camera with a Carl Zeiss lens. Never mind vertical smearing, or low light lack of response, or its tendency to go towards the reds the camera is great but the lens is cheap. It even changes exposure (film term) when you zoom and losses definition in wide angle (you have to stop down, never zoom out in low light). I also found that you have to be very, very precise in setting the correct iris (f stop: exposure) for each scene. A lot more than with professional video cameras. Never mind film! You are off by half an f stop (specially up) and you are in trouble and there is very little post can do for you, because its latitude (ability to handle big contrast) is very narrow. But with proper lighting, and if you don’t have to pull focus (just impossible), the images you can get with this little camera are just great. I use it via a capture card and its texture is special (you have to give it even a bit more light than with firewire capturing) somewhere in between film and 2/3” video. I have shot testimonial commercials for broadcasting with it and the agency loves them. In terms of value for money, you can go wrong with the PDX10. And it takes two of most popular video formats in the world today: DVcam and Mini DV. With a charger, two extra batteries, a wide angle adapter, a couple of good mikes (a lavalier and a shotgun with screen) and sound cables, a small boom, a tripod and a couple of Kinoflo with flags and cutters and stands and you are in business (Too much 5,000.oo USD?)

Its size is perfect and its XLR module, for pro sound recording, a wonderful option. Is the best second camera for any pro video crew (specially if your other camera is another DVcam camcorder), and a versatile main camera for a prosumer. Even its zoom control is better than most prosumer cameras.

But lately I have been having some doubts about its focus when zooming out. So I would love if any of you could do a focus test and write about its results here.

Get the best monitor you can find, better if it has S-Video connection. Focus on FULL TELEPHOTO on the center star of a focus chart (a newspaper with a cross in the center will do) placed diagonal and close to the camera (one meter more or less). Take note of the distance it shows in the viewfinder. You have to do it with little light so the lens is at its maximum aperture (f stop wide open), so its depth of field is minimal. Now zoom wide open. It should stay in focus. If when is wide open you can find better focus by changing the focus distance you set while on telephoto, something is wrong. Trying stopping down (closing down the iris) and you see how resolution improves and depth of field increases in front and behind your point of focus (that’s why you placed the chart diagonal). So if you have any problem you will find out with what aperture you will get away with. Good zoom lenses –theoretically, because it is really impossible- stay in focus all the time and maintain the same exposure, and resolution when zooming in and out. Inexpensive zoom lenses lose resolution when in wide angle unless stop down, and this is the case with the PDX10.

I am very worried because when I do this I found that I get better focus at infinity.

Thanks,

Jose
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Old October 31st, 2004, 07:30 AM   #2
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A bit of a mixed post from you Jose where on the one hand you're praising the little PDX10 to the skies and on the other you're criticising it heavily.

Of course there will be difficulties in getting differential focus with this cam, but it applies to all domestic camcorders using chips smaller than 1/3" and the PDX10 is not alone here. You call the lens 'cheap' but in reality this 12x Sony zoom stacks up very well and is certainly not surpassed by anything having Zeiss written on it. Zeiss lenses cost the same as Sony lenses and have to pass the same resolution tests, but the German branding sure helps shifts the kit in Europe.

You say the lens changes exposure as you zoom, but you're incorrect in this statement. It loses a stop and a half in maximum speed from wide to tele, but so do most zooms on camcorders these days.

You say you're doing your lens testing with the lens at maximum aperture. How do you know when you're at this point? Are you counting the clicks from the right on the exposure bar? If not, you may be shooting with gain-up, and this could be influencing your results. If your zoom really does change focus when you zoom to wide then I fear that it'll need attention, as the lens and chip block assembly is a sealed block, and there are no back focus adjustments available on this model as far as I know.

You say: "Inexpensive zoom lenses lose resolution when in wide angle unless stop down, and this is the case with the PDX10". But in fact the opposite is true, and at very short focal lengths such as 3.6mm, diffraction can quickly rob you of resolution as soon as you begin to stop down, regardless of what the lens costs. It is precisely for this reason that Sony use increasing amounts of ND filtration to control exposure rather than using smaller apertures.

tom.
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Old October 31st, 2004, 08:01 AM   #3
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I have to agree with all of Tom's points here. When you zoom out to full wide the depth of field is so huge on this little camera that I don't think the focus is particularly critical. In fact, as you turn the ring at full wide the indicator very quickly hops to infinity after a couple meters and it's just about impossible to set anything in between.

