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Old May 25th, 2010, 04:18 AM   #1
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Chromatic Aberations on EX3 question

I have been using the longest telephoto setting on my EX3 and have noticed a fair bit of Chromatic Aberations. I know this is a lens issue and that even more expensive lenses have this problem, albeit maybe to a lesser degree.

Can anyone suggest a way to lessen the problem or is there a software application that will re-register the colours. I have tried to correct this in Photoshop CS4 & CS5 (Extended edition) and it does work to a fashion but is not perfect. I have also tried After Effects CS5.

Alister Chapman stated that the EX1 & EX3 cameras have electronic correction for C/A, I have searched for this feature and can't find it. Does anyone know where it is located?

Thanks in anticipation
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Old May 25th, 2010, 05:09 AM   #2
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AFAIK the electronic correction is in-built and works automatically - it detects what lens is mounted and goes through a software algorythm to correct for its known defects.
As you say, it's a fact of life to a greater or lesser degree with HD lenses, in fact all lenses.
I was always told that in post the problem could be corrected to a pretty big extent - more or less selecting the colour of the fringing and telling the software to de-saturate that colour, but I'm no editor.
In scientific terms from what I read the aperture used should make no difference to the amount of fringing, but a lot of people reported it being worse the wider the aperture, the consensus then being that it showed up more with a wider aperture because the fringing was wider as it was more out of focus, while with a smaller aperture it was more sharply defined so less pixels wide, so that may help, stopping down a little. But of course stop down too much and you'll start to get softness due to diffraction - lesser of 2 evils I suppose.
Steve

ps I love it how my computer keeps underlining COLOUR to tell me I've spelt it wrong!
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Old May 25th, 2010, 05:47 AM   #3
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Thank you for your detailed reply Steve. I have tried several techniques for correcting this problem using After Effects, and yes you can selectively desaturate the two colours (Magenta & Green) but this does leave a desaturated shadow which looks just as bad. I will keep experimenting, the shots in question are needed for a project.

ps. you can change your computers default language from US to UK spelling, that will cure your "Color" problem
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Last edited by Vincent Oliver; May 25th, 2010 at 07:51 AM.
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Old May 25th, 2010, 07:32 AM   #4
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Have always been aware of the telephoto CA but never thought it could be fixed. Will try your idea Steve. Only now noticed that when cutting EX1 material on an SD timeline with 10 year old Digibeta pictures shot on a Fuji 20-1 SD lens that there is CA on X2 wildlife close ups. So in one respect for this project they match!
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Old May 25th, 2010, 07:56 AM   #5
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Hi Vincent,

If you have access to the Vortex Media PMW EX3 Field guide you will find that page 117 mentions lens files including how to store and retrieve them. I have fiddled with the RGB Flare adjustments for my Nikon 300mm f4 and noticed no change over the full range of adjustments so I returned to the original settings. However I was only using the viewfinder image to make my judgements.
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Old May 25th, 2010, 08:18 AM   #6
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I am not quite following you on this one Alastair. I am fully aware of how to store files etc.

Have been experimenting further with Photoshop and After Effects. Photoshop CS4/5 does have a very good fix and has produced a better looking clip than After Effects, it's still not perfect but better than before.

I perfected the C/A using Photoshop, feeling very pleased with myself - UNTILL !!


I just realised that Filters and C/A corrections will only work on one frame at a time, back to the drawing board.
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Old May 25th, 2010, 09:10 AM   #7
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As a follow up to my Photoshop and C/A experience, have now found the sollution.

Using Photoshop CS4/CS5 (Extended edition) Select the Video workspace (top right hand corner drop down list). An empty timeline appears at the bottom of the workspace. Open a video file, I have converted my EX3 files to QuickTime MOV files. The movie appears in the timeline and your Layers palette indicates a single Layer 1. This next step was the misssing link for me, Convert this Layer to a Smart Object. Now any filter that you apply will be applied to the entire clip, not just the first frame.

I used the filter, Distort > Lens Correction, to correct my C/A problem. It has worked very well. Photoshop CS5 has more options for more precise corrections.

Note this video editing ability is only available in the EXTENDED edition of CS4 and CS5
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Old May 25th, 2010, 09:26 AM   #8
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Sometimes you can separate each RGB layer, and realign them, though sometimes you might have to add a warp too.

Stopping down does help somewhat, so you use more of the centre of the lens overall in the image. Things are more rectilinear there.
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Old May 25th, 2010, 10:14 AM   #9
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Just to finish off, here are the fruits of my day's labour.

The file WindFarm is a reduced full size frame,

The file C/A is showing the before shot

The File C/A corrected has been through the Photoshop workaround

Click on the images to view a higher magnification
Attached Thumbnails
Chromatic Aberations on EX3 question-windfarm.jpg   Chromatic Aberations on EX3 question-ca.jpg  

Chromatic Aberations on EX3 question-ca-corrected.jpg  
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Old May 25th, 2010, 10:18 AM   #10
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[QUOTE=David C. Williams;1531191Stopping down does help somewhat, so you use more of the centre of the lens overall in the image. Things are more rectilinear there.[/QUOTE]

Stopping down doesn't mean you're using more of the centre of the image, only using a smaller sensor would do that.
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Old May 25th, 2010, 10:27 AM   #11
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Hi Vincent,

Looking at the before and after shots demonstrating the C/A, I am wondering if sharpening in camera is causing most of the problem, that is, of course if you have sharpening on.

To my eyes it, has the appearance (effect) of "unsharp mask" where adjacent pixels of high-contrast values are pumped up.

-Andrew
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Old May 25th, 2010, 12:11 PM   #12
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No, I have all the sharpening in camera turned off (Detail = 0)

The shot was taken on a very hot day and there is a lot of atmospheric distortion creeping in, this is a nice effect when you see the full clip.

I am now more than happy with the end result. I must stress that under normal viewing of the entire clip the C/A is not that apparent. The shot is required for broadcast so it had to be right (one shot in a series).

Now for the next problem to solve, but that is for another day. :-)
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Old May 25th, 2010, 12:25 PM   #13
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One thing to bear in mind, certainly true on the big broadcast cameras, is that Detail Off and Detail 0 are not the same thing.
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Old May 25th, 2010, 02:40 PM   #14
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There are a bunch of threads on the topic of sharpening & crispening as it is called in Sony parlance. Here is an illuminating thread on the matter.

I'm not stating that the problem is sharpening but it is worth knowing and considering some of the counter-intuitive sharpening related settings in the Sony camera as it could have contributed to the color/contrast shifts on those dark thin lines of the hydro tower.

-Andrew
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Old May 25th, 2010, 11:49 PM   #15
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I didn't know you could work on video files in photoshop.
Is this done often?
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