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Old July 24th, 2002, 08:53 PM   #1
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XL1s Lens Filters

Ok, I made the mistake of not buying filters with my new XL1s. My lens is the 16x Manual Servo. What filters do I need (can't live without)? Also, what brand do you recommened?

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Old July 24th, 2002, 10:48 PM   #2
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B+W and Heliopan are top end brand names. If it's made in Germany, it's probably pretty good.

Tiffen is a good quality medium price range filter. Probably best value for the dollar.

Don't buy any no-name crap for $10 off Ebay!

Get a UV filter. Then maybe a polarizer. After that don't buy anything until you absolutely need it, or you'll end up with a box of filters you've never used.
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Old July 25th, 2002, 03:50 PM   #3
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I would get a two stop ND filter. Cannon's built in ND filter always takes exposure down by six or more stops. That is just too big a change to be practical.

If I remember correctly, a .6ND filter corresponds to two stops. I would not shoot higher than f8 with an XL-1 if I could avoid it. Cameras that utilize 1/3" chips lose sharpness after about f8 or f11. A two stop ND filter would help out quite a bit in bright light.

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Old July 27th, 2002, 10:08 AM   #4
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When you say "higher" do you mean, for example f16 or f1.6?
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Old July 27th, 2002, 08:37 PM   #5
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Sorry Josh, I should have been more specific.

It is when you shoot with too small of an aperture that you lose sharpness. It has been recommended to me that a camera with 1/3" CCD's never be allowed to shoot with an aperture smaller than f11 and try to stick to f8 or f5.6. No mention was made with shooting at say f-2.8 so I assume that is okay. You get a shallower depth of field, but on an XL-1 it probably won't be a problem. The sharpness that is lost may be subtle, but I get such a large depth of field at f-8 that I don't mind not shooting at the extreme end. I have played around at f-16 and f-32 and dust particles on the lens end up in focus. That is when you want to turn on the ND filter but the built in one drops me from f-32 to f-2.8. That is why I would recommend a two stop filter and maybe a three.

As a side note, the smaller the CCD's the less depth of field you get. Of course you probably knew that one.

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Old July 27th, 2002, 10:36 PM   #6
 
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Lenses usually "optimize" out around f/5.6-f/8. Wide open apertures do not have the rez that a more closed aperture has. Below f/22, you begin to run into diffraction limits.
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Old July 27th, 2002, 10:50 PM   #7
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I see I see. My lens has two built in ND filters, and I have one in my so far unused filter kit. I hadn't noticed the above mentioned effects as related to aperature size, but I'll keep it in mind from now on. All that stopping up and stopping down business confuse me, especially since higher fstop number = less light but more depth of field.

One more thing, and I hope this isn't stupid. I'm using the manual 16x zoom lens. . .so will dust and particles and such still be visible at those low aperatures? The lens's minimum focus distance (I believe) is 3.5 feet.
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Old July 28th, 2002, 10:25 AM   #8
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Josh,

The dust particle are very easy to spot.

On a real bright sunny day, just point your camera off in the distance. I did this, without knowing it, while in Costa Rica working on my video project. There was a lot of beach footage that was shot at f-16 and f-32 and I could distinctly see the tiny specs of dust on the lens. If you haven't noticed them, it probably isn't a problem.


Bill,

You said wide open apertures usually don't have the resolution that a more closed aperture does. This contradicts my statement, but mine is second hand. Am I incorrect here?

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Old July 28th, 2002, 03:11 PM   #9
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Lenses usually perform their best between F5.6 and F11. Beyond F16 they start to be limited by diffraction, which will reduce overall picture quality. Diffraction is one of the 8 optical defects all lenses have. Below F5.6 and the lens will produce coma and astigmatism. So, use your ND filters and polarizers to keep your lens in the sweet spot.

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Old July 29th, 2002, 12:01 AM   #10
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Jeff (or anyone)
I and probably others could use a brief run though of the 8 optical defects of lenses if you don't mind and have the time.
Thanks!
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Old July 29th, 2002, 01:39 AM   #11
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I as well would like that list. Sometimes though, it just doesn't seem practical to stay in the sweet spot. Today I shot in a low light auditorium, and had no lighting kit with me. The only way to reach the sweet spot would have been to turn the gain up several notches, probably to +18 or so. . .producing noticable grain. I kept the gain at zero and opened the iris all the way instead.
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Old July 29th, 2002, 04:15 AM   #12
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It's often not possible to shoot in the best part of the lens. I have virtually never shot interiors at a 5.6. Many exceptionally shot films have been made with the lens set one stop over minimum aperture (at best) for interiors. All this means is that the optimum place in the lens is not practical, so you take the compromise.

