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Old August 15th, 2007, 10:15 AM   #31
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Originally Posted by Barry Green View Post
It is simply not possible for a ground glass to "overexpose", because a ground glass doesn't "expose" at all. It's glass. It's like a window -- can you "overexpose" a window? Windows don't expose.

(and yes, I've tested this, by taking a shot with a ground-glass adapter at one light level, and then at 256x that light level, compensating with internal ND filters and internal iris -- the results were identical).

The HVX's ND filters are not "electronic", they're physical filters that slide into position with the clunking of the ND filter switch, just like on a bigger broadcast camera. As to whether the ND filters are glass or gelatin I don't know.
Barry, the thing you are either unaware of, or forgetting is Sub-surface Scattering. You simply can't compare GG to perfectly crystal clear glass with an IOR of 1.0.

It's directly dependent on the material properties of the GG.


Last edited by Gene Crucean; August 15th, 2007 at 03:40 PM.
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Old August 15th, 2007, 04:42 PM   #32
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I'm not forgetting it; it's inherent to the way the ground glass "holds" the image. It's the very nature of the ground glass, and it's primarily the difference between ground glass and a window.

But it has nothing to do with the concept of a ground glass "exposing" or "overexposing". A ground glass can no more "overexpose" an image than, say, a projection screen could. I don't think I've ever heard anyone claiming that a rear-projection screen "overexposes" an image, but it's vaguely the same technique.
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Old August 15th, 2007, 05:14 PM   #33
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Except for the thickness, the material and the physical size of the screen. If you say so though. All I know is how my images look with and without.

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Old August 16th, 2007, 05:34 AM   #34
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the fact that most cameras use electronic ND filters as opposed to actual glass ND filters.
What cameras are you talking about? An "electronic ND" would be the same as negative gain - I don't think any camera with an ND filter switch/wheel would not have actual glass ND filters (on the DVX/HVX for example you can even see it's mechanical when you set the switch in between the right position).

I don't know about the adapter issue, but my experience with filters is that any filters in front of your lens might cause blurriness in full zoom, while I have never seen any image degradation with the built-in filters of either a DVX100, HVX200 or Sony DXC-D30/35/50. I don't think this would be any different with the HPX500 (that I haven't seen yet, but maybe soon)
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Old August 16th, 2007, 06:43 PM   #35
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You have not described a situation where you've compared with and without an external filter and explained the difference. I'm honestly eager to hear it.

On the last post you went on to your balcony and the effect didn't happen, but you thought maybe it wasn't bright enough.

- Lenny
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Old August 16th, 2007, 10:22 PM   #36
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There are some properties of our imaging elements that I can't discuss...and having said that, even if there was no difference on the imaging element side of things, I'd still do my shading/exposure control at the front of the optical chain where practical. Here's why.

Of the forms of lens flare (most being obvious) out there, hazing is the one that gives me the most grief. It's hard to see when you're shooting, can be unpredictable, and is easily taken care of by properly shading/exposing and in some cases stopping down the 35mm lens. Internal ND's will do nothing in this case. It would be extremelty difficult to predict bare lens behaviour in the field with incident light...there's too many variables. Also, AFAIK, no camera has an internal polarizer, and for me, that's a staple filter when shooting outdoors. On my list of things to do...a visual (with examples) guide to best practices on shooting with the Brevis.

So although imaging systems in adapters vary (I believe Barry was testing the Letus) and will predictably vary in behaviour with technology differences, no one can argue that proper shading/exposure control out front will never hurt your image quality, and in most cases will improve it. As a still photographer enthusiast for some 23 years, I am a firm believer in keeping non-image forming/unnecessary light off of my optics :-)
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