Modding 7D with optical low pass filter in front of the sensor to avoid Moire

M

Meierhans

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As we all know moire is a serious problem for DSLR filming. This is because the low pass filter mounted in front of sensor is ment to block details that could lead to moire when taking stills, not when recording video in reduced resolution (line skipping, binning.. .)
:violin:

But indeed there are two low pass filters mounted as you can see here: http://ghonis2.ho8.com/rebelmod450d18.html

They are simply the wrong strenght for video.

So I asked myself: If it is possible to replace the IR cut filter as these astro guys do, wouldn´t it be possible to do the same with the low pass filters? Sure this would mean you can not take high res stills anymore.. but seriously.. who would ever want to take stills? They don´t move, how boring.. ;)

Has it been done?
If yes, where can you get these filters?
 
Not just dslr, moire is a problem with ALL kind of cameras ( just more apparent on these ). Secondly if you shoot "people" you don't have to worry about it & if it's in your background just use a deeper d.o.f. Now if you are shooting objects then maybe you need a different kind of camera to avoid this all together
 
Thanks for your reply, but this is not really what I am asking for.

I know that moire apears on all cameras, I own a Sony Z1 as well and if you feed it with the wrong patterns (some clothes f.e...) it will also look ugly. But far less than with DSLR, because of the low pass filter beeing optimized for the video resolution.

And yes, I know how to open a lense to get the background out of focus. But this is not always possible and also quite limiting. What if you wanted to move the focus to the background because something is happening there...

I know there is Caprock filters to mount in front of lense, but you will need different ones for different focal lenght, and if you use zoom lenses it becomes really complicated. Especially if you want to work with (Vari-)ND + Mattebox. You end up with 4 Caprocks for about 500 $ + converter rings +++

So the question is: How to lower the MTF of the optical system by putting something directly in front of the sensor (where it belongs..)?

How to mod? Where to get the material.
 
Search around here, there are a couple of threads where someone tried this already on a T2i. They took the OLPF from an older DSLR with a resolution close to 1920x1080, and used it to replace the T2i's normal OLPF. If I recall correctly, all it did was horribly soften the image and did not negate the moire to any significant degree.
 
4100xpb said:
Search around here, there are a couple of threads where someone tried this already on a T2i. They took the OLPF from an older DSLR with a resolution close to 1920x1080, and used it to replace the T2i's normal OLPF. If I recall correctly, all it did was horribly soften the image and did not negate the moire to any significant degree.
Click to expand...

I seen that as well. It's just a problem with these Dslrs and you just have to try all of the tricks and different angles to try to avoid it. I also think there is a plugin that helps with this as well.


Since I shoot people and nature backgrounds I rarely have this problem, but if I shot other objects which did have this I would be using a different camera
 
a lot of the enhanced moire effect is the way it skips and reads pixels; it makes any moire all the more visible. its not just the OLPF.
 
yes it does, also you can turn contrast up a bit to enhance perceived sharpness to 'fake' a bit less moire. i try to avoid getting moire, when we shoot i always stress beforehand about stripes and try to shoot wider open so background moire is eliminated as much as possible. i have some unuseable footage from the T2i's at a wedding where it was not only moire from brick steps, but also the grooms suit, the ruffles on the table and in her dress, and even her hair which was streaked. too bad because the angle was great.
 
i have been shooting with sharpness all the way down, contrast all the way down as well as saturation. This only has minimal effect on removing moire and color aliasing. Unless, you intentionally nudge the focus a bit off, but this is not good practice. The caprock rescreener can effectively minimize it though.

I do a lot of wides in corporate and commercial work so I encounter this a lot on wide shots with 11-16 tokina and sigma 20-40, the caprock eliminates the moire but you must compensate contrast in post and maybe a pinch of unsharp mask. Using the caprock lowers contrast a bit but I find it ok since I find the canon's too contrasty even with it tuned all the way down.

The caprock gives it a bit of a black stretch look which is good for grading.
 
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Thx for your replies guys!
So you say it has been done, but the resulting decrease in moire does not make up for the sharpness you loose - because of line skipping/pixel binning? And the (quite expensive) caprocks are the only option?? Thats sad, would like to hear some other voices. We also do alot corporate stuff and sometimes the moire can´t be avoided when framing right, like when presenting the building.

So please, somebody tell me this is not a dead end.... maybe you could mount something caprock like inside the cam with a little distance to the sensor, so there would be no need to buy 4 of them. Also means no hassle with additional filters in front of lense... We are already dealing with ND/Pol/VariND and Gradient filters here, I just dont want to add another layer to this sandwich.

What is the plugin you are talking about? There was also a method to decrease at least the aliasing with a avisynth script, but I could not find the script itself anywhere and would really prefer to do it inside AFX if possible.
 
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