[marcusBMG]

So now I have a k-r I have been taking my little collection of manual lenses out for a run one by one to see how they do on the Pentax instead of the G1 mft. Definitely value the focus alert and live view facilities.

So this is a crop from this mornings pic of Conwy Castle using a tokina AT-X 28-135mm (for which I wrote a review)



The particular conditions and perhaps the camera showed up the CA more than I noticed on results from my G1. But what I really want to know is: why Purple Fringing down the right and Green Fringing along the top and down the left?

Finally I don't have photoshop: is there anyone who also uses serif software and can advise on correction.

[Adam]

So now I have a k-r I have been taking my little collection of manual lenses out for a run one by one to see how they do on the Pentax instead of the G1 mft. Definitely value the focus alert and live view facilities.

So this is a crop from this mornings pic of Conwy Castle using a tokina AT-X 28-135mm (for which I wrote a review)



The particular conditions and perhaps the camera showed up the CA more than I noticed on results from my G1. But what I really want to know is: why Purple Fringing down the right and Green Fringing along the top and down the left?

Finally I don't have photoshop: is there anyone who also uses serif software and can advise on correction.

Stuff in front of the plane of focus is green and stuff behind is red. This fringing doesn't look too bad given the lens, but stopping it down should reduce it even more. You can try using the selective color tool to eliminate it if you don't have a lens correction tool in your PP software.

[interested_observer]

Green, purple, blue or yellow - they're all examples of CAs particularly in digital imagery. All such colors and hues can be removed by essentially similar action in post processing. Fringing occurs when the colors of the light wave aren't all hitting the image sensor at a 90 degree angle (essentially it is a lens induced problem, as the light travels through the lens optics, each color is not equally treated). The different colors of fringing occur due to the individual light (color) frequencies, and "shift" accordingly. Commonly referred to as purple fringing, most prevalent, since purple is the furthest color from the sensor and depending on the f-stop can defocus.

If you are find fringing on one side of an image, check the other side automatically. And again after you have corrected the purple side. Green is the complementary color to purple, so when you have a chromatic aberration the color that shifts on one side will logically end up with a complementary color shifting (or bleeding) on the other.

Sometimes the post processing CA capability can't help you without introducing other/additional problems - for instance, if you have blue on one side, but not matching yellow on the other side, then sometimes fixing the blue can create a yellow fringe on the other... or if not, it may put a line around the edge on the opposite side, somewhat like what you see with over-sharpening. If you have that problem, then often you can fix it by creating a new layer on top of the original layer and changing the blend mode to "color" - then select the color next to the object that has the fringing with the eye dropper tool, then a soft brush and color over it - the fringe should disappear. This, however, like any other fix, may introduce extra problems so you have to be careful. It can be a game of wack-a-mole.

Most post processing utilities/packages have the capabilities to correct CA. Check the manual or search on line for instructions for the particular utility you are using. Sorry, I didn't read the last line of your post. PhotoShop (but its very expense), LightRoom, really any of the packages. Most of these packages offer something like a free 10 - 30 day trial, so that you can see how it performs and if their workflow appeals to you. I would first start out with something like LightRoom, or Corel Aftershot.

[marcusBMG]

Thanks for those informative replies. FYI this shot was at f5.6 and I was bracketing the focus to check how the focus confirm was working relative to the lens. I also notice (wikipedia) that the prevailing conditions (bright hazy sky) can produce strong reflected uv. yeah I'll just have to get stuck in and see how some processing techniques work in Serif photoplus (which seems to be a reasonably well specified package, looking at online comparisons)

[Anvh]

Chromatic aberrations

[interested_observer]

Thanks for those informative replies. FYI this shot was at f5.6 and I was bracketing the focus to check how the focus confirm was working relative to the lens. I also notice (wikipedia) that the prevailing conditions (bright hazy sky) can produce strong reflected uv. yeah I'll just have to get stuck in and see how some processing techniques work in Serif photoplus (which seems to be a reasonably well specified package, looking at online comparisons)

http://www.serif.com/media/community/pdfs/photoplusx4-usa.pdf

page 23, 25 and 62

[ihasa]

I would advise getting PS elements, which has good correction tools in the RAW import and within the programme itself if you are working with jpegs.

[Na Horuk]

Isn't that lateral chrom ab? If you are shooting jpeg with a Pentax Lens, the camera can deal with it automatically (there is an option for this). If you shoot raw, you can go and fix it with chromatic aberration sliders (Lightroom has this under the "Lens correction" ) or even use a lens profile that removes distortion and other chrom abs. Higher quality lenses and primes tend to have less of these problems. On film it is less noticeable than on digital, especially because with digital you can do things like 300% crop, which is pretty unrealistic to begin with - nobody will look at the photo at that size and condemn it for such details. If you show it at a normal size it will be almost unnoticeable and most people won't be bothered by it, except for other photographers

[marcusBMG]

Thanks for the pointers Interested_Observer and Anhv very good article on CA and I didn't have the photoplus manual.

I agree with you basically Na Horuk, in fact FYI the orig jpg is now here
http://www.tremyfoel.co.uk/photography/IMGP4900.JPG

This post was out of technical interest, and I have an interesting old tamron , an early 80-250mm which is sharp but has much more noticeable CA partic at the long end. Its all good stuff...

[vonBaloney]

Lateral chromatic fringing that is generally found on the edges can be very well corrected with software tools (Lightroom 4 does it with a single checkbox). And it can actually be *corrrected* instead of just covered up -- you will actually see those sections of the image become sharper in post processing. Most other kinds of CA can't actually be fixed easily with current technology, only masked. The Topaz Denoise plug-in has a "clean color" slider that does the best easy fix of this I've seen -- it will get rid all but the worst false color in an image (including color noise at high isos, which is really what it is actually intended for I think). The Lightroom and Photoshop color noise filters are similar but don't do as good of a job (and sometimes don't seem to do much of anything). But Lightroom 4 also has good fringing tools for manually picking out and isolating the colors so they can be desaturated.

[Anvh]

Isn't that lateral chrom ab? If you are shooting jpeg with a Pentax Lens, the camera can deal with it automatically (there is an option for this). I

Indeed but not with the older lenses he is shooting with.
Also this Tokina lens, and only Pentax lenses have this support.

[wildman]

Ran it through ACR 7.2 with no special handling just defaults. Took no more than a couple of mins...

[vonBaloney]

Ran it through ACR 7.2 with no special handling just defaults. Took no more than a couple of mins...

Ran it through how?

[wildman]

how?

I think this should make it self evident - nothing complicated.,,

[vonBaloney]

I think this should make it self evident - nothing complicated.,,

Yeah, you said "with defaults" -- I can do it in LR4, but have to select the fringes, etc. I think it works better with RAW files but haven't compared. (I have LR4, but still CS5 PS, so no ACR 7)