The cheapest cure for iris control and aliasing on the 5D?

joe 1008

joe 1008

Veteran
So Canon shot itself into the foot by not giving us full manual contros. It seems, that one of the steps the user can undertake to regain forbidden ground is to use Nicon compatible lenses with an adapter. By doing so you get reportedly full iris = DOF control. But there might be more: Buy cheap & soft Sigma glass and you maybe have even less aliasing problems. (I would especially appreciate comments on that point!)

Canon: It's time for a firmware upgrade for more manual controls or even reduced aliasing - or you will sell less glass.
 
the softness you get from using cheap glass isn't really the kind you want for low pass filtering in my opinion. it's worse near the edges, it tends to smooth out low contrast detail while the high contrast is still fairly sharp, the end result is probably just gonna be a softer vignetted image still with aliasing. maybe a silk stocking behind the lens could work? i'm gonna try that with my d90, problem is that when you remove detail on the d90 you don't get a smoother image, you get more blockiness due to the constant quality rather than constant bitrate encoding...

/matt
 
btw you can't really remove the aliasing in firmware, unless you soften the image quite a bit, down to almost half res, and i'm sure you don't want that. the low pass filter in front of the sensor is made for 4000 lines but in video mode only 1000 are sampled.

/matt
 
I think softenind the image in an intelligent mode is the way to go for now. Even if we end up with 720p footage on the 5D. Let me know about your test results! :)
 
mattsand said:
btw you can't really remove the aliasing in firmware, unless you soften the image quite a bit, down to almost half res, and i'm sure you don't want that. the low pass filter in front of the sensor is made for 4000 lines but in video mode only 1000 are sampled.

/matt
Click to expand...

Excuse me Matt that I'm scuandering around on things I don't really know about: But the pattern that is responsible for the aliasing is a fixed one, it never changes, each frame has it. Maybe that could be the point of depart for a render fix ( by a firmware upgrade or with a sofware application in post)?
 
yes, it's a fixed pattern but we don't have the data between the lines so to recreate it we need to blend the lines somehow, a process that by definition blurs the image no matter how intelligently you do it. the stairstep problem on the d90 is a different problem that's caused by digital scaling, a process that is almost losslessly reversible, only every 10 lines have to be resampled rather than all of them. of course the d90 has the same aliasing problem even if you fix that so yeah we'll see how the silk stocking trick works. i'll let you know.

/matt
 
OK, but woulnd't it be a blurry image with a much higher resolution? I mean, the 5D reads out every 3rd line. So filling the space between the lines would give a blurry image with 3240 lines (3x1080), wouln't it? Downsizing it would give us a sharper image again - or am I completely wrong?
 
if you could somehow increase the resolution by making the image bigger the world would be a great place but alas the res would at best be the same, plus you'd introduce more artifacts. downsizing it again would either, if sampled using a nearest neigbor algorithm, recreate the aliasing exactly, or if sampled using a weighted average blur the image since the new lines are constructed from the adjacent ones and then merged into the result.

/matt
 
no, it's by design. the camera only samples every third line in video mode. of course sharpening will make it worse but it's always there.
 
I'm curious if the aliasing/moire effect occurs in standard definition recording. If it does, this might give a hint as to wether standard def on this camera is a downrez of the HD pixel array or not. If it doesn't have this effect, then we know SD is not a downsample. Would anyone agree with this thought process?

In regards to controling aperture on your EF EOS lenses, one trick is to put something over the contacts of the lens so that it can't be controlled by the camera, this will force the lens to stay wide open. I know the lens won't be at its sharpest wide open but this might not even make a difference in HD resoltutions.

I know I've read about a trick to get the Canon lenses to stay at a specific aperture but I forgot how. I think it might be by holding down the DOF preview button in manual mode and then taking the lens off of the body. After this reapeat step one so that the camera won't change it back.

Even with this workaround, this still doesn't solve the problem with auto ISO and shutter speed but its still a big start in getting the picture you want even if its not the perfect settings.
 
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