Which CA software did you use to get rid of the CA after you enlarged the canvas? I usually use the CA correction built into ACR, but that's not going to be possible if you need to enlarge the canvas first. Are you using another tool in PS, or are you using DXO after the canvas has been enlarged?
Ben Horne wrote:
I picked up a 45mm TS-E lens here on FM for use on a trip. I LOVE this lens. Now that I am use to the lens movements, I find it difficult to use "regular" lenses now. I have learned several things about this lens that I thought I should pass on. First of all, you really NEED the angle finder C in order to tell if you have the lens properly setup. Otherwise, it is difficult to tell in the viewfinder if you have the lens tilted and focused properly. Here is a test shot yesterday with the 45mm TS-E tripod mounted, tilted almost to the max. I believe the shot was taken at f/8. With a normal lens, you'd get only a small percentage of the shot in focus at f/8.
I was well aware that Chromatic Aberration would be an issue with this lens. It's quite a bit more than I thought, but it also isn't that difficult to get rid of. You can NOT use the CA fix in Adobe Camera Raw since this is a different style of CA. On a normal lens, you will find that the red channel is slightly larger yet centered. As a result, the further you get from the center of the lens, the stronger the CA will be. Photoshop can essentially shrink the red channel, yet keep the center aligned, and you will have proper alignment.
With a TS-E lens, your image circle is huge, and depending on how you have the lens tilted/shifted, you will see only a portion of the edge of the image circle. This means that the CA is not radial, and centered in the middle of the photo. With a little bit of experimentation, I found that if you shrink the red channel to 99.92% of it's original size (on the 1DsmkII), you will now have a red channel that is the same size as the blue and green channels. Then you just have to align it. In the shot with the rocks on the beach, I set the height to 99.92%, left the width at 100% (uncheck the constrain proportions box) since there were not any red channel alignment issues on the other axis. Here is a 100% crop before and after the red channel shrinkage.
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I also found that 99.92% worked for correct CA on this lens that results from shifting to the max.................Show more →
OK, someone has to ask the dumb questions so it's my turn today.
I'm not sure what you mean by shrinking the red channel so can you explain that in more detail? I've used the 24,45,90 for years now and have never done that so if I'm missing something that obviously appears to improve things, I'd like to understand it. I'm also quite familiar with PS, but as we all know, there are 100 ways to do the same thing...
jamesf99 wrote:
OK, someone has to ask the dumb questions so it's my turn today.
I'm not sure what you mean by shrinking the red channel so can you explain that in more detail? I've used the 24,45,90 for years now and have never done that so if I'm missing something that obviously appears to improve things, I'd like to understand it. I'm also quite familiar with PS, but as we all know, there are 100 ways to do the same thing...
thanks
Load a photo from one of these lenses that has some severe CA. Next, look at the channels pallet. Click the blue channel, then the green channel, then the red channel. You'll see that the blue and green channels are properly aligned, but the red channel is off. The light in the red spectrum does not focus properly, causing the info on the red channel to be slightly larger. This is why you see the color fringing --- it is because not all the colors are focusing on the same plane. By shrinking the red channel, now the color channels are all the same size. When aligned properly, the vast majority of the CA will be fixed.
Ben Horne wrote:
By shrinking the red channel, now the color channels are all the same size. When aligned properly, the vast majority of the CA will be fixed.
Yes, but how do you do that (shrink only the red channel)?
I can view it, select it, move it around relative to the other channels, but if I try to use Image>Image Size to shrink it (only red channel visible, active and selected), the entire image (G&B in addition to R) is affected. So clearly I'm doing something wrong. What?
monoprint wrote:
Yes, but how do you do that (shrink only the red channel)?
I can view it, select it, move it around relative to the other channels, but if I try to use Image>Image Size to shrink it (only red channel visible, active and selected), the entire image (G&B in addition to R) is affected. So clearly I'm doing something wrong. What?
Exactly. This doesn't make sense, perhaps because I have never tried to "shrink" a channel. Image resize affects everything, RGB channels combined. I know a lot about using channels, but obviously not this...
Click on the red channel (you should see a black and white image now), then use the keyboard shortcut to select all of the canvas (Control A on PC, or Command A on mac). Copy the image to the clipboard, then paste it into a new document. Resize the image, then copy it, and paste it back into the original red channel. Next, just move the pasted in copy of the red channel so it aligns properly.
Ben Horne wrote:
Click on the red channel (you should see a black and white image now), then use the keyboard shortcut to select all of the canvas (Control A on PC, or Command A on mac). Copy the image to the clipboard, then paste it into a new document. Resize the image, then copy it, and paste it back into the original red channel. Next, just move the pasted in copy of the red channel so it aligns properly.
Thanks. With all the people pretending to know what you meant, I'm relieved to know there is not something that mysteriously got by me regarding PS channel "resizing".
Basically, you can't do it. This is definitely not a straight forward technique and your really creating and combining two images. I'd have to play with it before attempting to do it but perhaps if I review my images shot with the 24, 45, and 90 I'll find something worth "repairing" in this way.
jamesf99 wrote:
Thanks. With all the people pretending to know what you meant, I'm relieved to know there is not something that mysteriously got by me regarding PS channel "resizing".
Basically, you can't do it. This is definitely not a straight forward technique and your really creating and combining two images. I'd have to play with it before attempting to do it but perhaps if I review my images shot with the 24, 45, and 90 I'll find something worth "repairing" in this way.
I setup an action to do it. Pretty much everything is automated and it takes a split second.
Ben,
I'm not sure that this is a big shortcut but you could resize a channel without copying. Click on the channel, Select all, Edit->Transform->Scale.
After finding out how to do the resizing - thanks Ben and Alex - I tried the technique on an extreme Architectural shot taken with the 24 on full shift. I couldn't get the correction quite right, although I did improve the terrible CA quite a bit. The final fix, which leaves the image "perfect", is to convert to Lab, use Dust and Scratches filter on the a channel, and then sensible sharpening on the L channel.
I tried something similar. I converted to LAB mode, then applied a slight blur to the a and b channels, and it seemed to help fix the remaining CA issues. Both of those channels got very pixelated, and softening it seemed to smooth that out.
I tried the PS lens correction, and it did work, but it did not seem to do much different than the technique that I have been using. Also, it was a bit slower.
This is a test shot for the 45mm TS-E that I have just acquired. Tilted 7 degrees to get the plane of focus between the Canon cap and "XP" letters and then used a small aperture to bring in maximum DOF
