Triple scrim "could project moire pattern"

Moseph

Moseph

Veteran
I'm thinking about picking up one of these, mainly for outdoor use. But their descriptions say that it could cause a moire pattern, which sounds pretty undesirable. Does anyone have any experience with them, and do they actually cause a moire pattern? If so, I'll probably just get some cinescreen and an open-ended frame, unless anyone has any better ideas for a ~2 stop reduction in light. Thanks.
 
For the most part, with a scrim right up against the lens of the instrument, there's not much chance of a moire pattern on an object at a distance. Not with any kind of definition, anyway.

If you're outdoors, the easiest way to drop light two stops is to double the distance from the subject.
 
David Jimerson said:
For the most part, with a scrim right up against the lens of the instrument, there's not much chance of a moire pattern on an object at a distance. Not with any kind of definition, anyway.

If you're outdoors, the easiest way to drop light two stops is to double the distance from the subject.
Click to expand...

Depends on the instrument. This is not always true.
 
Well, yes; wouldn't be so true for, say, a Leko. In terms of the moire pattern, anyway -- it's very collimated, so it would be more likely to show.

Fresnels, open-face -- not so much. YMMV.

As for the inverse square rule, to what light doesn't that apply?
 
Paul Hudson said:
Depends on the instrument. This is not always true.
Click to expand...
What instrument do you have in mind? It's certainly true for fluos, for fresnels, for pars, for LEDs and for lekos and for candles; I can't think of a fixture where the inverse square rule doesn't apply. Maybe a laser?
 
The inverse square law doesn't apply if the light beam is absolutely collimated (all rays parallel to each other). In real life, this pretty much only strictly applies to lasers. But Lekos can get close to that, and if you stay within a range where the diameter of the projected light beam is only a small multiple (say 2:1) of the diameter of the lens on the fixture, then the falloff is less than predicted by 1/(distance * distance). This is true because the subject is being illuminated from a range of different angles passing through different points on the lens, rather than by a strictly defined point source. However, such a tight beam isn't very useful for general photographic applications, although you may see it in theatrical follow spots sometimes.

It's even possible to get greater brightness at a distance than close to the source if the beam converges (by means of a big lens) from a wide source to a focused spot as it passes through space.

- Greg
 
David Jimerson said:
For the most part, with a scrim right up against the lens of the instrument, there's not much chance of a moire pattern on an object at a distance. Not with any kind of definition, anyway.
If you're outdoors, the easiest way to drop light two stops is to double the distance from the subject.
Click to expand...
I was thinking more along the lines of the sun.
 
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