optical low-pass filter

rabsamir wrote on 8/15/2012, 7:26 AM

Hi
Some time ago I came up with a flickering problem in my videos. Many of you helped me to understand why and proposed solutions.
I do not remember having read about OLPFs then and happened to bump on this article not long ago.

http://www.red.com/learn/red-101/resolution-aliasing-motion-capture?utm_source=newsletter&utm_medium=email&utm_campaign=news27

(The video w strong aliasing looks very much like my video-problems :-( )

What do you think of that?
And, do OLPFs really exist? I mean mounted on a ring and ready to use in a camera.
Are they then named differently maybe (I haven't seen any in the market) ?

Regards

Jorge

Comments

farss wrote on 8/15/2012, 7:46 AM

"do OLPFs really exist?"

Yes, pretty well every digital cameras has to have one.
You will not see them "in the market" because they are largely useless in front of the lens, they have to go immediately in front of the sensor. Not something you can do yourself. They also have be designed specifically for the sensor.

You can get filters that do much the same as an OLPF to screw onto the front of the lens however for them to be effective you'd need quite a variety and have to select the right / best one based on focal length and aperature. Bit of a PIA to be doing. Best solution, start with a camera that's had it all done by the engineers that designed the thing.

Bob.

rabsamir wrote on 8/15/2012, 9:30 AM

Thanks Bob

very interesting.

Looks like I didn't discover America after all... :-)

Jorge

rabsamir wrote on 8/15/2012, 12:35 PM

> Best solution, start with a camera that's had it all done by the engineers that designed the thing.

Just for curiosity. How does one know if any camera has some kind of filtering? From the specifications? In mine there is no mention of this at all (but from the results I gather that it has none - Panasonic TM 900)
But does no mentioning in other cameras mean no filtering?

Thanks

Jorge

Laurence wrote on 8/15/2012, 2:32 PM

The problem is that the filter on a DSLR camera is set for it's highest still resolution, not the much lower video resolution. Worse than that, pixels are being skipped on capture in HD video. This effect is at it's worst in outdoor wide shots where all sorts of man-made details are made small by distance and create a myriad of these artifacts. Like I said in the other thread, I bought a Tamron lens that goes through it's complete zoom range with f-stops variable from f-2.9 to f-32. At f-32 the diffraction of the lens acts like a low pass filter and effectively gets rid of all these artifacts while still leaving plenty of clarity for HD video. I use this only on outdoor wide shots like the ones in the linked example, but it works really well for those shots. Maybe not a perfect solution, but it will tide me over until the technology at the low end that I can afford catches up to what we want.

Three large sensor still/video cameras that get around this are the Canon 5D Mark 3, the Nikon D800, and the Panasonic GH2.

rabsamir wrote on 8/15/2012, 3:22 PM

Hi Laurence.

Is the linked example you mention in another thread? Which one?

Thanks

Jorge

Laurence wrote on 8/15/2012, 3:31 PM

I was referring to the link in your first post. Someone else posted the same link a while back:

http://www.sonycreativesoftware.com/forums/ShowMessage.asp?ForumID=4&MessageID=822568