Regarding the lens, the HC-1000 which replaced the TRV-950 (the PDX-10's consumer cousin) has a lens branded as a Carl Zeiss Vario-Sonnar T. But evidently it's the exact same lens as the PDX-10 and Sony paid a licensing fee to Zeiss for the use of their name. Would it make you feel better if Sony had done this with the PDX-10? Evidently Panasonic does the same thing with Leica. I think Tom hit the nail on the head here: it's a marketing ploy.

Just about all of the prosumer cameras have the crummy infinitely spinning focus rings which make manual focus difficult at best. Happily Sony seems to have taken a step in a new direction with the FX-1.
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Old October 31st, 2004, 11:36 PM   #4
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Tom, if you only zoom out, without stopping down or rising light level, no matter what gain setting you might have, optics have to function the same way and focus should stay in the same place. Most lenses perform at their best one or two f stops above its widest aperture. In general around f 4 at that aperture there is no diffraction. Boyd, is no a matter of depth of field. Of course the more you zoom out the greater it gets (specially with a 3.6 m/m lens as the PDX-10 has at its widest). That’s why when you test a lens, on a test bench, you do it a very close distance and wide open (full aperture) to reduce depth of field to its minimum and be able to notice any change in focus, at a greater distance it would be just impossible.

I have had (and still do) many lenses. Some zoom lenses, for 16 m/m and 35 m/m film cameras. Angenieux, Canon, Nikon. And Carl Zeiss and Cooke fixed lenses. But I have never known of a zoom lens that losses a stop and a half of exposure when zooming. As I said no zoom is perfect, only in theory, but a stop and half is a lot of light. I just sold a 20-120 Angenieux zoom lens in mint condition because to get the resolving power that agencies want nowadays you had to stop it down to f. 8, and just 10 to 15 years ago it was used on feature films in NY.

Believe me, when you want to know if a zoom lens is good, zoom to wide open and shoot at its widest aperture, because at telephoto and stopped down most zoom lenses perform well. That’s why there is some much price difference in between, for example, a 10-150 Angenieux zoom lens and a Carl Zeiss 10-100 both, of course, for 16 m/m. And when you want to test a zoom for resolution it has to be done at its widest, at middle range and in full telephoto positions. And its best is very seldom –you could say never- at the extremes. In terms of physics and optics a wide-angle lens needs a much more precise mounting system than a tele. Ask for the price of a 135 m/m lens for an old fashion SRL still 35 m/m camera and compare it with the price of 28 m/m for the same camera. I know money is not everything, but it certainly it means something.

On the other hand, I tried the Panasonic 100 for a whole documentary and I must say I liked a lot the Leica zoom lens, but I prefer SONY electronics and DVcam format, especially for editing. Aim your camera towards the sun and you will see the shape of its iris. It should have more sides. Yes, I shouldn’t have used the word cheap referring the PDX-10 zoom lens; it’s a matter of linguistics. But we shouldn’t get personal. Nor unrealistic. Cameras are to get the most out of them and the best way to do it is to know its virtues and limitations. Everything can get improved. I am a great fan of Carl Zeiss lenses, I wish I could own a set of then for my Arri 2C (so does great many people in the film business), their definition is super and its contrast strong. Good for drama and comedy. If you want to be more romantic look go for a good old Cooke. So having any of these two names in the front element of my small video camera its like having SONY on its side. If you take into consideration the chip size of this camera –one of the smallest in the market (this also means less energy)-, its price and that you are into the DVcam environment you could only say that SONY did a great job, but my dream is this very same little camera with a better lens. Do you think it cold be done, even if it is a fixed one? (the chip block assembly must make it extremely compicated) Some people might say: “Well, buy the 170” But I like the feel, the body –and the price (to have several)- of the PDX-10.

