does OLPF for 7d exist

smelni

smelni

Veteran
I know that the rez tests for the 7d show the camera having less then HD rez before aliasing, and we cant change that. But is it possible to put a OLPF in front of the lens to at least prevent aliasing below that rez threshhold.

some people have suggested using promist or soft fx filters but those will also soften all edges - not just the high rez stuff -

does anyone know if they make OLPF that you can put in front of a lens?
 
An OLPF is, in effect, a blur filter. It's an optical low-pass filter, meaning it blurs out the highest-frequency details and lets the lower-frequency stuff pass.

There is an OLPF in there already, but it's tuned for still shots, not video work.

If you put an appropriate-strength OLPF in there it will blur out all the aliased stuff, leaving only the native res. Which isn't bad, it's about HVX200 level, so the net result is you get HVX200 sharpness with a built-in 35mm DOF look, for $1700. Awfully hard to argue with!

Perhaps what you want are the Caprock anti-moire filters. They go in front of the lens, not in front of the sensor, but they'll end up doing the same thing. I believe Isaac Brody is currently testing them to find which works best with the 7D.
 
one clarification - an olpf cant be the same as a blur filter because a blur filter would blur the edges of low frequency edges as well - an olpf has to JUST blur high frequency data - right?
 
Plus wouldn't it have to be a behind the lens filter?

Don't blur type filters increase with strength with the focal length of the lens?

-J
 
Barry,

Along these lines, I've been looking for a blurring filter for the T2i to take down the moire/aliasing.
As you said, it's like getting an HVX200 resolution camera with a 35mm DOF look for roughly $1500; I really have no complaints with losing some resolution if it gets rid of the aliasing.

I've been recommended these products:
http://www.caprockdev.com/antimoire.htm

Can anyone vouch for them?


So the blurring filter is multiplied by the focal length? Would it be possible to get a filter behind the lens then?
 
Quote:
So the blurring filter is multiplied by the focal length?
That doesn't make sense to me.

The blurring *effect* is multiplied by the focal length. A caprock 2 filter will appear stronger on a 200mm lens and will be almost nonexistent on an 18mm lens. So unless you have a full set of filters and have done extensive tests to determine the appropriate filter vs focal vs hd resolution... Then it will likely only work in very specific circumstances. It may otherwise have negligible effects, or it could be too strong rendering the image soft.
 
Here's Isaac Brody's test:
He concluded using the Caprock 2.0

Here's Barry Green's test:
He concluded using the Caprock 1.0, on the overall


This could mean the two of them have very different subjective opinions of what's an acceptable level of aliasing.

My alternate conclusion is that Isaac was shooting at 1080 and Barry was shooting at 720.
My logic is that 720 mode requires skipping more lines on the sensor so that it can achieve 60 fps. More lines skipped means a larger gap between active photosites for the video image. Therefore, 720 mode should require a Caprock filter with a stronger blurring strength than the 2.0 to cover the larger gap between active lines.

That's just my speculation on the matter. Isaac or Barry here to comment?


And if that's true, I wonder if the 640 mode would have different filter strength needs than the 720 or 1080 mode.
 
You must log in or register to reply here.
Back
Top