Hi-Zoom for DOF - why not? at DVinfo.net

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Old August 23rd, 2003, 10:48 AM   #1
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Hi-Zoom for DOF - why not?

I have been playing with my XL1 to get better DOF in my shots for a more film-like look. I know that staying away from the subject and zooming as much as possible with a wide-open iris works for this... but I don't see that done very often and I'm wondering why... the negatives I know are:

1. Logistics of camera position
2. Sound, if using the built-in mic
3. panning becomes more delicate...

I am always skeptical of getting something for free... so what are the other drawbacks/trade-offs to this approach?

btw, I was also unhappy to discover the the maximum open iris position closed as I zoomed in... I assume this is mandated by physics, but unfortunate...

Thanks in advance....
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Old August 23rd, 2003, 01:19 PM   #2
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Your lens is a variable aperture lens. Most cameras with attached lenses use variable aperture design, because it's cheaper. Pro lenses are usually a constant aperture, but cost thousands.

You might also want to read this thread on DOF. If you keep the subjects head etc. the same size, zooming in or out does not change DOF, only changing the aperture does. So, why be way back from your subject if you don't need to be. As you point out, audio and zooming can be more problematic.
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Old August 23rd, 2003, 02:03 PM   #3
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It is true about the subject-size=constant-DOF physics, but the reality is that they don't look the same. For those looking for the soft-background look, backing up and zooming in will result in a more "pleasing" look.

The DOF is constant at the given aperture, but what changes is the amount of magnification of the background elements. A telephoto lens "compresses" the space, bringing the background and foreground closer together. A wide angle "expands" the space, making it appear as if the background was further away.

So with the telephoto shot, the background will be bigger, more magnified -- and thus its out-of-focusness will be easier to see. The wide angle will push the background further away, so even though it may be optically just as out of focus, it will look a lot sharper.

The DVX100 loses about one and a half stops over the course of its zoom range -- wide angle is f/1.6, telephoto is f/2.8. When comparing a closeup head shot on full wide angle at f/1.6, vs. the same-sized subject at max telephoto but f/2.8, you may think that the wide-angle should have the shallower DOF because the aperture is significantly more open: but practical experience reveals that this just isn't so. The telephoto shot has a much softer-looking background than the wide angle, even with the smaller aperture.

So, back up and zoom in to get the best look -- where possible (obviously there are significant restrictions on doing this in interior locations). And if you're still not satisfied with how soft your background looks, consider using a SoftScreen (www.softscreen.us) for even more control over your background focus.
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Old August 23rd, 2003, 08:56 PM   #4
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When you zoom, you change angle of view. The change of angle of view may certainly effect the appearance of the background. Other factors that will effect the appearance of the background include, distance of subject to background, brightness and contrast of the background. Careful manipulation of the background will aid in obtaining an apparant shallow DOF.
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Old August 31st, 2003, 07:22 AM   #5
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I say if something works, do it. Also Jeff makes a great point... years and years ago when I first got into still photography I noticed how easy it is to forget about the background until the pictures are developed. Eventually you learn how to look at the whole shot rather then simply framing and making your subject pleasing. Now the first thing I do is look at the background, analyze it, and THEN take care of my subject. There is a lot you can do to pump up DOF if you take a moment to survey your shot.

When I had a 1/4" single chipper DOF was impossible to any real degree. Then I got a trv900 and DOF became somewhat possible. Now with the dvx, DOF is actually pretty darn good for a dv cam.

As a for instance. If you get a shot with some low foliage (pompous grass, maine grass, etc.) shooting from a couple feet, then have your subject about 10 feet out, then trees framing the shot (or skyline) off in the distance... the DOF will be outstanding. I've got a few shots out of this cam recently that appear to be 3D.

Your XL1 should easily be capable of the same thing. Also once you get a good wireless there will be no going back. I have an me66/softie setup which cost about the same as a used Lectro/Tram setup and so far the wireless has been kicking the 66's arse.
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