However, the less expensive (and lower grade) the lens, the more critical all this becomes--so it is probably more noticeable on a "prosumer" level video lens. Nevertheless, boosting the gain can be easily as destructive to the overall image. Josh, I think you did the right thing by not cranking the gain and shooting wide open. Anyone else?

p.s. the Panavision HD lenses for the Sony 900 were designed to work optimally at a wide-open aperture, to minimize the depth of field. I would be curious if the resulting compromise was that they fall apart at the smaller aperture end of the lens?
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Old July 29th, 2002, 04:29 AM   #13
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That's another thing: How much can you crank the gain (if any) before it becomes noticable? When I first go the camera I thought you could go to +18db (or whichever the third setting above 0 is), then I noticed I was wrong. It seems that in dark areas, you can see the little grainies swimming happily around, but it's barely noticable in brighter areas. I also see the little swimming pixels with no gain at all sometimes though, in darker areas.
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Old July 29th, 2002, 04:41 AM   #14
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Some of what you are seeing is the compression inherent in the DV format. However, even at a 0 db setting there is a certain amount of noise, a function of the electronics of the camera and the format (if you were to A/B the image directly from the camera and a tape playback of the same shot, you would notice the noise buildup). I've never seen proof of this, but I have often felt that the -3db setting is really more like a 0 gain (unity), and the 0 gain setting is an artificial, albeit minor boost to allow for more impressive low-light level specs.

I guess the answer to your question about how much you can crank the gain until it is noticeable is: crank it up until it becomes noticeable? Sort of an objective thing.

Remember though, that while you stay in the DV format (firewire editing, etc) the image will remain virtually identical to the original, but that once you output to VHS it will degrade substantially, and the noise will increase, so it's best to err on the clean side unless the image will be objectionally dark. Also, the theory of shooting dark and cranking in post vs upping the gain on the camera is suspect to me, because the former approach will magnify the compression artifacts.
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Old July 29th, 2002, 08:19 AM   #15
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The eight optical defects and what the cameraman can and cannot do to correctthe defect.

1. Astigmatism - The inability of the lens to bring to focus both vertical and horizontal lines on the same plane. Astigmatism is caused by axial rays (not parallel to the lens axis). It will appear that lines of equal density (darkness) are less dense horizontally or vertically. Astigmatism is improved by stopping down the lens (smaller lens opening, larger F number).

2. Coma - coma causes parallel oblique rays passing through a lens to be imaged (focused) not as a point, but as a comet shaped (oval) image. Coma can be improved by stopping down the lens.

3. Curvature of Field - The plane of sharpest focus becomes curved, not flat. It is caused by rays from the outer limits of the subject plane coming to focus nearer to the lens than the axial rays (image comes to focus in curved shape, away from the CCD). This defect is not improved by stopping down the lens.

4. Longitudinal Chromatic Aberration - The inability of a lens to focus all colors (wavelengths) at the same plane on the lens axis (shorter wavelengths come to focus in front of the CCD, longer behind). This defect is not improved by stopping down the lens. This is normally only noticable in long telephot lenses. It is reduced by the use of special glass elements, referred to as ED, ID, LD or Flourite.

5. Lateral Chromatic Aberration - lateral displacement of color images at the focal plane (CCD). Caused by different sizes of images by procuced by different colors even though the image is all on the same plane (CCD). Produces color fringing of red or blue. Not improved by stoping down.

6. Spherical Aberration - Inability of all rays to focus at the same point. Marginal rays (at the edge) through the lens come to focus closer to the lens than do paraaxial rays (rays parallel to the axis or center). This causes the focus to drift as you stop down the lens. This may be part of the XL1 focusing problems. However, it's just my opinion.

7. Distortion - distortion causes the image of a straight line, at the edges of the field (CCD) to bow in or out. Bowed in, pincushion, bowed out barrel distortions. Produced by variations of magnifications over the field of the lens, particulary at the ends of its range (max wide angle, max telephoto). It does not effect sharpness, only shape of the image. It is not improved by stopping down. Very common in extreme wide angles and lenses with WA adapters.

8. Flare - Flare is non-image forming light. Reduces contrast and color saturation. Flare is caused by very bright subject areas and produces internal reflections in the lens. Stacking of filters can increase flare. Lens coatings by the Mfg. keeps flare to a minimum. The use of a suitable hood (not the stock hood) can also aid in reducing flare.

9. Ghost Images - Not a true defect put is seen quit often and sometimes confused as one. Distinct images, usually in the shape of the diaphram or a very bright light source included in the scene. Caused by high intensity light producing rays which bounce around in the lens and form an image. Often multiple images appear in a row across the scene, starting at or near the source. Ghost images can be reduced by the use of a suitable lens hood.

Jeff
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