Thanks Tom for telling me about the lens and chip block assembly and about the gain setting. I thought I have turned off gain-up in the menu but now I think I was confused with another camera. Can it be done? And about the block assembly, it’s a great relief, because the real problem was that my beloved little camera fell of my hand. A short distance and it felt on a dense carpet, but I most be getting old. I thought I might have damaged the lens seating (something that affects more when in wide angle). This camera is not very popular here and I wanted to know if its performance has changed. A block assembly means better protection against shocks and blows. As you may notice I was trained in film (at the Poli of Central London, and the London Film School –back in the early 70s-) but the laws of optics are the same.

Thanks again,

Jose
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Old November 1st, 2004, 02:03 AM   #5
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Interesting post Jose - I enjoyed reading it and can agree with a great deal of what you say. Of course if you've been shooting movies using REAL cameras and lenses you won't have known that to limit the size, weight and cost of modern camcorders very nearly all zooms vary their maximum aperture as you zoom from one end to the other. The Canon XM2 loses over 1.5 stops, the Sony PD170 loses a stop and the Sony single chipper HC85E loses half a stop in its 10x Zeiss lens, but this is indeed unusual in camcorder circles.

I agree that to be called a zoom the lens should maintain accurate focus throughout the range. Vari-focal lenses (more popular in the 70s) had to be refocused at every focal length change, but they were lighter, cheaper and possibly sharper as a consequence.

As you understand test benches, aperture values and focal lengths, bring your fingers together so that they're just 3.6mm apart and marvel at this minute focal length. Then realise that many Sony camcorders have a minimum focal length of 2.3mm, and you'll see why the lens and chips are sealed solid in epoxy resin, simply to maintain the highly critical back focus adjustment. And of course to give the camcorder some sort of 'dropability' factor - as you've found out.

At these tiny focal lengths diffraction does indeed start as soon as you begin to stop down, and although using f4 will clean up the image simply because there's less flare and vignetting, the image is in fact losing resolution due to diffraction. Which is why Sony (and all the others) now use ND filters to control exposure, and can get away with using inefficient two bladed diaphragms (because they're not often used).

It's fascinating technology, and - in the quest for ever smaller and more compact camcorders - shows what can be achieved these days with amazingly controlled production build tolerances.

tom.
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Old November 1st, 2004, 08:42 AM   #6
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<<<-- Originally posted by Jose Pantin : I thought I have turned off gain-up in the menu but now I think I was confused with another camera. Can it be done? -->>>

The "auto gain" menu item allows you to limit the amount of gain the camera will apply in dim lighting while you're using auto exposure mode. It has no effect on the operation of the exposure wheel when you're in manual mode.
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Old November 1st, 2004, 11:58 AM   #7
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2.6 mm!!! Unbelievable. In 35 mm it’s around 52 mm depending on the make, it’s easier to work with but it can also give you a lot of trouble, most problems in focusing in films have to do with lenses mounting systems. Besides you don’t have the advantage of having back focus adjustment as many video cameras have, which makes switching lenses so much easier. So it has a lot of sense the idea of block assembly. Lens and chip an independent unit: perfect. It’s like a camera inside another camera. Obviously it makes lens swapping out of the question but manufactures can produce good and strong cameras at very affordable prices and concentrate spending on the electronics, which it’s what its new and what they are the best at.

I would like to buy another SONY DVcam camera (from the 250 upwards) mainly because of the lens, though it also has a bigger chip. But I don’t intend to get rid of my PDX10, or another one brand new. Because I also think it is a good choice if you want to have a multicamera set up for little money. Without its XRL sound module and a grip you can put it where very few camera of its type can go. Wonderful for cameracars with very little effort. I do some risky situations taping and I can hide my PDX10 in any koala and run –I still can if I am scared- and if it gets as bad as loosing it it’s easier to replace it. I think that when SONY designed this camera they actually had news cameramen in mind. Pros on the run. Little weight with good enough quality for dangerous situations. Isn’t its ability to do streaming for that? To send news quickly via Internet? To me, some cameras are like some people, you wish they were perfect, but you still love them.

Thanks friends,

Jose

PD. It is good to know that the auto gain-up only works with automatic exposure. Besides, it's no too difficult to notice when it starts to pump up exposure.
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