where's the sweet spot?

J

Jen

New member
Anybody have any recommendations on the "optimum f-stop" setting for the DVX100a? --not taking into account exceptionally bright or dark settings ...just general purpose shooting

Where (what settings) do you think it renders its best images? Specifically for film-like capture with the least amount of artifacts.... :)

thanks,
Jen
 
Re: where's the sweet spot?

Hmmm. Interesting question. I haven't heard of anyone conducting such tests.

Typically lenses are designed to perform at their sharpest somewhere around two to three stops down from wide-open, which on the DVX would put you in the ballpark of f/4 to f/5.6 or so. You typically get the worst performance at wide-open and at nearly-closed, so there's almost a bell curve of performance distribution.

However, lenses can be designed to perform differently: the Zeiss DigiPrimes are apparently optimized to deliver maximum sharpness at wide-open.

I've never heard it discussed before, and I've always kind of assumed that you're save as long as you stay f/4 to f/8, but that's just an assumption. Someone with lots of time and really good eyes should run a test!
 
Re: where's the sweet spot?

Thanks Barry...I don't think I've got the sharp eyes or the patience ;) to perform all the tests but I will definitely do some samples between the f/4 and f/6 range.
 
Re: where's the sweet spot?

And I sort of doubt that DV 25 has the resolution needed to actually resolve the differences between F stops as would a film camera.
 
Re: where's the sweet spot?

I don't know about that, based on the XL1 experience. The XL1 has notoriously low resolution and soft focus on some outdoors shots, and according to Chris Hurd, it was eventually traced to the use of f/32. Apparently f/32 was so tiny it was causing diffraction issues and a much softer image than f/16.

I used to use a Sony VX1000 a lot back when it first came out, and I remember there were times when the footage was sharp as could be, and times when it just looked awful. I never got around to seeing if it was related to an f-stop range, but now that I think back on it, I think it might have been.
 
Re: where's the sweet spot?

That could very well be true and everything is relative. I haven't really done any lens/f-stop sharpness tests. The basic rule of thumb from my 16mm days was two stops away from all the way open or all the way closes.

Not having the "all the way open" becuase of sharpness in DV hurts the whole DOF issue even more... unless you consider softness a DOF attribute... ;)

Michael
 
Re: where's the sweet spot?

What are the inherent problems with wide open?  I thought the bigger the aperture, the narrower the depth of focus, which is a telltale feature of film productions.  I had been thinking of keeping the aperture as open as possible for most things and using the ND filters to bring the exposure down to ideal levels (I have also read and experienced firsthand that video darks carry a LOT more information than lights, and shooting things intentionally dark is far better than overexposure).

Is there some sort of problem with the DVX100 when shooting wide open, other than too much light?  Some kind of distortion?
 
Re: where's the sweet spot?

Theoretically, all lenses should perform best when wide open. However in practice, most lenses have chromatic or spherical aberrations and coma at their maximum aperture. These aberrations can be reduced by stopping down the lens. Even though stopping down a lens corrects aberrations, you start to have problems with diffraction effects. In an optical system that is free from aberrations, the performance is limited solely by diffraction.

So for many (but not all) lenses, about two stops down from the widest aperture achieves the maximum reduction in aberrations and the minimum of any objectionable increase in diffraction effects.

Michael's comment about the resolution of DV is a good one. Because of the limited resolution of the DV standard, lens aberrations at maximum aperture are going to be much less noticeable.

If you *can* notice large differences in DV lenses across a range of apertures, you can be sure that the aberrations or diffraction effects are really bad.

With the DVX, I have not noticed any major degradation in image quality when the lens is used wide open. So if you want shallow DOF (such as it is with the DVX), I wouldn't hesitate to use the lens wide open.
 
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